CAITLIN MALONE: Thank you
very much for having us.
We're very excited to be
here and it's great
to see so many people.
So I guess as Ibrahim said, our
format is sort of-- the
first part I guess I think of
it as sort of a story time.
So there's been a lot in the
news, especially in the last
six months or so, as we've gone
through the Higgs boson
discovery process.
And that's something that we
were both at CERN for.
I've been there for a couple
years and Jens
has been there for?
JENS DOPKE: Ages.
CAITLIN MALONE: A long time.
JENS DOPKE: Too long.
CAITLIN MALONE: Yeah.
And so I guess our purpose to
come and talk to you today is
to speak a little bit informally
with you, to tell
you about what it was
like to be there.
Because it was actually a
really, really interesting
process to go through, a
discovery like this, maybe
teach you a little bit of
science, if we can sneak it in
between the edges, and then
answer whichever questions you
have for us.
So that having been said, if you
have questions as we go,
please feel free to interrupt,
because every once in a while
we can slip into jargon.
And it's best if you catch
us when we're doing that.
So with that, I'll begin.
So the place that I want to
start is in 1963, actually,
which is when the Higgs boson
was first theorized by Peter
Higgs and a handful of other
theorists, who were just a
little bit less lucky in
getting their name
tapped onto the boson.
And that's really what it is.
But they were looking at what we
call the standard model of
particle physics, which is a
collection of theories that
describe all the particles that
we know about, and the
way that they interact, their
masses, their couplings with
one another, things like this.
And one of the things about the
standard model that was a
major flaw in the model at the
time-- and this is what the
Higgs boson solves--
is that there's no mechanism
in the standard model for
particles to have mass.
We all know that particles
have mass.
Moreover, if they didn't, then
nothing would work properly.
And so what Higgs and his
contemporaries were able to do
was to do a manipulation of
the equations, basically a
change of variables, that
introduced a mass term to the
equations of the standard model,
and therefore sort of
endowed all the particles
with mass.
And the term that allows you to
do this introduces what we
call the Higgs field,
which is a field.
Sort of like an electromagnetic
field is one
type of field or an electroweak
field is another
less-known type of field.
And the Higgs field permeates
sort of all the space/time.
And as particles travel through
it, they interact with
it, and that's how they
pick up mass.
And so when we have fields
like this one, one of the
things that we know about them
is that they have to be
conveyed by particles.
And so the particle that's
corresponding to the Higgs
field is Higgs boson.
So the Higgs boson is now
on the scene in 1963.
And the question is can
we discover it?
So when I say discover the Higgs
boson, what I mean is a
very specific thing, which
is that what we
do is we don't discover--
well, actually, let's
start with CERN.
Can you pull up the
slide of CERN?
Thanks.
Sorry.
So let me step back a moment.
So we're experimental
particle physicists.
So what we do is we try to
create the particles that
we're looking for in high-energy
particle
collisions.
JENS DOPKE: What's
[INAUDIBLE]?
CAITLIN MALONE: The circles.
AUDIENCE: JENS DOPKE: Oh.
CAITLIN MALONE: Yeah, that one.
Thanks.
So we do is we have a particle
accelerator.
It's 27 kilometers.
It runs along the French/Swiss
border outside of Geneva.
And we run protons through the
accelerator in two different
directions.
It's a ring.
And at four points around the
periphery of the ring, the
protons will actually collide
with each other.
And we create all kinds
of new things that
we're trying to study.
So underground at the different
locations, we then--
let me draw a picture
for you here.
And the accelerator is sort of
going in a ring like this.
We have four interaction
points going around the
detector, where the beams
come into collision.
And then what we do is we're
part of a collaboration.
We build a detector basically
around the collision point so
that we can detect the
particles that
come out of the collision.
It's a cylindrical detector.
Sort of encompasses the
collision point like this.
And we call it Atlas.
Now, we have some compatriots
across the ring on the other
side, which are our competitors,
but in a friendly
way, called CMS.
And they will figure prominently
in the story.
So just very briefly, when
we're searching for a new
particle, what we're actually
looking for is not the
particle itself, but for the
particles that it decays into.
So for something like the Higgs
boson, it only lives for
a fraction of a second
and then breaks
apart into other particles.
Sometimes those particles
then break apart
into still more particles.
And so what you need to do is
you actually get sprays of
particles that come out from the
collision point, and then
you detect them as they traverse
your detector.
And from that, you
kind of reverse
engineer the Higgs boson.
And so what you're looking for
is for excesses of events in
the specific decay branches.
And once you see enough of them,
then you say, OK, it
looks like there's indications
in this particular decay
channel that there's
a particle here.
And then once you reach a
certain statistical confidence
in that statement,
you can say we've
discovered a new particle.
Could you pull up the branch
interactions that we had up
just a moment ago?
Thank you.
So there are three decay modes
of the Higgs that are really
important for this talk today.
So what this is showing is
basically the different ways
that the Higgs boson
can decay.
And I'll just point out a couple
of these to you that
are the most important.
They can decay in any one of
these different channels.
But for our story today, the
most important ones are WW,
it's this green line, ZZ,
and gamma-gamma, this
purple one down here.
So let me point out a couple
of things to you that are
important about these.
And these are the reasons why
these are so important.
So ZZ, I'll start with ZZ.
As it happens, the
Higgs is at 125.
So the ZZ is a pretty
good branching
fraction of maybe 30%.
ZZ is really nice because it's
a very clean channel.
You can detect all of the decay
products that are coming
out of the Higgs collision.
And it's a very low background
channel.
So this is a channel where you
can actually make a discovery
with dozens of events,
which is really nice.
Gamma-gamma is also
very clean.
We can pick up both gamma
rays in our detector.
So that's really nice.
And we can completely
reconstruct the Higgs.
A little bit higher background,
but still
relatively low background
compared to some
of the other ones.
The problem with gamma-gamma
is how low the branching
fraction is.
Only one out of 1,000 Higgs
bosons decays to gamma-gamma.
And when you're only producing
something like a few Higgs
bosons every hour, this might
not be all that many events.
You have to collect lots and
lots of data to be able to see
enough of them in gamma-gamma.
And then WW is a really nice
channel because it has this
nice high branching fraction,
even to 100%, depending on
what the mass of the Higgs is.
But the thing about WW is that
when the Ws decay in our
detector, one of the particles
that they decay to is a
neutrino, which is basically
impossible for us to detect.
And you need specialized
detectors to see them.
And so what this means is that
you can't completely
reconstruct the W, because
you're missing one of the
particles that you would
need to reconstruct it.
And so you get kind of funny
blobs where you had Ws.
And then when you take your Ws,
add them together to try
to get Higgs, you get kind
of a fuzzy blob.
But these are the three channels
that we have to work
with to make a discovery.
So now I'm gong to fast
forward to 2011.
So the Higgs--
yes?
AUDIENCE: Is there a
significance behind the names
of those channels?
CAITLIN MALONE: Yes.
So these are the particles that
the Higgs is decaying to.
So gamma-gamma is two photons.
And WW and ZZ are just different
kinds of particles
they can decay to.
So then let's fast
forward to 2011.
So at this point, the LHC has
been on for a couple of years.
And the LHC, there's a twofold
purpose to it, I would say, to
first order.
The first is to look for any
kind of physics beyond the
standard model.
And second, or maybe even first,
depending on how you
want order these things, is
to find the Higgs boson.
So the real focus of the
collaboration at this point is
to find the Higgs boson.
And there are hundreds of people
who are working on the
different decay channels looking
for excesses in each
of their channels.
And in 2011, I had just been at
CERN for a couple of weeks,
and it was a very interesting
weekend.
It was Easter weekend,
actually.
And so it was the Thursday
before Easter weekend.
And so everyone's kind of--
they're starting to go home.
People are ready to have
a four-day weekend.
And there's an email that goes
out that there's a group.
There's a small group of people,
three or four people,
who have been analyzing
some data
independently, on their own.
Not part of one of the major
efforts, but sort of as a
project that they're doing
independently.
And they see an excess in
one of the channels.
So this is big news.
And so what's going on here is
a little bit of skiing off
piste, I think.
They weren't doing anything
that was inappropriate.
But at the same time, now all of
a sudden the collaboration
is really focused on what's
going on in this channel and
might this be actually
a discovery.
One of the things that was
really intriguing about it
also was that the mass point
that they happened to be
seeing an excess at was a place
where there had been a
little bit of an interesting
excess on a previous
experiment, before that
experiment was closed down.
So maybe this is corroborating
proof of something that we
already had a hint at before.
And then something very dramatic
happened, which was
this internal document telling
about this hint that they had
seen was posted to a blog.
