Observation of ηc(2S) →pp¯ and search for X(3872) →pp¯ decays

Physics Letters B 769 (2017) 305–313 Contents lists available at ScienceDirect Physics Letters B www.elsevier.com/locate/physletb Observation of ηc(2S) →p¯ pand search for X(3872) →p¯ pdecays .LHCb Collaboration a r t i c l e i n f o a b s t r a c t Article history: Received 22 July 2016 Received in revised form 23 February 2017 Accepted 23 March 2017 Available online 28 March 2017 Editor: M. Doser The first observation of the decay ηc(2S) →p¯ pis reported using proton–proton collision data corresponding to an integrated luminosity of 3.0fb −1recorded by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The ηc(2S)resonance is produced in the decay B+→[c¯ c]K+. The product of branching fractions normalised to that for the J/ψ intermediate state, Rηc(2S), is measured to be Rηc(2S)≡ B(B+→ηc(2S)K+)×B(ηc(2S)→p¯ p) B(B+→J/ψ K+)×B(J/ψ →p¯ p)=(1.58 ±0.33 ±0.09)×10−2, where the first uncertainty is statistical and the second systematic. No signals for the decays B+→ X(3872)(→p¯ p)K+and B+→ψ(3770)(→p¯ p)K+are seen, and the 95% confidence level upper limits on their relative branching ratios are found to be RX(3872)<0.25 ×10−2and Rψ(3770)<0.10. In addition, the mass differences between the ηc(1S)and the J/ψ states, between the ηc(2S)and the ψ(2S)states, and the natural width of the ηc(1S)are measured as MJ/ψ −Mηc(1S)=110.2±0.5±0.9MeV, Mψ(2S)−Mηc(2S)=52.5±1.7±0.6MeV, ηc(1S)=34.0±1.9±1.3MeV. ©2017 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. 1. Introduction Charmonium has proved to be a remarkable laboratory for the study of quantum chromodynamics in the non-perturbative regime. By comparing theoretical predictions with experimental results one can verify and tune the parameters of theoretical models in order to improve the accuracy of the predictions. In addition, in recent years, many exotic charmonium-like states have been observed, renewing interest in charmonium spectroscopy above the open-charm threshold [1,2]. The B+→p¯ pK+decay1offers a clean environment to study intermediate resonances, such as charmonium and charmonium-like states decaying to p¯ p. The presence of p¯ pin the final state allows intermediate states of any quantum number to be studied. The first radial excitation ηc(2S)of the charmonium ground state ηc(1S)was observed at the Bfactories [3–5] and, to date, 1The inclusion of charge-conjugate modes is implied throughout the paper. only a few of its decay modes have been observed. LHCb has previously measured, using data corresponding to an integrated luminosity of 1fb −1, the decay B+→p¯ pK+and the branching fractions of its intermediate charmonium contributions. Upper limits on the ηc(2S), X(3872)and X(3915)branching fractions were also provided [6]. The BESIII Collaboration has also recently searched for the ηc(2S) →p¯ pdecay in ψ(2S)radiative transitions [7], and set an upper limit on the product of branching fractions B(ψ(3686) →ηc(2S)γ) ×B(ηc(2S) →p¯ p). The ηc(1S)state is the lowest-lying S-wave spin-singlet charmonium state and has been observed in various processes. The measurements of the ηc(1S)mass and width in radiative charmonium transitions show a tension with those determined in different processes such as photon–photon fusion and Bdecays [8]. Detailed investigations of the line shape of the magnetic dipole transition by the KEDR [9] and CLEO [10] Collaborations indicate that additional factors modify the naïve k3dependence on the photon momentum, k, assumed in earlier measurements. This would affect the measurements of the mass and width in radiative charmonium transitions. http://dx.doi.org/10.1016/j.physletb.2017.03.046 0370-2693/©2017 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. 306 LHCb Collaboration / Physics Letters B 769 (2017) 305–313 In this paper, the first observation of ηc(2S) →p¯ pdecay and a search for ψ(3770) →p¯ pand X(3872) →p¯ pdecays are reported. The measurements of the branching fractions are relative to that of the B+→J/ψ(→p¯ p)K+decay. Additional measurements of the ηc(1S)and ηc(2S)mass and the ηc(1S)width are reported. This new measurement of the ηc(1S)resonance parameters in exclusive B+→[c¯ c]K+decays, where [c¯ c]stands for a generic charmonium resonance, is independent of the above-mentioned line-shape complications. 