Searching for stealthy supersymmetry

Supersymmetry is a theory that predicts that all known particles have as-yet-undiscovered partner particles, or superpartners. These superpartners, according to this theory, could be produced in proton-proton collisions at the Large Hadron Collider at the European Laboratory for Particle Physics, CERN. Scientists have been actively exploring the nature of supersymmetry for over 40 years, in part because it can help explain the Higgs boson’s mass, which is currently measured to be about 125 times the mass of the proton. Searches for new partner particles with the CMS and ATLAS experiments at the LHC most often look for a large imbalance of energy resulting from supersymmetric particles that escape without detection. So far, these searches have found no sign of supersymmetry.

One team working on these searches comprises U.S. CMS physicists from Fermilab and associated universities collaborating under the umbrella of the Fermilab LHC Physics Center, which is also known as the LPC. This team is the first to perform a new kind of search for “stealthy” supersymmetry that does not result in an obvious signature of large energy imbalance. Instead, the LPC team is looking for collisions that result in an unusually large number of particles in the CMS detector. The LPC team uses a special machine-learning technique in which two neural networks, pitted against each other, discover subtle differences between signal and background events. Those differences are then used to help identify the few interesting collisions that may come from stealthy supersymmetry from the billion collisions per second that the LHC produces.

CMS recently published a physics briefing describing this analysis. In it, you can read more about stealthy supersymmetry, the importance of dueling neural networks and what the LPC team has learned from the data.

Jim Hirschauer is a Fermilab scientist.

Fermilab is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science.

After 10 years as executive director of Universities Research Association, Marta Cehelsky has announced her intent to step down in the latter part of this year.

“It has been a privilege and a pleasure to serve as URA executive director over the past 10 years,” Cehelsky said in announcing her plans. “I have had the good fortune to work with two excellent Fermilab directors; a succession of outstanding URA officers, trustees and staff; and with the extended URA university community. Working with our exceptional colleagues at Fermilab has been a special pleasure. It has also been a privilege to work with the highly accomplished and dedicated members of the Fermi Research Alliance Board of Directors, and our counterparts at the University of Chicago.”

Marta Cehelsky came to URA in 2008 as vice president of the organization following a career in the federal government that included service as the executive secretary of the National Science Board at the National Science Foundation. Earlier, she left an academic career to work at NASA. She then assumed a position as a congressional staff member, and later as senior advisor on science and technology to the InterAmerican Development Bank.

“Marta Cehelsky has been a friend and colleague since the day I arrived at Fermilab,” said Fermilab Director Nigel Lockyer. “She has always been a great supporter of the lab program, a proponent of our early career scientists and a booster of excellence. As executive director of URA, she provided valuable advice and oversight to Fermilab along with the University of Chicago. I wish her much success in the future.”

Reflecting on Fermilab’s extraordinary global mission in neutrino research and exciting new frontiers in quantum science, artificial intelligence and cosmology, Cehelsky said that Fermilab will continue to be the nation’s preeminent physics laboratory, making world-class contributions to science.

“This is a good time for a new person to step in at URA,” Cehelsky said. “In addition to our continuing responsibilities at Fermilab, URA has a new role contributing to the excellence of science and technology at Sandia National Laboratories. URA’s future is bright and full of opportunities.”

Fermilab is managed by the Fermi Research Alliance LLC for the U.S. Department of Energy Office of Science. FRA is a partnership of the University of Chicago and Universities Research Association Inc.