And we still don't
know who did it.
But this was actually a big
problem, because it puts a lot
of pressure on us to then very
quickly figure out what's
going on and not work in our
usual comfort zone, which is
very slow and deliberate.
And so as turns out, this
was a false alarm.
It took a couple weeks of truly
working around the clock
to figure this out.
But we learned something very
important from this
experience, which was that we
had to be very careful about
what we said.
Because as soon as anyone said
Higgs in public, a lot of eyes
all of a sudden came
on to CERN.
And so we wanted to be very sure
that we knew what to say
when they started asking
those questions.
So we continued to
run the detector.
We continued to collect
more data.
And in general, the more data
that you have, the more
confidence you can have in
detecting a particle.
And then there's a round of
conferences that come around
in the winter.
And before those conferences,
we wanted to have sort of a
status update on the
Higgs boson search.
And so this was too early for us
to say that we thought that
there was anything.
There wasn't enough data that
we would be able to say
anything definitive anyway,
but just to
give a status update.
And there was a little nudge
in the most interesting
channels at 125 or so GeV.
So it's right at this
point here.
Now, I'll just stop for a second
to point something out
to you, which is that 125
is actually really nice.
Because if you draw a vertical
line at 125, you hit all of
these lines.
So you have all of the decay
channels that can
come into play here.
Whereas if you're down here or
you're up here, then there's a
lot less flexibility that you
have for looking for it in
different decay channels.
But since we're looking now at
125, we have gamma-gamma, we
have WW, we have ZZ.
So all of the major players
are now in the game.
But there wasn't enough data
that we could say with great
confidence that we thought there
was something there.
There was something like a 1
in 100 chance that what we
were seeing was due to a
statistical fluctuation in the
data, which is simply not enough
for us to say anything.
The thing that was really
interesting for me, personally
I remember at the time, was that
CMS, which were sort of
our doppelganger on the other
side of the collider, they saw
peaks in the same channels
at the same mass.
So it's not just us.
If it were just us, I think
people would have been much
less excited.
But the fact that CMS was
seeing something too was
pointing towards that there
might be something physical
that's actually going on
in the detectors here.
So now we'll fast forward a
little bit further, about six
months, to June of 2012.
So we're working our way
up to the-- yes?
AUDIENCE: [INAUDIBLE]?
CAITLIN MALONE: Everything
is basically as
independent as can be.
So let me continue
to tell my story.
And then ask your question
again, if I
haven't answered it.
Because one of the things that's
really important is
sort of the interplay between
the two experiments during the
discovery process.
So in June of 2012, there was
a conference that was coming
up in mid-July.
And everyone knew that there was
going to be a Higgs update
that was given, one by
Atlas and one by CMS.
So at this point, we should have
enough data to be able to
say something fairly
conclusive.
And the magic number that we
needed to be working towards
is 5 sigma significance.
This is 5.
So if we can reach this number,
then we can say that
we have a discovery.
And this number is the number
that corresponds to basically
there's one in a 3 and 1/2
million chance that what we're
seeing is due to a statistical
fluctuation.
So it's a pretty high
degree of certainty.
And the reason we want to do
that is, like I said, because
you don't have a false alarm.
And because there are 3 sigmas
and 4 sigmas that
have come and gone.
So 5 sigma seems to be safe.
And this 5 sigma corresponds to
the combination of all the
decay channels together.
So maybe you see
3 sigma in ZZ.
That's not enough.
But if you see 3 sigma in
gamma-gamma also, then you can
put those two together
statistically, and you can say
potentially, depending on how
the channels are correlated,
that have 5 sigma overall.
So 5 sigma is the
magic number.
And we were at something
like to 2 to
2.5, I think, in December.
And so I was at a summer
conference in France with a
bunch of my friends.
And some of them are on CMS
and some of are on Atlas.
And this is something we
shouldn't have done, but we
were excited enough that
we did it anyway.
Which was that I as an
Atlas member saw
some of the CMS data.
So what CMS had been doing--
and this is what Atlas does too,
is they blind their data.
So they specifically set aside
the data where they think the
signal might be hiding.
And they look in side bands or
control regions to optimize
the entire analysis.
And only once that's complete
do they unblind and finally
look for the particle.
And the reason that we do that
is because we don't want to
bias ourselves and accidentally
get excited about
something that we see in the
data and then amplify it and
sort of bias ourselves
that way.
And so CMS was unblinding.
And so there was this big
call which had 300
people on the line.
And we were all dialed in, and
we were huddled around an
iPhone, looking to see what
the CMS results were.
And the CMS results looked
really, really good.
It was really, really
exciting.
And so we knew that if CMS was
seeing something that was this
good, then Atlas
should be too.
And sure enough, the next week,
Atlas unblinded their
gamma-gamma, and it looked
really good.
It was something like
3 and 1/2 sigma.
And then analogously in ZZ,
now ZZ is starting to come
online a couple weeks later.
And ZZ now sees something
like 2 and 1/2 sigma.
So at this point--
and this is the last that I
heard of the CMS results until
the 4th of July.
So there is some bleeding in
between the two of them.
But we tried very hard,
especially at this point, to
partition the two collaborations
so that the
excitement of one doesn't
sort of amplify the
efforts of the other.
So now the race is on to try
to get the results for the
conference in the summer.
So we have a hard deadline
that's in the middle of July.
And there was a lot of
excitement within CERN about
what the two collaborations
were seeing.
And there were rumors that were
flying back and forth a
little bit.
And so the director general of
CERN then called a meeting in
late June between the
spokesperson of Atlas, the
spokesperson of CMS, and the
director general of CERN, in
which the spokespersons sort of
tipped their hands to one
another-- and this was
by agreement--
and to the director general,
and said, this is
what we see so far.
And at this point, the director
general of CERN said,
this looks like it will probably
be good enough that I
think we want to have an
announcement that's coming out
of CERN, rather than having the
announcement that's coming
out of this conference,
which last year
happened to be in Australia.
Because we kind of feel a little
bit of possession, I
guess, of this discovery.
And we want it to be ours to
give to the world as sort from
our own home.
So this is taken as a very good
sign, that all of sudden
there's now a special seminar
that's been planned at CERN
for the 4th of July.
And this at this point is
several weeks in the future.
And so the question is, what
are you going to be able to
get done before the
4th of July?
So at this point the
accelerator, as it happens, is
running really, really well,
and we're getting lots and
lots of data every day.
And we need every bit of data
that we have to be able to get
enough confidence in these
channels that maybe we can
combine them and get
the magic number.
We can get the 5 sigma.
And usually as the data comes
in, we have to a round of
processing on it, basically, and
calibrations and make sure
that there was nothing wrong
with the detector conditions
when it was taken.
And there's this whole rigmarole
that the data gets
put through.
And it usually takes something
like a couple months.
And so at this point, there's
this massive mobilization at
CERN to bring dozens and dozens
of people online from
whatever they're working on, to
start working on the data
processing, so that we can get
the data out in a matter of
days and weeks, instead
of in weeks or months.
And it was really magnificent to
see this big effort kind of
come out of CERN because we had
to get all this data just
through as fast as we could.
And they did it.
They added it in really,
really quick.
It was magnificent to see
how fast they were
adding in the data.
They were taking it one
week and it was in a
plot the next week.
And that's absolutely
unheard of.
So we're getting more and
more data every day.
The numbers are being updated,
more and more
and more every day.
The reason I say this is because
I wish I could tell
you exact numbers and bring you
through the progression in
numbers as we were watching
the significance of these
channels grow.
But it was hard to keep track,
honestly, at this point.
Every day there's a new number
coming in, depending on which
channel it is, which data
set they're using.
Everything's looking
really good.
And so there's one channel that
I haven't mentioned in a
little while, and it's WW.
And WW is also in play.
But WW had yet to unblind,
because they had been a little
bit behind the curve, because
they hadn't gotten some data
sets as soon as they
needed them.
And so it was only five or six
days before the July 4th
announcement that we
know is coming.
And so the question is
what to do with WW.
So the decision was made that
they would talk about
unblinding WW, try to decide
whether they were ready to
look at the data yet in
the sigma region.
But before they did the
unblinding deliberation, they
had to decide whether they were
going to include WW in
the combination.
So is this channel, regardless
of what we do, and we know
personally amongst ourselves
this is something that we're
going to be ready to tell
the world about
on the 4th of July.
And the decision was that it
should not be included in the
final calibration, because there
was simply not enough
time to do all the checks that
you would want to do in those
four or five days before
the seminar.
And you have to be extremely
careful here, because this is
where some of those lessons that
we learned the first time
around come into play.
