Search for lepton number violating decays of D _s ⁺ → h ⁻h ⁰e ⁺e ⁺

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 νm is conducted in the lepton-number-violating decays of Ds+ → h−h0e+e+. Here, h− represents a K− or π−, and h0 represents a π0, KS0 or ϕ. No significant signal is observed, and the upper limits of their branching fractions at the 90% confidence level are determined to be B(Ds+ → ϕπ−e+e+) < 6.9 × 10−5, B(Ds+ → ϕK−e+e+) < 9.9 × 10−5, B(Ds+→KS0π−e+e+) < 1.3 × 10−5, B(Ds+ → KS0K−e+e+) < 2.9 × 10−5, B(Ds+ → π−π0e+e+) < 2.9 × 10−5 and B(Ds+ → K−π0e+e+) < 3.4 × 10−5. The Majorana neutrino is searched for with different mass assumptions within the range [0.20, 0.80] GeV/c2 in the decay of Ds+ → ϕe+νm with νm → π−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.