LHCb CollaborationAdeva Andany, BernardoDosil Suárez, ÁlvaroFernández Albor, Víctor ManuelGallas Torreira, Abraham AntonioGarcía Pardiñas, JuliánLemos Cid, EdgarLucio Martínez, MiriamMartínez Santos, DiegoPlo Casasus, MáximoPrisciandaro, JessicaRomero Vidal, AntonioSaborido Silva, Juan JoséSanmartín Sedes, BraisSantamarina Ríos, CibránVázquez Regueiro, PabloVázquez Sierra, CarlosVieites Díaz, María2020-05-192020-05-192016Aaij, R., Beteta, C. A., Adeva, B., Adinolfi, M., Affolder, A., Ajaltouni, Z., ... & Ali, S. (2016). First observation of the decay D0→ K− π+ μ+ μ− in the ρ0–ω region of the dimuon mass spectrum. Physics Letters B, 757, 558-5670370-2693http://hdl.handle.net/10347/22436A study of the decay D0→K−π+μ+μ−is performed using data collected by the LHCb detector in proton–proton collisions at a centre-of-mass energy of 8TeV, corresponding to an integrated luminosity of 2.0fb−1. Decay candidates with muon pairs that have an invariant mass in the range 675–875MeV/c2are considered. This region is dominated by the ρ0and ωresonances. The branching fraction in this range is measured to be B(D0→K− π + μ + μ − ) = (4.17±0.12 (stat)±0.40 (syst))×10−6. This is the first observation of the decay D0→K−π+μ+μ−. Its branching fraction is consistent with the value expected in the Standard Model.eng©2016 CERN for the benefit of the LHCb Collaboration. 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.2016.04.0291873-2445open access