Searching for Sterile Neutrinos with the CAPTAIN-Mills Detector at the Los Alamos Neutron Science Center

Sterile neutrinos are non-Standard Model neutrinos whose existence would significantly change our understanding of particle physics. The MiniBooNE and LSND experiments have shown compelling evidence for sterile neutrinos in short baseline neutrino oscillation experiments. In these experiments, an excess of electron neutrino appearance was observed from a pure muon neutrino beam, and if these data are interpreted as sterile neutrino oscillations, the mass scale is Δm² ∼ 1 eV². Analogous muon neutrino disappearance measurements have shown no anomalies, but these experiments have been performed at a different energy scale compared to LSND and MiniBooNE. CAPTAIN-Mills is a new experiment to search for neutrino disappearance at the LSND energy scale. CAPTAIN-Mills will use a 10-ton liquid argon scintillation detector to leverage the enhanced cross section from coherent elastic neutrino-nucleus scattering. CAPTAIN-Mills will operate at the Lujan Center at LANSCE which is a 100-kW stopped pion source that nominally delivers an 800-MeV proton beam onto a tungsten target at 20 Hz with a pulse width of 290 ns. This fast pulsing is crucial for isolating the monoenergetic muon neutrino in time and reducing neutron backgrounds. In this talk, I will describe the current state of sterile neutrinos, describe the CAPTAIN-Mills detector and the Lujan Center, and show results from our neutron background survey.