The 2-3 mixing and mass split: atmospheric neutrinos and magnetized spectrometers

TL;DR

This paper analyzes how atmospheric muon neutrino fluxes depend on neutrino mixing parameters, deriving expressions and estimating the sensitivity of magnetized detectors like ICAL to these parameters and potential CPT violation.

Contribution

It provides analytic formulas for the effects of 2-3 mixing deviations and octant asymmetry, along with sensitivity estimates for ICAL detector capabilities.

Findings

ICAL can detect 2-3 mixing deviations >6° at 3σ confidence

Sensitivity to octant improves for θ13 > 3°

ICAL can measure Δm² differences with 0.8×10⁻⁴ eV² accuracy

Abstract

We study dependence of the atmospheric $\nu_\mu$ and $\bar{\nu}_\mu$ fluxes on the deviations of the 2-3 mixing from maximal, $|45^\circ - \theta_{23}|$, on the $\theta_{23}$-octant and on the neutrino mass splitting $\Delta m_{32}^2$. Analytic expressions for the $\theta_{23}-$deviation effect and the octant asymmetry are derived. We present conservative estimations of sensitivities of the iron (magnetized) calorimeter detectors (ICAL) to these parameters. ICAL can establish the $\theta_{23}$-deviation at higher than 3$\sigma$ confidence level if $| 45^\circ - \theta_{23}| > 6^{\circ}$ with the exposure of 1 Mton$\cdot$yr. Sensitivity to the octant is low for zero or very small 1-3 mixing, but it can be substantially enhanced for $\theta_{13} > 3^\circ$. ICAL can measure the difference of $\Delta m_{32}^2$ in $\nu$ and $\bar\nu$ channels (the CPT test) with accuracy $0.8\times 10^{-4}$ eV$^2$ (3$\sigma$) with 1 Mton$\cdot$yr exposure, and the present MINOS result can be excluded at $>5\sigma$ confidence level. We discuss possible ways to further improve sensitivity of the magnetized spectrometers.