Improved Neutron Lifetime Measurement with UCNtau

Alexander Komives, DePauw University
et al.


We report an improved measurement of the free neutron lifetime τn using the UCNτ apparatus at the Los Alamos Neutron Science Center. We count a total of approximately 38×106 surviving ultracold neutrons (UCNs) after storing in UCNτ’s magnetogravitational trap over two data acquisition campaigns in 2017 and 2018. We extract τn from three blinded, independent analyses by both pairing long and short storage time runs to find a set of replicate τn measurements and by performing a global likelihood fit to all data while self-consistently incorporating the β-decay lifetime. Both techniques achieve consistent results and find a value τn=877.75±0.28stat+0.22/−0.16syst 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.