LHCb CollaborationAdeva Andany, BernardoBorsato, MartinoChobanova, VeronikaCid Vidal, XabierDosil Suárez, ÁlvaroFernández Prieto, AntonioGallas Torreira, Abraham AntonioGarcía Pardiñas, JuliánLemos Cid, EdgarMartínez Santos, DiegoPlo Casasus, MáximoPrisciandaro, JessicaRamos Pernas, MiguelRomero Vidal, AntonioSaborido Silva, Juan JoséSanmartín Sedes, BraisSantamarina Ríos, CibránVázquez Regueiro, PabloVieites Díaz, MaríaVázquez Sierra, Carlos2020-05-202020-05-202017Aaij, R., Adeva, B., Adinolfi, M., Ajaltouni, Z., Akar, S., Albrecht, J., ... & Cartelle, P. A. (2017). Observation of the Ξb−→ J/ψΛK− decay. Physics Letters B, 772, 265-2730370-2693http://hdl.handle.net/10347/22485The observation of the decay Ξ−b→J/ψΛK−is reported, using a data sample corresponding to an integrated luminosity of 3 fb−1, collected by the LHCb detector in ppcollisions at centre-of-mass energies of 7and 8 TeV. The production rate of Ξ−bbaryons detected in the decay Ξ−b→J/ψΛK−is measured relative to that of Λ0bbaryons using the decay Λ0b→J/ψΛ. Integrated over the b-baryon transverse momentum pT<25 GeV/cand rapidity 2.0 <y <4.5, the measured ratio is fΞ − b fΛ0 b B(Ξ − b → J/ψΛK− ) B(Λ0 b → J/ψΛ) = (4.19±0.29 (stat)± 0.15 (syst))×10−2, where fΞ−band fΛ0bare the fragmentation fractions of b →Ξ−band b →Λ0btransitions, and Brepresents the branching fraction of the corresponding b-baryon decay. The mass difference between Ξ−band Λ0bbaryons is measured to be M(Ξ − b )− M(Λ0 b ) = 177.08±0.47 (stat)± 0.16 (syst)MeV/c2.eng©2017 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3.http://creativecommons.org/licenses/by/4.0/journal article10.1016/j.physletb.2017.06.0451873-2445open access