The Atmospheric Neutrino Flavor Ratio from a 3.9 Fiducial Kiloton-Year Exposure of Soudan 2

TL;DR

This study measures the atmospheric neutrino flavor ratio using Soudan 2 data, finding a lower ratio than expected, with results confirmed by multiple analysis methods, advancing understanding of neutrino oscillations.

Contribution

First measurement of atmospheric neutrino flavor ratio in iron medium with multiple analysis methods confirming results.

Findings

Measured flavor ratio is 0.64 ± 0.13 of expected.

Results consistent across three independent analysis approaches.

Supports neutrino oscillation hypotheses.

Abstract

We report a measurement of the atmospheric neutrino flavor ratio, R, using a sample of quasi-elastic neutrino interactions occurring in an iron medium. The flavor ratio (tracks/showers) of atmospheric neutrinos in a 3.9 fiducial kiloton-year exposure of Soudan 2 is 0.64 +- 0.11 (stat.) +- 0.06 (syst.) of that expected. Important aspects of our main analysis have been checked by carrying out two independent, alternative analyses; one is based upon automated scanning, the other uses a multivariate approach for background subtraction. Similar results are found by all three approaches.