Improved Neutron Lifetime Measurement with UCNτ

Abstract

We report an improved measurement of the free neutron lifetime τ n using the UCNτ apparatus at the Los Alamos Neutron Science Center. We count a total of approximately 38 × 10 6 surviving ultracold neutrons (UCNs) after storing in UCNτ's magnetogravitational trap over two data acquisition campaigns in 2017 and 2018. We extract τ n from three blinded, independent analyses by both pairing long and short storage time runs to find a set of replicate τ n measurements and by performing a global likelihood fit to all data while selfconsistently incorporating the β-decay lifetime. Both techniques achieve consistent results and find a value τ n ¼ 877.75 AE 0.28 stat þ 0.22= − 0.16 syst s. With this sensitivity, neutron lifetime experiments now directly address the impact of recent refinements in our understanding of the standard model for neutron decay.

First-generation new physics in simplified models: from low-energy parity violation to the LHC

“…Alternatively, V ud can be extracted from neutron decay [163,164], in which case the additional nuclear uncertainties are absent, leaving the same hadronic effects as for superallowed β decays. In this case, significant improvements in precision measurements of the neutron life time τ n [165,166] and the asymmetry parameter λ [89] have been achieved in the last years, so that, with ref. [166] for τ n , a gain of another factor 2 in precision in λ would render the neutron-decay extraction competitive with superallowed β decays.…”

“…In this case, significant improvements in precision measurements of the neutron life time τ n [165,166] and the asymmetry parameter λ [89] have been achieved in the last years, so that, with ref. [166] for τ n , a gain of another factor 2 in precision in λ would render the neutron-decay extraction competitive with superallowed β decays. Finally, pion β decay π ± → π 0 e ± ν e [167][168][169] is currently not measured sufficiently precisely to impose meaningful constraints, but might become relevant in the future [170] in particular in combination with K 3 decays [169].…”

Dark Matter interpretation of the neutron decay anomaly

“…• The 'bottle method' measures the total neutron decay width, with the result Γ tot n = 1/(878.3 ± 0.3) s, by storing ultra-cold neutrons in a magnetic bottle and counting their remaining number after some time [1][2][3][4][5][6][7][8].…”

Neutron Stars with Baryon Number Violation, Probing Dark Sectors

“…We consider the most precise beam lifetime result, 887.7 ± 1.2 (stat) ± 1.9 (sys) s [41], the most recent PDG average of the neutron lifetime determined from bottle and trap experiments, 879.4 ± 0.6 s [30], and the most precisely measured neutron lifetime, determined in a magnetic trap experiment, 877.75 ± 0.28 (stat) +0. 22 −0.16 (sys) s [51]. The numerical difference between the beam and bottle/trap measurements constitutes the neutron lifetime anomaly.…”