That if you get too aggressive
with WW, and you include it
because you unblind it, you
say oh, this looks really
good, let's include it.
But you haven't done
all your checks.
Maybe there's a problem, and
you've accidentally just
discovered a particle that
isn't really there.
Likewise, let's say you
unblind it and there's
different kind of problem, and
WW actually sees less than
they should.
Well then, let's say you're
at 5 sigma before.
Now you add in WW, and you've
taken yourself down to 4.5.
So you just undiscovered
a particle.
You really want to know what's
going on with WW.
And the decision was we're not
confident that we can do all
those checks we need to do.
So WW--
this is now the Wednesday
before--
this is six days before
the announcement.
They make the decision
to unblind WW.
But it's going to stay within
the collaboration, and it's
not going to be included
on the 4th of July.
And so this is where the story
diverges a little bit in an
interesting way.
Because now there are two
different things that we need
to keep track of.
One is what's going to be
included on the 4th of July,
what we're going to be able to
tell everyone, whether we can
say the Higgs boson has
been discovered.
And then the other one is sort
of what we privately know as
collaborators and as people
who are privy to this
information, whether we know
that the Higgs boson has been
discovered.
So let's say that we only have
4.2 sigma on the 4th of July.
But we know the WW is waiting
in the wings and WW has 3
sigma, and that's going to push
it over the threshold.
So at that point, we
can't say we've
discovered the Higgs boson.
But let's be honest, we're going
to know for ourselves
whether we've discovered
the Higgs boson.
So this Wednesday afternoon was
really, really exciting.
Actually, when they unblinded
WW at about noon.
And so that afternoon, you're
just kind of sitting there,
and you're like, I'm pretty sure
they're discovering a new
particle right now.
That's really neat.
And so the next day,
the unblinding
had finished running.
There was an official talk
to be given on Friday.
So this was four days before
the announcement, but the
rumor started to go around.
And so they said that they
had unblinded and it
looked really good.
So we're all saying oh, we
should have put it in, we
should have put it in.
So regardless of what
we can say the next
week, we found it.
This is it.
So now the issue is what
are we going to be
able to say next week?
And what's happening now is that
you need to look at the
updates to the gamma-gamma.
You need to look at the ZZ.
You have a little bit of
information from last year's
analyses that you can mix in.
But gamma-gamma and ZZ are
the powerhouse channels.
And so it's just an issue of
like putting those together
and seeing if you have
the magic number.
And so I have a particularly
well-connected friend at CERN,
or maybe she was just in the
right meeting, I don't know.
And so we were eating lunch
with her on Thursday.
And we were all gossiping
about this, because, of
course, we're gossiping
about this.
And so one of my friends
kind of leans in.
We're speaking very quietly,
because it's a cafeteria
that's 50% Atlas and 50% CMS.
And if you want to learn secrets
at CERN, just go sit
in the cafeteria and listen for
somebody who's too noisy.
And so one of my friends, she
said they've done the global
combination, they know what the
number is for next week.
They're going to have it
in a meeting tomorrow.
But if you know the
right people, you
can find out today.
So one of my friends kind of
leans in, and he's like how
many sigma do they have?
And she goes [KNOCKING SOUND]
and kind of catching herself.
So at this point, you know
it's the bag, right?
We know it for ourselves
because we have the WW.
Like if the WW had been mixed in
at that point, it's like, I
don't even know, 6.56
sigma or something.
We're fine.
But not only that, but we
get to tell everyone.
So this perfect.
At the same time, the question
is, what does CMS have?
Because I'm pretty sure
that there's a Higgs
boson at this point.
And if there's a Higgs boson,
if we can see it,
they can see it.
And so now the competition comes
into it, back again a
little bit.
Because OK, so we had 5 sigma.
But what do they have?
Do they have 6 sigma?
I hope they don't have
6 sigma, because I
want to find it.
So even though we sort of had
all the physics cards on the
table, even up until the morning
of July the 4th, there
was still reason to go to
seminar because you only have
half the story, and you want
to see what other guy has.
So we go to talk to the next
day, and WW looks pretty good.
But they're not going
to be including it.
They need to run some more
checks, and it's going to be
out in a couple of weeks.
They do the global fit, and
it's 5.1 sigma, I think
something like that.
And we all go home, and we
have a quiet weekend.
But it's a really cool time,
because you know that it's
going to be a big deal in
like in three days.
And there's 5,000 people in the
world who know this, and
you're one of them.
Oh, this is going
to be so great.
So the word had sort of started
sneaking out at this point.
There were people there--
Peter Higgs said had been called
a few weeks before.
And they said, you probably
shouldn't plan any vacation
for early July.
We need you to come
to the CERN.
So now we're seeing Peter Higgs
in the CERN cafeteria,
and this is a very
promising sign.
So there's this announcement.
It's going to be made
on the 4th of July.
And everybody wants a seat
in the seminar room.
And the seminar holds--
I don't know.
It's reasonably big,
but it's not huge.
It's 500 people, maybe
300 people.
And half of those seats are
going to go to people who
funded the experiment and
the higher-ups on the
collaborations, as
they should.
But a fraction of the small
space is going to be reserved
for the schmucks like us.
And we had learned our lesson
from the December talk because
the December talk's seats
were hard to come by.
And we had showed up four
hours early for that.
JENS DOPKE: Is this the point
at which I should bring up
another picture?
CAITLIN MALONE: Yeah.
Why don't you start bringing
up pictures.
We have a bunch of pictures.
Jens and I were both
at this talk.
So there's Jens, sitting
there on the floor
for hours, I'm sure.
And we just slept there the
night before, honestly.
They locked the doors to the
seminar room because they knew
that people like us were
going to do this.
And so we all lined up in the
hallways, and we watched "The
Lion King," and we tried to
sleep, and got very excited,
and read internal notes because
we wanted to get all
the plots again, because
they looked so great.
JENS DOPKE: We should stress
here that this was at 5:00 AM,
where people came in thinking
they were early enough to get
into the auditorium.
CAITLIN MALONE: Yeah, I don't
know what they were thinking I
don't know what they
were thinking.
I think the latest you could get
there and get a seat was--
JENS DOPKE: 4:30.
CAITLIN MALONE: --4:30, maybe.
And so then seminar starts.
And we're all trying to stay
awake, actually, because we
have been up all night.
And the CMS talk was first.
And so the CMS talk actually
was really interesting.
Because CMS had done slightly
better than Atlas in the
respect that they had
more data in more
channels that was ready.
So their WW was more updated
than ours, for example.
And CMS, if they did the global
combination with all of
their channels minus one I
think, they got to 5.1 sigma.
And then they had a little bit
of a downer fluctuation in the
last channel.
And it bumped them to 4.9.
And it's just like, oh---
I mean, 4.9.
I mean, come on, you discovered
a particle.
But I thought that was
interesting, just because this
is a case of where you can
get a little bit unlucky.
And like I said 4.9,
you're fine.
But they did happen to get a
little bit unlucky there.
And then Atlas does the second
presentation, which, of
course, is less of a surprise,
because we've seen all the
slides already.
But we're, as it happens,
able to say the
magic words of 5 sigma.
And of course if you were to
Atlas and CMS together, you
would be at, I don't even know,
8 sigma or something.
Like there's no doubt
at this point.
Atlas was just a little bit
lucky in that we got to, like
I said, say the magic words.
And it was very exciting because
I think especially
crossing that 5 sigma
threshold was really
meaningful, I think.
And there was a big round of
applause, and especially for
Atlas that I remember.
CMS definitely got one too.
But I particularly remember the
Atlas one, because it went
on forever, just for like four
minutes of just-- like this is
starting to get ridiculous,
guys.
And it was all very nice, with
congratulations from
all over the world.
And Mr. Higgs was there and may
or may not have wiped a
tear from his eye at the
moment that they
flashed up the slide.
And it was really great.
So in the afternoon, we're all
kind of exhausted, and some of
us went home for naps.
The ones who had a little bit
more stamina stuck around for
the free champagne.
And there's a series more of
additional studies that we had
to do at this point.
I mean, the big discoveries--
I mean, this is sort of the
exciting part is now coming to
an end a little bit.
But one thing that I want to
spend just a moment talking
about now and sort of gesture
towards the future is like,
OK, so we found a particle,
now what?
And the first series of
questions that had to be
answered was, is it
the Higgs boson?
Because it looks like
a Higgs boson, and
it seems about right.
But you need to do things
like measure all of
these branching fractions.
You need to do things like
measure the spin of the
particle, which is just one
of its quantum mechanical
properties.
But if it has the wrong spin,
it's not a Higgs boson.
It's something else, and it's
maybe even more interesting.
