Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session Q2: Fundamental Symmetries (in Few-Body Systems) |
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Sponsoring Units: DNP GFB Chair: Allena Opper, The George Washington University Room: Thurgood Marshall East |
Monday, February 15, 2010 1:30PM - 2:06PM |
Q2.00001: Measuring the Neutron Lifetime Invited Speaker: Precision measurements of neutron beta decay parameters address basic questions in nuclear and particle physics, astrophysics, and cosmology. As a basic semileptonic decay system, the free neutron plays an important role in understanding the physics of the weak interaction, and improving the precision of the neutron lifetime is fundamental to testing the validity of the theory. Currently, there are two main strategies for measuring the lifetime. Experiments using confined, ultracold neutrons determine the lifetime by counting neutrons that remain after some elapsed time; experiments using cold neutrons measure the absolute specific activity of a beam by counting decay protons and the neutron flux simultaneously. The status of the recent lifetime measurements using these methods is discussed along with prospects for future experiments using new techniques. [Preview Abstract] |
Monday, February 15, 2010 2:06PM - 2:42PM |
Q2.00002: Results from a Search for the Permanent Electric Dipole Moment (EDM) of $^{199}$Hg Invited Speaker: Observation of a nonzero EDM would imply CP violation beyond the Standard Model. Additional sources of CP violation are expected to help explain the matter-antimatter asymmetry observed in our universe and naturally arise in extensions to the standard model such as supersymmetry. Our group has recently reported a new upper limit: $|d_{Hg}|$ $<$ 3.1$\times$10$^{-29}$\ e-cm for the EDM of $^{199}$Hg. The experiment compared the spin precession frequencies in four spin-polarized Hg vapor cells: two cells lie in parallel magnetic and anti-parallel electric fields, resulting in EDM-sensitive spin precession while the remaining two cells, at zero electric field, serve to cancel noise generated by magnetic field gradients and test for systematic errors. A frequency shift, linear in the applied electric field, due to the Stark mixing of atomic states has been identified and measured. A description of the EDM experiment and measurements that led to our recent result will be presented. [Preview Abstract] |
Monday, February 15, 2010 2:42PM - 3:18PM |
Q2.00003: CP-violating Moments in Few-body Systems Invited Speaker: The existence of a permanent electric dipole moment (EDM) would reflect direct violation of time-reversal (T) and parity (P), and thus CP-violation through the CPT theorem. Several experimental programs are pushing the limits on EDMs in the neutron, nuclei, and atoms. There are two mechanisms for P,T-violation in the nucleus; one driven by P,T-violation in the individual nucleons, and a second by a P,T-violating nucleon-nucleon (N-N) interaction. Searches for EDMs in neutral atoms are sensitive the CP-violation in the nucleus only through the screened Schiff moment. The latter is suppressed in light nuclei and enhanced in some heavy nuclei, rendering light nuclei unsuitable for this class of experiments. However, a new scheme for measuring EDMS of stripped nuclei in a magnetic storage ring suggests that few-body nuclei could be used to set accurate limits on the CP-violation N-N interaction. In this talk, I review the situation in few-body versus many-body systems, and examine the physics determining the different CP-violating moments in nuclei. [Preview Abstract] |
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