2. Detector and simulation The LHCb detector [11,12] is a single-arm forward spectrometer covering the pseudorapidity range 2 <η<5, designed for the study of particles containing bor cquarks. The detector includes a high-precision tracking system consisting of a silicon-strip vertex detector surrounding the pp interaction region, a large-area silicon-strip detector located upstream of a dipole magnet with a bending power of about 4Tm, and three stations of silicon-strip detectors and straw drift tubes placed downstream of the magnet. The tracking system provides a measurement of momentum, p, of charged particles with a relative uncertainty that varies from 0.5% at low momentum2to 1.0% at 200 GeV. The minimum distance of a track to a primary vertex (PV), the impact parameter (IP), is measured with a resolution of (15 +29/pT)μm, where pTis the component of the momentum transverse to the beam, in GeV. Different types of charged hadrons are distinguished using information from two ring-imaging Cherenkov detectors. The online event selection is performed by a trigger, which consists of a hardware stage, based on information from the calorimeter and muon systems, followed by a software stage, which applies full event reconstruction. At the hardware trigger stage, events are required to have high transverse energy in the calorimeters. For hadrons, the transverse energy threshold is 3.5 GeV. The software trigger requires the presence of a two-, three- or four-track secondary vertex with significant displacement from the primary pp interaction vertices. At least one charged particle must have pTlarger than 1.7GeV and be inconsistent with originating from a PV. Amultivariate algorithm [13] is used for the identification of secondary vertices consistent with the decay of a bhadron. Non-resonant B+→p¯ pK+events are simulated, uniformly distributed in phase space, as well as resonant modes such as B+→ ηc(2S)(→p¯ p)K+, B+→X(3872)(→p¯ p)K+, B+→ψ(2S)(→ p¯ p)K+and B+→J/ψ(→p¯ p)K+to optimise the signal selection and to evaluate the ratio of the efficiencies for each considered channel with respect to the normalisation mode. In the simulation, pp collisions are generated using Pythia 8 [14] with a specific LHCb configuration [15]. Decays of hadronic particles are described by EvtGen [16], in which final-state radiation is simulated using Photos [17]. The interaction of the generated particles with the detector, and its response, are implemented using the Geant4 toolkit [18] as described in Ref. [19]. 3. Event selection The selection of the B+candidates is done in two stages. First, a selection using loose criteria to reduce the background, is performed, followed by a multivariate selection. The three finalstate charged particles are required to have a track-fit χ2/ndf <3, where ndf is the number of degrees of freedom. They must also have p >1500 MeV, pT>100 MeV, and χ2 IP >1with respect to 2Natural units with c=1are used throughout the paper. any primary vertex in the event, where χ2 IP is defined as the difference in the vertex-fit χ2of a given PV reconstructed with and without the considered track. Moreover, the sum of the transverse momenta of the final-state particles is required to be greater than 4500 MeV and the sum of their momenta is required to be greater than 20 GeV. Particle identification (PID) requirements, based on the RICH detector information, are applied to pand ¯ pcandidates. The discriminating variables between different particle hypotheses (π, K, p)are the differences between log-likelihood values  lnLαβunder particle hypotheses αand β, respectively. The p and ¯ pcandidates are required to have  ln Lpπ>−5. The reconstructed B+candidates are required to have an invariant mass in the range 5.08–5.48 GeV. The PV associated to each B+candidate is defined to be the one for which the B+candidate has the smallest χ2 IP. The B+candidate is required to have a vertex fit with a χ2/ndf <12 and a flight distance greater than 3 mm, aχ2for the flight distance greater than 500, an χ2 IP <10 with respect to the associated PV and a pT>1000 MeV. The angle between the reconstructed momentum of the B+candidate and the B+flight direction (θfl)is required to be θfl>0.632 mrad. The reconstructed candidates that meet the above criteria are further filtered using a Boosted Decision Tree (BDT) algorithm [20,21]. The BDT is trained on a signal sample of simulated B+→p¯ pK+decays and a background sample of data taken from the upper B+-mass sideband in the range 5.34–5.48 GeV. The upper sideband is exploited