Non-standard interactions and the CP phase measurements in neutrino oscillations at low energies

TL;DR

This paper analyzes how non-standard interactions (NSI) impact CP phase measurements in low-energy neutrino oscillations, showing significant potential corrections and proposing a combined experiment to mitigate degeneracies and improve sensitivity.

Contribution

It introduces an analytic formalism to quantify NSI effects on CP phase measurements at low energies and proposes the TNT2K experiment to reduce degeneracies and enhance CP sensitivity.

Findings

NSI can cause 20-30% correction in oscillation probabilities.

CP phase correction can reach up to 50 degrees, affecting sensitivity.

Combining T2(H)K with $$Kam reduces NSI-CP degeneracy.

Abstract

We study the effects of non-standard interactions (NSI) and the genuine CP phase $\delta_D$ in neutrino oscillations at low, $E_\nu \lesssim 1\,\mbox{GeV}$, and very low, $E_\nu \lesssim 0.1\,\mbox{GeV}$, energies. For experimental setup with baseline and neutrino energy tuned to the first 1-3 oscillation maximum, we develop a simple analytic formalism to show the effects of NSI. The vacuum mimicking and its violation as well as the use of the separation basis play a central role in our formalism. The NSI corrections that affect the CP phase measurement mainly come from the violation of vacuum mimicking as well as from the corrections to the 1-3 mixing angle and mass-squared difference. We find that the total NSI correction to the $\nu_\mu - \nu_e$ probability $P_{\mu e}$ can reach $20\% - 30\%$ ($1 \sigma$) at T2(H)K. Correspondingly, the correction to the CP phase can be as large as $50^\circ$ and hence significantly deteriorates the CP sensitivity at T2(H)K. The proposed TNT2K experiment, a combination of T2(H)K and the short baseline experiment $\mu$Kam that uses the Super-K/Hyper-K detector at Kamioka to measure the oscillation of the antineutrinos from muon decay at rest ($\mu$DAR), can substantially reduce the degeneracy between NSI and the genuine CP phase $\delta_D$ to provide high CP sensitivity. The NSI correction to $P_{\mu e}$ is only $2\%$ ($1 \sigma$) for $\mu$DAR neutrinos.