Muon capture on light isotopes in Double Chooz

Abstract

Using the Double Chooz reactor neutrino detector, we have measured the products of μ- capture on 12C, 13C, 14N and 16O. Over a period of 490 days, we collected 2.3 × 106 stopping cosmic μ -, of which 1.8 × 105 captured on these nuclei in the inner detector. The resulting isotopes were tagged using prompt neutron emission (when applicable), the subsequent beta decays, and, in some cases, β-delayed neutrons. Production of these βn isotopes, primarily 9Li, which are backgrounds, was found at a significance of 5.5σ. The probability of 9Li production per capture on natC is (2.4 ± 0.9(stat) ± 0.1(syst)) × 10-4. We have made the most precise measurement of the rate of 12C(μ-, ν)12B to date, 6.57+0.11-0.21 ×103 s-1, or (17.35+0.35-0.59)% of nuclear captures. By tagging excited states emitting gammas, the ground state transition rate to 12B is found to be 5.68+0.14-0.23 ×103 s-1.