Neutron Lifetime and Axial Coupling Connection

Experimental studies of neutron decay, n→peν, exhibit two anomalies. The first is a 8.6(2.1) s, roughly 4σ difference between the average beam measured neutron lifetime, τₙᵇᵉᵃᵐ=888.0(2.0) s, and the more precise average trapped ultracold neutron determination, τₙᵗʳᵃᵖ=879.4(6) s. The second is a 5σ difference between the pre2002 average axial coupling, gA, as measured in neutron decay asymmetries gAᵖʳᵉ²⁰⁰²=1.2637(21), and the more recent, post2002, average gAᵖᵒˢᵗ²⁰⁰²=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 τₙ and gA values using a (slightly) updated relation τₙ(1+3gA²)=5172.0(1.1) s. Consistency with that relation and better precision suggest τₙᶠᵃᵛᵒʳᵉᵈ=879.4(6) s and gAᶠᵃᵛᵒʳᵉᵈ=1.2755(11) as preferred values for those parameters. Comparisons of gAᶠᵃᵛᵒʳᵉᵈ 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.