3:30–4:45 pm MCP 201
Neutrons, when liberated from a nucleus, are unstable. A free neutron spontaneously decays into a proton (of a lighter mass), electron, and an anti-neutrino, with a lifetime of approximately 10 minutes. This process is the basis of all nuclear beta-decays, which, together with neutron captures and alpha decays in stellar environments, made the diverse nuclear isotopes in the universe. The neutron decay rate is also the key input to estimate the rate of nuclear fusion and energy production in the sun, and it can be used to search for physics beyond the Standard Model. There exists, however, a 10-second discrepancy in the neutron lifetime as determined by two modern techniques. By counting the decays in a beam of neutrons, the lifetime is 887.7 +/- 2.2 s [PRL 111, 222501 (2013)]; by counting surviving ultracold neutrons stored in a bottle, it is 878.8 +/- 0.3 s [PRC 111, 045501 (2025)]. I will describe the challenges of these measurements and the innovations for meeting these challenges.