So there were a series
of studies that
then had to be done.
So we certainly partied
on the 4th of July.
But we were back at work on
the 5th of July trying to
figure this stuff out.
And they finally wrapped up
those studies, at least the
first round of them, enough that
a couple weeks ago at the
Moriond conferences, which is
another set of conferences
that they have in March, they
were able to say definitively
this is a Higgs boson.
So now we can say things like
we found the Higgs.
But there's still a lot more
that they're trying to find.
So I think I'll take the last
few minutes here just to
gesture towards what we're
looking at in the future as
far as things like the
Higgs is concerned.
And that is something
like looking for
additional Higgs bosons.
And the reason that I bring
this up in particular is
because it's something
that I work on.
This is my thesis topic, is
looking for under certain
classes of theories that go
beyond the standard model, so
these are the kinds of theories
that we're most
interested in investigating,
there's not just one Higgs
boson, but there's five.
And so it's my job to
find the second one.
And so there's a number of
different efforts on these
sorts of fronts, that now we
have this great new toy that
we can play with and try to
crack open the standard model
a little bit more.
And so that's just one gesture
towards some of the additional
ways that we'll be
doing at CERN.
So technologically, just very
briefly I'll bring in Jens to
say a couple things about--
yeah, just a couple minutes.
And then I think we'll be ready
for questions in just a
minute or two.
So CERN right now, it's at
an interesting point.
We've stopped taking data.
The whole goal was to find the
Higgs boson in round one, and
we've done that.
And now what we're doing is
upgrading and repairing parts
of the accelerator and upgrading
and repairing parts
of the detector.
So there actually won't be a
whole lot of new data being
taken at CERN for the
next two years.
But the data analysis of the
data that we've already
collected will be continued
for the next two years.
And so hopefully there'll
be a couple more
surprises to find in there.
This is something that Jens is
particularly involved in.
So Jens, do you want to say
a couple words about what
they're doing?
JENS DOPKE: I don't
want to say much.
I mostly came here
to show pictures.
So what Caitie has not shown
you is pictures.
And I encourage everyone,
because you're in Zurich, and
particularly the people in the
room are in Zurich, get over
there and get downstairs.
We have a long shutdown
now for two years.
The caverns are open.
So if you're interested, you can
just sign up for a visit
at CERN and go about 100 meters
underground and see the
experiments.
AUDIENCE: Do you have a website
that we can go to and
sign up for?
JENS DOPKE: You should look
at cern.ch and then you'll
probably find something like
"visits" or how to get there.
CAITLIN MALONE: Talk
to us, we can--
JENS DOPKE: Talk to us, yeah.
AUDIENCE: [INAUDIBLE].
JENS DOPKE: Say again?
AUDIENCE: Can you
come as a group?
CAITLIN MALONE: Yeah.
JENS DOPKE: Well, you
can come as a group.
For typical underground visits,
we're limited to 12
persons per visit, which
is about 45 minutes.
So if you're coming in with 500
people, then better plan
for a long week.
AUDIENCE: [INAUDIBLE]
question.
Could you repeat the
question for group?
CAITLIN MALONE: Yes,
of course.
The question was how
to get underground.
JENS DOPKE: The question here
in the room was how to visit
and how to get underground.
OK.
CAITLIN MALONE: Yeah.
But there's ways through the
CERN visit service that they
can do these arrangements,
yeah.
JENS DOPKE: To give an outline,
we have about 80,000
visitors per year.
And that's only the number
that we know of.
People like Caitie and I, we
typically get our family
there, our friends there,
or whatever, and
we guide them around.
And that's not included in
the official numbers.
So we're talking about a little
more than 100,000
visitors per year.
That does not include CERN open
days, which will happen,
for example, in September, I
think this year, which is
where we have two days on the
weekend which are open, one
for the families and friends of
CERN people and one for the
general public, which
has another 80,000
visitors in two days.
So that's roughly what
we're talking about.
What you get to see at CERN
is things like this.
And I cannot really point
at it, but maybe--
CAITLIN MALONE: Here--
--Caitie can point at it.
CAITLIN MALONE: --let
me take the laser.
JENS DOPKE: So what you get to
see on the ground is pretty
large structures.
The photos that I took here are
partially from 2007, 2008
when the cavern was still empty,
which you see here,
because the big structures
are missing.
CAITLIN MALONE: The gap
here, for example.
JENS DOPKE: There's
a large gap.
What we do is we build really
large detectors on the ground,
and they fill the caverns.
In the case of Atlas, we
built it underground.
That means we're bringing parts
down and building like a
ship in a bottle basically.
Whereas CMS builds everything
upstairs and then brought it
down in nine slices, the central
slice being about
3,000 tons and being
lowered 100 meters.
They rented a shipyard
crane for this.
The biggest structures Atlas
had, you're going to see in
one of those pictures, is 280
ton magnets, which are 11
meters in diameter.
The hall above the surface is
roughly 11 meters high, and
the crane is inside the hall.
So if you want to attach the
crane to the structure, you
have to lower the structure
halfway into the hole and then
attach the crane.
That was funny moments
back in 2007.
As you might realize,
Caitie does data
analysis, while I do hardware.
So I typically have
good photographs,
she has better plots.
We're going to get to some plots
too, because we have
some that might explain how
the discovery works.
This is the structure
I was talking about.
That's an 11-meter
diameter magnet.
So the thing that looks metallic
in the center,
supported by this orange
structure.
It can slide into
the detector.
CAITLIN MALONE: Like so.
JENS DOPKE: So you can
actually move this.
It has pneumatic feet, where
we put in pressure.
And then it's supported like a
hovercraft and can slide in.
It's not as simple to
move, but kind of.
The structure that you see aside
of it, which looks like
a large piece of cake, is a
22 meter muon chamber in
diameter, which can also slide
over it, suspended on rails at
the top of the cavern.
And it can slide over it to
seal off the detector.
This is Caitie and another
colleague from Great Britain
standing on a platform
inside the detector.
To give you an impression, we
have 11 stories on the C side
of our detector.
There's a C and an A side.
The A side has 12 stories
inside the cavern.
You get to climb up four floors
to be where we were
standing at that time, through
detector material.
So you're climbing between
active detectors.
And in this particular case,
you're standing next to a
1,000-ton calorimeter that's
filled with liquid argon gas.
We have developed 90,000 liters
of liquid nitrogen,
40,000 liters of liquid
argon in this cavern.
And it's a very particular
feeling if you're down there.
I think Caitie enjoyed
the day very much.
CAITLIN MALONE: I did.
It's like a big, radioactive
detector tree house.
It's really great.
JENS DOPKE: The first time I was
there was in summer 2006.
I keep getting back there
whenever I can because it's
the greatest place on Earth.
This is when we transported
the part that I
worked on at the time.
This was lowering a
four-kilogram detector itself,
with lots of support structure,
which had to be
inserted as the very last
component, into the center of
the detector.
The transportation effort alone
was complicated as such,
because we couldn't
crush it anywhere.
We couldn't just roll it over to
the cavern and then attach
it to the crane because it had
to be suspended, such that it
wouldn't suffer from shocks
during the transport.
So we couldn't just
roll it over.
It was craned over from one
hall into the other.
Also we had only a half an hour
window where the weather
forecast was good enough to get
it over without it being
drowned in rain.
CAITLIN MALONE: So just for a
sense of scale, let me just
jump in here for a second,
because I just learned this
recently, and I think
it's really cool.
So you have a sense now that the
detector is the size of a
large building.
But the alignment of the
components within the detector
is known to the width of
a few human hairs.
So it's very large, but it's
very precisely aligned.
And so if you have something
like you roll over a pebble
wrong, then it can mess
up that alignment.
That's why we have to be so
careful in the installation.
We should probably take
questions in a
few pictures here.
JENS DOPKE: We're almost there.
OK.
So this is where it arrived.
But I mean, we're done.
CAITLIN MALONE: Oh, OK.
Perfect.
We overspoke a little bit.
But we get carried away.
JENS DOPKE: If you want to see
results, we do actually
[INAUDIBLE]
results.
Because physicists typically
focus on getting data analyzed
and then getting papers out.
Making this easy to understand
for the general public is a
tough job and takes a lot of
time, that we need to make
time for that.
That's our weekends.
So I suppose that someone messed
up this weekend when
generating--
and made GIFs like this.
CAITLIN MALONE: Right.
We can just let this play
in the background.
But let me just introduce you to
it before I take a couple--
so this is the ZZ.
So what you're looking for is
you're looking for an excess
of events that's not explained
by basically these colored
structures.
So the colored structure is the
background Monte Carlos.
