A New Approach to Probe Non-Standard Interactions in Atmospheric Neutrino Experiments

Download Talk

Conference: The 22nd International Workshop on Neutrinos from Accelerators (NuFact 2021), Cagliari, Italy

Presentation mode: Online

Abstract: We propose a new approach to explore the neutral-current non-standard neutrino interactions (NSI) in atmospheric neutrino experiments using oscillation dips and valleys in reconstructed muon observables, at a detector like ICAL that can identify the muon charge. We focus on the flavor-changing NSI parameter ε_μτ, which has the maximum impact on the muon survival probability in these experiments. We show that non-zero ε_μτ shifts the oscillation dip locations in L/E distributions of the up/down event ratios of reconstructed μ^- and μ⁺ in opposite directions. We introduce a new variable Δd representing the difference of dip locations in μ^- and μ⁺, which is sensitive to the magnitude as well as the sign of ε_μτ, and is independent of the value of Δm²₃₂. We further note that the oscillation valley in the (E, cosθ) plane of the reconstructed muon observables bends in the presence of NSI, its curvature having opposite signs for μ^- and μ⁺. We demonstrate the identification of NSI with this curvature, which is feasible for detectors like ICAL having excellent muon energy and direction resolutions. We illustrate how the measurement of contrast in the curvatures of valleys in μ^- and μ⁺ can be used to estimate ε_μτ. Using these proposed oscillation dip and valley measurements, the achievable precision on |ε_μτ| at 90% C.L. is about 2% with 500 kt$\cdot$yr exposure. The effects of statistical fluctuations, systematic errors, and uncertainties in oscillation parameters have been incorporated using multiple sets of simulated data. Our method would provide a direct and robust measurement of ε_μτ in the multi-GeV energy range.