Aaij, R.Alfonso Albero, AlejandroGarcia Moreno, PaulaGarrido Beltrán, LluísGironella Gironell, PereGomez Fernandez, S.Graugés Pous, EugeniLobo Salvia, AniolMarin Benito, CarlaMauricio, J.Vazquez Gomez, RicardoLHCb Collaboration2025-04-252025-04-2520231126-6708https://hdl.handle.net/2445/220622A search for the lepton-flavour violating decays B0 → K∗0µ ±e ∓ and B0 s → φµ±e ∓ is presented, using proton-proton collision data collected by the LHCb detector at the LHC, corresponding to an integrated luminosity of 9 fb−1 . No significant signals are observed and upper limits of B(B 0→ K∗0µ +e −) < 5.7 × 10−9 (6.9 × 10−9 ), B(B 0→ K∗0µ −e +) < 6.8 × 10−9 (7.9 × 10−9 ), B(B 0→ K∗0µ ±e ∓) < 10.1 × 10−9 (11.7 × 10−9 ), B(B 0 s → φµ±e ∓) < 16.0 × 10−9 (19.8 × 10−9 ) are set at 90% (95%) confidence level. These results constitute the world’s most stringent limits to date, with the limit on the decay B0 s → φµ±e ∓ the first being set. In addition, limits are reported for scalar and left-handed lepton-flavour violating New Physics scenarios. 25 p.application/pdfengcc-by (c) Aaij, R. et al., 2023http://creativecommons.org/licenses/by/4.0/Física de partículesHadronsParticle physicsHadronsinfo:eu-repo/semantics/article7577352025-04-25info:eu-repo/semantics/openAccess