Leptonic CP violation studies at MiniBooNE in the (3+2) sterile neutrino oscillation hypothesis

TL;DR

The paper investigates leptonic CP violation within a (3+2) sterile-neutrino framework by comparing νμ→νe and ¯νμ→¯νe appearance at MiniBooNE, constrained by a global short-baseline plus atmospheric data fit. It formulates the CP-violating oscillation probabilities with a single phase φ45 and samples the seven-dimensional parameter space using Markov chain Monte Carlo, incorporating atmospheric data and practical MiniBooNE flux/cross-section effects. The results show that CP-violating (3+2) models do not significantly improve the fit over CP-conserving ones, but all φ45 values are allowed at 99% CL and CP violation could lead to large ν–¯ν appearance differences, potentially up to a factor of three in MiniBooNE. The work highlights the potential observational signatures of CP violation at short baselines and discusses cosmological tensions related to a heavy sterile state, noting possible loopholes if thermalization is avoided.

Abstract

We investigate the extent to which leptonic CP-violation in (3+2) sterile neutrino models leads to different oscillation probabilities for $\barν_μ\to\barν_e$ and $ν_μ\toν_e$ oscillations at MiniBooNE. We are using a combined analysis of short-baseline (SBL) oscillation results, including the LSND and null SBL results, to which we impose additional constraints from atmospheric oscillation data. We obtain the favored regions in MiniBooNE oscillation probability space for both (3+2) CP-conserving and (3+2) CP-violating models. We further investigate the allowed CP-violation phase values and the MiniBooNE reach for such a CP violation measurement. The analysis shows that the oscillation probabilities in MiniBooNE neutrino and antineutrino running modes can differ significantly, with the latter possibly being as much as three times larger than the first. In addition, we also show that all possible values of the single CP-violation phase measurable at short baselines in (3+2) models are allowed within 99% CL by existing data.

Figures (5)

• Figure 1: Flavor content of neutrino mass eigenstates in (3+2) models. Neutrino masses increase from bottom to top. The $\nu_e$ fractions are indicated by red (right-leaning) hatches, the $\nu_{\mu}$ fractions by green (left-leaning) hatches, the $\nu_{\tau}$ fractions by blue crosshatches, and the $\nu_s$ fractions by no hatches. The flavor contents shown are schematic only. Sorel:2003hf
• Figure 2: Expected oscillation probability asymmetry at MiniBooNE for neutrino and antineutrino running modes, for CP-conserving (3+2) models. The yellow (light gray) region corresponds to the 90% CL allowed region; the blue (dark gray) region corresponds to the 99% CL allowed region. See text for details.
• Figure 3: Illustration of expected oscillation probabilities at MiniBooNE in neutrino and antineutrino running modes, for CP-violating (3+2) models with atmospheric constraint. Here, the neutrino masses and mixings are fixed to their best-fit values and the only parameter that is allowed to vary is the CP-violating phase, $\phi_{45}$.
• Figure 4: Expected oscillation probabilities at MiniBooNE in neutrino and antineutrino running modes, for CP-violating (3+2) models. The yellow (light gray) region corresponds to the 90% CL allowed region; the blue (dark gray) region corresponds to the 99% CL allowed region. See text for details.
• Figure 5: Current limits on the CP-violating phase $\phi_{45}$ from current short-baseline results, and CP asymmetry measurement expected at MiniBooNE, $A_{p/\bar{p}}$, as a function of $\phi_{45}$. The yellow (light gray) region corresponds to the 90% CL allowed region; the blue (dark gray) region corresponds to the 99% CL allowed region. See text for details.