The CMS Department is a physics powerhouse

For researchers interested in unlocking the mysteries of the universe, having access to the most powerful high-energy accelerator on the planet, a world-class detector, and young, fresh, and enthusiastic minds are a winning combination – and the Fermilab CMS Department has all three.

The Large Hadron Collider is the highest-energy particle accelerator ever built, and the CMS detector is a superb instrument in which the Fermilab group played and is continuing to play leading roles to design, build and help operate.

No matter the quality of the experimental equipment, it is the people that make the Fermilab CMS Department a vibrant intellectual community. Nearly 100 researchers in the Fermilab Particle Physics and Scientific Computing divisions work with an even larger number of engineers, technicians and computer professionals to make the experiment a success. And since the CMS detector will operate for at least another two decades, the Fermilab CMS group is preparing for the future. Perhaps the longest-term impact of the CMS Department is its impressive cadre of research associates, or RAs — future leaders of the field. In addition to doing their own research, Fermilab physicists are currently training 17 of these next-generation leaders.

The Fermilab CMS Department’s research associates are a driving force in the CMS experiment and future leaders in the field of particle physics. Not pictured: Aram Apyan, Jennet Dickinson, Martin Kwok, Cristina Mantilla Suarez, Nick Smith.

By any measure, the CMS experimental program is highly successful. CMS is the first particle physics collaboration to ever publish over 1,000 papers. About half of those papers were made possible by algorithms and techniques that were either developed at Fermilab or optimized by Fermilab researchers. And CMS’ 1,000th paper described the observation of collisions in which three heavy bosons were produced. At Fermilab, current RAs Hannsjoerg Weber and Karri DiPetrillo contributed to this analysis, as did former RA Mia Liu, currently an assistant professor at Purdue University.

Other analyses led by Fermilab physicists include investigations into “dark QCD,” a theory that says dark matter is more complex than has long been thought. Current RAs Karri DiPetrillo, Thomas Klijnsma and Chris Madrid are contributing to this investigation, including a search for “soft bombs,” events with lots of mostly low-energy (soft) particles, a phenomenon that would elude traditional analyses.

Another exciting effort searches for long-lived particles that represent uncharted territories in data. RAs Allison Hall and Cristian Pena are developing new and innovative algorithms, for example in tracking and muon reconstruction to probe these exotic signatures.

While the Fermilab CMS Department is involved in many innovative investigations into new and exotic physics, Fermilab RAs also study the Standard Model, including studies of the Higgs boson (Apyan, Dickinson, Smith), and participate in searches pursuing more classical models of new physics (Cremonesi, Heller, Herwig, Ravera).

On the detector side of things, RA Aram Apyan has been playing a key role in the installation and operations of the CMS hadron calorimeter, while Matteo Cremonesi and Nick Smith are leaders in CMS computing, working in collaboration with SCD colleagues. Incoming RAs Yongbin Feng and Martin Kwok will join the team soon.

Looking toward the future, CMS is undertaking a series of upgrades that will ensure that the detector will continue its world-class performance for the coming decades.

In the high-luminosity environment of the upgraded LHC, event reconstruction will be incredibly difficult. Each interesting proton-proton collision will be accompanied by, on average, over a hundred other collisions. (As a comparison, at peak operation, CDF and DZero had about seven multiple interactions at once. At peak luminosity, CMS will see 200 on average.) The result is that the CMS detectors will see not only particles originating from the desired collision, but over a thousand other particles passing through the detector.

To help mitigate these confusing signals, the CMS Department is making major contributions to the construction of four unprecedented detectors: the first tracker capable of providing tracking information 40 million times per second, the first silicon-based hadron calorimeter providing “images” of particles, the first MIP timing detector that will determine the time when particles pass through the detector with a precision of about 35 picoseconds, and a novel trigger system.

Fermilab RAs are a driving force behind these modern detectors. Jennet Dickinson, Lesya Horyn, Fabio Ravera and Hannsjoerg Weber will be pivotal in building and qualifying over 2,500 sophisticated tracker modules and over 6,000 chip-to-sensor assemblies. Aram Apyan and Cristina Mantilla Suarez are doing equally important work on the calorimeter, for which Fermilab will build 550 of the 15-square-foot “cassettes,” over 1,000 silicon photomultiplier on-tile modules, and an ASIC that concentrates events for further processing. Karri DiPetrillo, Ryan Heller, Chris Madrid and Cristian Pena are engaged in the MIP timing detector, with Fermilab leading the development of the front-end chip and of the modules. The combination of these detector improvements will ensure CMS remains a world-class instrument for at least the next two decades.

To fully exploit the novel capabilities of the upgraded detector, the Fermilab CMS group is pioneering many modern and sophisticated event selection and reconstruction techniques. One advance that could change how future collider experiments are done is a heavy intellectual investment into the development of machine learning and artificial intelligence. Machine intelligence is what drives facial and handwriting recognition software and the increasingly convincing chatbots.

Artificial intelligence has been used in data analysis for decades now, but Fermilab scientists are pushing the envelope. The trend in artificial intelligence has been to involve it earlier and earlier in the detection process. While AI once was used primarily in offline reconstruction, it is now not only used in computer-based triggering, but is also beginning to be deployed onto programmable chips, known as FPGAs, and even in chips, such as ASICS, that are designed specifically for this application. Machine learning could well be crucial for selecting the particle collisions that contain the signature of the next physics breakthrough, and RA Christian Herwig is optimizing this approach.

Another innovation for which the Fermilab CMS group is leading the way is in the field of heterogeneous computing. RA Allison Hall, Thomas Klijnsma, and other Fermilab researchers and computer professionals use a variety of different computer processors to optimize the detector performance. Most commonly, graphics processing units, called GPUs, are included to benefit from their unique capabilities.

More broadly, Fermilab researchers are exploring what are called intelligent detectors, which integrate modern information technologies.

While Fermilab researchers are making important contributions to data analysis, detector and computing operations, as well as future upgrades, Fermilab is also the lead CMS institution in the United States. The U.S. CMS operations program manager is a Fermilab scientist, as is the manager of the U.S. CMS Detector Upgrade Project. The upgrade project is a $239 million responsibility, and it covers all DOE and NSF contributions to the CMS upgrade, while the operations program totals to $36 million per year.

Although 2020 has been a tough year for interpersonal interactions, the LHC Physics Center, hosted by Fermilab and co-coordinated by a lab scientist, continued being the social and academic hub of CMS interactions in the U.S. The LHC Physics Cemter holds a major data analysis school (over 100 participants) and hundreds of other events every year, training graduate students and new researchers, as well as building knowledge among experts. The school has been so successful that it has been reproduced in many countries throughout the world. While these events have been conducted virtually this year, the transfer of information, techniques and ideas has been instrumental in keeping the LPC a vibrant intellectual place.

The Fermilab CMS Department is an exciting place to be. The CMS collaboration has a huge data set, which has led to over 1,000 papers and the discovery of the Higgs boson. These achievements are impressive, and the collaboration is just getting started. When the LHC resumes operations in 2022, CMS will begin a period of operations that will record over 30 times more data than it has recorded so far. The future is bright, and the CMS powerhouse will continue to move forward.

Fermilab scientist Anadi Canepa is the head of the Fermilab CMS Department. Fermilab scientist Don Lincoln is on the CMS experiment and a member of the CMS Department.

CMS Department communications are coordinated by Fermilab scientist Pushpa Bhat.