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

Abstract

We study dependence of the atmospheric νμ and ${\bar{\nu }_\mu }$ fluxes on the deviations of the 2–3 mixing from maximal, |45° − θ ₂₃|, on the θ ₂₃-octant and on the neutrino mass splitting ∆m ²₃₂ . 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 3σ confidence level if |45° − θ ₂₃| > 6° with the exposure of 1 Mton·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°. ICAL can measure the difference of ∆m ²₃₂ in ν and $\bar{\nu }$ channels (the CPT test) with accuracy 0.8 × 10⁻⁴ eV² (3σ) with 1 Mton·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.