This is our model of what a
background will look like in
this channel.
This axis here is the
reconstructed mass of the Higgs.
So if you start to see a bump,
then that's the mass of the
particle that you're
looking for.
And so what this is doing is
it's scrolling through time
and it's adding more and more
data to the histogram.
And so you can start to see that
there is-- yeah, if you
can reset it--
that there will be a peak that
will start to emerge right
here that isn't apparent from
sort of the red background.
And so once you start to see a
peak that isn't explained by
any of the background,
and that's
what has to be a signal.
So this is actually watching
where the points here or the
data, actually watching the
Higgs peak grow in real time.
And then at some point, it'll
zoom in on this exact excess
and then fill in the Higgs
underneath it with sort of the
signal Monte Carlo.
Say that's what a Higgs
would look like.
OK, I think with that we've
overspoken by probably 10
minutes or so.
But--
AUDIENCE: [INAUDIBLE].
CAITLIN MALONE: --15 minutes
for questions.
AUDIENCE: [INAUDIBLE]?
CAITLIN MALONE: As many
questions as you
can ask in 15 minutes.
But thank you very much
for your attention.
It's been a lot of fun.
We hope you've learned
something.
AUDIENCE: This questions can
be about this topic or--
CAITLIN MALONE: This topic
or anything else really.
JENS DOPKE: We're young.
We answer questions
most of the time.
AUDIENCE: So [INAUDIBLE]
organizer of the Australian
conference [INAUDIBLE]?
CAITLIN MALONE: They
were understanding.
AUDIENCE: Could you repeat
the question?
CAITLIN MALONE: Oh, I'm sorry.
The question was what did the
Australian conference think
about their thunder being
slightly stolen?
I think they understood.
They could see that it was
maybe going to come.
I can't imagine they were that
happy, because it would be
great if you can be the person
who makes the announcement.
But we did have a direct line to
Melbourne for the seminar.
And so a lot of our colleagues
were in Australia at that
point for the conference,
which was
starting the next day.
And so they called in, and they
congratulated us very nicely.
And the people who were
organizing the conference were
a subset of the people who
made the discovery.
So it was a very collegial
feeling.
AUDIENCE: How big is the
next accelerator?
CAITLIN MALONE: How big is
the next accelerator?
JENS DOPKE: I prepared
a picture for that.
So the question was the
size of the next
machine that we're building.
AUDIENCE: [INAUDIBLE]?
JENS DOPKE: We are not building
the next machine yet.
We're thinking about building
next machines and, well,
upgrading the machine that we
currently have, which you see
on this picture in white.
That's the LHC.
That's nine kilometers in
diameter, 27 kilometers in
circumference.
We're thinking about upgrading
that sometime in 2022 maybe,
running up to 2030.
That's going to deliver a lot
of data to exclude a lot of
things that we're--
CAITLIN MALONE: Or discover
a lot of things.
JENS DOPKE: Well, we're
mostly excluding.
CAITLIN MALONE: We have many
more ideas than we have actual
particles that we found.
JENS DOPKE: We're
very exclusive.
CAITLIN MALONE: Yeah.
JENS DOPKE: But then
the thing is we
need a precision machine.
So the LHC is a thing that
collides protons.
Protons are particle
combinations of multiple quarks.
And so we never know how much
energy we actually get in a
collision, because what's
colliding is not the proton,
but the quarks.
So depending on how much
fraction of momentum of the
total proton one of the quarks
has as they collide, you get
more or less boost
in one direction.
What we used to have in the past
and what we should have
again in the far away future,
kind of, on my lifetime span
measured, or hers, is an
electron positron collider.
Because those are fundamental
particles.
They are not made up of other
structures as far as we know.
So what we got in the large
electron positron collider
previously was collisions where
we could adjust the
energy of the incident particles
and thereby create a
collision at a fixed energy.
We would never get something
else but the
energy that we put in.
Because as the two particles
collide, they disappear
completely.
So all of their momentum goes
into the collision.
And using those machines, you
can much more precisely
measure the outcome.
The energy we need to properly
measure Higgs bosons you can
roughly grasp from the scales
that are shown in this
picture, is 500 GeV center
of mass is nice.
That is because we can most
probably create Higgs bosons
only in associations
with Z bosons.
And that means we need to get
up to an energy of 240 GeV
instead of 125 to create both
particles and make them
detectable.
And then the other thing we
want to do is produce some
very heavy quarks in pairs and
measure them precisely.
So producing top quarks in pairs
require some 340, 350
GeV center of mass energy.
So that's the rough scale
we want to go to.
And then you want to be able to
go slightly beyond, just to
measure the full spectrum and
not just end exactly what you
want to measure.
There are also plans for
building something like a
compact linear collider and
not just the standard
international linear collider.
A standard concept is the one
shown in yellow, that's like
30 kilometers long in
a straight line.
The other concept is the compact
linear collider,
that's in light blue.
That's 42 kilometers.
It's only compact because it has
a lot more energy in the
same length.
CAITLIN MALONE: Wait.
I should say very quickly too,
one of the things that's
tricky about electrons and
positrons, they give you very
nice, clean collisions, and
they're very tunable.
The thing is that when you try
to run them in circles, they
radiate away their energy.
And if you were to put electrons
into the LHC, they
would radiate away as much
energy in a turn as you could
put back in through
the accelerator.
So the way that we avoid
this problem is
by not turning them.
So that's why you want to
build a linear collider.
But that technically
more difficult.
So that's what motivates
the geometry there.
JENS DOPKE: Linear collider
geometry is the problem.
As you see from the size of the
structures, it's kind of
hard to find a place where you
can actually drill a tunnel
that's this long.
You want to typically build a
tunnel such that it's easier
to control access, such that
you don't have radiation at
far ends that comes
out and disturbs
people, which it does.
So that's why we generally put
structures underground.
Japan is thinking about
looking into that.
The time scale for this
is roughly 2030.
And then there's other
ideas around.
We're not very fond of
just having one idea.
So this here, I zoomed out, is
ideas for an 80-kilometer
storage ring.
That would actually be
in the Geneva region.
And either it would pass, as
seen on the left, underneath
the lake of Geneva and beyond
the next mountain range that
we can see from the CERN
cafeteria or it would pass
into the [INAUDIBLE], both of
which will be complicated
because you're going through
multiple layers of different
types of rock and so drilling
tunnels in there is kind of
complicated.
But then you need the
preacceleration structures to
get proper energies
into these rings.
So that you only get here.
CAITLIN MALONE: I
think I heard a
question over here maybe?
AUDIENCE: I was just going
to ask [INAUDIBLE]
collider [INAUDIBLE] you're to
do a straight [INAUDIBLE]?
JENS DOPKE: So the question is
whether the tunnel has to be
straight or can be slightly bent
on the Earth's surface?
CAITLIN MALONE: Oh, to follow
the curvature of the Earth
over the distance.
JENS DOPKE: Curvature
of the Earth is not
really a big deal.
But it would most presumably be
a straight tunnel, just to
not deal with bending magnets.
We'd have to refocus
at some points.
And we'd probably get something
that we call more
like a kicker magnet that
adjusts the beam.
But it's really fixed focusing,
and it's not about
bending the particle path.
There must be a bending
somewhere in there, because at
the point where you want to
collide the beams, you don't
want to shoot the positron
beam into the electron
acceleration line.
So that at that point,
you have like a one
degree angle or so.
AUDIENCE: [INAUDIBLE]?
CAITLIN MALONE: Ah,
the question was
about the third detector.
So there are four points
around this ring.
And the two that I haven't
spoken about are LHCb and one
called ALICE.
LHCb and ALICE are both--
so CMS and Atlas we call sort of
general purpose detectors.
LHCb and ALICE are
more focused on
particular types of physics.
The LHCb is there and doing
wonderful physics.
They focus on the physics
of B hadrons.
And the reason that B hadrons
are interesting is because
we're trying to understand, not
to put too fine a point on
it, but why the universe is
made of matter instead of
antimatter.
Because there's no physical
reason why we should be made
of matter, instead
of antimatter.
And B hadrons, as it turns
out, show some asymmetry
between Bs and anti-Bs.
And so it's a very interesting
laboratory for studying the
answer to this question.
And then ALICE, just briefly
while we're talking about
other detectors, is designed
to do heavy ions.
So for a couple months every
year, they take all the
protons out of the LHC and
they put in lead nuclei.
And they smash them together to
try to basically create the
environment that existed just
a fraction of a second after
the Big Bang, when quarks and
gluons were not joined
together into protons and
neutrons but were actually
sort of floating free.
And this was obviously a very
interesting laboratory for us
to try to understand the very
beginning of the universe.
