Study of the atmospheric neutrino flux in the multi-GeV energy range

TL;DR

This study measures the atmospheric neutrino flux and its angular dependence in the multi-GeV range using Super-Kamiokande, revealing significant flavor ratio distortion and zenith angle asymmetry indicative of neutrino oscillations.

Contribution

It provides detailed measurements of neutrino flavor ratios and zenith angle distributions, offering new insights into neutrino oscillation effects in the multi-GeV energy range.

Findings

Measured mu/e ratio as 0.66 with uncertainties

Observed strong zenith angle distortion in mu-like events

Found upward/downward mu event ratio significantly less than expected

Abstract

The flavor ratio of the atmospheric neutrino flux and its zenith angle dependence have been studied in the multi-GeV energy range using an exposure of 25.5 kiloton-years of the Super-Kamiokande detector. By comparing the data to a detailed Monte Carlo simulation, the ratio $(\mu/e)_{DATA}/(\mu/e)_{MC}$ was measured to be $0.66\pm0.06(stat.)\pm0.08(sys.)$. In addition, a strong distortion in the shape of the $\mu$-like event zenith angle distribution was observed. The ratio of the number of upward to downward $\mu$-like events was found to be 0.52$^{+0.07}_{-0.06}(stat.)\pm0.01(sys.)$, with an expected value of $0.98\pm0.03(stat.)\pm0.02(sys.)$, while the same ratio for the $e$-like events was consistent with unity.