Hello, and welcome to the Physics World Weekly
podcast. I'm Hamish Johnston.
In this episode, I'm in conversation with Tim
Gershon,
who is a particle physicist based at The
UK's
University of Warwick.
Tim is a long time member of the
LHCb
collaboration,
which operates an experiment on the Large Hadron
Collider at CERN.
And Tim is currently the collaboration's
spokesperson elect.
Earlier this year, the UK government announced that
it would no longer fund
its share of a crucial upgrade to LHCb.
This came as a shock to Tim and
his colleagues, and he explains
that this major cut puts the experiment
and UK particle physics in jeopardy.
We also talk about some of LHCb's
research highlights
over the past year and look forward to
what the experiment could do in the future.
Hi, Tim. Welcome to the podcast.
Hi, Hamish. I'm delighted to join you.
So Tim, can we start off talking a
bit about LHCb
itself?
So so can you describe the experiment, and
what distinguishes
it from other experiments
on the LHC?
Yeah. So LHCb
is one of the four main experiments at
CERN's Large Hadron Collider.
But as you said, it's not the same
as all the others. In fact, it has
a unique design,
and, that design gives it a unique physics
program. So let me start with the design.
LHCb is designed to be optimal for the
study of particles that are produced in Large
Hadron Collider collisions,
that contain
either the beauty or the charm quarks or
in some cases both.
Now because these quarks are relatively light compared
to the energy of the proton proton collisions
at the LHC,
they're produced at small angles relative to the
beam direction.
So while the other detectors at the LHC
tend to have a kind of cylindrical design
surrounding the interaction point and looking at particles
produced at large angles,
LHEB, on the other hand, covers the forward
region.
So you can really see this difference if
you just look at pictures of the detectors.
So why is it,
designed in that way? Well, that is to
give it a physics program which allows us
to study what we call flavor physics, really
the the physics of how these different
quarks behave. And in particular,
one interesting question in flavor physics is to
study matter antimatter asymmetries.
And this is really important as we need
to try to understand how the matter dominated
universe evolved in the very early moments after
the big bang.
But also through studying rare decays of these,
flavored particles,
we can test the standard model through, precision
measurements.
So that's sort of the core physics program,
but it turns out by serendipity that if
you design a detector to be able to
do these things really well, you're able to
do a vast number of other things very
well, in addition.
And in particular,
we have been able to discover huge numbers
of new hadrons, including the so called
exotic hadrons, pentaquarks and tetraquarks,
and much, much more besides. In fact, so
far, we have over 800 publications,
which includes several major discoveries.
I see. And Tim, you you are by
no means the only British,
physicist working on LHCb. Can you can you
talk a bit about The UK's
participation in the experiment?
Yeah. So one of the the features of
the way particle physics is organized in The
UK is that we tend to focus our
effort on fewer experiments compared to some other
countries of similar
size. So Germany, France, and Italy, for for
example.
So LHCb is a good example of that.
The UK has a a really strong,
involvement in LHCb because it's one of the
experiments that we've chosen to focus on, and
this has been extremely successful,
allowing The UK to make a really strong
impact in LHEB.
That means leadership of the key detectors and
computing projects as well as physics exploitation and
indeed the overall collaboration.
So the overall,
leader of the collaboration is a position that
we call the spokesperson
in particle physics. And in LHCb, The UK
has provided four of the eight spokespersons,
which includes myself, recently elected to be the
next spokesperson.
So we're providing about, half of the overall
leaders of the project, but from,
about 18%
of the the the members and authors,
of the the collaboration.
The the collaboration is a is a large
one, I should say. LHCb is approaching 2,000
members,
from over a 100 institutes in currently 28
countries.
A good example of UK leadership in LHCb
is that we initiated
and developed plans for an upgrade to the
experiment,
which will allow LHCb to continue taking data
until the end of LHC operations,
the so called high luminosity
era
high luminosity
era of the LHC.
I see. And,
before we we talk about,
the sort of funding issue that's come up
recently,
this high loo luminosity
upgrade, that's something that's being done to the
LHC.
It's something that's being done to
the experiments
on the LHC. It's it it really is
a big deal, isn't it?
