Department Research Update - Duke Physicists at the LHC
Professor Mark Kruse spent November 29-December 3 at the Large Hadron Collider at CERN in Geneva. “The atmosphere there is pretty incredible right now,” he says. “Everyone’s getting very excited. The beam is circulating and they’ve managed to produce proton-proton collisions in the last few days—at a lower energy than designed, but still a huge milestone toward that goal.”
Now that the LHC is operational again, thousands of scientists, engineers, and students have converged on the place. “There are probably 5,000 people there,” Kruse says. “The CERN cafeterias were always fairly busy but now they’re absolutely packed. It’s just sardines from 11 o’clock to 2.”
Three Duke post-docs—Andrea Bocci, Esben Klinkby, and Jared Yamaoka—are in residence at the LHC, holding almost-daily video meetings with their colleagues in Durham. The post-docs are working with the TRT (Transition Radiation Tracker), a part of the ATLAS detector that was designed and constructed by Duke physicists in collaboration with colleagues at Indiana University. Duke ATLAS team leader Seog Oh says, “It was a huge undertaking and it’s quite meaningful for us because it’s one of the really important detectors there.” The Duke team built the TRT at Duke (which took about four years, not counting R&D and prototyping), shipped it to CERN, integrated it with the other ATLAS detectors, and commissioned and tested it.
The testing is an ongoing process of learning how different particles leave their traces in the TRT. “It takes time to understand it,” Oh says. “Every detector is unique. It’s like a person—it has its own characteristics, problems, hiccups.” Undergraduate Ariana Minot, under the mentorship of Klinkby and Kruse, spent the summer studying the tracks of cosmic rays in the TRT. (For more information about the LHC and Minot’s work on the TRT, click here. )
Kruse says, “We’ve done the groundwork—we’ve generated a lot of knowledge of how particles interact with that detector.” He and his students are now beginning to theorize how the tracks of new, as-yet unobserved particles might look in the detector. Discoveries of such particles will help physicists confirm or reject theories of what lies beyond the standard model of physics (which involves four fundamental forces and 12 fundamental particles). Kruse says, “There are problems with the standard model. It’s still valid in lower energy regimes, but at higher energies—which we’re beginning to explore at the LHC—it’s probably a subset of a grander theory. All of the new models require new particles.”
Oh says, “One of the aims of the LHC is to complete the standard model by the discovery of the Higgs particle. But the more important question is, ‘What lies after the standard model?’ This is the question we have been asking for more than 30 years. And the only thing that can answer that is new experiments.”
Once the data begin flowing out of ATLAS and the other experiments at the LHC, Oh says, theorists can use it to generate new ideas, which will in turn lead to new experiments. Oh predicts it will probably take five to 10 years to see begin seeing glimpses of what’s beyond the standard model.
As part of the ATLAS project, Oh is searching for super-symmetry particles and heavy gauge bosons decaying to a pair of leptons or gauge bosons. Kruse is searching for stable massive particles and conducting a global search for new physics using dilepton events. Kruse has recently rotated out of the leadership position of the Higgs group at Fermilab in Chicago, freeing up some time for him to spend on ATLAS work. Although it may turn out that the Higgs will be discovered (if it does indeed exist) at the Tevatron at Fermilab before the LHC gets up to full speed, Kruse says the higher-energy LHC will be able to generate more information about the Higgs particle.
“Once the LHC is running at full energy it will be producing the Higgs particles much more copiously than the Tevatron,” he says. “It will be able to measure properties of the Higgs particles—like spin, mass, charge, and the different ways it decays. Assuming we find a Higgs particle, these properties will be clues in determining whether it is the Higgs of the standard model or not, giving us a deeper understanding of how the universe works.”
The Duke ATLAS Team
Douglas P. Benjamin
William L. Ebenstein
Andrew J. Fowler, Jr.
Alfred T. Goshaw
Ashutosh V. Kotwal
Thomas J. Phillips