Badalov, AlexeyCalvo Gómez, MíriamCamboni, AlessandroCoquereau, SamuelFernandez, G.Garrido Beltrán, LluísGascón Fora, DavidGraciani Díaz, RicardoGraugés Pous, EugeniMarin Benito, CarlaPicatoste Olloqui, EduardoRives Molina, Vicente JoséSánchez Gonzalo, DavidVilasis-Cardona, XavierLHCb Collaboration2019-05-062019-05-062017-05-110031-9007https://hdl.handle.net/2445/132740A search for the rare decays Bs0→μ+μ- and B0→μ+μ- is performed at the LHCb experiment using data collected in p p collisions corresponding to a total integrated luminosity of 4.4 fb-1. An excess of Bs0→μ+μ- decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be B (Bs0→μ+μ- )=(3.0 ±0. 6-0.2+0.3) ×10-9 , where the first uncertainty is statistical and the second systematic. The first measurement of the Bs0→μ+μ- effective lifetime, τ (Bs0→μ+μ- )=2.04 ±0.44 ±0.05 ps , is reported. No significant excess of B0→μ+μ- decays is found, and a 95% confidence level upper limit, B (B0 →μ+μ-) <3.4 ×10-10 , is determined. All results are in agreement with the standard model expectations.11 p.application/pdfengcc by (c) CERN; LHCb Collaboration, 2017http://creativecommons.org/licenses/by/3.0/es/Física de partículesExperimentsParticle physicsExperimentsinfo:eu-repo/semantics/article6779972019-05-06info:eu-repo/semantics/openAccess