The ultimate goal of physics is really quite ambitious.
We hope to do nothing less than understand all of the laws of nature- every one of them-
so we can explain everything we observe- from quarks to the cosmos, so to speak.
And that is a very big goal.
To make progress requires very big teams of scientists and the largest and most sophisticated
equipment.
At Fermilab, we have a long history exploring this frontier of knowledge, including a full
quarter century when we hosted the Tevatron, which was at the time the highest energy particle
accelerator in the world.
That changed in 2011, when a newer and larger particle accelerator came online.
That accelerator is called the Large Hadron Collider, or LHC, and it is located at the
CERN laboratory just outside of Geneva, Switzerland.
Now you might think that might make a Fermilab scientist like me sad, and I guess it does,
kind of.
After all, I spent decades doing research using the Tevatron.
It was like losing an old friend.
But luckily, particle physics has always been highly collaborative, with individuals, universities,
laboratories, and even countries collaborating with one another.
For decades now, Fermilab scientists have contributed knowledge, equipment, and effort
to make the LHC research program a success.
And it goes both ways, with CERN researchers working to help build the Fermilab-hosted
Deep Underground Neutrino Experiment, or DUNE, which will dominate neutrino research for
the next few decades.
DUNE is definitely cool, but I’m an LHC guy, so I thought I’d tell you about what
Fermilab is doing to help upgrade the LHC accelerator and detector complex so it can
explore the energy frontier well into the 2030s.
CERN has embarked on what is called the High Luminosity Large Hadron Collider Upgrade,
or HL-LHC.
In particle physics lingo, luminosity simply means the brightness of the beams, which can
be accomplished by injecting more particles into the beams and by focusing the beams more
tightly.
Using techniques like these, the high luminosity LHC upgrade will increase the beam luminosity
ten-fold.
This will result in more particle collisions, with a corresponding increase in the opportunity
to discover rare subatomic particles and their interactions.
Fermilab’s superb staff of scientists, engineers, and technical professionals have always worked
at the frontier of high energy research, and we followed that tradition by identifying
a number of key high luminosity LHC projects on which to work.
For instance, in order to focus the particle beams to achieve the desired higher luminosity
will require a series of focusing magnets that are half again more powerful than the
existing LHC bending magnets.
In collaboration with researchers from other U.S. Department of Energy laboratories and
CERN, Fermilab scientists designed a new type of magnet using a superconducting material
called niobium 3 tin.
These magnets can make a magnetic field in the range of 11 or 12 Tesla, which is crazy
strong.
They’re going to make a big difference in improving LHC luminosity.
Fermilab is also working on what are called CRAB cavities, which are accelerator components
that briefly alter the direction of the two beams of protons that are circulating in opposite
directions to ensure that that the beams are hitting head-on.
This technology will also increase the luminosity of the LHC beams.
The actual components for the upgrade will be built at a number of different places around
the world.
While some components are made here, perhaps Fermilab’s key contribution is the knowledge
and experience to make these accelerator upgrades a reality.
Although increasing the collision rate of the beams is a crucial goal of the LHC research
program, improving the accelerator is not enough.
After all, there are also particle detectors arrayed around the accelerator ring and they
were designed for the original LHC.
The original detectors can’t handle the increase in luminosity.
Fermilab is a leader on the Compact Muon Solenoid, or CMS.
CMS is one of the two huge particle detectors on the LHC and we used it to discover the
Higgs boson back in 2012.
Now CMS is big- really big.
It’s five stories tall and it weighs fourteen thousand tons.
After the upgrades are complete, it will be like a two billion pixel camera capable of
taking 40 million pictures per second.
The parts of the detector near the point where the beams collide in the center of the detector
experience a lot of radiation damage due to the huge rate of particles hitting the detector.
The radiation environment will be even more daunting in the high luminosity LHC era, so
we have to give much of the detector an overhaul, especially the parts near where the beam passes
through the center of the detector.
After considerable thought, Fermilab researchers decided which projects were the ones on which
we could make the biggest impact.
We picked a few.
