Background Characterization and Rejection for a Precision Measurement of Electron Neutrino Appearance with the Short Baseline Neutrino Program Far Detector (ICARUS)*

The LSND and MiniBooNE experiments both observed low-energy excesses of νe like events. One solution is the existence of one or more sterile neutrinos with Δm2 ~ 1eV2. The Short Baseline Neutrino Program (SBN) consists of three liquid argon time projection chambers (TPCs) along the Booster Neutrino Beam. We will cover the sterile allowed oscillation parameter space with ~5σ sensitivity. In particular, we will measure νμ disappearance and νe appearance. The latter is more challenging given the low rate and susceptibility to backgrounds. Each of the SBN detectors will operate at shallow depth, exposed to a large flux of cosmic rays. For ICARUS, 3m of concrete overburden will absorb charged hadrons and γ's. The remaining μ's passing through or near the TPC can produce γ's which mimic a genuine νe charged current interaction. Additionally, γ's produced by beam interactions in nearby materials pose a similar background. Several methods exist to reject these events using the TPC alone. ICARUS will be equipped with a cosmic ray tagging system (CRT), a tracking detector external to the cryostat. Work is underway to optimize the complementarity of the CRT and TPC for maximum sensitivity.