A New Proposal of Beam Neutron Lifetime Experiment in Superfluid Helium-4 Scintillator

A large discrepancy in the measured neutron lifetime between the beam and bottle methods remains as a puzzle. More beam experiments of high precision, but with a different set of systematic effects, can greatly help in resolving the puzzle. In this report, we propose a new beam experiment at a sensitivity goal of 0.1% or sub-1 second by counting electrons from neutron beta decays in a superfluid helium-4 scintillation detector at 0.5 K, and monitoring the neutron flux simultaneously by the helium-3 captures in the same volume. In order to eliminate scattering with superfluid helium and suppress background events, the cold neutron beam must be of wavelength $\lambda$>16.5 {\AA}.