Physics with Ultracold and Thermal Neutron Beams: Testing and Possible Application of 'Low Temperature Fomblin' in a Neutron Lifetime Experiment

摘要

This project has been focused on a measurement of the mean lifetime (tau)(sub n) of the free neutron with a precision better than 0.1%. The neutron (beta)-decay n (yields) p + e(sup -) + (bar (nu))(sub e) + 783 keV into a proton, electron and electron antineutrino is the prototype semi-leptonic weak decay, involving both leptons and hadrons in the first generation of elementary particles. Within the standard V-A theory of weak interaction, it is governed by only two constants: the vector coupling constant g(sub V), and axial vector constant g(sub A). The neutron lifetime has been measured many times over decades, and the present (2004) world-average, (tau)(sub n) = 885.7 (+-) 0.8 s, has a weighted error of (approx)0.1% while individual uncertainties are typically 2-10 seconds for high precision data. The highest precision claimed by an individual measurement is (approx)0.15%. An improvement is required to resolve issues of the Standard Model of the electro-weak interaction as well as of astrophysics and of Big Bang theories. The focus in astrophysics is the solar neutrino deficit problem, which requires a precise value of g(sub A). Big Bang theories require a precise (tau)(sub n)-value to understand the primordial He/H ratio. The strong interest of particle physicists in (tau)(sub n) is mainly based on a possible difficulty with the Cabibbo Kobayashi Maskawa (CKM) matrix, which describes the mixing of quark mass states by the weak interaction.