Muon capture on light isotopes measured with the Double Chooz detector

Abstract

Using the Double Chooz detector, designed to measure the neutrino mixing angle ?13, the products of ?- capture on C12,C13,N14, and O16 have been measured. Over a period of 489.5 days, 2.3×106 stopping cosmic ?- 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 ? decays, and, in some cases, ?-delayed neutrons. The most precise measurement of the rate of C12(?-,?)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 ?s, 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(?-,??)Li8,C13(?-,?n?)Li8, and C13(?-,?n)B12 are measured. Further, a population of ?n decays following stopping muons is identified with 5.5? significance. Statistics limit our ability to identify these decays definitively. Assuming negligible production of He8, the reaction C13(?-,??)Li9 is found to be present at the 2.7? level. Limits are set on a variety of other processes. © 2016 American Physical Society.