First measurement of the yield of 8He isotopes produced in liquid scintillator by cosmic-ray muons at Daya Bay

Abstract

<p>Daya Bay presents the first measurement of cosmogenic 8He isotope production in liquid scintillator, using an innovative method for identifying cascade decays of 8He and its child isotope, 8Li. We also measure the production yield of 9Li isotopes using well-established methodology. The results, in units of 10−8⁢𝜇−1⁢g−1 cm2, are 0.307±0.042, 0.341±0.040, and 0.546±0.076 for 8He, and 6.73±0.73, 6.75±0.70, and 13.74±0.82 for 9Li at average muon energies of 63.9 GeV, 64.7 GeV, and 143.0 GeV, respectively. The measured production rate of 8He isotopes is more than an order of magnitude lower than any other measurement of cosmogenic isotope production. It replaces the results of previous attempts to determine the ratio of 8He to 9Li production that yielded a wide range of limits from 0% to 30%. The results provide future liquid-scintillator-based experiments with improved ability to predict cosmogenic backgrounds.<br></p>