Neutron Lifetime and Axial Coupling Connection

Experimental studies of neutron decay, $n\ensuremath{\rightarrow}pe\overline{\ensuremath{\nu}}$, exhibit two anomalies. The first is a 8.6(2.1) s, roughly $4\ensuremath{\sigma}$ difference between the average beam measured neutron lifetime, ${\ensuremath{\tau}}_{n}^{\mathrm{beam}}=888.0(2.0)\text{ }\text{ }\mathrm{s}$, and the more precise average trapped ultracold neutron determination, ${\ensuremath{\tau}}_{n}^{\mathrm{trap}}=879.4(6)\text{ }\text{ }\mathrm{s}$. The second is a $5\ensuremath{\sigma}$ difference between the pre2002 average axial coupling, ${g}_{A}$, as measured in neutron decay asymmetries ${g}_{A}^{\mathrm{pre}2002}=1.2637(21)$, and the more recent, post2002, average ${g}_{A}^{\mathrm{post}2002}=1.2755(11)$, where, following the UCNA Collaboration division, experiments are classified by the date of their most recent result. In this Letter, we correlate those ${\ensuremath{\tau}}_{n}$ and ${g}_{A}$ values using a (slightly) updated relation ${\ensuremath{\tau}}_{n}(1+3{g}_{A}^{2})=5172.0(1.1)\text{ }\text{ }\mathrm{s}$. Consistency with that relation and better precision suggest ${\ensuremath{\tau}}_{n}^{\text{favored}}=879.4(6)\text{ }\text{ }\mathrm{s}$ and ${g}_{A}^{\text{favored}}=1.2755(11)$ as preferred values for those parameters. Comparisons of ${g}_{A}^{\text{favored}}$ 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.

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