Hello, and welcome to the Physics World Weekly
podcast. I'm Hamish Johnston.
The European Organization
for Nuclear Research
or CERN
was founded in Geneva in 1954.
Today, it's most famous for the Large Hadron
Collider,
which accelerates
protons and nuclei
in opposite directions
around a 27
kilometer ring before smashing them together
at high energies.
In 2012,
'2 experiments on the LHC
announced the discovery of the long sought after
Higgs boson.
And that's just one of the many important
breakthroughs
made at the lab.
But CERN isn't just about colliding particles.
It's a leader in the study of antimatter,
the place where the world wide web was
invented.
And CERN was home to John Bell,
whose famous theorem
marked a profound
step forward in our understanding
of quantum physics.
In this podcast, I'm joined by my physics
world colleague, Margaret Harris, who is back from
a visit to CERN with an update on
the exciting
physics that's being done there.
Hi, Margaret.
Welcome to the podcast.
Hi, Amish.
Now if there's one lab that every physicist
should visit once in their lifetime, it's got
to be CERN,
the the sort of preeminent,
particle physics lab in Europe and and maybe
in the world.
What was it like? How would you describe,
your trip? What's it like being at CERN?
Certainly, at the moment, it is the world's
premier high energy physics laboratory.
And I was told by one of my
tour guides,
Sarah Aldewelt, who's an early career researcher at
the University of Edinburgh when she's not working
at the ATLAS detector at CERN. She said
that this is an interesting time to visit
CERN, and I hope to have her on
the podcast at some point to explain this
in more detail.
But, essentially, if you're a particle physicist, you
have several possible modes of operation.
You can be in data taking mode. You
can be in data analysis mode, so dealing
with the data you've already got, and you
can be in the upgrading the experiment mode,
or you can be thinking about future upgrades.
And future in that in this case could
mean five years from now or could mean,
in extreme cases, you know, up to fifty
years away.
And right now, CERN is operating in all
but one of those modes. There wasn't any
data collection when I was going on because
the collider shut down over the winter.
This is to save on electricity costs,
and also to help avoid putting too much
demand on the French or Swiss
electrical grids at a time when demand for
heating is already high.
The it's funny. The the LHC actually requires
as much electricity as the entire city of
Geneva when it's running. This is the Large
Hadron Collider, the main collider at CERN. Wow.
So so there's no new science data being
generated during the winter,
but absolutely everything else is happening right now.
In a couple months months, there'll be spring.
The LHC will restart.
But then in 2026, it will enter a
longer shutdown, one that will last all the
way until 2030,
during which it will get what will probably
end up being its last major upgrade.
So unlike a previous upgrade where they went
from colliding protons at energies of five oh,
so sorry. Seven teraelectron
volts
TeV
to clotting them at 14 TeV,
this upgrade isn't an energy increase.
Instead, it's an increase in luminosity.
Now what's that mean? Well, the the beep
beams of the LHC are made up of
bunches of protons,
and every bunch contains about a hundred billion
protons.
But because protons are so small, the vast
majority of them don't collide when you cross
the beams.
You might get a few tens of collisions
per crossing.
Now that might sound really low, but because
those crossings happen 40,000,000 times per second, you
do still get a lot of data.
In fact, you get so much data that
CERN pioneered the handling of big data, and
they have really complex algorithms to help them
decide which data points to keep for future
analysis
and which to throw away because they're not
gonna be very interesting.
But the high luminosity
upgrade is going to bring that up to
200 collisions per crossing. So now you're talking
about an order of magnitude more data that
could be generated per unit time.
And and this high luminosity upgrade, I mean,
it's not just simply a matter of pumping
more,
protons into the accelerator. I mean, I'll I
mean, just about am I right in thinking
that just about every aspect
of the LHC and and the experiments that
are on it have to be
modified
or tweaked in some way
just to to to achieve this?
Certainly, the the two main,
biggest experiments,
ATLAS and CMS, have have to undergo major
tweaks for this.
So but I think there's actually 17 different
work packages involved, and I saw only two
of them. So I can tell you about
those two. I don't know about the the
totality of the upgrades going on.
But the first upgrade that I saw on
my tour involved something called a crab cavity.
And what these cavities do is that they
tilt the proton bunches
so the protons in them appear to be
moving sideways like a crab walks.
Oh, that's why it's called a crab cavity.
Yeah. That's why it's called a crab cavity.
I always wondered about that. Well, listeners, you
learn something new every day.
They don't look anything like a crab.