Yeah. That's right. So the the main, upgrade
of the accelerator,
and of, two of the experiments of the
main experiments at the LHC, the ATLAS and
CMS experiments,
that will take place in the next few
years.
So the LHC will continue taking data until
halfway through 2026.
And at the end, the June,
we will have the final collisions of the
LHC in its current incarnation,
and start a long shutdown period during which
the accelerator
and ATLAS and CMS experiments are upgraded.
We're expecting that we will start taking data
again in 2030,
and the next run period
of the LHC so called run four,
will continue until 2033
when there will be another long shutdown, which
will allow the other two experiments, including LHCb,
to be upgraded.
And and just for our listeners who are
not, I suppose, you know, sort of up
on the lingo of particle physics, the the
high luminosity,
essentially, that means that you're going to be
colliding
many more protons. So you're going to be
you're going to have to your detector is
going to have to process
many more collisions.
And,
that means that you probably will see
some rare interactions
that you couldn't see before. Is that a
sort of a fair
assessment?
Yeah. Absolutely. So, luminosity, I think most people
will be familiar with the the word in
the the context of how bright a light
is. But in the context of particle colliders,
it's, essentially how bright the beams are. So
as we collide together,
beams at higher luminosity, that means that we
get more collisions
and, a higher rate of of data to
be processed.
So that allows us, as you said, to
see rarer processes that we're not able to
see, but it also allows us to collect
more data and, make measurements at higher precision.
And that's really important in particle physics because,
essentially,
these particle colliders are microscopes
to look at nature at the the smallest
scales.
And increasing the luminosity
is like improving the resolution of your microscope.
So it allows to see things at, even
smaller scales compared to to what has been
present to date. So there is a a
very exciting,
range of, of physics
challenges that we believe will be addressed,
by the high luminosity upgrade of the LHC
and its experiments.
Okay. Well, that that that's a great,
description of LHCb. I think it really sets
the scene
for,
talk talking about funding.
And, I mean, I suppose you and your
colleagues,
over the past
month or so perhaps have sort of received
an unfortunate bombshell
when it comes to funding. It appears that
UK research and innovation,
which pays for physics research in The UK,
will not continue funding
the high luminosity
upgrade
of LHCb.
What is your current understanding
of the funding
situation?
Yeah. So indeed, we've we've had this bad
news. To explain it, I'm going to have
to go a little back a little bit
back into into the the history and and
add a little bit more context to to
to what you've described.
So the the most relevant part of the
history here is that in 2022,
UKRI announced that it would invest in the
LHCb upgrade with an allocation of almost £50,000,000
from its infrastructure fund.
Now the infrastructure fund at the time was
a relatively new scheme that had been set
up by UKRI intended to provide a long
term stable source of funding for developments of
new research,
infrastructures, not only for physics, but across all
of, UK, research.
So this was a new way of allocating
funding, whereas previously,
UKRI distributes funds to the its research councils.
And one of those,
STFC,
is the research council that supports particle physics
as well as astronomy and and nuclear physics.
We'll we'll we'll come back to that in
a moment.
Let me let me just mention also that
the 50,000,000
that was allocated from the infrastructure fund was
to cover both capital,
so that means the cost of the detector
hardware, but also the staff to to build
this upgraded detector.
And the split between the two is around
about $50.50.
Now this very positive statement that we got
in in 2022
allowed UK scientists,
including myself, to really take, leadership roles shaping
the international project and and the design of
the overall,
international LHCb
upgrade,
and bringing our international partners on board. And
this had actually been really successful. By the
2025,
we had all major international partners agreeing to
contribute to this project, which meant that in
addition to The UK capital investment, we had
over a £100,000,000
worth of,
contributions from other countries essentially,
more or less signed up, and ready to
go.
This is great news for The UK. This
is a UK led project at The UK's
lab for particle physics because remember that CERN
is our lab that we operate together with
with our partners.
So things were looking pretty good.
We were planning to move on to preparing
detailed technical design reports on the subdetectors during
2026.
That's a a necessary step before we move
on to the construction phase of the project.
