UChicago plays ‘instrumental’ role in high-energy physics
By Steve Koppes
Photo courtesy of Argonne National Laboratory
In the Big Science world of high-energy physics, scientists often revolve about the nuclei of assorted experimental collaborations. Sometimes they move from one collaboration to the next in overlapping sequence, other times they work in two independent research groups with large but partially shared memberships.
UChicago physics professors Frank Merritt and Mark Oreglia, for example, formerly belonged to the OPAL (Omni-Purpose Apparatus at LEP) collaboration at the Large Electron-Positron collider, the predecessor to the Large Hadron Collider in Geneva. But even before the OPAL experiment shut down in 2000, they had joined the LHC’s ATLAS (A Toroidal LHC ApparatuS) collaboration. ATLAS is one of two frontier experiments in high-energy physics that employ the Large Hadron Collider at CERN, the European particle physics laboratory.
Physics professor Henry Frisch is a member of the Collider Detector at Fermilab collaboration. Although not directly involved with research at the Large Hadron Collider, one of his former students, Joseph Incandela, AB’81, MS’85, PhD’86, heads its CMS (Compact Muon Solenoid) experiment.
“The interesting thing is, the technology of his thesis apparatus was not in high-energy physics. It was in low-temperature physics,” Frisch notes. Incandela received his doctoral degree searching for magnetic monopoles, which is similar to the Higgs search in that both are major problems in physics involving hypothetical particles.
“The technique was different, but it’s experimenting. You learn how to experiment, and then you go out and ask the questions you want to ask,” Frisch says.
Physicists at Fermi National Accelerator Laboratory, which is heavily invested in the CMS experiment that Incandela leads, have one scientist affiliated with ATLAS. She is Young-Kee Kim, Fermilab’s deputy director and UChicago’s Louis Block Professor in Physics. Kim also is a member and former co-leader of the Collider Detector at Fermilab collaboration.
Kim notes that her contributions to ATLAS come mostly via her postdoctoral scientists and students. “My job at ATLAS really is meeting one-on-one with my postdocs and students on weekends,” says Kim, whose weekdays are consumed with her Fermilab administrative duties. “I have very smart postdocs. They help with my graduate students and my undergraduate students.”
Kim’s team is assisting the effort led by Melvyn Shochet, the Elaine M. and Samuel D. Kersten Jr. Distinguished Service Professor in Physics, to develop an improved electronic trigger — the FastTracKer — for the ATLAS detector.
ATLAS’s existing trigger is one of two important electronic components that the UChicago ATLAS team has developed and built for the experiment. The other component is called the tile calorimeter, a device that measures particle energies. The trigger’s job is to manage the massive data flow gushing from the collider, which generates billions of collisions each second.
Each of those billions of collisions, in turn, generates events that produce multiple short-lived particles, but ATLAS computers can save the data for only a few hundred events per second. The trigger thus must quickly decide which collisions have generated data interesting enough to record for later analysis. To further complicate the matter, collisions that look interesting to physicists may change from day to day as they complete one analysis, then move on to another.
The smarter, faster, more flexible FastTracKer technology has its roots in trigger technology developed for the Collider Detector at Fermilab experiment. “The concept really came from CDF, but of course the technical challenges for the ATLAS trigger are much greater,” Kim says.
CERN will shut down the Large Hadron Collider for two years starting in late 2012. During the shutdown period, engineers will make adjustments to the collider that will allow it to operate at higher energies. They also will install the new FastTracKer in the ATLAS detector.
The new trigger will enable ATLAS physicists to reconstruct particle trajectories approximately a thousand times faster than the one currently operating. “This will be a quite essential ingredient in making sure that we have the best sensitivity possible to whatever new phenomena will be discovered over the next years,” Shochet says.