Neutron Lifetime and Axial Coupling Connection.

Abstract

Experimental studies of neutron decay, n→peν[over ¯], exhibit two anomalies. The first is a 8.6(2.1)s, roughly 4σ difference between the average beam measured neutron lifetime, τ_{n}^{beam}=888.0(2.0) s, and the more precise average trapped ultracold neutron determination, τ_{n}^{trap}=879.4(6) s. The second is a 5σ difference between the pre2002 average axial coupling, g_{A}, as measured in neutron decay asymmetries g_{A}^{pre2002}=1.2637(21), and the more recent, post2002, average g_{A}^{post2002}=1.2755(11), where, following the UCNA Collaboration division, experiments are classified by the date of their most recent result. In this Letter, we correlate those τ_{n} and g_{A} values using a (slightly) updated relation τ_{n}(1+3g_{A}^{2})=5172.0(1.1) s. Consistency with that relation and better precision suggest τ_{n}^{favored}=879.4(6) s and g_{A}^{favored}=1.2755(11) as preferred values for those parameters. Comparisons of g_{A}^{favored} with recent lattice QCD and muonic hydrogen capture results are made. A general constraint on exotic neutron decay branching ratios, <0.27%, is discussed and applied to a recently proposed solution to the neutron lifetime puzzle.