* Corresponding author. Present address. Hamilton College, Clinton, NY 13323, USA. Tel.: #1-315-859-4697; fax: #1-315- 859-4696. E-mail address: gjones@hamilton.gov (G.L. Jones)  Present address: National Central University, Chung-Li 32054, Taiwan.  Present address: NIST, Gaithersburg, MD 20899, USA.  Present address: Abacus Concepts, Inc., Berkeley, CA 94704, USA. Nuclear Instruments and Methods in Physics Research A 440 (2000) 648}652 Time reversal in polarized neutron decay: the emiT experiment G.L. Jones*, J.M. Adams, J.M. Anaya, T.J. Bowles, T.E. Chupp, K.P. Coulter, M.S. Dewey, S.J. Freedman, B.K. Fujikawa, A. Garcia, G.L. Greene, S.-R. Hwang, L.J. Lising, H.P. Mumm, J.S. Nico, R.G.H. Robertson, T.D. Steiger, W.A. Teasdale, A.K. Thompson, E.G. Wasserman, F.E. Wietfeldt, J.F. Wilkerson National Institute of Standards and Technology, Gaithersburg, MD 20899, USA Los Alamos National Laboratory, Los Alamos, NM 87545, USA University of Michigan, Ann Arbor, MI 48109, USA Lawrence Berkeley National Laboratory, Berkeley, CA 4720, USA University of Notre Dame, Notre Dame, IN 46556, USA University of Washington, Seattle, WA 98195, USA Abstract The standard electro-weak model predicts negligible violation of time-reversal invariance in light quark processes. We report on an experimental test of time-reversal invariance in the beta decay of polarized neutrons as a search for physics beyond the standard model. The emiT collaboration has measured the time-reversal-violating triple-correlation in neutron beta decay between the neutron spin, electron momentum, and neutrino momentum often referred to as the D coe$cient. The "rst run of the experiment produced 14 million events which are currently being analyzed. However, a second run with improved detectors should provide greater statistical precision and reduced systematic uncertain- ties.  2000 Elsevier Science B.V. All rights reserved. Keywords: Neutron beta decay; Angular correlation; Weak interaction 1. Introduction CP violation, observed so far only in the neutral kaon system, can be explained in the standard model using a Kobayashi}Maskawa phase [1]. This phase is small, however, and its e!ects are highly suppressed in processes involving only the lighter quarks. The small standard-model values of time-reversal violating observables in beta decay provide an opportunity to search for interactions 0168-9002/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 9 9 ) 0 1 0 5 6 - 6