Measurement of a small atmospheric $\nu_\mu/\nu_e$ ratio

TL;DR

This study measures the ratio of muon-like to electron-like atmospheric neutrino interactions using Super-Kamiokande data, finding a smaller ratio than theoretical predictions, which supports neutrino oscillation phenomena.

Contribution

First precise measurement of the small atmospheric $ u_$ to $ u_$ ratio with detailed Monte Carlo analysis, confirming previous experimental results and challenging existing models.

Findings

Measured ratio $(/)_{DATA}/(/)_{MC} = 0.61 \u00b1 0.03(stat.) .05(sys.)

Result consistent with prior experiments, smaller than theoretical expectations

Supports evidence for neutrino oscillations

Abstract

From an exposure of 25.5~kiloton-years of the Super-Kamiokande detector, 900 muon-like and 983 electron-like single-ring atmospheric neutrino interactions were detected with momentum $p_e > 100$ MeV/$c$, $p_\mu > 200$ MeV/$c$, and with visible energy less than 1.33 GeV. Using a detailed Monte Carlo simulation, the ratio $(\mu/e)_{DATA}/(\mu/e)_{MC}$ was measured to be $0.61 \pm 0.03(stat.) \pm 0.05(sys.)$, consistent with previous results from the Kamiokande, IMB and Soudan-2 experiments, and smaller than expected from theoretical models of atmospheric neutrino production.