to avoid partially reconstructed background mainly due to B(+,0)→p¯ pK+π(0,−)decays, where the pion is not correctly reconstructed, with reconstructed masses smaller than the measured B+mass. The variables used by the BDT to discriminate between signal and background candidates are: the pTof each reconstructed track; the sum of the transverse momenta of the final-state particles; the sum of their χ2 IP with respect to the primary vertex; the IP of the final-state particle with the highest pT, with respect to the primary vertex; the number of final state particles with pT>900 GeV/c; the maximum distance of closest approach between any two of the final-state particles from the B+decay; the IP of the B+candidate with respect to the primary vertex; the distance between primary and secondary vertices; cos θfl; the χ2/ndf of the secondary vertex; a pointing variable defined as Psin θ Psin θ+ipT,i, where Pis the total momentum of the three-particle final state, θis the angle between the vector sum of the momenta of the final-state particles and the direction of the flight distance of the B+, with ipT,ithe sum of the transverse momenta of the final-state particles; and the log likelihood difference for each daughter between the assumed PID hypothesis and the pion hypothesis. The selection criterion on the BDT response is chosen by maximising the significance of the χc1→p¯ psignal yield in data. The number of events from this well-known transition provides a control sample comparable in size to that of the ηc(2S). With this optimisation 90% of the B+→p¯ pK+signal candidates are retained while reducing the combinatorial background level by 83%. 4. Invariant mass spectra and event yields An extended unbinned maximum likelihood fit is performed to the p¯ pK+invariant mass distribution shown in Fig. 1. The shapes of the different contributions are determined from simulation. The signal peak is parameterised using an Apollonios probability density function (PDF) [22]. The yield, mean and resolution are allowed to vary freely in the fit, while the tail parameters are fixed to the values obtained from simulation. The combinatorial background component is parameterised by an exponential function. Partially reconstructed background is parameterised using an ARGUS PDF [23] convolved with a Gaussian resolution function. LHCb Collaboration / Physics Letters B 769 (2017) 305–313 307 Fig. 1. Invariant mass spectrum of the p¯ pK+candidates. The total fit curve and individual fit components are superimposed on the data. The parameters of the ARGUS PDF and of the Gaussian resolution function are fixed to the values obtained from simulation. The misidentified background due to B+→p¯ pπ+decays, where the charged pion is misidentified as a kaon, is parameterised with a bifurcated Gaussian PDF [24] and parameters fixed to the values obtained from simulation. The yields of partially reconstructed and misidentified backgrounds are determined from data. The backgrounds observed in the p¯ pK+mass distribution are subtracted using the sPlot technique [25] to extract the p¯ pmass spectrum in B+→p¯ pK+decays. Signal yields for the resonant contributions are then determined from an extended unbinned maximum likelihood fit to the p¯ pmass spectrum. To improve the p¯ pinvariant mass resolution, the fit to the B+decay vertex is performed with the B+mass constrained to the known value [8] and the B+candidate pointing to the PV [26]. The p¯ p mass spectrum is also used to determine the mass differences MJ/ψ −Mηc(1S)and Mψ(2S)−Mηc(2S)and the natural width of the ηc(1S)state. In order to have accurate mass measurements, acalibration is applied to the momenta of the final-state particles. Large samples of B+→J/ψ K+decays with J/ψ →μ+μ−are used to calibrate the momentum scale of the spectrometer [27]. Possible reflections due to B+→p¯ →p¯ pK+decays are investigated using simulations, which show that no narrow structures are induced in the p¯ pspectrum. Six charmonium resonances are included in the nominal fit to the p¯ pinvariant mass spectrum: ηc(1S), J/ψ, χc0, χc1, ηc(2S)and ψ(2S). Alternative fits including the ψ(3770)or the X(3872)resonances are performed in order to estimate upper limits on their branching fractions. The J/ψ and ψ(2S)peaks are parameterised with a double Gaussian PDF. The ηc(1S), ηc(2S), χc0and ψ(3770)shapes are modelled with a relativistic Breit–Wigner PDF convolved with a Gaussian PDF. The