Lepton number violation in D meson decay

Understand

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.