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Michael Büker: Yes, alright, thank
you very much, okay. I’m glad

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that you all found your way here
and it’s been mentioned already,

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this is Comic Sans, which as you
know is the official type-font

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of awesome particle physics stuff.
*laughter*

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But in the interest of our mental
sanity, I will keep it to other fonts.

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So from here on Comic Sans
is just a bad memory.

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Okay, two things: First the
title, Breaking Baryons,

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which of course is an allusion
to Breaking Bad, was inspired

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by the wonderful talk from last year which
was called “How I Met Your Pointer”.

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And which was also very successful
and you can check out that talk,

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I got the link there. And this
talk goes especially well

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with another talk that we’ll have
tomorrow by a real particle physicist,

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at least a bit more than myself.

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And it’s called “Desperately Seeking
SUSY” which is about particle theories

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and the real cutting edge physical
questions. This is going to be

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happening tomorrow. Allright, so
we’re going to start out with my talk

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and I’m going to be talking about the
questions of “what are we doing?”,

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“why?” and “what kind of stuff do we
use?”. And I’m gonna spend some time

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on explaining this last part
especially. What is it that we do

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and how does this work? So, what
we do is we give a very high energy

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to small particles which
we call accelerating.

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But from a certain level of energy
this doesn’t really make sense,

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because we don’t actually make them go
faster. Once they reach the speed of light

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they can’t go any faster. We just
turn up the energy and the speed

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doesn’t really change. This is technically
useful but it also gives rise

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to doubts about the term accelerating,
but anyway, we just call it ‘accelerate’.

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There’s 2 basic types of devices that
you see there, you have storage rings,

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which are the circular facilities that
most of you know. And then there is

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linear accelerators which are in
comparison very boring, so I’m

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not going to be talking about them
a lot. We make the particles collide

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which is the reason for giving them high
energies, we want them to smash head-on.

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And then this last part which is about
the most difficult thing is we just

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see what happens. Which is not
at all as easy as it might sound.

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So why are we doing this? You all
know this formula but I’m going to try

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and put it in terms which are
a little bit closer to our hearts,

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as we are here at Congress.
I might postulate that

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parts, like electrical parts, building
parts, are actually the same as a device.

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Now this is not quite wrong but it
doesn’t feel exactly right, either.

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I mean, if you have some parts and then
build a device from it, it’s not the same.

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It’s made from the same thing but you do
require a certain amount of conversion.

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You have a building process, you have
specific rules how you can assemble

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the parts to make a device and
if you do it wrong it will not work.

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And this is actually pretty similar to the
notion of energy being equivalent to mass,

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because energy can be converted into mass
but it’s not at all easy and it follows

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a lot of very strict rules. But
we can use this principle

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when we analyze how particle
reactions are used to take a look at

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what mass and what energy forms
there are. Now suppose we are

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thinking about a device
which is very, very rare,

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such as a toaster that runs Net-BSD.
*laughter*

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Now as you can see from the photo
and the fact that you see a photo,

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I’m not making this shit up. There
is a toaster that runs Net-BSD but

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that’s beside the point. Now if we
are particle physicists and we want

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to research this question, we know
that parts are the same as a device,

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so if we just get enough parts and
do the right kind of things to them,

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there might just turn out, out of
nowhere a toaster that runs Net BSD.

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So let’s give it a try. We produce
collisions with technical parts

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and if we do enough of it, and if we
do it right, then there is going to be

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this result. Now from these pictures
you can see, that doesn’t seem

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to make a lot of sense. You will not
get a toaster from colliding vehicles.

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*laughter*
But as particle physics go,

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this is the best we can do. We
just smash stuff into each other

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and we hope that some other stuff
comes out which is more interesting.

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And that’s what we do. So to
put it in the technical terms,

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we use storage rings which are this
one circular kind of accelerator

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to produce collisions. Lots
of them with high energy.

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And then we put some enormous
experimental devices there

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and we use them to analyze what
happens. Now first let’s talk about

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these storage rings. This schematic
view is what a storage ring is

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mostly made of, and you can see right
away, that it’s not actually a circle.

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And this is true for any storage ring.
If you look at them closely they are

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not a perfect circle, you always
have acceleration parts which are

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not actually curved. So we
have the 2 basic elements

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of a curved part which is just “the
curve” and then you have a straight part

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which is there for acceleration. Now you
have this separation, it would be nicer

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to have a ring but it’s much more easy
this way. You have the acceleration

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where it is straight and because it is
straight you don’t need to worry about

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making the particles go on a curved
path. So you can just leave out

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the magnetic fields. We
need magnetic fields

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to keep them on a curve, but we need
electrical fields to accelerate them.

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Now we could try and assemble these
into one kind of device. A device

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that uses an electric field to accelerate
the particles and at the same time

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uses a magnetic field to keep them on
a curved path. Now this is the first thing

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that was tried. These kinds of
accelerators where called cyclotrons,

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but they were very inefficient, you
couldn’t go to high energies, it was

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very difficult. So the evolution went to

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this way where you just
physically separate the 2 tasks.

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You have a straight part for acceleration,
you have a curved part for the curve

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and then that’s much more easy.
Okay, so let’s take a look at the

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acceleration part of things. You
may know computer games

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where you go racing about and then
you have some kind of arrows

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on the ground and if you go over them in
the right direction they make you faster.

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This is a kind of booster if you will.

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If you happen to go around the wrong
way and you go onto these arrows,

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they will slow you down, which makes sense
because you’re going the wrong way,

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you shouldn’t be trying that. And this is

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the same effect we can think of when we
think about what an electrical field does

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to a charged particle. If a charged
particle moves through an electrical field

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in the ‘right’ direction so to speak
it will speed the particle up,

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taking energy from the field and to the
particle making it go faster. But if you

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go the wrong way, then this particle
will slow down and it will

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give off energy. If we where to try and…

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let’s say we have a level editor,
right? And we can edit this level

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where this little vehicle is going and
we want to make it go really fast.

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So what do we do? We just take this
acceleration path, we just take

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these arrows and we put them in a long
line. Let’s put 4, 5, 10 of them

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in a row, so if we go over them
we’ll be really fast at the end.

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Now suppose the level editor
does not allow this. It’s just

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by the rules of the game it’s not possible
to put a bunch of arrows in a row.

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Which sucks, because then we can’t
really make them go really fast.

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But then we just ask an engineer
who’s got this shit together.

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And what is he going to suggest?
You know what he’s going to suggest.

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Can I hear it? Come on, “inverse the
polarity”, that’s what he always does!

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*laughter and applause*

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So we inverse the polarity. And we are
going to make our track look like this.

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So we have an arrow which gives us a boost
in the right direction and then there’s

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an arrow in the wrong direction.
If we go over the track in this way,

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we’ll speed up and slow down and speed
up and slow down. And in the end

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we won’t win anything. But here is where
Geordi comes into play, because

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we’ll be switching polarities at just the
right moment and if we switch polarities

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at the precise moment that we are
in between two of these fields,

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then the next one will be an accelerating
field. And it goes on and on like this,

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we always switch the direction
of the arrows at the right moment

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when we are in between the two. And
from the point of view of the vehicle

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it will look like there is an accelerating
field followed by an accelerating field,

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followed by an accelerating field.
Which is the same as we tried to build

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but which the game, or in the case
of real accelerators the universe

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just wouldn’t allow. So we’re tricking
the universe by using Geordi’s tip

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and inversing the polarity at just the
right moments. And this is what is done

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in particle accelerators and this is
called Radio Frequency Acceleration.

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Now this kind of device that you see
there is the device that is used

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for this actual process in actual
accelerators. It’s about as big

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as a human child, but it
weighs a bit more, it weighs

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several hundred kilograms.
And in contrast to a child

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it’s made of a metal called Niobium.
Now Niobium is a rare metal,

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but it’s not super rare, and it fulfills

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3 basic requirements that
we have for these devices.

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It’s ductile, which means you can
easily shape it, because you see

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that this shape is really weird, you got
these kind of cone things going on,

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and they must be very precise. If these
cones on the inside of the cavity

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are off by just micrometers the whole
thing won’t work. So you need a metal

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which can be formed very well.

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Then you must be able to make it
superconductive, to cool it down

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to a temperature where it will
lose its electrical resistance.

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The electrical resistance will go down
to almost zero, some nano-Ohms

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is what’s left. So that’s the second
requirement for this metal,

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and the third one is: it shouldn’t
be ‘super’ expensive. I guess

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you could use platinum or something but
then you couldn’t pay for the accelerator

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and as we are going to see, the
accelerator is expensive enough as it is.

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So Niobium is what is used
for this kind of device and

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as I said, we cool it down to about
4 Kelvins, which is -269°C

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or 4°C above absolute Zero.
And at this temperature,

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the electrical resistance of the metal
is almost zero which we need

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for the high frequency
fields that we put in.

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What we used to cool these things is
liquid helium, so when they’re in use

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inside the accelerator they’re not
naked, exposed like you see here,

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they are enclosed by huge tanks
which are super tight and must

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hold on to large pressures and
be super temperature efficient,

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very well insulating
because these must keep

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the liquid helium inside. But on
the outside there is the tunnel

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of the accelerator and that’s where people
walk around. Not while the accelerator is

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running, but people walk around to do
maintenance and stuff. So you must have

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a temperature differential between room
temperature next to the accelerator

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and 4 Kelvin inside the tank
where this cavity is sitting.

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So you have a temperature difference
of 300 degrees, which this tank

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around the cavity must keep. So that’s
a very hard job, actually cooling

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is one of the more difficult things

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from an engineering point of view.
The thing which feeds the fields

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– the actual changing electrical
fields are polarity switched –

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into these cavities are called klystrons.
There’s a picture of a klystron,

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it’s the longish device sitting on the
bottom. And they’re usually about

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as big as a refrigerator or two.
And these klystrons produce

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radio waves not very much unlike that

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which you hear in your car when you just
turn on the radio. It’s not modulated

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in the same way, so there’s no
sound information encoded,

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but it’s extremely strong.
You can see on the bottom

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that one of these klystrons as it is in
use at the LHC has a transmitting power

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of 300 Kilowatts. Now if you think of the
transmitting power of the Fernsehturm

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like the Hertz-Turm which is right next
- no, that way -

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which is right next to the conference
center, or even the Fernsehturm in Berlin.

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It has about half the transmitting
power of one of these klystrons.

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Now for the LHC accelerator
16 of them are used.

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So that’s a lot of transmitting power.
And because the power is so high

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we don’t actually use cables.
Usually you transfer your…

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when you have some oscillator and
you’re checking out some signals,

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you just put cables between
your source and your device.

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This is not what’s used here, because
cables get way too complicated

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when you have these high energies.

