Muon capture on light isotopes measured with the Double Chooz detector

Abstract

Using the Double Chooz detector, designed to measure the neutrino mixing angle θ[subscript 13], the products of μ[superscript −] capture on [superscript 12]C, [superscript 13]C, [superscript 14]N, and [superscript 16]O have been measured. Over a period of 489.5 days, 2.3 × 10[superscript 6] stopping cosmic μ[superscript −] have been collected, of which 1.8 × 10[superscript 5] 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 [superscript 12]C(μ[superscript −], ν) [superscript 12]B to date is reported: 6.57[+0.11 over −0.21] × 10[superscript 3] s[superscript −1], or (17.35[+0.35 over −0.59])% of nuclear captures. By tagging excited states emitting γs, the ground state transition rate to [superscript 12]B has been determined to be 5.68[+0.14 over −0.23] × 10[superscript 3] s[superscript −1]. The heretofore unobserved reactions [superscript 12]C(μ[superscript −], να) [superscript 8]Li, [superscript 13]C(μ[superscript −], νnα) [superscript 8]Li, and [superscript 13]C(μ[superscript −], νn) [superscript 12]B 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 [superscript 8]He, the reaction [superscript 13]C(μ[superscript −], να) [superscript 9]Li is found to be present at the 2.7σ level. Limits are set on a variety of other processes.