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

Le résumé fourni par la source

Daya Bay presents the first measurement of cosmogenic $^{8}\mathrm{He}$ isotope production in liquid scintillator, using an innovative method for identifying cascade decays of $^{8}\mathrm{He}$ and its child isotope, $^{8}\mathrm{Li}$. We also measure the production yield of $^{9}\mathrm{Li}$ isotopes using well-established methodology. The results, in units of ${10}^{\ensuremath{-}8}{\ensuremath{\mu}}^{\ensuremath{-}1}{\mathrm{g}}^{\ensuremath{-}1}\text{ }\text{ }{\mathrm{cm}}^{2}$, are $0.307\ifmmode\pm\else\textpm\fi{}0.042$, $0.341\ifmmode\pm\else\textpm\fi{}0.040$, and $0.546\ifmmode\pm\else\textpm\fi{}0.076$ for $^{8}\mathrm{He}$, and $6.73\ifmmode\pm\else\textpm\fi{}0.73$, $6.75\ifmmode\pm\else\textpm\fi{}0.70$, and $13.74\ifmmode\pm\else\textpm\fi{}0.82$ for $^{9}\mathrm{Li}$ at average muon energies of 63.9 GeV, 64.7 GeV, and 143.0 GeV, respectively. The measured production rate of $^{8}\mathrm{He}$ 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 $^{8}\mathrm{He}$ to $^{9}\mathrm{Li}$ 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.

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