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So what is used, is waveguides and that
is what you can see on the top there

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in this picture. It looks like an
air duct, it looks like there’s some

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sort of air conditioning system and the
air moves through. That’s not what it is.

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It is a waveguide which is designed
to have the radio waves inside

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radiate in a certain direction.
Think of a series of mirrors,

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long rectangular mirrors and you put
them all with the mirroring area inside.

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So you have a tube which is mirroring
inside. And then at one side

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you shine in a bright light. Now the
light can’t escape anywhere and it

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always hits the mirrors so it
goes on in a straight path.

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You’ve built yourself a waveguide
for light. Now this here,

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this clunky looking metal
part is a waveguide

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but for high frequency, high energy radio
waves which are fed into the cavities.

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And that’s how acceleration happens.
Now let’s talk about the curves.

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This is where it gets less
fidgety and more… boom!

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So these devices you see here, there’s
2 devices sitting next to each other,

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identical devices. These
are the cryo-dipoles.

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Again, they have the word “cryo” in
them because they are also cooled

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by liquid helium down to
a temperature of about -270°C.

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They’re 40 meters long, they weigh
35 tons and each of these babies

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costs about half a million Swiss Francs.

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And as you can see one line above that,
there’s 1200 of these curve dipoles

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in the LHC. So there you have
a cost of 1.5 to 2 billion dollars

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00:13:54,719 --> 00:13:57,850
in the curve magnets alone.
We’re not talking acceleration,

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we’re not talking about power use, we are
not talking about the helium that you need

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for cooling or the power that you need for
cooling. It’s just building these things,

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just building the curve, 27 kilometers.

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And that’s what you have there as a
cost. Now what they do is, they make

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00:14:12,250 --> 00:14:15,420
a huge magnetic field, because in
a magnetic field a charged particle

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will go on a curve. That’s
what we want, right? But

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to make these particles with a very high
energy and keep them on a tight curve…

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now in particle physics’ terms
let’s say that 27 kilometers

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00:14:27,009 --> 00:14:30,920
to go around one way is a tight curve.

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We need a current of 12,000 amps.
Which is a large current

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that goes through these dipoles.
Which is the reason why we have them

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00:14:38,579 --> 00:14:44,850
superconductingly cooled, because
otherwise you put 12,000 amps

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through a piece of metal and it just melts
away. You don’t get a magnetic field,

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00:14:48,460 --> 00:14:52,820
maybe for a microsecond or 2.
But you want to sustain a stable field

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of 8.5 Tesla to make these
protons go around on a curve.

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So, yeah, that’s a big thing.
There’s also niobium in there,

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not the big clunky parts like the cavity
we saw, but thin niobium wires,

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actually half niobium, half titanium
most of the time. But since

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there are so many magnets and it’s
so long a curve, there is 600 tons

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of atomic niobium in this
entire accelerator thing.

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And this was a fourth of the
world production of niobium

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which comes mostly from Brazil by the way.
This was a fourth of the world production

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of niobium for 5 years.
So that’s where it all went.

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It just went into the accelerator.
And now if we have this running,

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we have it up, we have it cooled, we have
a large current going, we got our nice

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00:15:39,259 --> 00:15:43,109
big magnetic fields. And
there is energy stored.

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I mean we put in a lot of power and the
magnetic fields are up and they’re stable

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00:15:46,910 --> 00:15:50,920
and that means that there’s magnetic
energy stored in this. And the amount

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of energy that is stored in the curve
magnets alone of the LHC when it’s running

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is 11 gigajoules. Sounds like a lot,

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let’s compare it to something: If we
have an absurdly long freight train

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00:16:03,770 --> 00:16:07,699
with let’s say 15,000 tons. I hear that
normal freight trains in Germany

243
00:16:07,699 --> 00:16:11,811
or England have about 5000 tons.
So let’s take a big freight train

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and multiply it by 3. If this
freight train goes at 150 km/h,

245
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then the kinetic energy, the
movement energy of this train

246
00:16:21,899 --> 00:16:26,839
is equivalent to the magnetic
energy that is stored in the LHC.

247
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And that is why we don’t want
any problem with the cooling.

248
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*laughter*

249
00:16:33,740 --> 00:16:39,740
Because if we get a problem with
the cooling, bad things happen.

250
00:16:39,740 --> 00:16:44,469
This is a photograph of what at CERN
at the LHC they just call “the incident”.

251
00:16:44,469 --> 00:16:47,089
*laughter*

252
00:16:47,089 --> 00:16:50,059
Which was a tiny mishap that
happened just a few weeks

253
00:16:50,059 --> 00:16:54,060
after the LHC was taken into
operation for the first time in 2008.

254
00:16:54,060 --> 00:16:57,230
And it shut the machine
down for about 8 months.

255
00:16:57,230 --> 00:17:00,390
So that was a bad thing. It’s
a funny story when they where

256
00:17:00,390 --> 00:17:03,290
constructing these magnets; now
what you see here is the connection

257
00:17:03,290 --> 00:17:07,850
between 2 of these magnets. I told you
that each of them weighs 35 tons.

258
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So here you have a connection between
2 parts that are 35 tons in weight each.

259
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And they’re shifted by almost half
a meter. So it takes a bit of boom.

260
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So what happened was: the cooling broke
down and the helium escaped and

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00:17:21,630 --> 00:17:25,569
the sheer force of the helium expanding,
because if you have liquid helium

262
00:17:25,569 --> 00:17:29,810
and it instantly evaporates into gaseous
helium then the volume multiplies

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00:17:29,810 --> 00:17:33,650
by a very large amount.
And what they had was…

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what I hear is that the tunnel of the
LHC, which has a diameter of about

265
00:17:36,720 --> 00:17:41,010
let’s say 6 or 7 meters was
filled with nothing but helium

266
00:17:41,010 --> 00:17:44,510
which pushed away the air
for about 100 meters

267
00:17:44,510 --> 00:17:48,140
around this incident. So the helium
evaporated, it pushed everything away,

268
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it made everything really cold, some
cables broke and some metal broke.

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And the funny thing now is, the
engineers that built the LHC,

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00:17:57,010 --> 00:18:00,210
before they did that, visited
Hamburg. Because here there is

271
00:18:00,210 --> 00:18:03,511
a particle accelerator which is
not quite as large. The LHC

272
00:18:03,511 --> 00:18:07,770
has 27 kilometers; here in Hamburg we
have a particle accelerator called HERA

273
00:18:07,770 --> 00:18:12,490
which had 6.5 kilometers. So it’s
the same ballpark, it’s not as big.

274
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And in HERA they had a safety system
against these kinds of cryo failures,

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they’re called quenches.
They had a protection system,

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which protects this exact part.
Now we’re talking about “Yeah,

277
00:18:23,480 --> 00:18:26,710
how should we build this? Should
we have a quench-protection

278
00:18:26,710 --> 00:18:31,030
at the connection between the dipoles?”
And the HERA people in Hamburg said:

279
00:18:31,030 --> 00:18:34,690
“Well we have it, it’s a good thing,
you shouldn’t leave it out,

280
00:18:34,690 --> 00:18:38,630
if you build the LHC.” Well,
they left it out. *laughter*

281
00:18:38,630 --> 00:18:43,470
They ran out of time, they ran out of
money, the LHC project was under pressure.

282
00:18:43,470 --> 00:18:45,950
Because they had promised to build
a big machine by that time and

283
00:18:45,950 --> 00:18:49,450
they weren’t really finished, so they
cut some edges. Well this was

284
00:18:49,450 --> 00:18:53,930
the edge they cut and it cost them
8 months of operation. Which says

285
00:18:53,930 --> 00:18:59,360
that they really should have listened to
the people of Hamburg. Okay, so,

286
00:18:59,360 --> 00:19:03,940
in summary of the operations of
a storage ring we can just say this:

287
00:19:03,940 --> 00:19:07,040
They get perfectly timed kicks
with our polarity switching

288
00:19:07,040 --> 00:19:11,700
at just the right moment by radio waves
generated in these large klystrons

289
00:19:11,700 --> 00:19:16,110
from the funny looking metal
tubes that we called cavities.

290
00:19:16,110 --> 00:19:18,461
And some big-ass superconducting
magnets keep them on a curve

291
00:19:18,461 --> 00:19:22,780
when they are not being accelerated.
Now the trick is, one of these kicks

292
00:19:22,780 --> 00:19:26,430
like moving through the cavity once, may
not give you all the energy you want,

293
00:19:26,430 --> 00:19:30,160
in fact it doesn’t. But if you
make them go round in the ring,

294
00:19:30,160 --> 00:19:34,150
they come by every couple of
nanoseconds. So you just have them

295
00:19:34,150 --> 00:19:37,660
run through your acceleration all the
time. Which is the big difference

296
00:19:37,660 --> 00:19:40,620
between the storage ring and a linear
accelerator. A linear accelerator

297
00:19:40,620 --> 00:19:44,400
is basically a one shot operation but
here, you just give them an energy kick

298
00:19:44,400 --> 00:19:48,880
every time they come around, which
is often, we’re going to see that.

299
00:19:48,880 --> 00:19:52,880
So that’s the summary of what
the storage rings do. Now,

300
00:19:52,880 --> 00:19:56,570
the machine layout, if you
look at a research center

301
00:19:56,570 --> 00:20:01,160
which has a bunch of accelerators,
it almost always goes like this:

302
00:20:01,160 --> 00:20:05,030
You have some old, small storage
rings and then they built

303
00:20:05,030 --> 00:20:08,620
newer ones which were
bigger. So this is just

304
00:20:08,620 --> 00:20:12,420
a historical development, first
you build small machines, then

305
00:20:12,420 --> 00:20:14,920
techniques get better, engineering gets
better, you build bigger machines. But

306
00:20:14,920 --> 00:20:18,640
you can actually use that, it’s very
useful because the older machines,

307
00:20:18,640 --> 00:20:22,640
you can use as pre-accelerators.
For a variety of reasons it’s useful

308
00:20:22,640 --> 00:20:26,370
to not put in your particles with
an energy of zero and then

309
00:20:26,370 --> 00:20:30,180
have them accelerated up to the energy you
want. You want to pre-accelerate them,

310
00:20:30,180 --> 00:20:33,460
make them a little faster at a time.
That’s what you do, you just

311
00:20:33,460 --> 00:20:37,840
take the old accelerators. And if
we look at the accelerator layout

312
00:20:37,840 --> 00:20:42,200
of some real world research centers,
you can actually see this. On the left

313
00:20:42,200 --> 00:20:47,020
you have CERN in Geneva and on the
right you have DESY here in Hamburg.

