Neutral-current background induced by atmospheric neutrinos at large liquid-scintillator detectors. I. Model predictions

The experimental searches for diffuse supernova neutrino background and proton decay in next-generation large liquid-scintillator (LS) detectors are competitive with and complementary to those in the water-Cherenkov detectors. In this paper, we carry out a systematic study of the dominant background induced by atmospheric neutrinos via their neutral-current (NC) interactions with the C-12 nuclei in the LS detectors. The atmospheric neutrino fluxes at the location of Jiangmen Underground Neutrino Observatory (JUNO) are used, as the JUNO detector is obviously a suitable representative for future LS detectors. Then, we implement the sophisticated generators GENIE and NuWro to simulate the neutrino interactions with the carbon nuclei, and the package TALYS to deal with the deexcitations of final-state nuclei. Finally, the event rates for the production of additional nucleons, gamma's, alpha's, pions, and kaons are obtained and categorized, and the systematic uncertainty of the NC background represented by a variety of data-driven nuclear models is estimated. The implications of the NC background from atmospheric neutrinos for the detection of diffuse supernova neutrino background and proton decay are also discussed.