Measurement of the neutrino-oxygen neutral-current quasielastic cross section using atmospheric neutrinos at Super-Kamiokande

Abstract

Neutral current (NC) interactions of atmospheric neutrinos on oxygen form one of the major backgrounds in the search for supernova relic neutrinos with water-based Cherenkov detectors. The NC channel is dominated by neutrino quasielastic (NCQE) scattering off nucleons inside 16 O nuclei. In this paper we report the first measurement of NCQE cross section using atmospheric neutrinos at Super-Kamiokande (SK). The measurement used 2,778 live days of SK-IV data with a fiducial volume of 22.5 kiloton water. Within the visible energy window of 7.5-29.5 MeV, we observed 117 events compared to the expected 71.9 NCQE signal and 53.1 background events. Weighted by the atmospheric neutrino spectrum from 160 MeV to 10 GeV, the flux averaged NCQE cross section is measured to be ð1.01 AE 0.17ðstat:Þ þ0.78 −0.30 ðsys:ÞÞ × 10 −38 cm 2 .

Measurement of neutrino and antineutrino neutral-current quasielasticlike interactions on oxygen by detecting nuclear deexcitation γ rays

“…Note that the definition of energy in the present work differs from the previous T2K work [20], where the electron mass (0.511 MeV) was added to the visible energy. The current definition is consistent with recent low energy analyses in SK [21,53]. The interaction vertex and direction are inferred from the PMT hit pattern and timing.…”

“…The resulting excited nuclei relax to the ground state with the emission of γ rays promptly. These γ rays are available as a probe to study the NCQE interaction as has been demonstrated at T2K [20] and SK [21]. Previous studies at T2K measured the neutrino-oxygen NCQE interaction cross section with a data set of 3.01 × 10 20 protons-ontarget (POT) and SK measured this process with its atmospheric neutrino data, which is a mixture of neutrino and antineutrino interactions.…”

“…In this work the signal is termed "NCQE-like," to highlight the fact that the event selection may contain contributions from NC two-particle-two-hole (2p2h) interactions where two nucleons are involved in the interaction via mesonexchange currents. Previous studies [20,21] may have also included such events, though they were not addressed specifically. Further descriptions will be given in Sec.…”

Inclusive nucleon decay searches as a frontier of baryon number violation

“…The de-excitation particles accompanying nucleon decay could be searched for as a model-independent signature [94][95][96][97]. Such signals, however, could be plagued by typical radioactive background within experiments as well as neutrino interactions that result in similarly excited nuclear states [98].…”

Measurement of gamma-ray emission from neutron-$^{16}$O reactions with an 80 MeV quasi-mono energetic neutron beam

“…The results presented here represent valuable inputs to the modelling of gamma-ray production via neutron- 16 O reactions. Such reactions are of particular relevance to neutrino-16 O neutral-current scattering measurements in water Cherenkov detectors, since they often accompany secondary neutrons which produce gammarays that mimic those of the primary neutrino interaction [11,34]. Similarly, these data are expected to be beneficial to water Cherenkov experiments seeking to measure the final state neutron multiplicity of neutrino interactions, such as the ANNIE experiment [35,36], because understanding neutron transport and subsequent gamma-ray production are essential for identifying the signal.…”