Characterization of Scintillation Light produced in Superfluid Helium-4

Experiments that place strict limits on the electric dipole moment of the neutron (n-EDM) represent one of the most promising opportunities to search for physics beyond the standard model. Over the last several years, a collaboration based at Los Alamos National Laboratory has been working toward the development of an apparatus that is expected to improve the current n-EDM limit by two orders of magnitude. A key feature of the proposed experiment involves the detection of ultraviolet scintillation light produced as a result of neutron capture on 3He in superfluid liquid 4He (l-4He). Typically such events give rise to a large prompt flash of light followed by a train of delayed photons ('after-pulses'). We recently performed an experiment to examine correlations between the amplitude of the initial light pulse and the number of after-pulses that are produced when a dilute mixture of 3He in l-4He is irradiated with a neutron beam. Data from this experiment suggest that events associated with reaction products from neutron capture on 3He can be distinguished from background events associated with other forms of ionizing radiation such as gamma rays. A sample of data from our experiment is presented