And that's something that
ALICE specializes in.
Yes?
AUDIENCE: I have question.
Are there risk parameters
[INAUDIBLE]?
CAITLIN MALONE: Like, like-- oh,
things like black holes,
risks like black holes.
JENS DOPKE: Just a quick vote
in the audience, like who's
heard of black holes?
CAITLIN MALONE: I've heard
of black holes.
I've heard of black holes.
Yeah, yeah, yeah, yeah.
JENS DOPKE: That's good.
Is it clear that when we're
talking about black holes in
the context of the LHC that
A, we have to assume
very special theories.
And B, we're talking about
microscopic black holes.
We're not talking about the
thing that eats up suns.
We're talking about something
that's very, very tiny.
AUDIENCE: [INAUDIBLE]
JENS DOPKE: In the beginning.
Yeah, yeah, yeah.
Yeah.
It does suck for a while and
then it grows bigger.
CAITLIN MALONE: So to first
order, we're pretty sure that
they wouldn't be there.
There are smarter people that
me who crunch the numbers,
that says we just don't
have enough energy.
But let's suppose we got that
equation wrong and we do
create a microscopic
black hole.
Stephen Hawking, one of the
things that he sort of made
his name theorizing was
that black holes
can actually evaporate.
And as it happens, small ones
evaporate quite quickly.
So they would only live for
a fraction of a second.
Now, let's suppose that Stephen
Hawking is wrong and
we have a stable black hole,
stable microscopic black hole
that's floating around the
inside of the detector.
And then they did a calculation
like it's doing a
little PacMan through the
detector and it's just
gobbling up atoms as it
gets close to them.
And how long would it have to go
before it would be, I don't
know, the size of an atom
or something like that?
And it was millions of years.
AUDIENCE: So there could
be one in there.
JENS DOPKE: Well--
CAITLIN MALONE: And
that is why we--
here we go.
I think we promised something
like wild and irresponsible
speculation.
And I am glad you're here to
provide it for everyone.
JENS DOPKE: Let's go further
into wild speculations.
We do know about objects like
neutron stars, which are
roughly the mass of the Sun or
two, but the size, a diameter
of a kilometer.
So what these feel like is
matter in the core of an atom,
the nucleus of an atom,
just the size of
one kilometer diameter.
The moment a microscopic black
hole would exist, it would hit
a neutron star, and it would
just be dissipated.
The neutron star would go away
at that very moment.
Now, we know that cosmic
radiation exists.
We have some very fancy
experiments, for example, in
Argentina that has 3,000 square
kilometers of Earth's
surface monitored for energy
deposition from the sky.
We look into the sky with
telescopes to find gamma ray
bursts in the upper
atmosphere.
We have a South Pole telescope
that monitors the cosmic
microwave background.
We have quite a few things
that know that
there's cosmic radiation.
And we see cosmic radiation in
an energy range that we will
never reach with any accelerator
that we can build
on this planet, because
the planet's diameter
is not large enough.
So we have a pretty good idea
that if microscopic black
holes would exist and were
stable, that they would be
created a lot more often and
a lot bigger in cosmic
radiation, hitting anything
that's in their way.
So if neutron stars exist, then
we can safely assume that
microscopic black holes, if they
existed, were not stable.
Because otherwise, they'd be
eaten up the moment they
existed by something
that hits them.
AUDIENCE: I think [INAUDIBLE]
energies in the black holes.
JENS DOPKE: Has anyone ever
heard about RHIC?
RHIC used to be a heavy ion-- is
still a heavy ion collider
at Brookhaven National
Lab on Long Island.
In the '90s I think, when it
ramped up the STAR experiment,
there was a rumor that they
would create black holes and
destroy the universe.
I think the rumor about the
black holes came up ever since
someone fancied the theory that
it would contains black
holes, because black
holes are cute.
But the problem is the moment
someone comes up with a cute
idea that sounds kind of
vicious, someone else comes up
and goes to an American lawyer
and says, I want to
get money for this.
This is mostly how it works.
People are more easily scared
than assured of being safe.
And that's the big deal.
That's why we actually have
to take care of publishing
results the way we communicate
with the general public.
Because the general public tends
to receive the negative
message much better than
the positive message.
CAITLIN MALONE: That having been
said, there are analyses
that are searching
for black holes.
I mean, we're looking
for them.
I wish we had found them,
but we haven't.
AUDIENCE: How safe is the beam
itself and can you slice bread
with it [INAUDIBLE]?
CAITLIN MALONE: We've tried.
JENS DOPKE: So the question
was about beam safety.
So we've done--
AUDIENCE: That means you can
slice bread with it.
CAITLIN MALONE: So we're very
clear about the bread, yeah.
JENS DOPKE: Let's be clear.
No, you cannot slice
bread with it.
You can--
AUDIENCE: Melt.
JENS DOPKE: Melt--
you can melt a cubic meter of
copper with the energy that's
within the beam.
AUDIENCE: [INAUDIBLE]?
JENS DOPKE: No.
You can cut the bread with it.
But you'd have to get the
beam to the bread.
We did test studies
with copper.
And we can shoot very nice
holes into copper.
When we're talking about beam
safety, we have two so-called
beam guns, one for each
direction, which are sitting
in Point 6 of the LHC, that's
somewhat pointing towards
Zurich on that ring.
No, but the pointing direction
then is towards the UK and
towards Italy.
So they are sitting on the side
of Zurich of the ring,
but pointing in different
directions.
Beam dumps are basically a large
structure that can be
cooled, that heats up to 700
degrees Celsius if you dump
the beam into it, which
are there for safety.
So if we have the full LHC
filled with protons, we're
talking about 2,808 packages per
direction, with about 100
billion to 200 billion
protons inside.
The protons themselves don't
have much energy as such.
But there's just so many
of them that it
makes for a large impact.
When we, for any reason, which
we do very often because every
now and then we have electric
glitches or whatever, dump the
beam, we realize there's
something wrong with the
machine so we are not sure we
can keep the beam in shape.
And that moment, it takes three
turns of the protons to
dump them into the beam dump.
Three turns is less than
a millisecond.
And the time constant that all
the magnets have that we have
there, we have the largest
magnets that you
can find in the world.
Magnets tend to be slow
in whatever they do.
We pump them up with, what,
eight kiloamps, 10 kiloamps?
So--
CAITLIN MALONE: Yeah.
JENS DOPKE: --the time it takes
for this current to go
down, and if the current goes
down, the magnetic field
itself induces more current as
it collapses, so the time
constant of these magnets is
so large that within their
time constants, if we would just
cut the wire between one
end and the other, and the
current could not flow, A, the
current would continue to
flow wherever it can.
And B, the magnetic
field would still
be there for a while.
And this while is long enough
that we dump the beam.
We have to defocus the beam.
We have to shoot the packages
into different directions in
the beam dump, so as
to not shoot holes
into the beam dump.
But yes, the beam itself is
not a very nice thing.
No one is underground
when this happens.
We have interlocked
doors everywhere.
So if anyone for any reason
manages to open the door, that
will cause the beam
to be dumped.
And those doors are either above
surface or at least like
six meters of concrete away
from the actual beam line.
AUDIENCE: [INAUDIBLE]?
JENS DOPKE: Yeah, we do shoot
holes into stuff.
AUDIENCE: [INAUDIBLE]
how big would it
go [INAUDIBLE]?
JENS DOPKE: I have no idea.
The beam dump itself is a
structure that's like 10
meters long or so,
so as to be safe.
CAITLIN MALONE: It's roughly
analogous to shooting a bolt
of lightning into something.
That gives you an idea.
It's a lot of [INAUDIBLE].
JENS DOPKE: We're talking 1,800
megajoule, if anyone
wants to do the calculations.
I'm not very good at calculus.
AUDIENCE: Speaking of the other
[INAUDIBLE], slightly
off topic here, faster
than light.
CAITLIN MALONE: Oh right, faster
than light neutrinos.
What was the problem?
AUDIENCE: [INAUDIBLE]?
JENS DOPKE: Sadly, I don't
have a picture of CNGS.
CAITLIN MALONE: So the
neutrinos, just a brief word
on neutrinos, the faster
than light neutrinos.
So what is a neutrino?
A neutrino is just a fundamental
particle.
It's very light.
It's almost impossible
to detect.
We need dedicated detectors
to do it.
Atlas can't see them.
And so that's why, if you
remember at the very
beginning, WW was so hard was
because we can't see the
neutrinos coming out of there.
But we have dedicated
experiments where we make
neutrino beams at CERN
and elsewhere.
But the one in question
came from CERN.
