Research in Elementary Particle Physics

University Of Chicago, Chicago IL

Investigators

Abstract

The Chicago High Energy Physics Group is engaged in three major experiments, ATLAS, CDF and KTeV, and concluding a fourth, OPAL. In addition, the group is planning a reactor neutrino experiment and is continuing work toward a Linear Collider. Each of these subgroups is integrated into the larger whole with the shared goals of understanding Electroweak Symmetry breaking, CP violation, and the basic structure of space-time. Education and outreach are integrated into this effort, with involvement in programs at the elementary, high school, undergraduate, and public levels. The ATLAS experiment at the CERN LHC is expected to begin operation during the period of this request. It will be the world's premier facility for exploring the high energy frontier with the most obvious physics targets being the mechanism for mass generation (Higgs boson) and the explanation of the mass hierarchy (supersymmetry). The Chicago group is involved in calorimetry and is also developing a proposal for a hardware track trigger that will allow rapid selection of events containing b quarks or tau leptons. The CDF experiment at Fermilab is studying ppbar collisions with the world's highest energy accelerator. CDF has made precise determinations of the top quark and W boson masses, and broad searches for physics beyond the Standard Model. Run II is in progress, with the goal of collecting 50 times more data than in Run I. The Chicago trigger electronics is working well and we are now working on Run IIb trigger/DAQ upgrades. Studies of top quark properties and searches for new physics are underway, with the first Chicago Run II papers submitted for publication. The KTeV experiment at Fermilab was designed to measure direct CP violation in Kpp decays and search for very rare K decay modes. The Chicago-led analysis of half of the total KTeV data yielded a 7-sigma observation of direct CP violation; the group is now completing the (e/e) analysis using the full data sample. Among dozens of other results from KTeV, the most notable is the recent determination of |Vus| by the Chicago group based on measurements of KL branching fractions and semileptonic decay form factors. These measurements show very large deviations from previous world averages and are consistent with unitarity of the CKM matrix. Over its lifetime, LEP was the world's premier facility for studies of the electroweak interaction. On the OPAL experiment, the Chicago group was heavily involved in both the detector and physics analysis. In the past few years, Chicago physicists completed a measurement of the W boson mass, searched for non-standard Higgs boson decay modes, and studied semileptonic b decay. New initiatives for the group include a significant new effort in neutrino physics. Chicago has helped form a collaboration of several universities to perform an experiment at a nuclear reactor to measure theta13, the last unmeasured mixing angle of the neutrino mixing matrix. Design studies are underway. Work is also in progress toward an international linear collider, both in the organizational effort and in detector R&D.