Theoretical study of lepton events in the atmospheric neutrino experiments at SuperK

TL;DR

This paper provides a theoretical analysis of lepton events in atmospheric neutrino experiments at Super-Kamiokande, focusing on nuclear medium effects in sub-GeV energy interactions, and compares predictions with experimental data.

Contribution

It introduces a detailed nuclear medium effects model for sub-GeV atmospheric neutrino interactions, improving the understanding of lepton event production in this energy range.

Findings

Nuclear medium effects significantly alter lepton event predictions.

Model results align closely with Super-Kamiokande observations.

Comparison with Monte Carlo simulations highlights the importance of nuclear effects.

Abstract

Super-Kamiokande has reported the results for the lepton events in the atmospheric neutrino experiment. These results have been presented for a 22.5kT water fiducial mass on an exposure of 1489 days, and the events are divided into sub-GeV, multi-GeV and PC events. We present a study of nuclear medium effects in the sub-GeV energy region of atmospheric neutrino events for the quasielastic scattering, incoherent and coherent pion production processes, as they give the most dominant contribution to the lepton events in this energy region. We have used the atmospheric neutrino flux given by Honda et al. These calculations have been done in the local density approximation. We take into account the effect of Pauli blocking, Fermi motion, Coulomb effect, renormalization of weak transition strengths in the nuclear medium in the case of the quasielastic reactions. The inelastic reactions leading to production of leptons along with pions is calculated in a $\Delta $- dominance model by taking into account the renormalization of $\Delta$ properties in the nuclear medium and the final state interaction effects of the outgoing pions with the residual nucleus. We present the results for the lepton events obtained in our model with and without nuclear medium effects, and compare them with the Monte Carlo predictions used in the simulation and the experimentally observed events reported by the Super-Kamiokande collaboration.