But the reason they they want to make
the move sideways is because at the moment,
the beams of the LHC cross
I mean, it's not at right angles exactly.
It's more like a sort of flattened x
shape,
but the area overlap isn't huge.
But once the crab cavity is installed, they'll
get a much fuller overlap. So if you
can imagine this difference between placing your two
fists in a cross at the wrists and
aligning your hands so that your entire arms
are sort of all crossing in front of
you.
And that means every proton in a bunch
is gonna have to pass through the whole
length of the bunch moving in the opposite
direction.
And that on its own will increase the
number of collisions per crossing
by around 20%.
Now of course if you're getting more collisions
you're also gonna need a detector and readout
electronics that can handle that. And that's where
the other work package I saw, the inner
tracker or ITK
systems upgrade
comes in. And this is gonna become the
new heart of the ATLAS detector. I guess
you could say the detector is having a
heart transplant effectively.
And right now, this inner tracker doesn't look
like much. It looks like an empty tube.
It's about as tall as I am with
slots in it, and these slots are gonna
be filled by long
strip like silicon based sensors.
I see. And I have to say, Margaret,
I'm very, very jealous that you got to
see,
ATLAS. I mean, I I I suppose that's
one of the bonuses of visiting CERN when
the,
collider isn't running, that you could actually
go down and see the experiment.
So what what what was that like? Was
it I mean, you you hear stories of
it being huge.
How huge is it? Can you can you
can you give us, I don't know. Is
is is it small office building huge or,
what's the story? Yeah. It's I don't know
the exact numbers. It's several stories tall. It's
a hundred meters underground.
To get in there, you have to go
through a security system that's sort of like
walking into a if you can imagine that,
an old fashioned telephone booth with a door
on the front and a door in the
back. So you walk into the the front
of the telephone booth. You stand on a
a square
that is apparently like testing your weight as
well as sort of scanning you like an
airport scanner.
And
then the doors open, you get to go
out. And if you're carrying anything and you
want to carry some tools or a backpack
or anything like that, it has to go
through a separate slot.
And they they were a little bit cagey
about exactly what this is doing, but it's
essentially making sure
that everybody is counted in and counted back
out and that the same people go in
as come out and they're not they're not
carrying
undue amounts of extra stuff with them while
either on the way in
or on the way out.
So you can, you know, appreciate the sort
of security. It's it's both for security and
also for safety. You don't want there to
be an incident. You forget that there's one
of your people is still down a hundred
meters underground. Yeah. So so it's got there's
a lot a lot of preamble or build
up to it. And then you get down
to the detector itself, and it's absolutely enormous.
And I think
the thing that that most impressed me about
it, this enormous machine, it's probably one of
the biggest machines
that humankind has ever constructed.
The thing that most impressed me about it
was the cable ties. And that's not because
cable ties were impressive or because they were
really fancy or whatever. It's because each of
those cable ties, and I could probably see
hundreds from just where I was standing, each
of them was put in place by a
human being who knew exactly what he or
she was was doing,
and they had to be put together in
this whole giant machine was fabricated entirely by
hand, by human hands and human brains who
knew exactly what they were doing. And that's
just, I think that's that's the thing that
got me about the detector, not its sheer
size or the fact that there's, you know,
above you, there's a hole in the ceiling
that lets new new components be lowered down.
It was seeing those cable ties and just
realizing
the immense amount of effort that went into
to making this this machine.
And I I I suppose the information that
flows through a lot of those cables is,
you know, just a tiny bit of the
information that the the detector produces, and then
that that's all put together
Yeah. You know, to tell you, you you
know, to tell physicists about,
the details of a of a collision. Yeah.
It is it is just amazing, really. I
mean, I've never seen ATLAS. I have seen
CMS, which I don't I don't think is
quite as big, but it was,
it was definitely impressive. So so was ATLAS
was it more or less intact when you
saw it, or had they was it taken
apart? Was it in pieces on the floor
or sort of halfway in between?
I mean, it looked pretty intact to me.
There wasn't a big, gigantic chunk missing, which
is absolutely what will happen when they put
this, this new ITK,
inner tracker in.
And one of the advantages of this new
design that goes in is that it should
be more
radiation hard than the inner detector that's in
Atlas now.
The scientists have showed me around the Integration
Hall where this, inner tracker is being assembled
before it gets lowered through that that
hole in the roof down a hundred meters
underground.
They said that the existing detector would actually
need replacing anyway even if they weren't doing
this high luminosity upgrade
because it's absorbed so much radiation over the,
you know, decade or more that it's been
in ATLAS.
