From oscillation dip to oscillation valley in atmospheric neutrino experiments

Abstract

Atmospheric neutrino experiments can show the “oscillation dip” feature in data, due to their sensitivity over a large L/E range. In experiments that can distinguish between neutrinos and antineutrinos, like INO, oscillation dips can be observed in both these channels separately. We present the dip-identification algorithm employing a data-driven approach – one that uses the asymmetry in the upward-going and downward-going events, binned in the reconstructed L/E of muons – to demonstrate the dip, which would confirm the oscillation hypothesis. We further propose, for the first time, the identification of an “oscillation valley” in the reconstructed ($$E_\mu $$ E μ ,$$\,\cos \theta _\mu $$ cos θ μ ) plane, feasible for detectors like ICAL having excellent muon energy and direction resolutions. We illustrate how this two-dimensional valley would offer a clear visual representation and test of the L/E dependence, the alignment of the valley quantifying the atmospheric mass-squared difference. Owing to the charge identification capability of the ICAL detector at INO, we always present our results using $$\mu ^{-}$$ μ - and $$\mu ^{+}$$ μ + events separately. Taking into account the statistical fluctuations and systematic errors, and varying oscillation parameters over their currently allowed ranges, we estimate the precision to which atmospheric neutrino oscillation parameters would be determined with the 10-year simulated data at ICAL using our procedure.

A new approach to probe non-standard interactions in atmospheric neutrino experiments

“…The wide range of neutrino energies and baselines available in atmospheric neutrino experiments offer an opportunity to study the features of "oscillation dip" and "oscillation valley" in the reconstructed µ − and µ + observables, as demonstrated in [32]. These features can be clearly identified in the ratios of upward-going and downward-going muon events at ICAL.…”

“…non-zero mixing of neutrinos, then the valley in both µ − and µ + is approximately a straight line. The location of the dip, and the alignment of the valley, can be used to determine ∆m 2 32 [32]. These features may undergo major changes in the presence of NSI, and can act as smoking gun signals for NSI.…”

“…A major impact of NSI is observed on the feature corresponding to the first oscillation minima, seen in the figure as a broad blue/black diagonal band. We refer to this broad band as the oscillation valley [32]. In the SI case, the oscillation valley appears like a triangle with straight edges, while in the presence of NSI, its edges seem to acquire a curvature.…”

“…In this study, we generate the charged-current interactions of ν µ andν µ , similar to ref. [32], using neutrino and antineutrino fluxes calculated at the Theni site by Honda et al [38,39] and the neutrino event generator NUANCE [40]. The reconstructed energy (E rec µ ) and zenith angle (θ rec µ ) of muons produced in neutrino and antineutrino interactions will be used in the analysis.…”

“…For log 10 [L rec µ /E rec µ ], we use the same binning scheme as used in ref. [32], which is shown in table 3 in the range 0-4. The downward-going events (D, cos θ rec µ > 0) are not affected significantly by oscillations or by additional NSI interactions.…”