From oscillation dip to oscillation valley in atmospheric neutrino experiments

TL;DR

This paper introduces a novel data-driven method to identify the atmospheric neutrino oscillation dip and the first proposal of an oscillation valley in reconstructed muon data, enhancing the visualization and testing of neutrino oscillation parameters.

Contribution

It presents a new dip-identification algorithm based on asymmetry in upward and downward events and introduces the concept of an oscillation valley in the ($E_$, $\,os heta_$) plane for detectors like ICAL.

Findings

Successful demonstration of dip detection using the proposed algorithm.

First identification of an oscillation valley in reconstructed muon data.

Estimated precision of oscillation parameters with 10-year ICAL data.

Abstract

Atmospheric neutrino experiments can show the "oscillation dip" feature in data, due to their sensitivity over a large $L/E$ range. In experiments that can distinguish between neutrinos and antineutrinos, like INO, oscillation dips can be observed in both these channels separately. We present the dip-identification algorithm employing a data-driven approach -- one that uses the asymmetry in the upward-going and downward-going events, binned in the reconstructed $L/E$ of muons -- to demonstrate the dip, which would confirm the oscillation hypothesis. We further propose, for the first time, the identification of an "oscillation valley" in the reconstructed ($E_\mu$,$\,\cos\theta_\mu$) plane, feasible for detectors like ICAL having excellent muon energy and direction resolutions. We illustrate how this two-dimensional valley would offer a clear visual representation and test of the $L/E$ dependence, the alignment of the valley quantifying the atmospheric mass-squared difference. Owing to the charge identification capability of the ICAL detector at INO, we always present our results using $\mu^{-}$ and $\mu^{+}$ events separately. Taking into account the statistical fluctuations and systematic errors, and varying oscillation parameters over their currently allowed ranges, we estimate the precision to which atmospheric neutrino oscillation parameters would be determined with the 10-year simulated data at ICAL using our procedure.