314
00:20:47,020 --> 00:20:51,140
And you can see that there are smaller
accelerators, which are the older ones,

315
00:20:51,140 --> 00:20:54,140
and you have bigger accelerators
which are connected to them.

316
00:20:54,140 --> 00:20:59,410
And that’s this layout of the machines.
Okay, now let’s talk about collisions.

317
00:20:59,410 --> 00:21:03,411
This is a nice picture of a collision.
It’s not actually a proton collision

318
00:21:03,411 --> 00:21:08,270
but a heavy-ion collision, which
they do part of the time in the LHC.

319
00:21:08,270 --> 00:21:11,520
They are extremely hard to produce, we’re
going to see that, but still we make

320
00:21:11,520 --> 00:21:15,690
an awful lot of them.
So let’s see, first of all

321
00:21:15,690 --> 00:21:19,330
let’s talk about what the beam looks like,
because we’re going to be colliding beams.

322
00:21:19,330 --> 00:21:23,220
So what are these beams? Is it
a continuous stream of particles?

323
00:21:23,220 --> 00:21:27,780
Well it’s not. Because the acceleration
that we use, these radio frequency,

324
00:21:27,780 --> 00:21:31,960
polarity shifting mechanisms, they
make the particles into bunches.

325
00:21:31,960 --> 00:21:35,730
So you don’t have a continuous stream,
you have separate bunches.

326
00:21:35,730 --> 00:21:38,610
But how large are these bunches?
Is there one particle per bunch?

327
00:21:38,610 --> 00:21:41,150
You’ve got a particle, you wait
a while, there’s another particle?

328
00:21:41,150 --> 00:21:44,650
Well, it’s not like that.
Because if it were like that,

329
00:21:44,650 --> 00:21:49,300
if we had single particles coming after
one another, it would be impossible

330
00:21:49,300 --> 00:21:52,750
to hit them. You have to aim
the beams very precisely.

331
00:21:52,750 --> 00:21:56,620
I mean, think about it. One comes
around 27 kilometers around the ring.

332
00:21:56,620 --> 00:21:59,950
The other comes around 27
kilometers going the other way.

333
00:21:59,950 --> 00:22:03,480
And now you want them to hit. You have
to align your magnets very precisely.

334
00:22:03,480 --> 00:22:07,060
You can think of it like this:
You have a guy in Munich

335
00:22:07,060 --> 00:22:10,790
and you have a guy in Hamburg and
they each have a rifle. And the bullets

336
00:22:10,790 --> 00:22:14,550
of the rifle are let’s say one centimeter
in size. So the guy in Hamburg

337
00:22:14,550 --> 00:22:17,390
shoots in the air and the guy in Munich
shoots in the air, and they are supposed

338
00:22:17,390 --> 00:22:22,490
to make the bullets hit in the
middle, over, let’s say Frankfurt.

339
00:22:22,490 --> 00:22:25,720
Which they’re not going to manage.
And which is actually way too simple.

340
00:22:25,720 --> 00:22:32,200
Because if the bullet is really
one centimeter in size,

341
00:22:32,200 --> 00:22:37,360
then the equivalent distance that the two
shooters should be away from each other,

342
00:22:37,360 --> 00:22:40,650
if we want to make it the same
difficulty as these protons,

343
00:22:40,650 --> 00:22:45,050
would not be between Hamburg and Munich.
It would be from here to fucking Mars.

344
00:22:45,050 --> 00:22:49,470
*laughter and applause*
I calculated that shit.

345
00:22:49,470 --> 00:22:54,200
*applause*

346
00:22:54,200 --> 00:22:57,650
We don’t even have rifles on Mars
anyway. *laughter*

347
00:22:57,650 --> 00:23:01,690
So what we got is, we got large
bunches, very large bunches.

348
00:23:01,690 --> 00:23:04,890
And in fact there’s 10^11
protons per bunch, which is

349
00:23:04,890 --> 00:23:11,030
100 Billion. This is where I called Sagan
“ you going Millions of Millions“

350
00:23:11,030 --> 00:23:15,120
Okay, so you got 100 Billion
protons in one bunch.

351
00:23:15,120 --> 00:23:19,270
And the bunches go by one after the other.
Now, if you stand next to the LHC

352
00:23:19,270 --> 00:23:23,160
and you were capable of observing these
bunches, you would see one fly by

353
00:23:23,160 --> 00:23:28,170
every 25 nanoseconds. So you go “there’s
a bunch, now it’s 25 nanoseconds,

354
00:23:28,170 --> 00:23:32,770
there is the next one”. And there’s about
7.5 meters between the bunches.

355
00:23:32,770 --> 00:23:36,760
Now, 7.5 meters corresponds to
25 nanoseconds, you see that

356
00:23:36,760 --> 00:23:42,940
the speed is very big and indeed
it’s almost the speed of light.

357
00:23:42,940 --> 00:23:45,590
Which is just, we accelerate them
and at some point they just go

358
00:23:45,590 --> 00:23:48,640
with the speed of light and we just push
up the energy, we don’t make them

359
00:23:48,640 --> 00:23:53,750
go any faster actually. And if you
were to identify the bunches,

360
00:23:53,750 --> 00:23:58,940
which actually you can, you would
see that there are 2800 bunches

361
00:23:58,940 --> 00:24:02,890
going by; and then when
you have number 2809,

362
00:24:02,890 --> 00:24:06,620
that’s actually the first one that you
counted which has come round again.

363
00:24:06,620 --> 00:24:10,160
Per direction! So in total
we have over 5000 bunches

364
00:24:10,160 --> 00:24:15,470
of 100 Billion protons each. So
that’s the beam we are dealing with.

365
00:24:15,470 --> 00:24:19,610
Oh, and a funny thing: you get charged
particles moving, it’s actually a current,

366
00:24:19,610 --> 00:24:22,680
right? In a wire you have
a current running through it,

367
00:24:22,680 --> 00:24:27,150
there’s electrons moving or holes moving
and you get a current. If you were

368
00:24:27,150 --> 00:24:31,800
to measure the current of the
LHC, it would be 0.6 milliamps,

369
00:24:31,800 --> 00:24:34,330
which is a small current, but
we’re doing collisions anyway

370
00:24:34,330 --> 00:24:38,270
and not power transmission,
so that’s fine. *laughter*

371
00:24:38,270 --> 00:24:42,780
This is a diagram of what the actual
interaction point geometry looks like.

372
00:24:42,780 --> 00:24:46,340
You get the beams from different
directions, think of it like the top one

373
00:24:46,340 --> 00:24:50,010
coming from the right, the bottom
one coming from the left;

374
00:24:50,010 --> 00:24:53,480
and they are kicked into intersecting
paths by magnets. You have

375
00:24:53,480 --> 00:24:57,590
very complicated, very precise
magnetic fields aligning them,

376
00:24:57,590 --> 00:25:01,850
so that they intersect. And it’s
actually a bit of a trying-out game.

377
00:25:01,850 --> 00:25:05,970
I’ve heard this from
accelerator operators.

378
00:25:05,970 --> 00:25:09,410
You shift the position of the beams
relative to each other by small amounts

379
00:25:09,410 --> 00:25:12,880
and you just see where the collisions
happen. You go like: “Ah yeah, okay,

380
00:25:12,880 --> 00:25:17,220
there’s lots of collisions, ah, now
they’re gone, I’m going back.”

381
00:25:17,220 --> 00:25:20,440
And you do it like that. You can save the
settings and load them and calculate them

382
00:25:20,440 --> 00:25:24,300
but it’s actually easier
to just try it out.

383
00:25:24,300 --> 00:25:28,350
If we think of how much stuff we’ve
got going on: you got a packet,

384
00:25:28,350 --> 00:25:31,240
a bunch of 100 Billion
protons coming one way,

385
00:25:31,240 --> 00:25:35,100
you got another packet of 100 Billion
protons coming the other way.

386
00:25:35,100 --> 00:25:39,640
Now the interaction point area is as small
as the cross section of a human hair.

387
00:25:39,640 --> 00:25:43,270
You can see that, it’s one hundredth
of a square millimeter.

388
00:25:43,270 --> 00:25:46,110
Now how many collisions do
you think we have? We’ve got…

389
00:25:46,110 --> 00:25:48,120
Audience: Three!
*Michael laughs*

390
00:25:48,120 --> 00:25:51,850
Michael: …it’s actually not that bad.
We got about 20 in the LHC.

391
00:25:51,850 --> 00:25:56,450
And the funny thing is, people
consider this a bit too much.

392
00:25:56,450 --> 00:25:59,600
The effect is called pile-up. And the
bad thing about pile-up is you’ve got

393
00:25:59,600 --> 00:26:03,590
beams intersecting, you’ve got bunches
‘crossing’ – that’s what we call it.

394
00:26:03,590 --> 00:26:06,720
And there’s not just one collision which
you can analyze, there is a bunch of them,

395
00:26:06,720 --> 00:26:10,110
around 20. And that makes that
more difficult for the experiments,

396
00:26:10,110 --> 00:26:15,720
we’re going to see why. Well, and if we
have 20 collisions every bunch crossing

397
00:26:15,720 --> 00:26:19,580
and the bunches come by every
25 nanoseconds, that gives us a total

398
00:26:19,580 --> 00:26:24,690
of 600 Million collisions per
second. Per interaction point.

399
00:26:24,690 --> 00:26:27,770
Which we don’t have just one of. We
have 4 experiments, each experiment

400
00:26:27,770 --> 00:26:31,371
has its own interaction point. So
in total, we have about 2 Billion

401
00:26:31,371 --> 00:26:36,660
proton-proton collisions happening
every second when the LHC is running.

402
00:26:36,660 --> 00:26:39,580
Now let’s look at experiments.
*laughs*

403
00:26:39,580 --> 00:26:44,070
Yeah, this is a photograph of one part of
the ATLAS experiment being transported.

404
00:26:44,070 --> 00:26:47,690
And as for the scale of this thing, well,
in the physics community, we call this

405
00:26:47,690 --> 00:26:53,700
a huge device.
*laughter*

406
00:26:53,700 --> 00:26:57,150
I have a diagram of the experiment
where this is built in and

407
00:26:57,150 --> 00:27:00,510
you’re going to recognize the part
which is the one I’ve circled there.

408
00:27:00,510 --> 00:27:04,290
So the real thing is even bigger.
And down at the very bottom,

409
00:27:04,290 --> 00:27:08,190
just to the center of the
experiment, there’s people.

410
00:27:08,190 --> 00:27:12,860
Which if I check it like this,
they’re about 15 pixels high.

411
00:27:12,860 --> 00:27:16,490
So that’s the scale of the experiment.

412
00:27:16,490 --> 00:27:20,250
The experiment has the interaction point
at the center, so you got a beam line

413
00:27:20,250 --> 00:27:23,570
coming in from the left, you got the other
beam line coming in from the right.