However,
on the 12/19/2025,
we received letters from the chief executive of
UKRI,
Sir Ian Chapman,
stating that the infrastructure fund investment in the
LHEB upgrade was,
to use his words, no longer prioritized.
This was a complete shock to us. Not
only were we working on LHEB,
not consulted,
the advisory bodies
for STFC,
which had previously prioritized the project were not
consulted,
and even CERN management,
have not, been consulted.
So,
we didn't even know that the the funding
was at risk. We didn't know that any
kind of review was going on.
If we had have known, we would have
still been very confident of continuation
since the progress on the product has been
so successful. And indeed, the case for investment
is, if anything, even stronger than it was
in 2022,
when the funding was was awarded.
So it's been a big shock, and we've
been working to try to to understand the
situation. Our current understanding of the situation well,
there's many aspects to this, but I'll try
to to keep it relatively brief.
So we know that the LHCb upgrade was
one of four, infrastructure fund projects that have
been
deprioritized
or to use a simpler word, cut.
Three of those are STFC projects,
and two of those are within the area
of particle physics, astronomy, and nuclear physics, which
we collectively refer to as PPAN. The other
one, by the way,
is for UK contribution to the electron ion
collider, which is proposed, in in America.
So it appears to have been an intentional
choice by UKRI to reduce the number of
STFC projects.
And the reason for that seems to be
concerns that STFC had taken on too much,
although, projects were only approved together with UKRI.
And in particular, it seems to be a
concern that the running costs of new facilities,
might be more than had previously been anticipated,
and that could be, become unaffordable due to
increased staff and electricity costs.
These reasons, however, don't explain why it is
that the PPAN projects in particular have been
targeted
and really make no sense at all as
regards the LHB upgrade because perhaps uniquely amongst
the, projects,
this is one where The UK is already
committed to paying the dominant part of the
running costs. Cost because The UK is committed
to paying the CERN subscription,
which funds the operation of the accelerator,
which is essentially what we need in order
to to to be able to do the
LHCb upgrade. In fact, it will be running
anyway,
for the, Atlas and CMS,
experiments.
Also, the LHCb upgrade project is on budget.
So although we understand that there are concerns
on how public money is invested
and, funding is always tied,
the funding going into UKRI is at a
record high,
because the government recognizes the importance of research
and innovation,
and how it contributes to the economy.
So these cuts don't appear to have been
motivated by purely financial reasons, and it's really
very hard to to understand what the reason
actually was.
We've been told by UKRI that the decision
is final, but we still hope that sense
might prevail.
And, Tim, The UK is a is a
a big contributor
to CERN,
probably one of the biggest.
So I'm guessing that
that taking this money out of the LHCb
upgrade
budget
is is is going to be a big
problem,
not just for for UK physicists, but also
for
any particle physicist,
who works on the experiment.
Have you have you been able to, you
know, sort of talk to your,
colleagues and and work out what this is
going to mean for the LHCb upgrade? Is
it is it just gonna have to not
happen?
So,
so indeed so there's several, aspects to that.
Let me, first of all,
put it in context of the CERN subscription.
So indeed that The UK is one of
the largest contributors to CERN through the the
CERN subscription,
and that pays for the construction and operation
of the accelerators, but it doesn't pay
for, for the experiments apart from, essential support
to the experiments which is provided by by
the host lab. So experiments are funded by,
member states and and other partners coming on
board and agreeing,
to make contributions to them, and that was
the process that we were going from.
And as you said, within LHCb,
The UK is a major partner. And as
I've described previously, the entire plans
for the LHB upgrade have been,
built essentially around, this UK contribution.
So the infrastructure fund award was to cover
both the capital contribution
and for project staff to construct the detector.
And it's important to stress that this is
not money that is just sent as a
check to to CERN. This is money that
will be spent predominantly,
via grants in The UK institutes.
There's 11 universities in the REL National Laboratory
that are involved, in in LHEB.
And in addition, we would have been working
with UK industry in order to to maximize
the the benefit and constructing as much of
the the detector as we would, here in
The UK.
The upgrade project would have provided opportunities for
hundreds of students to be involved in developing
cutting edge technologies, both in the the detector
hardware and in in the software.
