The Upgraded Measurement of the Neutron Lifetime Using the In-Beam Method

Precision measurements of neutron beta decay can provide answers to some of the most fundamental questions in particle physics, astrophysics and cosmology. Neutron beta decay is the simplest semi-leptonic decay; therefore, it provides a clean test of the charged current sector of the Standard Model (SM). A precise measurement of the neutron lifetime and λ, the ratio of axial vector and vector coupling constants of the weak interaction, allows for a determination of the Cabibbo-Kobayashi-Moskawa (CKM) matrix element V_ud that is free from nuclear structure effects. The SM predicts that the CKM matrix is unitary; therefore, the measurement of the neutron lifetime provides an important test of the SM. The neutron lifetime is also an important input parameter into early universe Big Bang Nucleosynthesis calculations. The neutron lifetime remains one of the most uncertain parameters in the calculation of cosmic ⁴He abundance. The in-beam method of measuring the neutron lifetime requires the absolute counting of decay protons in a neutron beam of precisely known flux. Improvements in the neutron and proton detection systems as well as the use of a new analysis technique and apparatus upgrades allow for a rigorous re-examination of the systematic effects associated with this method. This work will discuss the development and optimization of new analysis techniques that provide improved proton energy resolution as well as an absolute timing comparison to simulation. The results of new proton systematic studies and a new simulation model will also be discussed.