Abstract
At upcoming medium baseline reactor neutrino experiments the spallation 9Li background will be somewhat larger than the inverse β decay reactor neutrino signal. We use new FLUKA simulations of spallation backgrounds to optimize a class of veto strategies and find that surprisingly the optimal veto for the mass hierarchy determination has a rejection efficiency below 90%. The unrejected background has only a modest effect on the physics goals. For example Δχ2 for the hierarchy determination falls by 1.4 to 3 points depending on the muon tracking ability. The optimal veto strategy is essentially insensitive to the tracking ability, consisting of 2 meter radius, 1.1 second cylindrical vetoes of well tracked muons with showering energies above 3 to 4 GeV and 0.7 second full detector vetoes for poorly tracked muons above 15 to 18 GeV. On the other hand, as the uncertainty in θ 12 will be dominated by the uncertainty in the reactor neutrino spectrum and not statistical fluctuations, the optimal rejection efficiency for the measurement of θ 12 is 93% in the case of perfect tracking.
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Grassi, M., Evslin, J., Ciuffoli, E. et al. Vetoing cosmogenic muons in a large liquid scintillator. J. High Energ. Phys. 2015, 32 (2015). https://doi.org/10.1007/JHEP10(2015)032
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DOI: https://doi.org/10.1007/JHEP10(2015)032