The Search for Low Energy Single Photons in MicroBooNE

Abstract

The MiniBooNE experiment is a Cherenkov based experiment located on the Booster Neutrino Beam. It observed an unexplained excess of $\nu_e$ charged current quasi-elastic (CCQE) event candidates in the reconstructed $E_{\nu}^{QE}\approx 200-475$ MeV region known as the ``Low Energy Excess'' (LEE). These $\nu_e$ CCQE event candidates were in the form of lone showers, a signature left by both electrons and photons indistinguishably in the MiniBooNE detector. For this reason the identity of the MiniBooNE LEE as a photon or electron excess is currently unknown. Liquid argon time projection chambers (LArTPCs) are a relatively new type of detector able to distinguish between photons and electrons. The MicroBooNE detector is one such LArTPC and is situated on the same beamline and at a similar baseline as the MiniBooNE detector. This makes MicroBooNE an ideal experiment to test the photon and electron interpretations of the MiniBooNE LEE. This thesis presents the search for a photon LEE using an enhanced rate of neutrino-induced neutral current (NC) $\Delta$ production and subsequent radiative decay (NC $\Delta$ radiative) as the candidate source. A multi-stage NC $\Delta$ radiative event selection has been developed which takes full advantage of MicroBooNE's photon-electron discrimination capability. The ability of the search to select NC $\Delta$ radiative events in MicroBooNE and validation of the search with 4.8$\times 10^{19}$ protons-on-target worth of data are presented. Also shown are preliminary studies of MicroBooNE's sensitivity to a NC $\Delta$ radiative interpretation of the LEE.