Searching for lepton number violating $\Lambda$ baryon decays mediated by GeV-scale Majorana neutrino with LHCb

We consider the lepton-number-violating processes in Λb/Λc decays mediated by on-shell GeV-scale sterile neutrino. We calculate the branching ratio for the following processes: Λb0→B+μ-μ-π+, where B+ is Λc+ or proton, and Λc+→Λμ+μ+π- as function of the mass of the sterile neutrino mN and the heavy-light mixing coefficient of the extended Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix |UμN|2. The effect of finite detector size is included in our calculation. After comparing the theoretical effective branching ratio with the expected experimental ability of LHCb, we give the sensitivity upper bounds on |UμN|2 on the (|UμN|2-mN) plane. These channels give comparable results with the bounds given by different search strategies (e.g., at Belle, NuTeV, DELPHI, and BEBC) in the mass region mN≃0.25 GeV–4.5 GeV, and the limits are stronger in the mass range 2 GeV<mN<4.5 GeV.