Muon Spallation in Double Chooz

This report presents my work for Double Chooz at MIT during the 2009 Summer REU program, funded by Columbia University. Double Chooz is a reactor neutrino experiment that aims to measure the mixing parameter θ13. The experiment detects electron antineutrinos via inverse beta decay. Neutrons and light nuclei made in muon spallation are a major background to the experiment. The delayed neutron emitter Li is especially problematic because it mimics the inverse beta decay signal. For this reason I studied muon spallation in Double Chooz, focusing on the production and subsequent decay of Li. There are two key differences between Li decay and inverse beta decay. The first is that Li is a β− decay, so it emits an electron, whereas inverse beta decay emits a positron. The second difference is the energy of the neutrons emitted. In Li decay the neutron energy is on the order of MeV, whereas the inverse beta decay neutron has a negligible kinetic energy. Since Double Chooz does not distinguish charge, the positrons and electrons are not easy to distinguish. First, I ran simulations of electrons and positrons in the Double Chooz detector and constructed a late light variable to distinguish them from electrons. This proved insufficient, so I wrote general software to simulate radioactive decays in the Double Chooz detector. In this report I present the deposited energy spectra of a few important decays.