Zoom in muon survival probability with sterile neutrino for CP and T-violation

Abstract

We present the approximated analytic expressions for the muon survival probability in a $3+1$ mixing scenario in the presence of matter effect using the S-matrix formalism. We find that all the individual terms contributing to the muon survival probability can significantly reduce to just three contributions. The leading order contribution comes from the three flavor muon survival probability followed by the two sub-leading contributions arising from active-sterile mixing. Furthermore, to more simplify the results we adopt the well known series expansion relations about mass-hierarchy parameter $\alpha = \Delta m^2_{21} / \Delta m^2_{31}$ and the mixing angle $\sin \theta_{13}$ in the vanishing limit of $\alpha^2$. We discuss the relevance of muon survival probability to probe the CP and T-violation studies coming from the new physics. We also compare the analytic relation between vacuum and matter contributions to the muon survival probability at the leading order. Finally, we comment on the probability behavior at the various long baselines relevant to understand the atmospheric-neutrino sector and to resolve the existing mass-hierarchy problem.