Improved Neutron Lifetime Measurement With Ucn Tau

We report an improved measurement of the free neutron lifetime tau(n) using the UCN tau apparatus at the Los Alamos Neutron Science Center. We count a total of approximately 38 x 10(6) surviving ultracold neutrons (UCNs) after storing tau's magnetogravitational trap over two data acquisition campaigns in 2017 and 2018. We extract tn from three blinded, independent analyses by both pairing long and short storage time runs to find a set of replicate tau(n) measurements and by performing a global likelihood fit to all data while self-consistently incorporating the beta-decay lifetime. Both techniques achieve consistent results and find a value tau(n) = 877.75 +/- 0.28(stat) + 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.