Background Studies for Double Chooz: Identifying $^9$Li Decay

Double Chooz is a reactor neutrino experiment that aims to measure the mixing parameter $\theta_{ 13}$. The experiment detects electron antineutrinos via inverse beta decay. Neutrons and light nuclei produced in muon spallation are a major background to the experiment. The delayed neutron emitter $^9$Li is especially problematic because it mimics the inverse beta decay signal. Since Double Chooz is not sensitive to the sign of the electric charge, an electron from $^9$Li decay is not easily distinguished from an inverse beta decay positron. However, the emitted neutron energies differ substantially between $^9$Li decay and inverse beta decay. The neutron from $^9$Li decay has energy on the order of an MeV, whereas the inverse beta decay neutron has a negligible kinetic energy. Furthermore, in three of the five neutron-emitting $^9$Li decay branches, an alpha particle is also emitted. To test whether Double Chooz can detect these differences, I developed general software to simulate radioactive decays in the detector. In this talk, I compare pulse timing information of each $^9$Li neutron-emitting decay branch to that of inverse beta decay.