BL3: The Next Generation Neutron Lifetime Measurement Using the Beam Method*

Neutron beta decay is one of the most fundamental processes in nuclear physics and provides sensitive means to uncover the details of the weak interaction. A precise measurement of the neutron lifetime, along with neutron beta decay correlations, can provide tests of CKM unitarity and is needed for Big Bang Nucleosynthesis models of the primordial 4He abundance, which correlates with other cosmological parameters. A next generation beam method experiment, BL3 at the NCNR, aims to improve the systematic precision of neutron lifetime measurements in order to resolve the discrepancy between in-flight decay and trapped neutron measurements. In BL3, the recoil protons from neutron beta decay are born in a quasi-Penning trap with magnetic and electric fields which transport them to a segmented silicon detector. The BL3 experiment will use a larger beam with higher neutron flux, which requires a new and improved apparatus to reach an ultimate precision of <0.3 s. We will discuss simulations of proton transport and components of the new BL3 apparatus.