And it's also worth noting that the majority
of our students then take those skills on
into into industry at great benefit to the
economy.
Specifically within The UK for, for the upgrade,
we were interested in the development of detectors
with ultrafast timing resolution,
developing novel silicon detector systems with reduced material,
and in managing
high throughput,
data processing.
So without this,
UK contribution, your question was, would the future
of LHEB be in jeopardy?
The answer to that, unfortunately, is is yes.
The entire project is developed around The UK
contribution. So if that's completely removed, the project
will simply collapse.
And you might wonder, well, surely,
other countries could step in and and cover
these essential roles. And with enough time, that
would be possible.
But as I mentioned earlier, our plan was
to move to complete technical design reports this
year and to start the construction phase next
year. And we simply now do not have
enough time to develop new plans that we
would be able to to manage without that,
and the time scale can't be changed because
it's fixed by the the LHC schedule.
So
the full exploitation of the LHC is that
the highest priority
in particle physics in both the the European
strategy, which is recently,
updated and in The UK roadmap. And the
LHCb upgrade is needed to achieve that because
of the uniqueness of the LHCb physics program.
So it's really essential that we find a
solution that allows The UK to continue to
be involved.
And and so what does that mean for
you and all your colleagues in The UK?
You know, senior people like you right down
to,
graduate students. Does that I mean,
if you're not if The UK isn't coming
up with the money, does that mean that
LHCB is going to say, you know, sorry,
Tim.
The British
can't
work on the experiment anymore. Is it is
it that harsh,
or is there going to be a workaround?
Well, it could be that harsh, and that's
what we're working still to try to understand.
So even without funding from the UKRI infrastructure
fund, in principle, there could be funding through
STFC,
which has been the the sort of historic
way that these types of projects have been
funded.
But, unfortunately,
at the same time as the infrastructure fund
project is cut,
UKRI has asked STFC
to to make 30% cuts to its PPAN
program in order to deal with what it's
calling cost pressures.
Now, again, it's unclear exactly what is causing
these cost pressures, but it seems to be
mostly staff and electricity costs at the facilities.
But whatever the reason is, the PPAN program
is facing these cuts at the level of
of 30%.
And since the particle physics, astronomy, and nuclear
projects tend to have long timescales,
the majority of these funds are are committed
in the the future, at least for the
next few years,
through international,
agreements.
So it is not straightforward,
to make cuts at that scale. In fact,
it's impossible to make cuts without reneging on
those international commitments.
So in this context, it's clearly going to
be extremely challenging
for SDFC to find a way to support
the upgrade.
That means that, yes, unfortunately, we are facing
a potentially a nightmare scenario
where the withdrawal of the infrastructure fund award
results in the LHCb upgrade collapsing and hence
the early termination of of LHCb
because the current detector will only be able
to operate up until 2033,
when it is,
expected it will reach its end of life
due to the radiation damage.
This would mean that the top priority of
The UK and European particle physics roadmaps is
not achieved, and it would be completely unprecedented
for a CERN member state to cause the
collapse of a CERN flagship experiment in this
way. So clearly, this will be a disaster
for UK science diplomacy.
It's gonna also have potentially huge ramifications for
particle physics in general, in particular in The
UK, as the LHB upgrade is the only
major construction project on the timescale of the
mid twenty thirties.
Without this project, it's gonna be really difficult
to maintain the continuity of expertise
in building and operating particle physics detectors.
And once those skills are lost, they're very,
very difficult to regain.
More generally, if 30% cuts to PPAN
really are enacted,
this will be a major loss of income
to university physics departments, which as we know
are already struggling with many, many financial challenges.
In fact, there was a report published by
the Institute of Physics towards the end of
last year that stated that a quarter of
UK physics departments are at risk of closure,
and that was before taking these potential cuts
into consideration.
Clearly, those can only make the situation even
worse.
So, Tim, are you and your colleagues,
I'm guessing you're organizing
to fight this?
What,
I mean, can you reveal any of your
plans to to try to get this decision
reversed or or changed or, you know, find
some sort of funding?