It's absorbed so much radiation from the all
the particle collisions and all the the debris
of those collisions that it's becoming harder to
supply enough voltage to deplete the silicon in
the detector itself. Oh, wow. Yeah. Yeah. So,
you know, this is is you don't think
I personally don't think of the LHC as
being that older device, but it's actually you
know, it's been going for quite a while,
and there's there are thing there are things
there there's,
you know, a lot of of science has
been done about the auxiliary systems that go
into it. You know, think of where silicon
semiconductor
electronics was in, I don't know, the early
two thousands when they were designing and building
this thing, and think about where it is
now. You know, there's a real reason for
upgrades that have, you know, all everything to
do with lots of different areas of of
science,
not just particle physics.
So the new system can deal with a
higher number of collisions,
as well as being able to to cope
with, the the radiation.
It's just far more granular, faster channels, faster
electronics.
Right. And the the the other thing I
I remember is
when you go to see these detectors,
you you actually have to leave the main
site of,
of CERN, don't you? At least with CMS.
So is did you have to get on
a bus and sort of go across the
border into France? And,
you know, did they tell you to
remember your passport just in case?
They didn't mention the passport. My phone was
going off all the time saying, welcome to
France. Welcome to Switzerland. You have this much
data on your your plan. So I guess
that that was actually the only indication I
had that we were crossing the border at
the particular places I went because it is,
you know, relatively open border. There are checkpoints,
but, you know, there's
it's part of Central Europe. There's a lot
of of freedom to cross the border, which
is good for the scientists to work there
because a lot of them live in France
and then work in Switzerland or vice versa.
But yeah. No. It it's I think one
people we I spoke to said that he
he compares it. He's from from Glasgow originally.
He compares it to Glasgow subway system in
terms of the the length of it. Oh,
that's famously a big loop, isn't it? The
Glasgow subway system. Yeah. Yeah. Yeah. Because I
I, you know, I I've been discerned twice,
and I think the first time was in
the nineties. And back then, you know, whatever
the arrangement was between France
and Switzerland,
there was actually a border
to cross, you know, there there was a
kiosk there with somebody,
you know, we I had to flash my
passport, and we drove through. But then the
second time, yeah, as you say, the the
border had magically disappeared
as it has in, yeah,
in a lot
of Europe.
It's certainly a softer border than it than
it has been sometimes in the past. Yeah.
So so Margaret, the
we've got this where we will have this
high luminosity
LHC running at some point in the future.
What what does that mean for the the
physics
that's being done at experiments like ATLAS?
Why is it important to to see more
collisions?
Well, it will allow the
the the two,
high energy physics experiments at the LHC, ATLAS
and CMS, to collect 10 times more data
than they have now,
and to explore the energy frontier with more
potential for discovery.
And this is kind of amazing to me.
You know, the LHC has been running off
and on since 02/2008,
but it's actually only collected 10% of the
data it's ever going to collect. It will
get the remaining 90%
during this high Lumi run, which is scheduled
last from 2030
through to about 2040 or thereabouts.
And
a key focus for the high luminosity LHC
will be studying something something called a dye
Higgs event, which is not where the Higgs
boson dies.
It's where you create not one Higgs boson,
but two of them at once.
And once you have two Higgs boson at
once, that means you can study what happens
when the Higgs interacts with itself.
Fabiola Giannati, who's the current CERN director general,
called this self interaction
a portal to exploring interactions in the early
universe.
So within about a picosecond or ten to
the minus twelve seconds of the big bang,
this is when the Higgs field first became
established.
And so understanding how that came about is
crucial to understanding how initially massless elementary particles
end up gaining mass by interacting with this
Higgs field and turning into the massive quarks
and electrons we see around us today,
which are what you need to be have
in order to form atoms.
And this Higgs pair production also has some
implications
for matter, antimatter asymmetry. So we might learn
about that too.
I see. And, I mean,
the LHC and, you know, that sort of
high energy particle physics is not the only
science
that's done at CERN. And, you know, to
me, I think one of the most interesting,
group,
of experiments that,
are being done there at the moment are
the antimatter
experiments. And I think you you also paid
a visit to the was it the antimatter
factory? Do I have that right? At Yeah.
At CERN. Yeah. The antimatter factory.
There's actually I think
it's a little bit,
question of what the boundary between different experiments
lies, but I think there's actually five experiments
at the antimatter factory.
