Cosmogenic 11C production and sentivity of organic scintillator detectors to pep and CNO neutrinos

Several possible background sources determine the detectability of pep and CNO solar neutrinos in organic liquid scintillator detectors. Among such sources, the cosmogenic {sup 11}C nuclide plays a central role. {sup 11}C is produced underground in reactions induced by the residual cosmic muon flux. Experimental data available for the effective cross section for {sup 11}C by muons indicate that {sup 11}C will be the dominant source of background for the observation of pep and CNO neutrinos. {sup 11}C decays are expected to total a rate 2.5 (20) times higher than the combined rate of pep and CNO neutrinos in Borexino (KamLAND) in the energy window preferred for the pep measurement between 0.8 and 1.3 MeV. This study examines the production mechanism of {sup 11}C by muon-induced showers in organic liquid scintillators with a novel approach: for the first time, we perform a detailed ab initio calculation of the production of a cosmogenic nuclide, {sup 11}C, taking into consideration all relevant production channels. Results of the calculation are compared with the effective cross sections measured by target experiments in muon beams. This article also discusses a technique for reduction of background from {sup 11}C in organic liquid scintillator detectors, which allowsmore » to identify on a one-by-one basis and remove from the data set a large fraction of {sup 11}C decays. The background reduction technique hinges on an idea proposed by Martin Deutsch, who suggested that a neutron must be ejected in every interaction producing a {sup 11}C nuclide from {sup 12}C. {sup 11}C events are tagged by a threefold coincidence with the parent muon track and the subsequent neutron capture on protons.« less