Yeah. I would, prefer to say that rather
than than fighting, we're trying to work together
with STFC and UKRI in order to to
find a solution. Because I we want to
avoid
the potentially catastrophic outcomes that I've mentioned,
and we don't believe that these are intentional
consequences of decisions being made at UKRI.
So this means not only within LHCb, but
in the the the particle physics and astronomy
and nuclear physics communities more more broadly.
Now, of course, we we hope that the
the cuts, specifically, that the cut of the
LHCb
upgrade, we hope that those cuts can be
reversed.
And again, it really seems impossible to believe
that that this could be an intended consequence
of decisions that have been made. But if
it turns out that the solution is is
something different to that, then then so be
it. So long as we can still find
a way that we can continue
with with with this project,
and avoid,
all of the the the negative,
possible outcomes which I've discussed previously.
In fact, you know, there's reasons for for
optimism. All of the the the chief executive
of UKRI, Soreen Chapman, as I mentioned earlier,
but also the science minister, Claude Valence, and
indeed the secretary of state for science and
innovation and technology,
which is Liz Kendall, all of them have
separately stated that curiosity driven science should be
protected in particular
in fields where we are world leading.
That sounds like a a very good ruling
principle to me. I would hope everybody would
agree with that. And clearly, LHCb is a
great example of world leading curiosity driven science
being led within The UK. It's a genuine
UK science success story.
We want to make sure that, LHEB in
particular, but PPAM Science also more generally, do
not become an exception to this rule that
The UK wants to remain world leading in
curiosity driven science.
And, Tim, I wanna end this interview on
a positive note.
I know here at Physics World,
we've covered a lot
of papers that LHCb
has published over the past decade or so.
In particular,
a a lot of work has come out
of the experiment regarding
exotic hadrons. I think you you you mentioned
them,
earlier. Can you just give us a flavor
of,
of some of that research and and some
of the
exotic particles that you've found. These are these
are very heavy particles with more than three
quarks, aren't they?
Yeah. That's right. So in fact, if I
can, let me first of all give you
some of examples of some of the the
research highlights that came out during 2025.
And then perhaps after that, we can talk
a bit about what what could come in
the future with the upgraded
LHEB because the,
part about exotic hadrons is is particularly relevant
for for the upgrade.
But during 2025, we had a number of
of really major, results.
So one was the first discovery
of CP violation in in baryon decays.
So CP violation
is, essentially asymmetry
between
matter and antimatter. And as I mentioned, right
near the start of our conversation,
that's something which is really important to to
understand,
the universe where the the universe, which is
essentially made up, predominantly most of the mass
in the universe is is from from baryons,
at least, of the visible matter. We're not
talking about dark matter, but for the time
being.
And there is an asymmetry that we see
only baryons and not antibaryons
naturally occurring,
in in the universe.
So CP violation is essential to this, but
all previous observations of CP violation going back
to the the first discovery in 1964
had involved mesons
rather than baryons. So mesons are particles that
are made up of a quark and an
antiquark,
whereas baryons involve three quarks and antibaryons, three
antiquarks.
So since the asymmetry of the universe is
in baryons, there should also be CP violation
in baryons. And now we've seen this for
the first time. And in fact, this is
something a good example of the uniqueness of
LHEB. This is the only experiment that that
can make those types of measurements.
Another highlight is a result which came out
towards the end of last year. It was
an updated study of, a particularly interesting rare
decay process
of a a neutral beam meson turning into
a,
an excited,
kaon and, mu plus, mu minus.
Now that may sound like a a lot
of particles, but this is a particularly interesting
process to test the standard model because there
are predictions
for,
the both the rates, but also the angular
distributions of the decay products.
And previous measurements had indicated that what we're
actually measuring was not consistent with the standard
model predictions.
So it was really highly anticipated to update
those measurements with, the data sample,
that that we have, available until now.
So we now have those new more precise
measurements, and they confirm what we've seen before.
