Background: Time-reversal-invariance violation, or equivalently CP violation, may explain the observed cosmological baryon asymmetry as well as signal physics beyond the Standard Model. In the decay of polarized neutrons, the triple correlation D<J_{
n}>cdot(p_{e}timesp_{ u}) is a parity-even, time-reversal- odd observable that is uniquely sensitive to the relative phase of the axial-vector amplitude with respect to the vector amplitude. The triple correlation is also sensitive to possible contributions from scalar and tensor amplitudes. Final-state effects also contribute to D at the level of 1e-5 and can be calculated with a precision of 1% or better. Purpose: We have improved the sensitivity to T-odd, P-even interactions in nuclear beta decay. Methods: We measured proton-electron coincidences from decays of longitudinally polarized neutrons with a highly symmetric detector array designed to cancel the time-reversal-even, parity-odd Standard-Model contributions to polarized neutron decay. Over 300 million proton-electron coincidence events were used to extract D and study systematic effects in a blind analysis. Results: We find D = [-0.94pm1.89(stat)pm0.97(sys)]e-4. Conclusions: This is the most sensitive measurement of D in nuclear beta decay. Our result can be interpreted as a measurement of the phase of the ratio of the axial-vector and vector coupling constants (CA/CV= |{lambda}|exp(i{phi}_AV)) with {phi}_AV = 180.012{deg} pm0.028{deg} (68% confidence level) or to constrain time-reversal violating scalar and tensor interactions that arise in certain extensions to the Standard Model such as leptoquarks. This paper presents details of the experiment, analysis, and systematic- error corrections.
We report the results of an improved determination of the triple correlation $D P cdot(p_{e}times p_{ u})$ that can be used to limit possible time-reversal invariance in the beta decay of polarized neutrons and constrain extensions to the Standard Mo
del. Our result is $D=(-0.96pm 1.89 (stat)pm 1.01 (sys))times 10^{-4}$. The corresponding phase between g_A and g_V is $phi_{AV} = 180.013^circpm0.028^circ$ (68 % confidence level). This result represents the most sensitive measurement of D in beta decay.
