LANSCE-PSR Short-Pulse Upgrade for Improved Dark Sector Particle Searches with the Coherent Captain Mills Experiment

Proton beam dumps are prolific sources of charged and neutral pions, enabling a powerful technique to search for dark matter, axions, sterile neutrinos, tests of short baseline anomalies, and precision measurements of coherent nucleus scattering neutrinos (CEvNS). The Lujan neutron elastic scattering center at the Los Alamos Neutron Science Center (LANSCE) consists of an 800-MeV, short-pulse, 100-kW proton and spallation neutron source where such searches are ongoing with the Coherent CAPTAIN Mills (CCM) 10-ton, liquid argon detector. The employment of fast timing coincidence of the beam with the detector is used to identify signals and reject background. The current beam time width is 300 ns with an intensity of $3.1 \times 10^{13}$ protons per pulse at 20 Hz. With upgrades to the Proton Storage Ring (PSR), the beam time width may be compressed to 30 ns with minimal intensity loss, allowing an increase in the signal to background (S/B) of more than 100 and an increase in the sensitivity for dark matter and sterile neutrino searches of an order of magnitude. This can be achieved with PSR accelerator upgrades on a time scale of a few years and at a modest cost.