There still seems to be this very intriguing
tension between our measurements and the standard model
predictions,
intriguing tension between our measurements
and the standard model predictions, but we still
do need more data to
be sure if the effect is due to
something beyond the standard model and not from
larger than expected corrections to the the standard
model predictions. So
So these are among the the results that
led to perhaps the third and last highlight
that I'd I'd I'd draw out,
which was the award of the 2025
breakthrough prize, in fundamental
physics,
which was this is sometimes called the the
Oscars of science,
and this prize was awarded to LHCb together,
with the other three large LHC experiment,
collaborations
in recognition,
of what had been achieved in, with the
exploiting the data collected
in in the first two runs
of, of the LHC.
But if I just add one more thing,
we have also been taking data in the
third run. And so perhaps even the most
important news last year has been how successful
this data taking has been, in the third
run. Means the sample size that we have
now and becoming available for analysis is at
least a factor of four larger than in
our publications to date. And in many processes,
it's even a much larger factor.
It's gonna take a while to convert the
data into into measurements, in particular when we're
talking about really precise measurements and we have
to control
systematic uncertainties,
very, very carefully. But first results are starting
to come through the pipeline, so you can
look forward to many exciting new results coming
later in 2026.
And the future, Tim, what, what can we
look look forward to for an upgraded LHCB?
Yeah. So it's worth noting that even with
this amazing performance and how well we've done
in data taking in 2024 and 2025,
we've not yet collected even 10% of the
total sample that we'll be able to accumulate
with the upgraded detector.
So this larger data sample will not only
allow us to advance the precision frontier, it
means that we'll be able to do various
things which are currently impossible.
So let's bring this back to talk about
the exotic hadrons, that that we talked about
before. So we've discovered a number of exotic
hadrons, so called tetraquarks and pentaquarks,
but so far these contain all contain charm
quarks and antiquarks.
With the LHCb upgrade, we expect to be
able to see the corresponding states that contain
beauty quarks, and this will provide unique understanding
of the binding force in in these particles.
Being able to compare the states that we
observe with charm to those with beauty will
really give us unique insight into into what
is going on with these exotic hadrons.
Another great example of what we'll be able
to do with the upgraded LHCb is that
we can actually bring together these two main
elements of our physics program. I've talked about
CP violation and rare decays, and we'll be
able to make CP violation measurements with rare
decays.
So one of the main highlights of the
first phase of LHB was the discovery
of the the decay of a a BS
meson into two muons.
This is particularly interesting because the final state
only contains muons, but it's a very, very
rare process occurs only a few times in
every billion b s meson decays.
Nonetheless, with the upgraded LHCb, we'll have a
large enough data sample that will have thousands
of these decays, and that will be enough
to make CP violation measurements providing a new
way to test the standard model.
And if I can give just one more
example Oh, go on. Go ahead.
So LHEB is the is the, only experiment
which can study CP violation in charm meson
decays. This is another
really huge result which has come out of
LHEB, the unexpected discovery of CP violation in
charm, which occurs at a rate that seems
to be inconsistent with the standard model expectation.
But, again, to know if this is really
due to something beyond the standard model or
due to larger than expected corrections,
we need more data and more independent measurements
to be able to confirm that. And that's
something that will only be possible with the
LHEB upgrade. In fact, in the current global
planning of particle physics, there's no other experiment
that will be able to do this for
at least another fifty years. So you see
the LHCb upgrade really is a once in
a lifetime opportunity to uncover new aspects of
the laws of nature.
We are determined that we're not gonna let
this opportunity slip, and that's why it's so
important that we find a solution to the
crisis that's been caused by the UKRI decision.
Well, thanks, Tim. Thanks so much for for
speaking to Physics World about this and explaining
the situation. And I'm sure within the physics
community, people are are behind LHCb in The
UK, and we hope that you can come
up with
some sort of resolution to move things forward.
So,
best wishes with that.
Thank thank you very much, Hamish. That's much
appreciated, and I hope that I'll be able
to come back with some good news sometime
soon.
That's great. Thank you, Tim.
I'm afraid that's all the time we have
for this week's podcast. Thanks to Tim Gershen
for an update on LHCb.
I'm Hamish Johnston, and our producer is Fred
Isles.
The theme music in this episode is called
one three seven, and it was composed and
performed by the physicist
Philip Moriarty.