And then we shot it through
the ground to Gran Sasso
laboratory in Italy.
And what you do is you basically
make measurements on
the beam at CERN, and at Gran
Sasso you look for changes in
the composition of the beam
between the two points.
And so as sort of a warm-up
measurement that they did on
this experiment was they tried
to measure just the time of
flight of the neutrinos.
And they came up with a number
that said the neutrinos were
traveling faster than the
speed of light, which is
something that Einstein
might disagree with.
And actually, it was an
interesting case, because as
it turns out, the reason that
they measured that was because
there was a problem.
There was a loose cable in their
data acquisition system.
And so there was a signal that
was traveling through
basically their electronics
crates a little bit slower
than they had calibrated
it to travel.
And this ended up looking like
a delay that the implication
was that the neutrinos looked
like they were traveling
faster than the speed
of light.
So after a couple of months of
very thorough and nervous
investigation, they found
this problem.
They reran the analysis.
The neutrinos do not
travel faster than
the speed of light.
It was a really interesting case
of that in particular.
So the collaboration that
did this was the OPERA
collaboration.
And there was a lot of criticism
of OPERA at the time
that they were irresponsible
for giving this result.
And I personally at least--
everyone has an opinion on
this-- but I personally at
least really admired what
they did there.
Because it was a
tricky result.
You put yourself in
their position.
You've done this analysis,
you've checked everything you
can think of to check.
OK, maybe you didn't
check your cables.
But that wouldn't be the
first thing that I
would think of either.
And you still have the result.
And you can't not release it.
And I don't know, maybe
neutrinos do travel faster
than the speed of light.
And you would feel like a fool
if you figured this out in six
months, and you were sitting
on it and then someone else
scoops the Nobel Prize from
you in the meantime.
And so if you look back at the
result as they presented it, I
thought they did it in quite a
responsible way, in the sense
that they went for it.
They said, look, this
is what we find.
It doesn't make a whole
lot of sense to us.
These are all the things
we've checked, and
it's not any of those.
So--
JENS DOPKE: Help us.
CAITLIN MALONE: --we said we
would give you a result.
This is our result.
And very pointedly not saying,
we think neutrinos travel
faster than the of light.
And so it was kind of
interesting then to watch both
the experimental community
trying to figure out what's
wrong with it and the
theoretical community is like,
ooh, if neutrinos can travel
faster than the speed of
light, then--
and following this through their
favorite theory and I
don't know, coming up with like
extra dimensions out of
it or something like that.
JENS DOPKE: What people should
understand here is what is
seen on the map now.
What we're doing is we're
taking protons from the
preaccelerator of the LHC, shoot
it into a target, where
they convert into muons.
And then we detect the
muons in two places.
And as the muons disappear from
one place to another, we
know that they must have left
a muon neutrino behind.
That's the way our
physics works.
That's the way we can explain
a lot of things.
So there must be a muon neutrino
whenever a muon
disappeared.
So at that point we can say
we've produced so many muon
neutrinos in this type
of distance.
And then we shoot them through
738 kilometers of rock and we
hit our target, the OPERA
detector, close to Rome in the
Gran Sasso underground
laboratory, with about two
centimeters of precision.
And they've measured the timing
of both the incident
beam at CERN and the arrival at
Gran Sasso to a little less
than two nanoseconds'
accuracy.
CAITLIN MALONE: Which is two
feet at the speed of light.
JENS DOPKE: They have GPS
receivers, which they have to
install above surface
to get this timing.
And then they have to
extrapolate at CERN 100 meters
under ground, and at
Gran Sasso through
the Gran Sasso tunnel.
So actually they had to block
half of the tunnel.
It has two lanes.
And they block one of those
lanes for quite some time just
to extrapolate length
measurements from the outside
to the inside and get the timing
right at the detector.
So measuring a 60-nanosecond
time difference in time of
arrival is complicated.
And I think they've put a
lot of effort into this.
CAITLIN MALONE: I think I
saw you had a question.
Yes?
AUDIENCE: You know you
had the results.
And then somebody from the media
or from a blog grabs it,
runs with it, then applies
some sweeping generations
[INAUDIBLE]?
JENS DOPKE: Are we talking
about god particles?
CAITLIN MALONE: Oh, yeah.
JENS DOPKE: So the question is
about media and how we get
around with them I guess.
CAITLIN MALONE: It depends very
much, I guess my opinion,
on how responsibly I feel like
the message has been conveyed.
So one example that I'll give
is that outlets like the BBC
or the "New York Times," usually
they have people who
when they come to us are
responsible about trying to
portray things accurately.
And sometimes it's not
perfect, but that's
all right with me.
I'm less crazy about--
sometimes bloggers take a little
bit more liberty than I
would have chosen.
I think that it certainly gets
people interested in talking.
And I think that that
is a good thing.
But for example, when there
was this sort of spurious
semidiscovery in 2011, the
reason that was a problem was
because it got onto a blog
and it got public.
And so that's an example of how
I think it kind of hurt us
to have something out there, but
then have to say, no, no,
no, no, no, don't pay
attention to that.
And then I guess on the
very far extreme are
kind of like crackpots.
And I guess what can you do?
People are going to say
what they're going
to say about whatever.
JENS DOPKE: Handing the question
back, how does Google
deal with it?
There was a question there.
AUDIENCE: So when LHC was first
supposed to go offline
back in what was it, 2007 or
2008, there were some--
JENS DOPKE: Here's a
question about the
LHC accident in 2008.
CAITLIN MALONE: What accident?
JENS DOPKE: So the accident.
CAITLIN MALONE: I'm
just kidding.
I know what accident.
JENS DOPKE: We only had one.
So again, to talk in numbers.
We have 1,232 dipole magnets,
which are in most places
connected to one another.
We're filling this whole
27-kilometer ring with magnets
or accelerating structure
or experiments.
But that's all there is.
And we only have so many.
When this accident happened,
what happened was there is an
interconnection between
multiple magnets.
Those are superconducting
magnets.
They run at a typical
temperature of like 1.9 Kelvin.
We're cooling them with what
we call superfluid helium,
which tends to crawl up the wall
and cover all surfaces
and has, as far as we can
measure, infinite heat
conductivity kind of.
Which is complicated
to measure at
almost absolute zero.
So we're cooling this all so far
just because we need the
coolant flow.
Because helium itself doesn't
have a large heat capacity, so
we need superfluid helium
to get there.
The problem is gases
tend to expand.
Well, liquid gases tend to
expand as they evaporate by
about a factor of 1,000, which
is kind of almost always true.
So depending on which gas you
have, that's more or less.
But a factor of 1,000
is good number.
What happened there was that
we had an interconnection
between two superconductors
which was slightly above the
resistance that it should have
been, plus that the heat
conduction at this place was
likely below the value that it
should have been.
So unfortunate, but what
happened was that the--
and it's not that simple.
There's someone making an
extending movement in the
background.
What happened was this
thing got hot.
It kind of burned through.
So the superconductor
didn't work anymore
because it was too warm.
So at that point, the typical
superconductor that we use is
niobium titanium.
And niobium and titanium are
both not very good conductors.
It's a wonderful
superconductor up to 10 Kelvin.
But as soon as it goes
beyond that, gone.
So what happened was the
current, those 8 kiloamps or
so, had to go somewhere else.
And typically what we have for
this is a copper surrounding.
So two U-profiles that slide on
top of one another, so that
if the magnets extend
or shrink they
can still have contact.
And if the current goes through
the copper, then at
least it can still continue.
And you immediately dump the
power of the magnet.
The problem was in this
case even the copper
contact wasn't there.
So what then happened--
tiny gap.
So the current go
somewhere else.
And what it did was it jumped
a little and hit the helium
vessel within the magnet.
So the helium and the
superconductor are not within
the same structure.
But they are connected
through metal.
What then happened was the
helium vessel opened.
The helium sees a sudden under
pressure and starts
evaporating, getting hot
and creating a cloud.
And this then pushed partially
the magnets
by 1 and 1/2 meters.
Each of those magnets is about
20 meters long and about 22
tons in weight.
And they are bolted into
concrete feet with screws
roughly the size of my arm.
CAITLIN MALONE: And that is why
you're not allowed in the
cavern when the beam
is running.
JENS DOPKE: That is why we
have interlocked doors.
CAITLIN MALONE: Yeah.
JENS DOPKE: It moved a total
of 55 magnets at the time,
which is a long distance.
Like a total of 400 meters,
I think, was damaged.
And it took a year to
fix it and get first
countermeasures installed.
And right now, we're in a
shutdown because we want to
install more countermeasures
to this.
Because we are kind of sure
that we've pinpointed the
problematic locations.