And all of them are in various ways
and with different techniques looking for differences,
actually, between the matter and look exploring this
matter antimatter asymmetry asymmetry
in a different way. They're looking for differences
between the behavior of matter and the behavior
antimatter,
whether that's the behavior antimatter under gravity as
with the alpha g, g bar, and AEGIS
experiments, or different magnetic moments as with the
base experiments or spectra as with, the
Asakusa experiments.
I see. And and and the reason this
is important,
is that what we know that at least
in the visible universe,
there's much more matter than antimatter.
And if we could we we could sort
of work out why by looking for differences
between the two, that could that could tell
us a lot
about, well, what we don't know
about physics.
So so what, I mean I mean, I
think, you know, the most famous experiment that
was that's been done there is, you know,
testing this idea
that does antimatter
fall up,
or, you know, does it somehow
respond to gravity
in a different way? And I think this
so far, the answer is no. But there's
lots of really interesting experiments there, aren't there?
Doing spectroscopy
on anti atoms and
I mean, it's some amazing stuff they do
there when you consider that antimatter doesn't really
want to hang around for too long.
No.
And I think this area of CERN actually
you know, I'm talking about the Hi Lumi
upgrade for ATLAS and CMS, but this area
of CERN actually had its big upgrade relatively
recently.
As recently as 2018,
each of those animator experiments got eight hours
of beam time per day, which is, you
know, a decent working day, but, you know,
you've got a machine. You could run it
twenty four seven if you wanted to.
But due to an upgrade of the Elena
ring
that provides actually slower
particles, everywhere else at CERN wants fast particles,
the antimatter factory wants slower particles.
This Elena ring upgrade provides half a million
anti protons per two minute shot,
and that became fully operational in 2021.
And now it delivers anti protons to four
experiments at once twenty four seven while it's
running.
And what that means is that alpha, which
is what I heard about most because my
tour guide, April Cridland, is a research fellow
at CERN who's part of the alpha collaboration.
What that means is whereas they used to
take make maybe 20 or 30 atoms of
anti hydrogen every four minutes,
now they're making more than a hundred, which
is a huge step because what used to
take
weeks now takes a day.
So so she was saying that, actually, there's
lots of alpha results due out later this
year, including,
sympathetically
cooling antimatter with beryllium. So putting antimatter into
contact with beryllium
to
maximize the number of anti hydrogen atoms trapped.
So definitely stay tuned on that.
Yeah. I I I mean, I think that's
really exciting. And, you know, we we we
shouldn't forget that, okay, we might see a
a huge breakthrough beyond the standard model of
particle physics
from the LHC, you know, in the high
luminosity
upgrade. But, you know, it's possible that,
the big, big discovery at CERN will come
from one of those antimatter
factories.
So, lot there's lots going on there. Isn't
there?
Yeah. And and people are also, you know,
starting to think about what the next machine
might look like. That's kind of the final
sort of component.
And that's interesting to me because the time
scales are so long on that Mhmm. That
the older generation of scientists will probably never
get to work on that next machine,
although they may live to see it built
after they've retired.
And even today's early career researchers will be
well into their careers, maybe even heading towards
retirement on their own before it gets going.
You have to have a long term perspective.
And you mentioned this question of antimatter following
up. This is this is kind of relevant
for me because one of the very first
stories I ever wrote as a science journalist,
as a student, an undergraduate,
was about a researcher
at my university who was interested in finding
out whether antimatter fell up.
And so when,
you know, the the antimatter experiments at CERN
found started finding evidence that it does in
fact fall down just like normal matter, I
mean, it's kind of disappointment. Right? Because you
wanna see some Oh, yeah. Unusual physics. But
it was also kind of, you know, it
felt very satisfying for me even as an
observer of this to sort of have finally
found the answer to a question
I was asking researchers,
you know, twenty years ago as a student.
So, you know, this is definitely,
you have to have a long term perspective,
I think, to be a particle physicist, to
think not just about the discoveries that are
happening now, but the discoveries
that are gonna be made in the future
and what you need to do to get
there to have that happen. And that's where
I think everything kinda comes together.
You you mentioned the sort of next generation.
So the I suppose the LHC is going
to run-in its high luminosity
mode and, you know, gather lots more data.
But at some point, it's it's just gonna
run out of of of road, I suppose.
