The emiT Experiment: A Search for Time-reversal Invariance Violation in Neutron Beta Decay


 H. P. Mumm for the emiT collaboration

Ionizing Radiation Division, National Institute of Standards and Technology



The emiT experiment tests time-reversal symmetry in the beta decay of polarized free neutrons by searching for the time reversal-odd, parity-even triple correlation between the neutron spin and momentum of both the electron and proton.  The detection of this correlation above the small calculable effect due to final state interactions would be a direct indication of time reversal symmetry violation, independent of charge conjugation-parity. To date the only observation of direct time-reversal violation comes from the decay of neutral kaons. This observation, however, can be incorporated within the Standard Model and cannot provide the time-reversal violation required to produce the baryon asymmetry observed  in the Universe.  Thus it remains important to search for time reversal violation in other systems.  Some of the most sensitive of these tests are searches for electric dipole moments (EDMs).  Yet a number of extensions to the Standard Model, such as lepto-quarks, can give rise to a triple correlation but do not generate measurable EDMs.  Consequently, the emiT experiment is complementary to EDM measurements, and, it is important to place the strongest possible limits in neutron decay. The emiT collaboration has published a result [1] from its first run.  A highly successful second run of the emiT experiment has recently been completed at the NIST Center for Neutron Research.  The analysis of and constraints on time reversal violation obtained from this greatly improved data set will be presented.


 [1] Phys. Rev. C. 62, 055501, (2000).




Presenting Author:


Hans Pieter Mumm

Mentor: Scott Dewey

Division: Ionizing Radiation (846)

Laboratory: Physics

Building and room address: 235/B185

Mail stop:  8461

Telephone: 8355

Fax: 926-1604


Sigma Xi member: No


Category: Physics