414
00:27:23,570 --> 00:27:27,280
And in the very core of the experiment
is where the interactions,

415
00:27:27,280 --> 00:27:31,140
where the collisions happen. And then
you got the experiment in layers,

416
00:27:31,140 --> 00:27:35,240
like an onion, going around
them in a symmetrical way.

417
00:27:35,240 --> 00:27:38,370
Inside you have a huge magnetic
field which is almost as big

418
00:27:38,370 --> 00:27:42,470
as the curve magnets we were talking about
when I was describing the storage ring.

419
00:27:42,470 --> 00:27:46,130
This is about 4 Teslas,
so it’s also a very big field.

420
00:27:46,130 --> 00:27:50,160
But now we got a 4 Tesla field
not just over the beam pipe

421
00:27:50,160 --> 00:27:54,340
which is about 5 centimeters in diameter,
but through the entire experiment;

422
00:27:54,340 --> 00:27:58,080
and this thing is like 20-25 meters.
So you’ve got a 4 Tesla field

423
00:27:58,080 --> 00:28:01,910
which should span more than 20 meters.

424
00:28:01,910 --> 00:28:07,410
And, just for shits and giggles,
it’s got 3000 kilometers of cables.

425
00:28:07,410 --> 00:28:11,060
Which is a lot; and if you just
pull some random plug

426
00:28:11,060 --> 00:28:16,270
and don’t tell anyone which one it
was you’re making a lot of enemies.

427
00:28:16,270 --> 00:28:19,980
So the innermost thing is what we
call the inner tracking. It is located

428
00:28:19,980 --> 00:28:23,210
just centimeters off the beam line,
it’s supposed to be very very close to

429
00:28:23,210 --> 00:28:26,290
where the actual interactions happen.

430
00:28:26,290 --> 00:28:29,180
And this thing is made to leave the
particles undisturbed, they should just

431
00:28:29,180 --> 00:28:32,590
fly trough this inner tracking detector.
And the detector will tell us

432
00:28:32,590 --> 00:28:35,910
where they were, but not actually
stop them or deflect them.

433
00:28:35,910 --> 00:28:40,050
This gives us precise location data,
as to how many particles there were,

434
00:28:40,050 --> 00:28:44,030
what way they were flying,
and, from the curve,

435
00:28:44,030 --> 00:28:47,570
what momentum they have. Outside
of that we’ve got calorimeters.

436
00:28:47,570 --> 00:28:51,300
Now these are supposed to be stopping
the particles. A particle goes through

437
00:28:51,300 --> 00:28:55,360
the inner tracking without being disturbed
but in the calorimeter it should stop.

438
00:28:55,360 --> 00:28:58,970
And it should deposit all its energy there
and which is why we have to put around it

439
00:28:58,970 --> 00:29:03,100
the inner tracking. You see, if we put the
calorimeter inside, it stops the particle,

440
00:29:03,100 --> 00:29:07,770
outside of that nothing happens. So we
have the calorimeters outside of that.

441
00:29:07,770 --> 00:29:12,070
And then we got these funny wing things
going on. That’s the muon detectors.

442
00:29:12,070 --> 00:29:15,490
They are there for one
special sort of particle.

443
00:29:15,490 --> 00:29:19,610
Out of the… 50, let’s say 60
– depends on the way you count –

444
00:29:19,610 --> 00:29:22,860
elementary particles that we
have. These large parts are

445
00:29:22,860 --> 00:29:26,250
just for the muons. Because the
muons have the property,

446
00:29:26,250 --> 00:29:29,990
the tendency to go through all sorts of
matter undisturbed. So you just need to

447
00:29:29,990 --> 00:29:33,270
throw a huge amount of matter
in the way of these muons, like:

448
00:29:33,270 --> 00:29:36,750
“let’s have a brick wall and then
another one”. And then you

449
00:29:36,750 --> 00:29:42,030
may be able to stop the muons,
or just measure them.

450
00:29:42,030 --> 00:29:45,060
This is to give you an idea of the
complexity of the instrument

451
00:29:45,060 --> 00:29:49,170
on the inside. This is the inner tracking
detector, it’s called a pixel detector;

452
00:29:49,170 --> 00:29:52,730
and you see guys walking around in
protective suits. That is not for fun

453
00:29:52,730 --> 00:29:56,920
or just for the photo, this is a very,
very precise instrument. But it’s sitting

454
00:29:56,920 --> 00:30:00,100
inside this huge experiment which – again,

455
00:30:00,100 --> 00:30:03,910
I calculated that shit – is about
as large as a space shuttle

456
00:30:03,910 --> 00:30:07,420
and weighs as much as the
Eiffel Tower. And inside

457
00:30:07,420 --> 00:30:12,030
they’ve got electronics, almost a ton
of electronics which is so precise

458
00:30:12,030 --> 00:30:16,030
that it makes your smartphone
look like a rock. So there you go,

459
00:30:16,030 --> 00:30:19,970
it’s a very, very complicated sort of
experiment. Let’s talk about triggering,

460
00:30:19,970 --> 00:30:24,360
because as I said there’s 600 Million
events happening inside this.

461
00:30:24,360 --> 00:30:27,600
That’s 40 Million bunch crossings.
Now: how are we going to analyze this?

462
00:30:27,600 --> 00:30:31,720
Is there a guy writing everything
down? Obviously not.

463
00:30:31,720 --> 00:30:35,540
So this experiment with all the tracking
and the calorimeters and the muons

464
00:30:35,540 --> 00:30:39,800
and everything has about
100 Million electronic channels.

465
00:30:39,800 --> 00:30:43,410
And one channel could be the measurement
of a voltage, or a temperature

466
00:30:43,410 --> 00:30:47,330
or a magnetic field or whatever. So
we’ve got 100 Million different values,

467
00:30:47,330 --> 00:30:52,540
so to speak. And that makes
about 1.5 Megabytes per crossing,

468
00:30:52,540 --> 00:30:57,220
per every event readout. Which
gives us – multiplied by 40 Million –

469
00:30:57,220 --> 00:31:01,260
gives us about 60 terabytes
of raw data per second.

470
00:31:01,260 --> 00:31:05,610
That’s bad. I looked it up, I guess

471
00:31:05,610 --> 00:31:10,340
the best RAM you can do is about
1 terabyte per second or something.

472
00:31:10,340 --> 00:31:14,950
So we’re obviously not going to tackle
this by just putting in fast hardware,

473
00:31:14,950 --> 00:31:18,690
because it’s not going
to be fast enough. Plus,

474
00:31:18,690 --> 00:31:24,450
the reconstruction of an event is done
by about 5 Million lines of C++ code.

475
00:31:24,450 --> 00:31:29,570
Programmed by some 2000-3000
developers around the world.

476
00:31:29,570 --> 00:31:33,330
It simulates for one crossing
30 Million objects, which is

477
00:31:33,330 --> 00:31:36,840
the protons and other stuff flying around.

478
00:31:36,840 --> 00:31:44,410
And it is allocated to take 15 seconds
of one core’s computing time.

479
00:31:44,410 --> 00:31:47,770
To calculate it all, you would
need about 600 million cores.

480
00:31:47,770 --> 00:31:50,330
That’s not happening. I mean,
even if we took over the NSA

481
00:31:50,330 --> 00:31:54,132
*laughter*
and used all of their data-centers

482
00:31:54,132 --> 00:31:57,440
for LHC calculations, it still wouldn’t be
enough. So we have to do something

483
00:31:57,440 --> 00:32:02,570
about this huge mass of data. And
what we do is, we put in triggers.

484
00:32:02,570 --> 00:32:07,170
The trigger is supposed to reduce the
number of events that we look at.

485
00:32:07,170 --> 00:32:10,830
The first level trigger looks at
every collision that happens.

486
00:32:10,830 --> 00:32:13,840
And it’s got 25 nanoseconds
of time to decide:

487
00:32:13,840 --> 00:32:17,410
Is this an interesting collision?
Is it not an interesting collision?

488
00:32:17,410 --> 00:32:21,830
We tell it to eliminate
99.7% of all collisions.

489
00:32:21,830 --> 00:32:26,480
So only every 400th collision
is allowed for this trigger to go:

490
00:32:26,480 --> 00:32:30,280
“Oh, yeah, okay that looks interesting,
let’s give it to Level 2 trigger”.

491
00:32:30,280 --> 00:32:34,150
So then we end up with about 100,000
events per second. Which get us

492
00:32:34,150 --> 00:32:38,660
down to 150 Gigabytes per second. Now
we could handle this from the data flow,

493
00:32:38,660 --> 00:32:43,450
but still we can’t simulate it. So
we’ve got another level trigger.

494
00:32:43,450 --> 00:32:46,720
This is where the two
experiments at the LHC differ:

495
00:32:46,720 --> 00:32:50,030
the CMS experiment has just a
Level 2 trigger; does it all there.

496
00:32:50,030 --> 00:32:53,301
The ATLAS experiment goes the more
traditional way, it has a Level 2 trigger

497
00:32:53,301 --> 00:32:57,500
and a Level 3 trigger. In the end these
combined have about 10 microseconds

498
00:32:57,500 --> 00:33:01,450
of time, which is a bit more and it gives
them a chance to look at the events

499
00:33:01,450 --> 00:33:05,920
more closely. Not just, let’s say:
“Was it a collision of 2 protons

500
00:33:05,920 --> 00:33:09,300
or of 3 protons?”; “Were there
5 muons coming out of it

501
00:33:09,300 --> 00:33:12,810
or 3 electrons and 2 muons?” This is
the sort of thing they’re looking at.

502
00:33:12,810 --> 00:33:16,370
And certain combinations the triggers
will find interesting or not.

503
00:33:16,370 --> 00:33:20,120
Let’s say 5 muons, I don’t give a shit
about that. “3 muons and 2 electrons?

504
00:33:20,120 --> 00:33:23,480
Allright, I want to analyze it”. So
that’s what the trigger does.

505
00:33:23,480 --> 00:33:27,640
Now this Level 2 and 3 trigger,
again, have to kick out about

506
00:33:27,640 --> 00:33:31,070
99.9% of the events. They’re
supposed to leave us with

507
00:33:31,070 --> 00:33:36,360
about 150 events per second. Which
gives a data volume of a measly

508
00:33:36,360 --> 00:33:40,030
300 Megabytes per second and that’s
something we can handle. We push it

509
00:33:40,030 --> 00:33:45,780
to computers all around the world.
And then we get the simulations going.

510
00:33:45,780 --> 00:33:50,900
This is a display, this is
what you see in the media.