And we're trying to measure--
you can try and go online and
figure out how to measure the
resistance of less
than a nanoamp.
That's complicated.
We've been managing
to measure that.
And the idea is now to either
exchange magnets where we
think that the resistances are
too high in these junctions
points or also install
overpressure valves.
Because the moment this just
happens again, we need to be
prepared that there's helium
again extending and expanding
and moving the magnets.
And that would be sad.
So that's what we're
doing right now.
AUDIENCE: How do
you test beams?
How do you--
JENS DOPKE: Come to CERN.
AUDIENCE: --test that's it's
working better than.
JENS DOPKE: Here is
the question then,
how do we test this?
This is all prototype.
Like we're not building
a second LHC.
So the first time we switch this
on is the first time ever
someone is trying this.
And we're only switching
on the real machine.
We don't have a second one
somewhere in the back yard
where we can try out stuff.
So this is our one playground.
That is why things
like this happen.
And they have to happen
to figure out why
stuff is not working.
We do have above surface
structures where we also have
superfluid helium to operate
the magnets.
But you can only operate so many
in a chain, because you
need the space.
So getting all of this assembled
and [INAUDIBLE] our
structure only happens
underground.
AUDIENCE: So basically,
[INAUDIBLE].
JENS DOPKE: We only have one
system, and that's the
production system.
There is a preproduction
sample.
But it never gives you
the full feeling.
It's like just having the engine
of Ferrari and then
trying to figure out
how it will drive.
There's a question here?
AUDIENCE: How many rounds of
design review [INAUDIBLE]?
JENS DOPKE: A good question,
in particular for the LHC.
CAITLIN MALONE: Yeah.
JENS DOPKE: I can tell you
that for detectors, the--
oh, the question was how
many rounds of design
reviews did we do?
So I can tell you that from the
detector side of things.
The technical design report for
the detector I worked on
was written in 1998.
The last changes to that were
made, I think, in 2007,
probably, just before
we installed.
Because what we did was
installed an additional heater
blanket for components
that couldn't be
operated very cold.
That was the last design
change that was made.
I don't think there's ever
been a state at which the
detector was clearly defined
up until the point where we
installed it.
We do go through a lot of
rounds of design reviews
because we're never sure, like
did we see everything.
So we have a lot of people
from, for example, other
experiments.
We can just go around and pick
up people from Atlas or from
LHCb and tell them here,
look this is what
we're going to build.
Is this sane?
Go through the documentation.
Go through the preproduction
samples that we have.
Like figure out whether we
overlooked something.
AUDIENCE: How many
[INAUDIBLE]?
JENS DOPKE: That depends
on the project.
For me, it's typically
electrical engineering.
So there's electrical
engineers.
There's physicists who want to
figure out whether, besides
the technical aspect of things
that will work for a
physicist, because you will
find that there's a big
difference between the
electrical engineer and the
physicist in approach of trying
to build the detector.
That's mostly it, I think.
It depends on the problem.
Like we have IT specialists
there.
We have kind of specialists
for everything there.
We have our own department
for glues.
AUDIENCE: There's five
more minutes
we will take questions.
CAITLIN MALONE: There's
one over there.
AUDIENCE: [INAUDIBLE]
is how reliable?
JENS DOPKE: The question
is how reliable
is the machine now?
And last year, last year's
operation was on time of, I
don't know.
We had a so-called [INAUDIBLE]
factor of
more than 40% I think.
CAITLIN MALONE: Yeah.
I think when it's running
really well--
it's a little bit stop and go at
the beginning as they sort
of get a feel for the machine.
Once it's sort of on that
plateau, though, it's running
maybe 70% of the time.
And then the rest of the time,
you're refilling or
calibrating, whatever.
JENS DOPKE: Once the machine is
on, it really operates 24/7
and nicely, actually.
Like all the data we've acquired
last year, it was
more than we initially were
told we would get.
And it was definitely
very good.
A question there?
AUDIENCE: So [INAUDIBLE], but
what are the remaining gaps in
the standard model remaining?
JENS DOPKE: I sure hope
that Caitie is going
to answer the question.
CAITLIN MALONE: I will try.
JENS DOPKE: What's the gaps
in the standard model?
Like what do we do now that
we have the Higgs boson?
CAITLIN MALONE: So there's a
large class of people who
looking for supersymmetry, which
is another sort of--
you take the standard model, and
you give it another sort
of dimension of freedom,
if you like.
And this gives you a whole new
set of particles that we can
be looking for that might have
escaped our attention so far
because we didn't have the
energy to see them or because
they don't interact with the
protons and the atoms that we
make our detector out of.
So maybe they sneak through
because they don't interact
with atoms that well.
So there's a large group that's
looking for that.
Other open questions that are
related, I think, are things
like searching for
dark matter.
Which is something that we
cosmologically has to exist,
because we look out there and
we see that 25% of the
universe is something
that we can't see.
And so some of the
supersymmetric theories in
particular have particles that
are candidates to be the dark
matter particles.
So we look for those.
There are some other exotic
searches that happen at the
LHC for things like magnetic
monopoles, extra dimensions,
black holes.
And then yeah, like the
other little things.
JENS DOPKE: [INAUDIBLE].
CAITLIN MALONE: And then there's
some other smaller
experiments that you don't hear
coming out of CERN as
much, but I think are maybe in
the long run more impactful on
people's lives.
So things like learning how to
make antihydrogen, and to trap
it, and to study its spectrum.
And things like that.
Potentially antihydrogen, as it
turns out, and antiprotons
have some really nice properties
if you want to
fight cancer.
As it happens, they're extremely
difficult to make.
And they're not well
studied at all.
The first time we ever made
antihydrogen was in 1996.
So this is not an old thing.
This is something that
we're really pushing
on the edges there.
But if they figure out how to
make it larger quantities,
then there's all kinds of cool
stuff you could do with
something like antimatter,
for example
JENS DOPKE: The general drive
is to kind of get the full
picture of the universe.
So if we're looking up into the
sky, and we see that like
97% of whatever is out there is
not what we understand in
our current models,
then we're upset.
AUDIENCE: [INAUDIBLE]?
CAITLIN MALONE: Right.
We as much as possible
interconnect the two as much
as we can, though.
But then we also have colleagues
in things like
astrophysics who can help
us [INAUDIBLE].
AUDIENCE: How long does
it take [INAUDIBLE]?
CAITLIN MALONE: You
want to do this?
JENS DOPKE: The question is how
long does it take to fill?
About half an hour.
So the filling procedure itself,
depending on how
stable it goes, is something
like 10 to 15 minutes to get
lots of packets of protons
into the ring.
Because you need to
like stagger it.
So you start at a very small
ring accelerator, accelerate
protons to medium energy.
Get them into the next
accelerator, higher energy,
and then eventually fill
them into the LHC.
But as these rings have
different radii, you can fill
only so many packages
into each ring.
And so the initial ring gives
you the maximum length that
you can fill into
the next ring.
And as we do this, the procedure
has to repeat a lot
of times before we completely
fill the LHC.
So that takes 10
to 15 minutes.
And then the ramp-up of energy
that happens in the LHC takes
another let's say 10
to 15 minutes.
CAITLIN MALONE: Yeah,
20 minutes maybe.
AUDIENCE: [INAUDIBLE]?
JENS DOPKE: Well, let's say the
energy itself in the LHC
doesn't actually cause any
energy consumption because the
magnets are superconducting.
So you only fill them
with current.
And you can actually withdraw
the current eventually.
Like you could get it back.
I don't think we do.
The energy consumption
initially, I don't know.
CERN has a proper power line.
We have problems when we switch
from the French to the
Swiss network, which is an 18
kilowatt line on one side and
an 18 kilowatt line
on the other side.
And in theory, this should
happen seamlessly.
It never does.
Whenever we're being told that
there's a switching of power,
then everyone shuts down all the
critical systems, because
it means less work when you
power them up again.
We have a maximum of 200
megawatts that we can consume.
In standard operation with the
LHC on, we're consuming
between 145 and 165 megawatts,
out of which 85 is just the
cooling system for the LHC.
RF power to keep the protons
at energy is 2.4 megawatts.
So that's where we're talking
order of the Canton of Geneva
in terms of power consumption.
That's 400,000 households.
This is why we're supposed to
switch off in winter, because
if we're drawing too
much current,
Geneva has trouble heating.
CAITLIN MALONE: [INAUDIBLE].
AUDIENCE: Yeah.
I know there's a lot
more questions.
But our guests, they have
some meetings set up.
One's starting in two minutes.
CAITLIN MALONE: Thank you
very much for having us.
Yeah, good questions.
