Determination of mass hierarchy with $\nu_\mu \to \nu_\tau$ appearance and the effect of nonstandard interactions

TL;DR

This paper explores how the neutrino mass hierarchy can be determined using muon to tau neutrino appearance probabilities and examines how non-standard interactions might influence this determination.

Contribution

It introduces the use of the asymmetry parameter in muon to tau neutrino oscillations as a method to identify the neutrino mass hierarchy and studies the impact of non-standard interactions on this approach.

Findings

The asymmetry parameter effectively indicates the neutrino mass hierarchy.

Non-standard interactions can significantly alter the asymmetry parameter.

Mass hierarchy determination remains feasible despite NSI effects.

Abstract

Crucial developments in neutrino physics would be the determination of the mass hierarchy (MH) and measurement of the CP phase in the leptonic sector. The patterns of the transition probabilities $P(\nu_\mu \rightarrow \nu_\tau)$ and $P(\bar{\nu}_\mu \rightarrow \bar{\nu}_\tau)$ are sensitive to these oscillation parameters. An asymmetry parameter can be defined as the difference of these two probabilities normalized to their sum. The profile of the asymmetry parameter gives a clear signal of the mass ordering as it is found to be positive for inverted hierarchy and negative for normal hierarchy. The asymmetry parameter is also sensitive to the CP phase. We consider the effects of non-standard neutrino interactions (NSI) on the determination of the mass hierarchy. Since we assume the largest new physics effects involve the $\tau$ sector only, we ignore NSI in production and study the NSI effects in detection as well as along propagation. We find that the NSI effects can significantly modify the prediction of the asymmetry parameter though the MH can still be resolved.