Lithium-9 Production from Stopped Muons in the Double Chooz Detector

Neutrino detectors rely on low background levels in order to detect rare neutrino interactions. A major background for the Double Chooz and other reactor neutrino experiments is 9Li, a beta delayed neutron emitter that mimics the inverse decay signal. Radioactive isotopes like 9Li are known to be produced by muon spallation processes on Carbon, but at Double Chooz depths production from muon capture on Carbon may be significant, as the branching ratio is unknown. The overall rate for 9Li production is sensitive to both the stopping and through-going muon rate, however only the rate from through-going muons is well understood. By evaluating the production rate of 9Li from muon capture we determine a limit on the branching ratio for this process.