Muon capture on light isotopes measured with the Double Chooz detector

Abstract

Using the Double Chooz detector, designed to measure the neutrino mixing angle θ13, the products of μ- capture on C12,C13,N14, and O16 have been measured. Over a period of 489.5 days, 2.3×106 stopping cosmic μ- have been collected, of which 1.8×105 captured on carbon, nitrogen, or oxygen nuclei in the inner detector scintillator or acrylic vessels. The resulting isotopes were tagged using prompt neutron emission (when applicable), the subsequent β decays, and, in some cases, β-delayed neutrons. The most precise measurement of the rate of C12(μ-,ν)B12 to date is reported: 6.57-0.21+0.11×103s-1, or (17.35-0.59+0.35)% of nuclear captures. By tagging excited states emitting γs, the ground state transition rate to B12 has been determined to be 5.68-0.23+0.14×103s-1. The heretofore unobserved reactions C12(μ-,να)Li8,C13(μ-,νnα)Li8, and C13(μ-,νn)B12 are measured. Further, a population of βn decays following stopping muons is identified with 5.5σ significance. Statistics limit our ability to identify these decays definitively. Assuming negligible production of He8, the reaction C13(μ-,να)Li9 is found to be present at the 2.7σ level. Limits are set on a variety of other processes.