Resolving CP Violation by Standard and Nonstandard Interactions and Parameter Degeneracy in Neutrino Oscillations

TL;DR

This paper explores how to distinguish standard and nonstandard CP violation effects in neutrino oscillations using a two-detector setup, demonstrating the potential to detect NSI parameters and CP violation with high sensitivity.

Contribution

It introduces a method to disentangle standard and nonstandard CP violation effects in neutrino experiments using near-far detectors and analyzes the discovery potential for NSI parameters.

Findings

Can identify non-standard CP violation down to |ε_{eμ}| ≈ a few × 10^{-3}

Can detect |ε_{eτ}| ≈ 10^{-2} at 3σ CL for small θ_{13}

Method improves understanding of NSI impact on neutrino oscillation measurements

Abstract

In neutrino oscillation with non-standard interactions (NSI) the system is enriched with CP violation caused by phases due to NSI in addition to the standard lepton Kobayashi-Maskawa phase \delta. In this paper we show that it is possible to disentangle the two CP violating effects by measurement of muon neutrino appearance by a near-far two detector setting in neutrino factory experiments. Prior to the quantitative analysis we investigate in detail the various features of the neutrino oscillations with NSI, but under the assumption that only one of the NSI elements, \epsilon_{e \mu} or \epsilon_{e \tau}, is present. They include synergy between the near and the far detectors, the characteristic differences between the \epsilon_{e \mu} and \epsilon_{e\tau} systems, and in particular, the parameter degeneracy. Finally, we use a concrete setting with the muon energy of 50 GeV and magnetized iron detectors at two baselines, one at L=3000 km and the other at L=7000 km, each having a fiducial mass of 50 kton to study the discovery potential of NSI and its CP violation effects. We demonstrate, by assuming 4 \times 10^{21} useful muon decays for both polarities, that one can identify non-standard CP violation down to | epsilon_{e \mu} | \simeq \text{a few} \times 10^{-3}, and | \epsilon_{e \tau} | \simeq 10^{-2} at 3\sigma CL for \theta_{13} down to \sin^2 2\theta_{13} = 10^{-4} in most of the region of \delta. The impact of the existence of NSI on the measurement of \delta and the mass hierarchy is also worked out.