College Park, Maryland      June 6 - 10 , 2004

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MP18: Search for Time-Reversal Violation in Neutron Beta Decay

H.P. Mumm (University of Washington), L.J. Broussard (Tulane University), T.E. Chupp, R.L. Cooper, K.P. Coulter (University of Michigan), M.S. Dewey (National Institute of Standards and Technology), S.J. Freedman, B.K. Fujikawa (University of California-Berkeley/LBNL), A. Garcia (University of Washington), S.R. Hwang (University of Michigan), G.L. Jones (Hamilton College), L.J. Lising (University of California-Berkeley/LBNL), J.S. Nico (National Institute of Standards and Technology), R.G.H. Robertson (University of Washington), A.K. Thompson (National Institute of Standards and Technology), C. Trull, F.E. Wietfeldt (Tulane University), J.F. Wilkerson (University of Washington)

The emiT experiment tests time-reversal symmetry in the beta decay of polarized free neutrons by searching for the triple correlation Dσ•p_e×p_p, where s is the neutron spin and p_e and p_p are the decay product momenta for the electron and proton, respectively. A nonzero D-coefficient above the small effect from final state interactions would be a signal of direct time reversal symmetry (T) violation, independent of charge conjugation-parity (CP) violation. Various extensions to the Standard Model, such as lepto-quarks and left–right symmetry, can give rise to a D-coefficient yet do not generate measurable electric dipole moments. Consequently, it is important to place the strongest possible limits in neutron decay. In December of 2003 the emiT collaboration completed a successful data run at NIST. In this run, more than 3x10⁸ neutron decays were measured, and a signal-to-background ratio of approximately 100:1 was obtained. Analysis of the data is underway, and the collaboration is optimistic that an improved limit on the D-coefficient will be achieved. Along with a discussion of theoretical motivation and the experimental technique, the status of the analysis and studies of systematic uncertainties will be presented. This work is supported by DOE, NSF, and NIST.

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