511
00:33:50,900 --> 00:33:55,360
If you take one of these events – just
one of the interesting events which

512
00:33:55,360 --> 00:34:00,740
actually reach the computers – because
those 40 million bunch crossings… well,

513
00:34:00,740 --> 00:34:04,150
most of them don’t reach the computers,
they get kicked out by the triggers.

514
00:34:04,150 --> 00:34:08,240
But out of the remaining 100 or 200
events per second, let’s say this is one.

515
00:34:08,240 --> 00:34:12,849
It’s an actual event and it’s been
calculated into a nice picture here.

516
00:34:12,849 --> 00:34:17,510
Now, normally they don’t do that, it’s
analyzed automatically by code

517
00:34:17,510 --> 00:34:21,089
and it’s analyzed by the physics data.
And they only make these pretty pictures

518
00:34:21,089 --> 00:34:25,339
if they want to show something to
the press. To the left you have

519
00:34:25,339 --> 00:34:29,330
what’s called a Feynman Diagraph.
That’s just a fancy physical way

520
00:34:29,330 --> 00:34:34,040
of saying what’s happening there. And
it involves the letter H on the left side,

521
00:34:34,040 --> 00:34:37,180
which means there’s a Higgs involved.
Which is why this event was particularly

522
00:34:37,180 --> 00:34:42,280
interesting to the people
analyzing the data at the LHC.

523
00:34:42,280 --> 00:34:47,230
And you see a bunch of tracks, you see
the yellow tracks all curled up inside,

524
00:34:47,230 --> 00:34:51,290
that’s a bunch of protons hitting
each other. The interesting thing is

525
00:34:51,290 --> 00:34:55,710
what happens for example above
there with the blue brick kind of things.

526
00:34:55,710 --> 00:35:00,050
There’s a red line going through
these bricks. This indicates a muon.

527
00:35:00,050 --> 00:35:05,480
A muon which was created in
this event there in the center.

528
00:35:05,480 --> 00:35:08,980
And it went out and the
bricks symbolize the way

529
00:35:08,980 --> 00:35:13,140
the reaction was seen by the experiment.

530
00:35:13,140 --> 00:35:16,880
There was actually just a bunch of bricks
lighting up. You got, I don’t know,

531
00:35:16,880 --> 00:35:21,320
500 bricks around it and brick 237
says: “Whoop, there was a signal”.

532
00:35:21,320 --> 00:35:24,300
And they go: “Allright, may have been
a muon moving through the detector”.

533
00:35:24,300 --> 00:35:28,700
When you put it all together you
get an event display like this. Okay,

534
00:35:28,700 --> 00:35:32,590
so we got to have computers analyzing
this. And with all the 4 experiments

535
00:35:32,590 --> 00:35:36,570
running at the LHC, which is not just
CMS and ATLAS I mentioned but also

536
00:35:36,570 --> 00:35:41,630
LHCb and ALICE, they produce about
25 Petabytes of data per year.

537
00:35:41,630 --> 00:35:46,230
And this cannot be stored at CERN alone.
It is transferred to data centers

538
00:35:46,230 --> 00:35:50,780
around the world by what is called
the LHC Optical Private Network.

539
00:35:50,780 --> 00:35:55,530
They’ve got a network of fibers going from
CERN to other data-centers in the world.

540
00:35:55,530 --> 00:36:00,430
And it consists of 11 dedicated
10-Gigabit-per-second lines

541
00:36:00,430 --> 00:36:04,410
going from CERN outwards. If we
combine this, it gives us a little over

542
00:36:04,410 --> 00:36:08,330
100 Gigabits of data
throughput, which is about

543
00:36:08,330 --> 00:36:11,880
the bandwidth that this congress has.

544
00:36:11,880 --> 00:36:14,560
Which is nice, but here it’s dedicated
to science data and not just porn

545
00:36:14,560 --> 00:36:20,250
and cat pictures.
*laughter and applause*

546
00:36:20,250 --> 00:36:23,930
*applause*

547
00:36:23,930 --> 00:36:27,580
From there it’s distributed outwards
from these 11 locations to about

548
00:36:27,580 --> 00:36:31,490
170 data centers in all the
world. And the nice thing is,

549
00:36:31,490 --> 00:36:35,090
this data, these 25 Petabytes
per year, is available

550
00:36:35,090 --> 00:36:38,310
to all the scientists working
with it. There’s about… well,

551
00:36:38,310 --> 00:36:41,440
everybody can look at it, but there’s
about 3000 people in the world

552
00:36:41,440 --> 00:36:45,270
knowing what it means. So all these
people have free access to the data,

553
00:36:45,270 --> 00:36:48,900
you and I would have free access to the
data, just thinking it’s cool to have

554
00:36:48,900 --> 00:36:53,260
a bit of LHC data on your harddrive maybe.
*laughter*

555
00:36:53,260 --> 00:36:57,850
All in all, we have 250,000
cores dedicated to this task,

556
00:36:57,850 --> 00:37:01,990
which is formidable. And about
100 Petabytes of storage

557
00:37:01,990 --> 00:37:05,730
which is actually funny, because
25 Petabytes of data are accumulated

558
00:37:05,730 --> 00:37:10,090
per year and the LHC has been
running for about 4 years.

559
00:37:10,090 --> 00:37:13,600
So you can see that they buy the
storage as the machine runs. Because

560
00:37:13,600 --> 00:37:17,540
100 Petabytes, okay, that’s what we have
so far. If we want to keep it running,

561
00:37:17,540 --> 00:37:21,730
we need to buy more disks. Right! Now,

562
00:37:21,730 --> 00:37:25,380
what does the philosoraptor
say about the triggers?

563
00:37:25,380 --> 00:37:29,110
If the triggers are supposed to eliminate
those events which are irrelevant,

564
00:37:29,110 --> 00:37:33,420
which is not interesting, well,
who tells them what’s irrelevant?

565
00:37:33,420 --> 00:37:37,230
Or to put it in the terms
of Conspiracy-Keanu:

566
00:37:37,230 --> 00:37:43,120
“What if the triggers throw away the
wrong 99.something % of events?”

567
00:37:43,120 --> 00:37:48,230
I mean, if I say: “If there’s an event
with 5 muons going to the left,

568
00:37:48,230 --> 00:37:52,500
kick it out!”. What if that’s actually
something that’s very, very interesting?

569
00:37:52,500 --> 00:37:56,010
How should we tell? We need to
think about this very precisely.

570
00:37:56,010 --> 00:37:59,320
And I’m going to tell you about
an example in history where

571
00:37:59,320 --> 00:38:02,800
this went terribly wrong, at least for
a few years. We’re talking about

572
00:38:02,800 --> 00:38:06,820
the discovery of the positron.
A positron is a piece of anti-matter;

573
00:38:06,820 --> 00:38:10,770
it is the anti-electron. It was
theorized in 1928, when

574
00:38:10,770 --> 00:38:15,440
theoretical physicist Dirac put up a bunch
of equations. And he said: “Right,

575
00:38:15,440 --> 00:38:20,030
there should be something which is like
an electron, but has a positive charge.

576
00:38:20,030 --> 00:38:22,470
Some kind of anti-matter.” Well,
that’s not what he said, but that’s

577
00:38:22,470 --> 00:38:26,740
what he thought. But it was
only identified in 1931.

578
00:38:26,740 --> 00:38:30,310
They had particle experiments back then,
they were seeing tracks of particles

579
00:38:30,310 --> 00:38:34,090
all the time. But they couldn’t
identify the positron for 3 years,

580
00:38:34,090 --> 00:38:37,210
even though it was there on paper.
So what happened? Well,

581
00:38:37,210 --> 00:38:41,230
you see the picture on the left. This
is the actual, let’s say baby picture

582
00:38:41,230 --> 00:38:44,460
of the positron. I’m going to
build up a scheme on the right

583
00:38:44,460 --> 00:38:48,440
to show you a bit more, to
give you a better overview of

584
00:38:48,440 --> 00:38:52,150
what we are actually talking about.
In the middle you’ve got a metal plate.

585
00:38:52,150 --> 00:38:55,200
And then there’s a track which is bending
to the left, which is indicated here

586
00:38:55,200 --> 00:39:01,890
by the blue line. Now if we analyze
this from a physical point of view,

587
00:39:01,890 --> 00:39:05,270
it tells us that the particle
comes from below,

588
00:39:05,270 --> 00:39:08,310
hits something in the metal plate
and then continues on to the top.

589
00:39:08,310 --> 00:39:12,900
So the direction of movement
is from the bottom to the top.

590
00:39:12,900 --> 00:39:17,310
The amount by which its curvature
reduces when it hits the metal plate

591
00:39:17,310 --> 00:39:21,780
tells us it has about the mass of
an electron. Okay, so far so good.

592
00:39:21,780 --> 00:39:26,020
But then it has a positive charge.
Because we know the…

593
00:39:26,020 --> 00:39:29,580
we know the orientation of the magnetic
field. And that tells us: “Well,

594
00:39:29,580 --> 00:39:33,280
if it bends to the left, it
must be a positive particle.”

595
00:39:33,280 --> 00:39:37,020
So we have a particle with the mass of
an electron, but with a positive charge.

596
00:39:37,020 --> 00:39:43,190
And people were like “Wat?”.
*laughter*

597
00:39:43,190 --> 00:39:46,160
So then someone ingenious came
up and thought of a solution:

598
00:39:46,160 --> 00:39:48,480
‘They developed the picture
the wrong way around!?’

599
00:39:48,480 --> 00:39:52,300
*laughter and applause*

600
00:39:52,300 --> 00:39:59,470
*applause*

601
00:39:59,470 --> 00:40:02,780
It’s what they thought. Well it’s wrong,
of course, there’s such a thing as

602
00:40:02,780 --> 00:40:08,500
a positron. And it’s like an electron,
but it’s positively charged. But…

603
00:40:08,500 --> 00:40:13,520
to put it in a kind of summary maybe:
you can only discover that

604
00:40:13,520 --> 00:40:17,180
which you can accept as a result.
This sounds like I’m Mahatma Gandhi

605
00:40:17,180 --> 00:40:23,200
or something but it’s just what we call
science. *laughter*

606
00:40:23,200 --> 00:40:27,740
Okay, so to recap: What have we
seen, what have we talked about?

607
00:40:27,740 --> 00:40:32,210
We saw from the basic principle,
that if we have energy in a place,

608
00:40:32,210 --> 00:40:36,190
then that can give rise to other forms of
matter, which I called ‘parts = a device’.

609
00:40:36,190 --> 00:40:39,360
You got your little parts, you do
some stuff, out comes a device.

