Neutrino oscillations at low energy long baseline experiments in the presence of nonstandard interactions and parameter degeneracy

Osamu Yasuda

doi:10.1093/ptep/ptaa033

Abstract

Abstract We discuss the analytical expression of the oscillation probabilities at low energy long baseline experiments, such as Tokai to HyperKamiokande (T2HK) and Tokai to HyperKamioka and Korea (T2HKK), in the presence of nonstandard interactions (NSIs). We show that these experiments are advantageous in the exploration of the NSI parameters ($\epsilon_D$, $\epsilon_N$), which were suggested to be nonvanishing to account for the discrepancy between the solar neutrino and Kamioka Liquid scintillator Anti-Neutrino Detector data. We also show that, when the NSI parameters are small, parameter degeneracy in the CP phase $\delta$, $\epsilon_D$ and $\epsilon_N$ can be resolved by combining data of the T2HK and T2HKK experiments.

Highlights

In the last two decades we have been successful in determination of the oscillation parameters in the standard three flavor framework [1]
We show how parameter degeneracy can be resolved by combining data at different baseline length and different energy in the T2HK and T2HKK system
Even after the approximation sin(∆E2(∓1 )L/2) ≃ ∆E2(∓1 )L/2 is used, the term with ǫN remains. This is an advantage of a long baseline experiment (L >∼ 1000km) at low energy (E

Summary

Introduction

In the last two decades we have been successful in determination of the oscillation parameters in the standard three flavor framework [1]. The mass hierarchy (whether the mass pattern is given by normal hierarchy or inverted hierarchy) and the octant of θ23 (whether θ23 is larger than π/4 or not) is not known, the normal hierarchy and the higher octant θ23 > π/4 are favored to some extent [2, 3, 4] The uncertainties in these oscillation parameters are expected to be much reduced in the future long baseline experiments, T2HK [5] at L=295km, T2HKK [6] at L=1100km and DUNE [7] at L=1300km. In the analysis of the long-baseline experiments and the atmospheric neutrino experiments, the dominant oscillation comes from the larger mass squared difference ∆m231 and the oscillation probabilities are expressed in terms of ǫαβ, which will be defined in Eq (3) below, in addition to the standard oscillation parameters. The situation of parameter degeneracy in low energy long baseline experiments is better than that at high energy, because the oscillation probabilities at low energy involve fewer numbers of the NSI parameters

Nonstandard interactions in propagation

Solar neutrino flavor basis

Oscillation probability in the Earth

Conclusions