X(3872)and the χc1are described with a Gaussian PDF since their natural width is much smaller than mass resolution. Due to the B+mass constraint in the vertex fit, the p¯ pmass resolution is effectively constant in the entire p¯ pspectrum. The mass resolution parameter, common to all the charmonium states, is found to be σp¯ p=(4.3 ±0.4)MeV, in good agreement with the simulations. The masses of the χc0, χc1, X(3872), ψ(3770)and X(3915)states are fixed to the known values [8]. The J/ψ and ψ(2S)peak positions (MJ/ψ and Mψ(2S)), the mass differences (MJ/ψ −Mηc(1S) and Mψ(2S)−Mηc(2S)), and the natural width of the ηc(1S)state (ηc(1S)) are free parameters and are obtained from the fit to the data. A Gaussian constraint to the average value for the natural width of the ηc(2S)is applied [8]. The p¯ pnon-resonant component is assumed to have no relative orbital angular momentum, J=0. The fit includes a possible interference effect between the ηc(1S)state and the J=0 non-resonant component. The amplitude is given by |A|2=|Anon-res +fe iδAηc(1S)|2, where Anon-res is the amplitude of the non-resonant component, Aηc(1S)is the amplitude of the ηc(1S)state, δis the phase difference and fa normalisation factor. The shape of the non-resonant component in the p¯ pmass spectrum follows a phase-space distribution [8]. The fit result is shown in Fig. 2. A zoom of the fit result in the range 3.55–4.00 GeV is shown by the inset in Fig. 2. Using Wilks’ theorem [28], the statistical significance for the ηc(2S)signal is computed from the change in the best fit likelihood when omitting the signal under scrutiny, 2ln(LS+B/LB), where LS+Band LBare the likelihoods from the nominal fit and from the fit without the ηc(2S)signal component, respectively. The statistical significance for the ηc(2S)signal is found to be 6.4 standard deviations. No evidence for the ψ(3770)and X(3872) resonances is found. The signal yields are reported in Table 1. Fig. 2. Invariant mass spectrum of the p¯ pcandidates. Background in the B+→p¯ pK+distribution is subtracted using the sPlot technique as described in the text. The total fit curve is superimposed. A zoom of the fit result in the range 3.55–4.00 GeV is shown by the inset. 308 LHCb Collaboration / Physics Letters B 769 (2017) 305–313 Table 1 Signal yields from the fit to the p¯ pmass spectrum in B+→p¯ pK+decays. The fit fractions of the ηc(1S)and the non-resonant component in the J=0amplitude are 25% and 65% respectively. The fit fractions do not include uncertainties due to the ambiguities in the relative phase of the interfering amplitudes. Uncertainties are statistical only. State Signal yield ηc(1S)+non-res. 11246 ±119 J/ψ 6721 ±93 χc084±22 χc195±16 ηc(2S)106±22 ψ(2S)588 ±30 ψ(3770)−6±9 X(3872)−14±8 5. Efficiencies and systematic uncertainties The branching fraction of the B+→[c¯ c](→p¯ p)K+decay for a specific [c¯ c]resonance relative to that of the J/ψ is given by R[c¯ c]≡ B(B+→[c¯ c]K+)×B([c¯ c]→p¯ p) B(B+→J/ψ K+)×B(J/ψ →p¯ p) =N([c¯ c]) N(J/ψ) ×J/ψ c¯ c ,(1) where N([c¯ c]) ≡N(B+→[c¯ c](→p¯ p)K+)and N(J/ψ) ≡N(B+→ J/ψ(→p¯ p)K+)are the numbers of decays and J/ψ /c¯ cis the total efficiency ratio. The total efficiency is the product of the detector geometrical acceptance, the trigger efficiency, the reconstruction and selection efficiency, the PID efficiency, and the BDT classifier efficiency. The ratio of the efficiencies between the signal and the normalising J/ψ channels is determined using simulated samples. To account for any discrepancy between data and simulation, the PID efficiencies of kaons and protons are calibrated from data samples of D∗+ →D0(→K−π+)π+and Λ0→pπ−decays. For each simulated candidate, its PID value is replaced by a value extracted randomly from the corresponding PID curves determined from control samples. The selection is then applied to the PID- corrected simulated sample to estimate the efficiency. Systematic uncertainties originate from the determination of the signal yields, efficiencies, selection procedure and branching fractions. Since the final state is common for all considered decays, most of the systematic uncertainties cancel in the ratios. Imperfect knowledge of the invariant mass distributions for the signal and background causes systematic uncertainties in the signal yield determination, the mass difference and width measurements. The contribution from the fit model is studied by using alternative shapes for