Atmospheric neutrinos as a probe of eV^2-scale active-sterile oscillations

Abstract

The down-going atmospheric ν_μ and {\bar{ν_μ}} fluxes can be significantly altered due to the presence of eV^2-scale active-sterile oscillations. We study the sensitivity of a large Liquid Argon detector and a large magnetized iron detector (like the proposed ICAL at INO) to these oscillations. Such oscillations are indicated by results from LSND, and more recently, from MiniBooNE and from reanalyses of reactor experiments following recent recalculations of reactor fluxes. There are other tentative indications of the presence of sterile states in both the νand {\barν} sectors as well. Using the allowed sterile parameter ranges in a 3+1 mixing framework in order to test these results, we perform a fit assuming active-sterile oscillations in both the muon neutrino and antineutrino sectors, and compute oscillation exclusion limits using atmospheric down-going muon neutrino and anti-neutrino events. We find that (for both ν_μ and {\bar{ν_μ}}) a Liquid Argon detector, an ICAL-like detector or a combined analysis of both detectors with an exposure of 1 Mt yr provides significant sensitivity to regions of parameter space in the range 0.1 < Δm^2 < 5 eV^2 for \sin^2 2Θ_{μμ}\geq 0.08. Thus atmospheric neutrino experiments can provide complementary coverage in these regions, improving sensitivity limits in combination with bounds from other experiments on these parameters. We also analyse the bounds using muon antineutrino events only and compare them with the results from MiniBooNE.