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

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.