Search for lepton number violating decays of $D_s^{+}\to h^{-}{h}^0{e}^{+}{e}^{+}$

Abstract

Based on 7.33 fb${}^{-1}$ of $e^{+}{e}^{-}$ collision data collected by the BESIII detector operating at the BEPCII collider at center-of-mass energies from 4.128 to 4.226 GeV, a search for the Majorana neutrino $\hat{I}{½}_m$ is conducted in the lepton-number-violating decays of $D_s^{+}\to h^{-}{h}^0{e}^{+}{e}^{+}$. Here, $h^{-}$ represents a $K^{-}$ or $\ddot{I}{€}^{-}$, and $h^0$ represents a $\ddot{I}{€}^0$, $K_S^0$ or $\ddot{I}•$. No significant signal is observed, and the upper limits of their branching fractions at the 90\% confidence level are determined to be $\mathcal{B}(D_s^{+}\to \ddot{I}•\ddot{I}{€}^{-}{e}^{+}{e}^{+})<6.9\times 10^{-5}$, $\mathcal{B}(D_s^{+}\to \ddot{I}•K^{-}{e}^{+}{e}^{+})<9.9\times 10^{-5}$, $\mathcal{B}(D_s^{+}\to K_S^0\ddot{I}{€}^{-}{e}^{+}{e}^{+})<1.3\times 10^{-5}$, $\mathcal{B}(D_s^{+}\to K_S^0{K}^{-}{e}^{+}{e}^{+})<2.9\times 10^{-5}$, $\mathcal{B}(D_s^{+}\to \ddot{I}{€}^{-}\ddot{I}{€}^0{e}^{+}{e}^{+})<2.9\times 10^{-5}$ and $\mathcal{B}(D_s^{+}\to K^{-}\ddot{I}{€}^0{e}^{+}{e}^{+})<3.4\times 10^{-5}$. The Majorana neutrino is searched for with different mass assumptions within the range [0.20, 0.80] GeV$/c^2$ in the decay of $D_s^{+}\to \ddot{I}•e^{+}\hat{I}{½}_m$ with $\hat{I}{½}_m\to \ddot{I}{€}^{-}{e}^{+}$, and the upper limits of the branching fractions at the 90\% confidence level are at the level of $10^{-5}-10^{-2}$, depending on the mass of the Majorana neutrino.