When you when you spoke to people at
CERN, did you have any feeling for what
they thought the next generation
collider would be? What I mean, are people
very keen on this humongous
collider that would sort of go under Lake
Geneva,
you know, this hue but much larger version
of the LHC
at CERN, I suppose, or, you know, maybe
a linear collider somewhere else, or is it
it is I mean,
so I I suppose the community has to
decide on what it wants to do, but
to to to people there, is it still
really far in the future, or are they
focusing on the LHC at the moment?
I think that, you know, it probably depends
on what level you're talking about. You know,
the
Fabiola Gianati and, actually, the the upcoming CERN
director general director general designate Mark Thompson, who
I think was on the podcast a couple
weeks ago. Mhmm. They're very much thinking about
the long term future as well as thinking
about how to run the the experiments
and the the collider in its current operational
phase. I think I get the impression that
the CERN is very much pushing for the
establishment of the future circular collider, as it's
called, this this big, even bigger version of
the LHC.
But I think that you're you're right. The
community still has to sort of decide because
it's clear that,
you know, we're we're gonna get,
you know, no more than
one or two big
ex additional big machines like this.
The Chinese government is talking about building some
sort of high energy facility there. It's a
question about whether that will happen independently
of what's going on in Europe or, you
know, maybe The US.
And these things just have to still still
have to sort of shake out in the
in the wash, really.
Yeah. Well, it it'll be very interesting to
see what happens.
And, you know, for I mean, for our
listeners,
I mean, I think you'd agree with me,
Margaret, that,
CERN is a great day out. And I
I don't think you have to be a
member of the press
to go. I think they do maybe do
they have an open day every year? I
know, certainly, one of our colleagues is gone
as a sort of a normal citizen.
Oh, yeah. You you can absolutely day. You
can absolutely tour tour CERN as as an
ordinary citizen. I believe it's actually the top
ranked activity in Geneva on TripAdvisor or maybe
the second after going to Lake Geneva itself.
So, you know, you may not be able
to go down and see the ATLAS detector
like I did, but you can certainly go
and, you know, have a look around the,
you know, the control center and look around
the the buildings on campus and as part
of a a public tour group. And, yeah,
it's it's whatever you get to see is
absolutely impressive. Mhmm. There's also really, a really
good museum there, the the CERN Gateway. Mhmm.
That's, I think that's probably, like, number four
on the list of things to do in
if you go to visit visit Geneva. So
that's also a a great attraction.
Great. Well, thanks for the update, Margaret.
You're welcome, Hamish. Nice to talk to you.
That was Margaret Harris, and there'll be much
more about CERN from Margaret in physics world,
so stay tuned.
Twenty twenty five is the international year of
quantum science and technology,
and celebrations
are well underway
here at Physics World.
Our latest contribution to the festivities
is a fun quiz about all things quantum,
and here are three of my favorite questions.
Which celebrity
was spotted in the audience
at a meeting about quantum computers and music
in London in December
2022?
Was it Peter Andre,
Peter Capaldi,
Peter Gabriel,
or Peter Schmeichel?
So which one of those Peters is interested
in quantum music?
The next question is which of the following
versions of the quantum hall effect
has not been observed
so far in the lab?
Is it the fractional quantum hall effect,
the anomalous
fractional quantum hall effect,
the anyonic
fractional quantum hall effect,
or the excitonic
fractional quantum hall effect?
So which of those effects
hasn't been observed in the lab?
And finally,
what destroyed
the Helgoland
guesthouse
where Werner Heisenberg
stayed in 1925
while developing
quantum mechanics.
Was it a bomb,
a gas leak, a rat infestation,
or a storm?
The quiz has 15 more questions to test
your quantum knowledge,
and you can find it on the Physics
World website.
Just look for the headline,
test your quantum knowledge in this fun quiz.
The commercial quantum technology sector is burgeoning,
and I'm sure that some podcast listeners are
keen on pursuing
quantum careers.
So if you'd like some inspiration
and a few tips for success,
check out our interview with Michelle
Lawley,
who is an advanced
laser scientist
at Quantinium.
There, she supports the design,
development,
and construction
of complex
optical systems
that will serve as the foundations of quantum
computers.
After studying finance at university,
Michelle worked for several years as an investment
banker.
But after reading a scientific paper about quantum
teleportation,
she packed that in to become a physicist,
gaining a PhD
in quantum optics.
You can read all about her career shift
in the article From Banking to Michelle
Lawley's
Unique Journey.
And you can find that on the Physics
World website.
I'm afraid that's all the time we have
for this week's podcast.
Thanks to Margaret Harris for speaking to me
today, and a special thanks to our producer,
Fred Isles.
We'll be back again next week. See you
then.