610
00:40:39,360 --> 00:40:43,100
We have storage rings which give
a lot of energy to the particles

611
00:40:43,100 --> 00:40:46,700
and in which they move around in huge
bunches. Billions of billions of protons

612
00:40:46,700 --> 00:40:51,020
in a bunch and then colliding. Which
gives in the huge experiments

613
00:40:51,020 --> 00:40:55,390
that we set up an enormous amount of data
ranging in the Terabytes per second

614
00:40:55,390 --> 00:40:59,740
which we have to program triggers
to eliminate a lot of the events

615
00:40:59,740 --> 00:41:03,750
and give us a small amount of data which
we can actually work with. And then

616
00:41:03,750 --> 00:41:07,190
we have to pay attention to the
interpretation of data, so that

617
00:41:07,190 --> 00:41:11,500
we don’t get a fuck-up like with the
positron. Which is a very hard job.

618
00:41:11,500 --> 00:41:16,780
And I hope that I could give you
a little overview of how it’s fun.

619
00:41:16,780 --> 00:41:20,250
And it’s not just about building
a big machine and saying:

620
00:41:20,250 --> 00:41:24,180
“I’ve got the largest accelerator of
them all”. It’s a collaborative effort,

621
00:41:24,180 --> 00:41:28,600
it’s literally thousands of people working
together and it’s not just about

622
00:41:28,600 --> 00:41:32,390
two guys getting a Nobel Prize. You
see this picture on the top left, that’s

623
00:41:32,390 --> 00:41:36,900
about 1000 people at CERN watching
the ceremony of the Nobel Prize

624
00:41:36,900 --> 00:41:40,600
being awarded. Because everybody felt
there’s two people getting a medal

625
00:41:40,600 --> 00:41:45,230
in Sweden, but it’s actually an
accomplishment… it’s actually an award for

626
00:41:45,230 --> 00:41:49,190
everybody involved in this enormous thing.
And that’s what’s a lot of fun about it

627
00:41:49,190 --> 00:41:53,991
and I hope I could share some of this
fascination with you. Thank you a lot.

628
00:41:53,991 --> 00:42:19,000
*huge applause*

629
00:42:19,000 --> 00:42:22,410
Before we get to Q&A, I’m going to be
answering questions that you may have.

630
00:42:22,410 --> 00:42:25,560
My name is Michael, I’m @emtiu on
Twitter, I’ve got a DECT phone,

631
00:42:25,560 --> 00:42:29,550
I talk about science, that’s
what I do. I hope I do it well.

632
00:42:29,550 --> 00:42:32,210
And you can see the slides and
leave feedback for me please

633
00:42:32,210 --> 00:42:36,770
in the event tracking system. And
tomorrow, if you have the time

634
00:42:36,770 --> 00:42:39,720
you should go watch the “Desperately
seeking SUSY” talk which is going to be

635
00:42:39,720 --> 00:42:43,480
talking about the theoretical side of
particle physics. Okay, that’s it from me,

636
00:42:43,480 --> 00:42:46,540
now on to you.
Herald: Okay, if you have questions,

637
00:42:46,540 --> 00:42:50,240
please line up, there’s a mic there and
a mic there. And if you’re on the stream,

638
00:42:50,240 --> 00:42:53,770
you can also use IRC and
Twitter to ask questions. So

639
00:42:53,770 --> 00:42:55,820
I’m going to start here,
please go ahead.

640
00:42:55,820 --> 00:43:00,490
Question: Thanks a lot, it was a very
fascinating talk, and nice to listen to.

641
00:43:00,490 --> 00:43:04,030
My question is: Did HERA
ever suffer a quench event

642
00:43:04,030 --> 00:43:08,030
in which the quench protection
system saved the infrastructure?

643
00:43:08,030 --> 00:43:11,250
Michael: No, actually it didn’t. There
were tests where they provoked

644
00:43:11,250 --> 00:43:15,040
a sort of quench event in order to
see if the protection worked. But

645
00:43:15,040 --> 00:43:18,100
even if this test would have failed it
would not have been as catastrophic.

646
00:43:18,100 --> 00:43:22,020
But there were failures in the
operation of the HERA accelerator

647
00:43:22,020 --> 00:43:25,790
and there was one cryo failure. Which
is actually a funny story. Which is

648
00:43:25,790 --> 00:43:30,140
where one part of the
helium tubing failed

649
00:43:30,140 --> 00:43:33,680
and some helium escaped
from the tubing part

650
00:43:33,680 --> 00:43:36,790
and went into the tunnel. Now what
happened was that the air moisture,

651
00:43:36,790 --> 00:43:41,180
just the water in the
air froze at this point.

652
00:43:41,180 --> 00:43:45,450
And the Technical Director of the HERA
machine told us this: at one point

653
00:43:45,450 --> 00:43:49,020
he sat there with a screwdriver and
a colleague, picking off… the ice

654
00:43:49,020 --> 00:43:53,120
off the machine for half the night before
they could replace this broken part.

655
00:43:53,120 --> 00:43:56,480
So, yeah, cryo failures
are always a big pain.

656
00:43:56,480 --> 00:44:01,790
Herald: Do we have questions
from the internet? …Okay.

657
00:44:01,790 --> 00:44:04,490
Signal Angel: We have
one question that is:

658
00:44:04,490 --> 00:44:09,500
“How are the particles
inserted into the accelerator?”

659
00:44:09,500 --> 00:44:13,420
Michael: They mostly start
in linear accelerators.

660
00:44:13,420 --> 00:44:19,310
Wait, we’ve got it here. So you
got the series of storage rings

661
00:44:19,310 --> 00:44:23,780
there at the top in the middle and
you have one small line there.

662
00:44:23,780 --> 00:44:26,900
That’s a linear accelerator. To get
protons is actually very easy.

663
00:44:26,900 --> 00:44:30,400
You buy a bottle of hydrogen which
is just a simple gas you can buy.

664
00:44:30,400 --> 00:44:34,380
And then you strip off the electrons.
You do this by ways of exposing them

665
00:44:34,380 --> 00:44:38,280
to an electric field. And what you’re left
with is the core of the hydrogen atom.

666
00:44:38,280 --> 00:44:42,670
And that’s a proton. Then you
accelerate the proton just a little bit

667
00:44:42,670 --> 00:44:47,650
into the linear accelerator and from there
on it goes into the ring. So that means

668
00:44:47,650 --> 00:44:52,780
basically at the start of these colliding
experiments is just a bottle of helium

669
00:44:52,780 --> 00:44:56,590
that somebody puts in there. And
at the LHC it’s about, you know,

670
00:44:56,590 --> 00:45:00,430
a gas bottle. It’s about this big and it
weighs a lot. At the LHC they use up

671
00:45:00,430 --> 00:45:03,531
about 2 or 3 bottles a year for
all the operations, because

672
00:45:03,531 --> 00:45:07,760
a bottle of hydrogen
has a lot of protons in it.

673
00:45:07,760 --> 00:45:11,020
Herald: You please, over there.

674
00:45:11,020 --> 00:45:15,120
Question: Actually I have
2 questions: One part is,

675
00:45:15,120 --> 00:45:18,790
you said there are 2 beams
moving in opposite directions.

676
00:45:18,790 --> 00:45:22,680
And you explained the way where you
switched polarity. How can this work

677
00:45:22,680 --> 00:45:26,010
with 2 beams opposing each other?

678
00:45:26,010 --> 00:45:31,160
Michael: That’s a good question. Now, if
I show you the picture of the cryo dipole,

679
00:45:31,160 --> 00:45:36,980
you will see that these 2 beams
are not actually in the same tube.

680
00:45:36,980 --> 00:45:40,650
There we go. You see a cryo dipole and

681
00:45:40,650 --> 00:45:44,210
on the inside of this blue tube, you
see that there’s actually 2 lines.

682
00:45:44,210 --> 00:45:47,760
You can’t see it very well but
there’s 2 lines. So they are

683
00:45:47,760 --> 00:45:51,980
inside the same blue tube, but then
inside that is another small tube,

684
00:45:51,980 --> 00:45:56,040
which has a diameter of just about
a Red Bull bottle. Say 5 or 6 centimeters

685
00:45:56,040 --> 00:45:58,860
in diameter. And this is where the beam
happens. And they are just sitting

686
00:45:58,860 --> 00:46:02,480
next to each other. So the beams
are always kept separate

687
00:46:02,480 --> 00:46:06,310
except from the interaction points
where they should intersect.

688
00:46:06,310 --> 00:46:10,090
And the acceleration happens
obviously also in separate cavities.

689
00:46:10,090 --> 00:46:11,740
Herald: You had a second question?

690
00:46:11,740 --> 00:46:15,890
Question: The second question is: The
experiments, where are they placed,

691
00:46:15,890 --> 00:46:18,750
on the curve or on the acceleration part?

692
00:46:18,750 --> 00:46:22,610
Michael: The interaction points are
placed between the acceleration

693
00:46:22,610 --> 00:46:25,930
on the straight path. Because, again,
it’s much easier if you had the protons

694
00:46:25,930 --> 00:46:30,130
going straight for 200m; then you
can more easily aim the beam.

695
00:46:30,130 --> 00:46:34,240
If they come around the curve then they
have – you know they have a curve motion,

696
00:46:34,240 --> 00:46:38,000
you need to cancel that. That
would be much more difficult.

697
00:46:38,000 --> 00:46:39,410
Herald: And the left, please.

698
00:46:39,410 --> 00:46:42,630
Question: Okay, so you got yourself
a nice storage ring and then

699
00:46:42,630 --> 00:46:44,970
you connect it to the power plug
and then your whole country

700
00:46:44,970 --> 00:46:48,120
goes dark. Where does the power come from?

701
00:46:48,120 --> 00:46:52,510
Michael: Well, in terms of power
consumption of, let’s say

702
00:46:52,510 --> 00:46:56,950
households, cities, or aluminum plants:

703
00:46:56,950 --> 00:47:00,620
accelerators actually don’t
use that much power. I mean

704
00:47:00,620 --> 00:47:03,370
most of us don’t run an aluminum
plant. So we’re not used to this

705
00:47:03,370 --> 00:47:07,370
sort of power consumption. But’s it’s not
actually all that big. I can tell you about

706
00:47:07,370 --> 00:47:11,290
the HERA accelerator that we had here
in Hamburg, which I told you is about

707
00:47:11,290 --> 00:47:15,880
6.5 kilometers, not the 27, so you
can sort of extrapolate from that.

708
00:47:15,880 --> 00:47:20,230
It used with the cryo and the
power current for the fields

709
00:47:20,230 --> 00:47:25,030
and everything – it used about
30 MW. And 30 Megawatts is a lot,

710
00:47:25,030 --> 00:47:29,270
but it’s not actually very much in
comparison to let’s say aluminum plants,

711
00:47:29,270 --> 00:47:34,140
our large factories. But in fact,
the electricity cost is a big factor.

