Aug. 4, 1999 CHAMPAIGN, Ill. -- An electronic device being designed and built at the University of Illinois will assist experimenters at a major accelerator by distinguishing between "good" and "bad" collisions.
The device is called a "trigger," and is part of an upgrade being performed on the Cornell Electron Storage Ring -- a synchrotron particle accelerator at Cornell University. Mats Selen, a professor of physics at the U. of I., is directing a team of scientists and engineers responsible for building the trigger, and for interfacing the device with the accelerator's CLEO detector and data-acquisition system.
"At CESR, electrons and positrons [a positron is the antiparticle of an electron] are accelerated to extremely high speeds," Selen said. "These tiny particles are then slammed together in head-on collisions, which in turn produce the even tinier bits of matter that we want to study."
Of course, there really are no good and bad collisions, Selen said, but there are some that are much more interesting than others. "Searching for the most interesting events is like panning for gold. Just as you need to sift through tons of sand to find that elusive gold nugget, we must sift through tons of collisions to find the ones we want. We are building a better sifter to help us find those events."
Selen's team is particularly interested in identifying collisions that create bottom quarks -- the second heaviest variety of these elementary particles. Like tiny Lego blocks, quarks compose all baryonic matter. Studying the way bottom quarks are produced and the way they decay into lighter quarks provides essential information about the fundamental rules for assembling matter.
"Collisions in CLEO can occur 20 million times a second, but we can only record the data one thousand times a second," Selen said. "The trigger's job is to monitor all aspects of the experiment and to distinguish between interesting and non-interesting collisions, and to do so very quickly."
Every 42 nanoseconds the trigger will take a "snapshot" of what it sees in the detector, and then process that information for about 2 microseconds before deciding whether to save or discard the data.
"The trigger will look at thousands of signals from various parts of the detector, and very quickly perform pattern recognition," Selen said. "When an interesting pattern is found, the trigger will tell the computer to save all the data."
Technically, by the time the trigger has made up its mind, the information already has come and gone, Selen said. "So the data must be stored temporarily until the decision is made to toss it or send it to the data-acquisition system."
Selen's U. of I. team includes research engineer Mike Haney, physics professor George Gollin, postdoctoral research associates Randal Hans and Jesse Ernst, and graduate students Tim Bergfeld, Ed Johnson, Charles Plager, Chris Sedlack and Jeremy Williams.
The trigger is being funded by the National Science Foundation and the U.S. Department of Energy.
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