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

Abstract

We study dependence of the atmospheric $ν_μ$ and $\barν_μ$ fluxes on the deviations of the 2-3 mixing from maximal, $|45^\circ - θ_{23}|$, on the $θ_{23}$-octant and on the neutrino mass splitting $Δm_{32}^2$. Analytic expressions for the $θ_{23}-$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 $θ_{23}$-deviation at higher than 3$σ$ confidence level if $| 45^\circ - θ_{23}| > 6^{\circ}$ 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 $θ_{13} > 3^\circ$. ICAL can measure the difference of $Δm_{32}^2$ in $ν$ and $\barν$ channels (the CPT test) with accuracy $0.8\times 10^{-4}$ eV$^2$ (3$σ$) with 1 Mton$\cdot$yr exposure, and the present MINOS result can be excluded at $>5σ$ confidence level. We discuss possible ways to further improve sensitivity of the magnetized spectrometers.