712
00:47:34,140 --> 00:47:38,530
Now you see the LHC is located at the
border between Switzerland and France.

713
00:47:38,530 --> 00:47:41,770
It gets most of its power from France.

714
00:47:41,770 --> 00:47:45,020
And you always have an annual shutdown of
the machine. You always have it off about

715
00:47:45,020 --> 00:47:47,890
1 or 2 months of the year. Where you do
maintenance, where you replace stuff,

716
00:47:47,890 --> 00:47:51,690
you check stuff. And they always
take care to have this shutdown

717
00:47:51,690 --> 00:47:55,500
for maintenance in winter. Because
they get their power from France.

718
00:47:55,500 --> 00:47:59,660
And in France many people use
[electrical] power for heating.

719
00:47:59,660 --> 00:48:03,670
There’s not Gas heating or Long
Distance heat conducting pipes

720
00:48:03,670 --> 00:48:07,480
like we have in Germany e.g. The people
just use [electrical] power for heat.

721
00:48:07,480 --> 00:48:11,500
And that means in winter the electricity
price goes up. By a large amount. So

722
00:48:11,500 --> 00:48:15,410
they make sure that the machine is off in
winter when the electricity prices are up.

723
00:48:15,410 --> 00:48:18,050
And it’s running in the summer where
it’s not quite as bad. So it’s a factor

724
00:48:18,050 --> 00:48:21,890
if you run an accelerator. And you
should tell your local power company

725
00:48:21,890 --> 00:48:25,130
if you’re about to switch it on!
*laughter*

726
00:48:25,130 --> 00:48:28,820
But actually, it won’t make the grid off,
even a small country like Switzerland

727
00:48:28,820 --> 00:48:30,890
break down or anything.

728
00:48:30,890 --> 00:48:35,150
Herald: Do we have more questions from
the internet? Internet internet, no,

729
00:48:35,150 --> 00:48:39,970
no internet. Okay. Then just
go ahead, Firefox Girl.

730
00:48:39,970 --> 00:48:43,000
Question (male voice): So you see a lot
of events. And I guess there’s many

731
00:48:43,000 --> 00:48:48,210
wrong ones, too. How do you select if
an event you see is really significant?

732
00:48:48,210 --> 00:48:51,470
Michael: Well, you have different kinds
of analysis. Like I told you there is

733
00:48:51,470 --> 00:48:57,750
100 Mio. channels you can pick from.

734
00:48:57,750 --> 00:49:01,960
With the simplest trigger that
you have, the Level 1 trigger,

735
00:49:01,960 --> 00:49:06,560
it can’t look at the data in much
detail. Because it only has 25 ns.

736
00:49:06,560 --> 00:49:09,910
But as you go higher up the chain,
as the events get more rare,

737
00:49:09,910 --> 00:49:13,320
you can look at them more closely. And
what we end up in the end, these 100,

738
00:49:13,320 --> 00:49:17,890
maybe 200 events per second, you can
analyze them very closely. And they get…

739
00:49:17,890 --> 00:49:20,990
they get a full-out computation. You
can even make these pretty pictures

740
00:49:20,990 --> 00:49:26,560
of some of them. And then it’s basically,
well, theoretical physicists’ work,

741
00:49:26,560 --> 00:49:29,161
to look at them and say: “Well, this
might have been that process…”, but

742
00:49:29,161 --> 00:49:33,060
still a lot of them get kicked out. When
the discovery of the Higgs particle

743
00:49:33,060 --> 00:49:37,540
was announced, it was ca. 1 1/2 years ago…

744
00:49:37,540 --> 00:49:42,470
Well, the machine had been running
for 2 1/2 years. And, like I told you,

745
00:49:42,470 --> 00:49:46,390
there’s about 2 Billion proton collisions
per second. Now the number of events

746
00:49:46,390 --> 00:49:51,150
that were relevant to the discovery
of the Higgs – the Higgs events –

747
00:49:51,150 --> 00:49:54,890
it was not even 100.
Out of 2 Billion per second.

748
00:49:54,890 --> 00:50:00,490
For 2 1/2 years. So you have to sort out
a lot. Because it’s very very, very rare.

749
00:50:00,490 --> 00:50:03,400
And that’s just the work of
everybody analyzing, which is why

750
00:50:03,400 --> 00:50:06,849
it’s a difficult task,
done by a lot of people.

751
00:50:06,849 --> 00:50:08,380
Herald: The right, please.

752
00:50:08,380 --> 00:50:13,060
Question: What I’m interested in: You
say ‘one year of detector running’.

753
00:50:13,060 --> 00:50:16,460
How much time in this year does
this detector actually run…

754
00:50:16,460 --> 00:50:18,140
…is it actually running?

755
00:50:18,140 --> 00:50:21,560
Michael: Well, yeah, like I said, we
have the accelerator off for about

756
00:50:21,560 --> 00:50:25,670
1 or 2 months. Then if something
goes wrong it will be off again.

757
00:50:25,670 --> 00:50:29,450
But you want to keep it running
for as long as possible, which…

758
00:50:29,450 --> 00:50:33,760
in the real world… let’s say it’s
9 months a year. That’s about it.

759
00:50:33,760 --> 00:50:35,260
Question: Straight through?

760
00:50:35,260 --> 00:50:38,570
Michael: Straight through – ah, well,
not in a row. But it’s always on

761
00:50:38,570 --> 00:50:41,350
at least for a week. And then you
get maybe a small interruption

762
00:50:41,350 --> 00:50:46,459
for a day or two, but you can also have
a month of straight operation sometimes.

763
00:50:46,459 --> 00:50:47,810
Herald: Internet, please!

764
00:50:47,810 --> 00:50:51,580
Signal Angel: Yeah, another question:
what would happen if they actually find

765
00:50:51,580 --> 00:50:54,820
what you are looking for?
*Michael laughs*

766
00:50:54,820 --> 00:50:58,690
Do we throw the LHC in the
dumpster or what do we do?

767
00:50:58,690 --> 00:51:01,930
Michael: That’s a good question!
It would be one hell-of-a waste

768
00:51:01,930 --> 00:51:06,310
of a nice-looking tunnel! *laughs*
You might consider using it for

769
00:51:06,310 --> 00:51:10,160
– I don’t know – maybe swimming
events, or bicycle racing.

770
00:51:10,160 --> 00:51:13,050
Well, but actually that’s a very good
question because the tunnel

771
00:51:13,050 --> 00:51:17,700
which the LHC sits in, this 27 km
tunnel, it was not actually dug,

772
00:51:17,700 --> 00:51:21,220
it was not actually made just for the LHC.
There was another particle accelerator

773
00:51:21,220 --> 00:51:25,620
inside before that. It had less energy,
because it didn’t accelerate protons

774
00:51:25,620 --> 00:51:30,030
but just electrons and positrons.
That’s why the energy was a lot lower.

775
00:51:30,030 --> 00:51:34,060
But they said: “Well, okay, we’re going
to build a very large accelerator,

776
00:51:34,060 --> 00:51:38,200
does anyone have a
30 km tunnel, maybe?”

777
00:51:38,200 --> 00:51:41,460
and then someone came up with:
“Yeah, well, we got this 27 km tunnel

778
00:51:41,460 --> 00:51:45,450
where this LEP accelerator is sitting in.
And when it’s done with its operations

779
00:51:45,450 --> 00:51:47,470
in…” – I don’t know, by that time,
let’s say in – “…10 years, we’re going

780
00:51:47,470 --> 00:51:51,900
to shut it off. Why don’t we put the next
large accelerator in there?” So you try

781
00:51:51,900 --> 00:51:55,860
to reuse infrastructure, but of course
you can’t always do that. The next big,

782
00:51:55,860 --> 00:52:00,470
the next huge accelerator, if we get the
money together as a science community,

783
00:52:00,470 --> 00:52:03,540
because the politicians are
being a bitch about it…

784
00:52:03,540 --> 00:52:06,920
if we get the money it’s going to be
the International Linear Collider.

785
00:52:06,920 --> 00:52:10,900
And that’s supposed to have
100 km of particle tubes

786
00:52:10,900 --> 00:52:16,240
and, well, you need to build
a new tunnel for that, obviously.

787
00:52:16,240 --> 00:52:20,050
Question: First off, couldn’t
you use it in something

788
00:52:20,050 --> 00:52:23,829
like material sciences, like
example with DESY?

789
00:52:23,829 --> 00:52:27,240
Well okay, if you are done with
leptons you can still use it

790
00:52:27,240 --> 00:52:30,590
for Synchrotron Laser
or something like this.

791
00:52:30,590 --> 00:52:33,500
Michael: That was thought of. The HERA
accelerator at DESY was shut off

792
00:52:33,500 --> 00:52:37,170
and people were thinking about if they
could put a Synchrotron machine inside it.

793
00:52:37,170 --> 00:52:41,670
But the problem there is the HERA
accelerator is 25 m below the ground.

794
00:52:41,670 --> 00:52:44,960
This is not enough space.
With particles accelerating

795
00:52:44,960 --> 00:52:48,730
you just need a small tube. But for
Synchrotron experiments you need

796
00:52:48,730 --> 00:52:51,810
a lot of space. So you would have
to enlarge the tunnel by a lot,

797
00:52:51,810 --> 00:52:56,210
and this was not worth it, in the case of
the HERA accelerator. But interestingly,

798
00:52:56,210 --> 00:53:00,000
one of the pre-accelerators of HERA,
one that was older is now used

799
00:53:00,000 --> 00:53:04,100
for Synchrotron science, which is
PETRA. Which used to be just an

800
00:53:04,100 --> 00:53:08,200
old pre-accelerator, and now it’s one of
the world’s leading Synchrotron machines.

801
00:53:08,200 --> 00:53:11,960
So, yeah, you try to reuse things
because they were expensive.

802
00:53:11,960 --> 00:53:15,630
Question: And may I just
ask another question?

803
00:53:15,630 --> 00:53:21,830
You said you get… you use just the matter

804
00:53:21,830 --> 00:53:25,420
from a bottle of hydrogen
or a bottle of helium.

805
00:53:25,420 --> 00:53:29,980
Well, most helium or hydrogen is protons

806
00:53:29,980 --> 00:53:33,850
or, in the case of helium, helium-4. But

807
00:53:33,850 --> 00:53:37,350
you have a little bit helium-3 or deuterium.

808
00:53:37,350 --> 00:53:41,150
And well, you are looking for
interesting things you don’t expect.

809
00:53:41,150 --> 00:53:44,880
So how do you differentiate if it’s really

810
00:53:44,880 --> 00:53:50,320
something interesting or: “Oh, one of
these damn deuterium nuclides, again!”

