BL3: The Next Generation Neutron Beam Lifetime Experiment

The BL3 experiment proposed at the NCNR aims to measure the neutron lifetime to 0.3 s and investigate the systematic effects of beamline-based measurements. A precision measurement of the neutron lifetime is needed to resolve the nearly 5σ discrepancy between beam and bottle method experiments. The resulting neutron beta decay correlations can be used to test CKM unitarity, and are required in Big Bang Nucleosynthesis calculations to determine the abundance of 4He in the early universe. In BL3, protons produced by neutron beta decay are collected in a quasi-Penning trap and are delivered to a segmented silicon detector via magnetic and electric fields. This experiment utilizes a larger beam with a higher neutron flux compared to previous iterations, requiring an improved neutron flux monitor and an upgraded alpha-gamma device for the absolute calibration of the flux monitor. This talk will include an overview of the measurement techniques in BL3 and an update of the ongoing construction of the new apparatus.