Testing the Standard Model
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| Final stages of assembly of the g-2 muon storage ring. This is the largest superconducting magnet ever built. Inside the ring are detectors and readout components for the measurement of the muon anomalous magnetic moment. |
Much of the progress that we have made in understanding the structure of matter and the origin of the universe has come from elementary particle experiments at accelerator laboratories. Our current knowledge is embodied in the Standard Model, which organizes the fundamental building blocks of matter into three families each of quarks and leptons. One of the highlights of the Minnesota and U.S. HEP program during the past few years was the direct observation of the last of the twelve fundamental particles of the Standard Model, the tau-neutrino, by the Direct Observation of Nu Tau (DONUT) experiment at Fermilab in which Professors Heller and Rusack collaborate.
Studies of heavy flavors (b and c quarks and tau lepton) have been crucial in developing this picture. Professors Kubota, Poling and Urheim work on the CLEO experiments which have charted out much of the heavy-flavor sector of the Standard Model, especially in the discovery and detailed measurements of particles composed of b quarks. Measurements of the decay couplings of b quarks to c and u quarks have been a Minnesota specialty. They provide important ingredients for tests of the Standard Model's description of CP violation, a key to understanding the matter/antimatter asymmetry of the universe. Detailed studies of this are currently under way at the B factories in California and Japan (without Minnesota involvement), but the definitive measurements may come from the BTeV experiment (Professors Kubota and Poling) at Fermilab later this decade.
Measurements of extremely rare processes, or of fundamental properties that can be predicted with great precision, provide powerful tests of the Standard Model. The g-2 experiment (Professor Cushman) at Brookhaven National Laboratory measures the deviation of the magnetic moment of the muon from its naive value of two. The Standard Model predicts this difference very precisely and by measuring it to within a third of a part per million the g-2 experiment provides a powerful constraint on physics beyond the Standard Model. CLEO's precise measurements of rare decays, like that of a b quark to an s quark and a photon, are a complementary probe of new physics.
Extracting fundamental physics from the complex events recorded in our detectors requires detailed understanding of the interactions of the particles produced. Measurements of the properties of quarkonia and other states of heavy quarks probe the workings of the strong interaction. Such measurements are the specialty of the elegant E835 experiment at Fermilab (Professor Rusack), and have been an important part of the CLEO program. They will be the centerpiece of CLEO-c, which will test the powerful theoretical technique of lattice gauge theory, potentially benefiting many measurements, including the refinement of quark-mixing measurements.
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