811
00:53:50,320 --> 00:53:54,100
Michael: You don’t get wrong isotopes
because you just use a mass spectrometer

812
00:53:54,100 --> 00:53:58,290
to sort them out. You have a magnetic
field. You know how large it is. And

813
00:53:58,290 --> 00:54:03,380
the protons will go and land – let’s say
– 2 micrometers next to the deuterons,

814
00:54:03,380 --> 00:54:07,230
and they just sort them out.

815
00:54:07,230 --> 00:54:11,240
Question: I have 2 questions. One is:

816
00:54:11,240 --> 00:54:15,100
I guess you mentioned that
basically once the experiment

817
00:54:15,100 --> 00:54:19,550
runs at speed of light you
just put more energy into it.

818
00:54:19,550 --> 00:54:22,380
But what is actually the meaning
of the energy that you put into it?

819
00:54:22,380 --> 00:54:25,230
What does it change in the experiment?
Like the Higgs was found

820
00:54:25,230 --> 00:54:28,260
at a particular electron volt…

821
00:54:28,260 --> 00:54:33,410
Michael: Yeah, it was
found at 128 GeV. Well,

822
00:54:33,410 --> 00:54:37,610
it’s more of a philosophical question.
There is a way of interpreting

823
00:54:37,610 --> 00:54:41,480
the equations of special relativity where
you say that, when you don’t increase

824
00:54:41,480 --> 00:54:45,930
the velocity you increase the mass.
But that’s just a way of looking at it.

825
00:54:45,930 --> 00:54:50,260
It’s more precise and it’s more
simple to say: you raise the energy.

826
00:54:50,260 --> 00:54:53,130
And at some low energies that
means that you raise the velocity.

827
00:54:53,130 --> 00:54:55,890
And at some high energies it means
the velocity doesn’t change anymore.

828
00:54:55,890 --> 00:55:00,110
But overall you add more energy.
It’s one of the weird effects

829
00:55:00,110 --> 00:55:07,769
of special relativity and there
is no very nice explanation.

830
00:55:07,769 --> 00:55:10,950
Question: Let’s assume there is
an asteroid pointing to earth.

831
00:55:10,950 --> 00:55:14,410
*Michael laughs*
Could you in theory point this thing

832
00:55:14,410 --> 00:55:17,980
on the asteroid and destroy it,
or would it be too weak?

833
00:55:17,980 --> 00:55:19,830
*laughter*

834
00:55:19,830 --> 00:55:24,290
*applause*

835
00:55:24,290 --> 00:55:26,750
Michael: I’m going to help you out.
Because it wouldn’t actually work

836
00:55:26,750 --> 00:55:30,430
because between the accelerator and the
asteroid there’s the earth atmosphere.

837
00:55:30,430 --> 00:55:33,750
And that would stop all the particles.
But even if there were no atmosphere:

838
00:55:33,750 --> 00:55:37,690
no, it would be much too weak. Well,

839
00:55:37,690 --> 00:55:40,620
you’d have to keep it up for a long time
at least. There was this one accident

840
00:55:40,620 --> 00:55:46,210
at the HERA accelerator where the
beam actually went off its ideal path

841
00:55:46,210 --> 00:55:50,300
and it went some 2 or 3 cm
next to where it should be.

842
00:55:50,300 --> 00:55:54,550
And it hit a block of lead – just,
you know, the heavy metal lead –

843
00:55:54,550 --> 00:55:59,070
and the beam shot into this
lead thing and the entire beam,

844
00:55:59,070 --> 00:56:02,960
which was a couple of Billions of
protons, was deposited into this lead

845
00:56:02,960 --> 00:56:06,670
and some kilograms of lead
evaporated within microseconds

846
00:56:06,670 --> 00:56:10,630
and there was a hole like pushed by
a pencil through these lead blocks.

847
00:56:10,630 --> 00:56:15,160
So, yeah, it does break stuff apart. But
even if you managed to hit the asteroid

848
00:56:15,160 --> 00:56:19,339
you would make a very small hole.
But you wouldn’t destroy it.

849
00:56:19,339 --> 00:56:26,800
It would be a nice-looking asteroid then.
*laughter*

850
00:56:26,800 --> 00:56:30,820
Question: Before you turned on the LHC
the popular media was very worried

851
00:56:30,820 --> 00:56:34,220
that you guys were going
to create any black holes.

852
00:56:34,220 --> 00:56:39,080
Did you actually see any black holes
passing by? *Michael laughs*

853
00:56:39,080 --> 00:56:43,080
Michael: Well, there may have been
some, but they were small, and

854
00:56:43,080 --> 00:56:48,810
they were insignificant. The interesting
thing is… sorry, I’m going to recap, yeah.

855
00:56:48,810 --> 00:56:52,010
The interesting thing is that whatever
we can do with the LHC – where

856
00:56:52,010 --> 00:56:56,869
we make particles have large energies
and then collide – is already happening!

857
00:56:56,869 --> 00:57:00,830
Because out in space there is black
holes with enormous magnetic fields

858
00:57:00,830 --> 00:57:04,450
and electrical fields. And these
black holes are able to accelerate

859
00:57:04,450 --> 00:57:08,320
electrons to energies much, much
higher than anything we can produce

860
00:57:08,320 --> 00:57:12,340
in any accelerator. The LHC
looks like a children’s toy

861
00:57:12,340 --> 00:57:16,370
in comparison to the energies that
a black hole acceleration can reach. And

862
00:57:16,370 --> 00:57:21,170
the particles which are accelerated in
these black holes hit earth all the time.

863
00:57:21,170 --> 00:57:24,630
Not a lot, let’s say one of these
super-energetic particles they come around

864
00:57:24,630 --> 00:57:28,840
about once a year for every
square kilometer of earth.

865
00:57:28,840 --> 00:57:31,470
But still, they’ve been hitting
us for Millions of years.

866
00:57:31,470 --> 00:57:34,900
And if a high-energy particle
collision of this sort were able

867
00:57:34,900 --> 00:57:39,140
to produce a black hole that swallows
up the earth it would be gone by now.

868
00:57:39,140 --> 00:57:45,499
So: won’t happen.
*applause*

869
00:57:45,499 --> 00:57:48,190
Question: Maybe more interesting
for this crowd: you talked about

870
00:57:48,190 --> 00:57:52,580
the selection process of the events.

871
00:57:52,580 --> 00:57:56,750
So I guess these parameters
are also tweaked to kind of

872
00:57:56,750 --> 00:58:00,430
narrow down like what
a proper selection procedure.

873
00:58:00,430 --> 00:58:04,040
Is there any kind of machine
learning done on this to optimize?

874
00:58:04,040 --> 00:58:07,230
Michael: Not that I know of. But there is
a process which is called ‘Minimum Bias

875
00:58:07,230 --> 00:58:11,690
Data Collection’. Where you
actually bypass all the triggers

876
00:58:11,690 --> 00:58:15,290
and you select a very small portion
of events without any bias.

877
00:58:15,290 --> 00:58:19,990
You just tell the trigger: “Take
every 100 Billionth event”

878
00:58:19,990 --> 00:58:22,940
and you just pass it through no matter
what you think. Even if you think

879
00:58:22,940 --> 00:58:28,150
it’s not interesting, pass it through.
This goes into a pool of Minimum Bias Data

880
00:58:28,150 --> 00:58:32,830
and these are analyzed especially in order
to see the actual trigger criteria

881
00:58:32,830 --> 00:58:37,230
are working well. So yeah,
there is some tweaking. And

882
00:58:37,230 --> 00:58:41,230
even for old machines
we have data collected

883
00:58:41,230 --> 00:58:44,910
and sometimes we didn’t know what we
were looking for. And some 20 years later

884
00:58:44,910 --> 00:58:48,800
some guy comes up and says: “Well,
we had this one accelerator way back.

885
00:58:48,800 --> 00:58:52,249
There may have been this and that
reaction. Which we just theorize about.

886
00:58:52,249 --> 00:58:56,200
So let’s look at the old data and see
if we see anything of that in there

887
00:58:56,200 --> 00:58:59,420
now, because it’s limited because
it goes through all the filters”.

888
00:58:59,420 --> 00:59:03,600
You can’t do this all the time with
great success. But sometimes,

889
00:59:03,600 --> 00:59:06,810
in very old data you find new
discoveries. Because back then

890
00:59:06,810 --> 00:59:11,980
people weren’t thinking about looking
for what we are looking now.

891
00:59:11,980 --> 00:59:16,470
Question: I always asked myself about
repeatability of those experiments.

892
00:59:16,470 --> 00:59:20,480
Seeing as the LHC is the biggest one
around there, so there’s no one out there

893
00:59:20,480 --> 00:59:23,320
who can actually repeat the
experiment. So how do we know

894
00:59:23,320 --> 00:59:26,440
that they actually exist, those particles?

895
00:59:26,440 --> 00:59:30,150
Michael: That’s a very good question.
I told you that there is 2 main

896
00:59:30,150 --> 00:59:33,940
large experiments. Which is the CMS
experiment and the ATLAS experiment.

897
00:59:33,940 --> 00:59:39,020
Now these both sit at the same ring.
They have some 10 km between them

898
00:59:39,020 --> 00:59:41,740
because they’re on opposite ends
of the ring. But still, obviously,

899
00:59:41,740 --> 00:59:46,690
they’re on the same machine. But these 2
groups, the ATLAS and the CMS experiment,

900
00:59:46,690 --> 00:59:51,910
operate completely separately. It’s not
the same people, not the same hardware,

901
00:59:51,910 --> 00:59:55,250
not the same triggers,
not even the same designs.

902
00:59:55,250 --> 00:59:58,760
They build everything up from scratch,
separate from each other. And

903
00:59:58,760 --> 01:00:02,700
it’s actually funny because when you
look at a conference and here is CMS

904
01:00:02,700 --> 01:00:05,570
presenting their results and here is
ATLAS presenting their results,

905
01:00:05,570 --> 01:00:08,300
they pretend like the other
experiment is not even there.

906
01:00:08,300 --> 01:00:11,730
And that’s the point of it: they’re
not angry at each other. It must be

907
01:00:11,730 --> 01:00:16,070
2 separate experiments because obviously
you can’t build a second accelerator.

908
01:00:16,070 --> 01:00:18,720
So you try to have redundancy in order

909
01:00:18,720 --> 01:00:22,900
for one experiment to confirm
what the other finds.

910
01:00:22,900 --> 01:00:27,900
Herald: Okay. It’s midnight
and we’re out of time.

911
01:00:27,900 --> 01:00:31,400
So please thank our awesome speaker!
*applause*

912
01:00:31,400 --> 01:00:39,163
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