CP violation in $B_s$ decays mediated by two nearly-degenerate Majorana neutrinos

TL;DR

This paper investigates CP violation in B_s decays mediated by nearly-degenerate Majorana neutrinos, showing potential for observation at LHCb and providing new constraints on neutrino mixing parameters.

Contribution

It introduces a study of CP violation in B_s decays involving two nearly-degenerate GeV-scale Majorana neutrinos, with experimental analysis and bounds on neutrino mixing.

Findings

CP violation could be significant if neutrino mass difference is around decay width.

LHCb upgrade II could observe such CP violation under current constraints.

New upper bounds on heavy-light neutrino mixing parameter |U_{μN}|^2 in 1-3 GeV mass range.

Abstract

We study the \textit{CP} violation in the lepton-number-violating process $B_s^0 \rightarrow D_s^- \mu^+ \mu^+ \pi^-$ and its \textit{CP}-conjugate process $\bar{B_s^0} \rightarrow D_s^+ \mu^- \mu^- \pi^+$ that are induced by two GeV-scale Majorana neutrinos with nearly-degenerate masses. Our result shows that the size of the \textit{CP} violation could become considerable if the mass difference between the two Majorana neutrinos is around the decay width of the neutrinos. We perform experimental analysis on the \textit{CP}-violating processes at LHCb within its upgrade II. The analysis shows that under current constraint on the heavy-light neutrino mixing parameter, it is possible that such \textit{CP} violation is observed with the LHCb experimental ability. We also give the upper bound on the heavy-light mixing parameter $|U_{\mu N}|^2$ under the assumption that no positive signal of the process is observed. The result shows that such modes can give complementary constraint compared with previous experiments such as NuTeV, BEBC, etc. in the mass region 1~GeV $< m_N <$ 3~GeV.