They are called the silicon tracking detector, the endcap hadron calorimeter, the trigger,
and a timing detector.
Now, to be clear, Fermilab isn’t working on these projects alone.
Many groups are involved.
But we’re a big institution with many people involved, and therefore we have a disproportionate
impact on the tasks we undertake.
Let me give you an idea of what these upgrades involve.
First the tracker upgrade.
When two protons collide in the LHC, hundreds of particles come out.
Even worse, perhaps one or two hundred pairs of protons can collide at the same time, which
means that at any one time, maybe ten thousand particles are flying through the detector.
In order to see the path followed by each particle, we need to use tiny, tiny, detector
elements to try to ensure that each element is hit by only one particle.
This approach was used in the original CMS detector with a vast array of very small individual
detectors made of silicon, but that detector is worn out and needs to be completely replaced.
Researchers at the Fermilab Silicon Detector Facility are working to build a new silicon
detector.
Then there’s the forward hadron calorimeter.
Calorimeters measure the energy that hits them and the energy environment near the beam
line is especially intense.
That’s what we call the forward direction.
CMS is removing the existing forward calorimeter and replacing it with one that uses silicon
detector technology in places where the radiation environment is high and another technology
called plastic scintillator in regions where the radiation is lower.
Since scintillator is less expensive than silicon, this approach achieves the required
performance for lower cost.
A third upgrade on which Fermilab is working is called the trigger.
Basically, CMS faces a real challenge.
Collisions occur about forty million times per second, but we can only record about a
thousand of them.
So, we need to decide which collisions to record and which to discard.
And we have to do it blindingly fast.
We do that by teaching electronics and computers to scan the data and keep the data of one
collision out of every forty thousand.
The equipment that does this is called a trigger.
Improvements in electronics and computer technology are allowing us to vastly improve our ability
to properly select and record only the most interesting collisions.
The fourth upgrade of the CMS detector on which Fermilab researchers are working is
called the timing detector.
Every time the two beams of protons pass through the CMS detector more than one collision occurs.
In fact, something like one or two hundred collisions simultaneously occur and all of
those tracks are simultaneously passing through the CMS detector.
Figuring out which of those tracks came from which collision is pretty hard.
However, if we can measure the time precisely enough, that can help us identify which tracks
are the ones we care about.
The goal of the timing detector is to measure things with a precision of thirty picoseconds,
which is a millionth of a millionth of a second, which will vastly improve our ability to sort
everything out.
Now, it would be dishonest if we didn’t acknowledge that these projects are not something
that Fermilab is working on alone.
CMS is an international project, with something like three thousand scientists working on
it.
But Fermilab has more collaborators working on CMS than any other institution beside CERN
itself, and we certainly take pride in our contribution.
However, we must admit that a project this big does, indeed, take a village.
And the contribution goes beyond the technical.
Fermilab is the institution that houses what is called the Project Office for work done
on CMS by U.S. institutions.
We have the administrative and organizational capabilities to make sure that money and resources
are responsibly used to achieve the experiment’s goals.
If that weren’t enough, Fermilab also houses the LPC, short for LHC Physics Center, which,
in addition to our own staff, hosts a hundred or so visiting researchers.
At any moment, hundreds of CMS researchers are collaborating in our corridors.
The High Luminosity LHC won’t start operations until the mid- or late-2020s at the earliest,
but when it does, it will operate for at least a decade – perhaps even into the 2040s.
This project is the flagship of the high energy frontier for the foreseeable future- certainly,
for the rest of my career.
We expect to collect at least ten times more data than we’ve collected so far, and it
will likely be more than that.
It always is.
It’s impossible to say what we might discover with all that data, and I don’t know about
you, but I’m chomping at the bit to start looking.
I liked this video, because it was a reminder that discoveries like the Higgs boson only
occur because of a huge effort and years of preparation to build the equipment that makes
it happen.
No accelerator and no detector means no discoveries.
And we kind of like discoveries.
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It sounds like the LHC will be studying physics for decades which works for me, because- as
you know- physics is everything.