Neutron Lifetime Measurement with Pulsed Cold Neutron Beam inside Superfluid Liquid Helium

The persistent discrepancy in free neutron lifetime measurements, known as the "neutron lifetime puzzle," highlights the need for new experimental techniques. We propose a novel method to measure the neutron beta decay lifetime (​ τ_β) using a pulsed cold neutron beam traveling through superfluid helium. A key advantage of this approach is that when the neutron wavelength is greater than 16.5 Å, neutron scattering on superfluid ⁴He is absent, which simplifies the measurement. Both neutron beta decays and neutron captures by trace amounts of ³He generate distinctive bursts of 16 eV UV photons. By counting the number of beta decays (△N_β​) and ³He captures (​△N_3He​) using a photon detection array, we can determine the neutron lifetime from the ratio △N_3He /△N_β​=τ_βn_3Heσ(v)v. In this equation, ​n_3He is the ³He concentration and σ(v) is the neutron-³He capture cross section at neutron speed v. This talk will detail the experimental strategy, emphasizing how we can reliably distinguish between the two types of events based on their unique photon signatures on the detector array.