Why does the space shuttle returning to Earth cause two separate sonic booms?
Professor Beck received his bachelor's degree in physics from the University of Saskatchewan in 1979, and his Ph.D. in physics from Massachusetts Institute of Technology in 1986. After working as a senior research fellow at the California Institute of Technology for two years, he joined the Department of Physics at the University of Illinois as an assistant professor in 1989. He was promoted to associate professor in 1994 and to full professor in 1999.
Professor Beck is the creator, spokesman, principal driving force, and intellectual leader of the G0 experiment at Thomas Jefferson National Accelerator Facility. This collaboration of more than 80 senior physicists from 18 institutions is designed to elucidate a detailed spatial distribution of charge and current densities for strange quarks. The Illinois group, under Professor Beck's leadership, is responsible for the main instrumentation for the experiment, a superconducting toroidal spectrometer. The $2M magnet for the spectrometer was designed and tested at Illinois before being successfully installed at JLab. The eight internal lead collimators for the magnet were also assembled and tested at Illinois.
We are completing a series of measurements of the neutral weak currents of the nucleon using parity-violating electron scattering. Together with the ordinary electromagnetic currents of the proton and neutron, they allow us to separately determine the contributions of the various quark flavors. We are particularly interested in the contribution of strange quarks, because they are exclusively part of the sea of virtual quarks and gluons in the nucleon. Up and down quark pairs in the sea apparently interact with the medium to the extent that they have different momentum distributions. The present measurements will help us understand whether the heavier strange quarks are similarly affected.
We have also begun work on development of an experiment to measure the neutron electric dipole moment. Electric dipole moments for 'fundamental' particles like the neutron violate both parity- and time-reversal symmetry. Although the standard model of particle physics predicts a small but non-zero value for this quantity, the effects from physics at energies potentially accessible at the LHC may be significantly larger. Time-reversal violation is, in fact, a critical ingredient in generating a small excess of matter over anti-matter in the early universe (providing for our own existence), and, in many models produces an observable effect in the neutron.
We have recently released (May 2009) the final data from the parity-violation experiment showing that the effects are generally small at the higher momentum transfers of the most recent measurement. In a related measurement of the effective parity-violating coupling of the photon, the results suggest there is a measurable effect from the weak interactions among quarks within the nucleon. In the neutron electric dipole moment experiment, we have successfully constructed a large aperture, superfluid-tight valve for liquid helium and we have measured and developed techniques to improve the relaxation time of polarized 3He on the materials (plastics, non-magnetic metals) and at the temperatures (~0.5 K) relevant for the experiment.
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