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RAPID COMMUNICATIONS PHYSICAL REVIEW D 94, 091102(R) (2016) ỵ þ Study of Bþ c decays to the K K final state and evidence ỵ for the decay Bỵ c → χ c0 π R Aaij et al.* (LHCb Collaboration) (Received 21 July 2016; published 30 November 2016) Bỵ c ỵ A study of K K þ decays is performed for the first time using data corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb experiment in pp collisions at center-of-mass ỵ þ energies of and TeV Evidence for the decay Bỵ c c0 K K ị is reported with a significance of 4.0 standard deviations, giving Bỵ cị Bỵ ị ỵ3.4 ỵ ì BBỵ c c0 ị ẳ 9.83.0 statị ặ 0.8systịị ì 10 Here B ỵ ỵ ỵ denotes a branching fraction while Bỵ c ị and B ị are the production cross sections for Bc and B ¯ weak annihilation is found for the region mK ỵ Þ < 1.834 GeV=c2 , with a mesons An indication of bc significance of 2.4 standard deviations DOI: 10.1103/PhysRevD.94.091102 Heavy-flavor physics involves studying the decays of hadrons containing at least one b or c valence quark, and offers the possibility of making precision measurements of Standard Model (SM) parameters and detecting effects of new physics The Bỵ c meson (bc), the only currently established hadron having two different heavy-flavor quarks, has the particularity of decaying weakly through either of its flavors.1 In the SM, the Bỵ c decays with no charm and beauty particles in the final or intermediate W ỵ uq (q ẳ d, s) states can proceed only via bc annihilation, with an amplitude proportional to the product of Cabibbo-Kobayashi-Maskawa matrix elements V Ãcb V uq Calculations predict branching fractions in the range 10−8 –10−6 [1–3] Any significant enhancement could ¯ annihilations involving particles indicate the presence of bc beyond the SM, such as a mediating charged Higgs boson (see, e.g., Ref [4,5]) Experimentally, the decays of Bỵ c mesons to three light charged hadrons provide a good way to study such processes These decay modes have a large available phase space and can include other processes such as Bỵ c D0 Kịhỵ (h ẳ , K) [6] mediated by b u and ỵ ỵ s transitions, Bỵ b d, c Bq h1 h2 Þh3 decays [7] mediated by c → q transitions, or charmonium modes ỵ Bỵ c hỵ c ẵc h1 Þh2 [8] mediated by the b → c transition [9] In this study, special consideration is given to decays leading to a K ỵ K ỵ final state in the region well below the D0 mass, taken to be mK ỵ ị < 1.834 GeV=c2 , where, after removing possible contributions from * Full author list given at the end of the article Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI Charge conjugation is implied throughout the paper 2470-0010=2016=94(9)=091102(10) ẵcc; B0s ị K þ K − , only the annihilation process remains The other contributions listed above are also examined The ¯ K ỵ K ị ỵ is used as a normalization decay Bỵ D mode to derive Rf Bỵ cị ì BBỵ c fị; Bỵ ị 1ị ỵ where B is the branching fraction, and Bỵ c ị and B ị ỵ ỵ are the production cross sections of the Bc and B mesons The quantity Rf is measured in the fiducial region pT ðBÞ < 20 GeV=c and 2.0 < yðBÞ < 4.5, where pT is the component of the momentum transverse to the proton beam and y denotes the rapidity The data sample used corresponds to integrated luminosities of 1.0 and 2.0 fb−1 collected by the LHCb experiment at and TeV centerof-mass energies in pp collisions, respectively Since the kinematics of B meson production is very similar at the two Bỵ cị energies, the ratio B ỵ ị is assumed to be the same for all the measurements discussed in this paper The LHCb detector is a single-arm forward spectrometer covering the pseudorapidity range < η < 5, described in detail in Refs [10,11] The detector allows the reconstruction of both charged and neutral particles For this analysis, the ring-imaging Cherenkov detectors [12], distinguishing pions, kaons and protons, are particularly important Simulated events are produced using the software described in Refs [1319] ỵ ỵ The Bỵ cị K K π decay candidates are reconstructed applying the same selection procedure as in Ref [20] A similar multivariate analysis is implemented, using a boosted decision tree (BDT) classifier [21] Particle identification (PID) requirements are then applied to reduce the combinatorial background and suppress the cross feed from pions misidentified as kaons The BDT and PID requirements are optimized to maximize the sensitivity to small event yields 091102-1 © 2016 CERN, for the LHCb Collaboration RAPID COMMUNICATIONS R AAIJ et al PHYSICAL REVIEW D 94, 091102(R) (2016) Events/(0.004 GeV/c2) The signal yield is determined from a simultaneous fit in three bins of the BDT output OBDT , 0.04
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