The Current Status of the UCNtau Neutron Lifetime Experiment and Plans For the Next Generation

The UCNτ experiment at the Los Alamos Neutron Science Center has provided the most precise value for the neutron lifetime to date. The current status of the Cabibbo Anomaly strongly motivates improving the precision of measurements of the CKM matrix element V_ud, which is currently most precisely determined from superallowed nuclear decays. A measurement of the neutron lifetime, together with an angular correlation measurement, provides a nuclear structure-independent determination of V_ud.

We provide an update on the most recent lifetime result published by the UCNτ collaboration and discuss experimental upgrades since the last publication. Specifically, we focus on the advantages of a buffer volume known as the round house (RH), the addition of a robust normalization monitor in the round house, and an improved main dagger detector in the trap.

In addition, we mention the upgrade to the UCNτ experiment, UCNτ+, which is aiming for roughly a factor of two improvement in the precision of the UCNτ experiment - potentially establishing the neutron lifetime input at the precision level to directly compete with superallowed nuclear decays.