Status of UCNτ Experiment to Measure Neutron Lifetime

Determining the lifetime of a free neutron is an essential experimental observable for developing our understanding of particle physics and cosmology, as it plays a significant role in determining the abundances of light elements in the early universe and provides input for testing physics beyond the Standard Model. The UCNτ experiment has produced the world’s most precise measurements of τ_n, the free neutron lifetime, by storing ultracold neutrons (UCN) in a magneto-gravitational trap designed to remove relatively high-energy UCNs and avoid neutron-wall collisions. The most recent result from UCNτ specifies a lifetime of 877.75 ± 0.28 (stat) +0.22/-0.16 (sys) seconds where the limiting factor is statistical precision. The goal for the upgrade from UCNτ to UCNτ+ is to reduce the lifetime uncertainty to the ~0.1 second level. To achieve this precision, the neutron delivery system to the trap is being replaced with a more efficient system using an elevator concept. Instead of removing a small section of the array and guiding the neutrons up into the trap, the new delivery system will fill a bin above the trap. The bin is then moved through the array, adiabatically transporting the UCN into the trap. This talk will present the concept of the UCNτ+ experiment and show progress of the experimental work towards the upgrade.