Badalov, AlexeyCalvo Gómez, MíriamCasanova Mohr, RaimonGarrido Beltrán, LluísGascón Fora, DavidGraciani Díaz, RicardoGraugés Pous, EugeniMarin Benito, CarlaPicatoste Olloqui, EduardoRives Molina, Vicente JoséRuiz, Hugo (Ruiz Pérez)Vilasis-Cardona, XavierLHCb Collaboration2019-05-092019-05-092015-07-280031-9007https://hdl.handle.net/2445/132875The first observation of the B 0 s → η ′ η ′ decay is reported. The study is based on a sample of proton-proton collisions corresponding to 3.0     fb − 1 of integrated luminosity collected with the LHCb detector. The significance of the signal is 6.4 standard deviations. The branching fraction is measured to be [ 3.31 ± 0.64 ( stat ) ± 0.28 ( syst ) ± 0.12 ( norm ) ] × 10 − 5 , where the third uncertainty comes from the B ± → η ′ K ± branching fraction that is used as a normalization. In addition, the charge asymmetries of B ± → η ′ K ± and B ± → ϕ K ± , which are control channels, are measured to be ( − 0.2 ± 1.3 ) % and ( + 1.7 ± 1.3 ) % , respectively. All results are consistent with theoretical expectations.9 p.application/pdfengcc by (c) CERN; LHCb Collaboration, 2015http://creativecommons.org/licenses/by/3.0/es/Física de partículesExperimentsParticle physicsExperimentsinfo:eu-repo/semantics/article6567592019-05-09info:eu-repo/semantics/openAccess