Lepton number violation in D meson decay

TL;DR

This paper investigates lepton number violating decays of D mesons mediated by a heavy Majorana neutrino, providing upper limits on branching fractions and constraints on neutrino mixing parameters based on current experimental bounds.

Contribution

It extends previous studies by analyzing specific D meson decay channels with on-shell heavy neutrinos, deriving new upper limits and constraints on neutrino mixing matrix elements.

Findings

Branching fractions for $D^0 o K^- au^+ au^+ ext{ or } e^+ e^+$ are at the order of 10^{-10} to 10^{-9}.

Constraints on the mixing matrix element $|V_{eN}|^2$ are competitive with those from B meson decays.

Upper limits are derived using the Narrow Width Approximation and current experimental bounds.

Abstract

The lepton number violating process can be induced by introducing a fourth generation heavy Majorana neutrino, which is coupled to the charged leptons of Standard Model. There have been many previous studies on the leptonic number violating decay processes with this mechanism, we follow the trend to study the process: $D \to K \ell \ell \pi$ with the same-sign dilepton final states. We restrict ourself to certain neutrino mass regions, in which the heavy neutrino could be on shell and the dominant contribution to the branching fraction comes from the resonance enhanced effect. Applying the Narrow Width Approximation, we found that upper limit for the branching fractions for $D^0 \to K^-\ell^+\ell^+\pi^-$ are generally at the order of $10^{-10}$ to $10^{-9}$, if we take the most stringent upper limit bound currently available in the literature for the mixing matrix elements. We also provide the constrains, which is competitive compared to the LNV B decays, on the mixing matrix element $|V_{eN}|^2$ based on the upper limit of $D^0 \to K^- e^+ e^+ \pi^-$ estimated from Monte-Carlo study at BESIII.