the B+component, for the [c¯ c]states and for the background. For the B+signal shape, a Gaussian PDF with powerlaw tails on both sides and the sum of two Gaussian PDFs with power-law tails are used as alternatives to the Apollonios PDF. The combinatorial background component in the p¯ pK+invariant mass is parameterised using a linear PDF. The effect of removing the peaking background due to misidentified B+→p¯ pπ+decays is investigated by checking the variation of the ratio of the branching fractions by including or neglecting this component in the fit. Incorrect modelling of the partially reconstructed background can also introduce a systematic uncertainty. This is estimated by removing the p¯ pK+invariant mass fit range below 5.20 GeV in order to exclude its contribution. In the fit to the p¯ pspectrum, for the J/ψ signal, the Apollonios PDF is used as an alternative to the sum of two Gaussian PDFs. The range of the p¯ pinvariant mass spectrum is also varied. The systematic uncertainty due to the variation of the fit range gives a negligible contribution to the Table 2 Systematic uncertainties in units of 10−4on the ηc(2S), X(3872)and ψ(3770) branching fraction measurements relative to that of the J/ψ. The efficiency contribution includes both the PID efficiency variation and the statistical error due to the finite size of the simulated samples. ηc(2S)X(3872)ψ(3770) Fit 5 3 5 BDT 8 2 11 Efficiency 2 1 1 Total 9 4 12 Table 3 Systematic uncertainties on the mass differences MJ/ψ −Mηc(1S), Mψ(2S)−Mηc(2S) and the ηc(1S)measurements. The systematic uncertainty associated to the momentum scale calibration is negligible for the total width ηc(1S)measurement. MJ/ψ −Mηc(1S) [MeV] Mψ(2S)−Mηc(2S) [MeV] ηc(1S) [MeV] Fit 0.90 0.10 1.20 BDT 0.21 0.55 0.40 Momentum scale 0.03 0.06 – Total 0.92 0.56 1.27 branching fraction measurement while it is the largest contribution to the MJ/ψ −Mηc(1S)difference. The largest variation in the ratio of the branching fractions due to the fit model is assigned as the corresponding systematic uncertainty. Possible biases related to the signal selection criteria are investigated by varying the BDT requirement and by checking the effect on the branching fraction ratio and on the efficiency ratio, after accounting for statistical fluctuations. The maximum variation in the ratio of the yields or the maximum variation in the mass difference and width measurements are considered as an estimate of the corresponding source of systematic uncertainty. In addition, variations in the procedure used to determine the PID efficiency and the uncertainty due to the finite size of the simulated samples, lead to an uncertainty on the efficiency ratio in the branching fractions evaluation. The total systematic uncertainties on the relative branching fraction measurements, determined by adding the individual contributions in quadrature, are listed in Table 2. The significance, including systematic uncertainties, of the signals is determined by convolving the profile likelihoods used in the yield determinations with a Gaussian with a width equal to the size of the systematic uncertainties that affect the yield. From the modified profile likelihood the significance of the ηc(2S)signal is found to be 6.0 standard deviations. The upper limits at 90% and 95% confidence level on the X(3872)and ψ(3770)ratio of branching fractions are determined from integrating the profile likelihood functions including systematic uncertainty. The measurements of the mass differences MJ/ψ −Mηc(1S)and Mψ(2S)−Mηc(2S)and the natural width of the ηc(1S)state are further affected by the uncertainty in the momentum scale calibration. This systematic uncertainty is small for the mass differences and negligible (< 0.003 MeV)for the natural width. Table 3 summarises the systematic uncertainties on the measurement of the MJ/ψ −Mηc(1S), Mψ(2S)−Mηc(2S)mass differences and on the ηc(1S)natural width. 6. Results and conclusions A search for the ηc(2S), ψ(3770)and X(3872)contributions in B+→p¯ pK+decays is performed using data corresponding to an integrated luminosity of 3.0fb −1recorded at centre-of-mass energies of √s=7TeVand 8TeV. The branching fractions are determined using the B+→J/ψ(→p¯ p)K+decay as normalisation channel. The ηc(2S) →p¯ pdecay is observed for the first time with LHCb Collaboration / Physics Letters B 769 (2017) 305–313 309 a total significance of 6.0 standard deviations. The relative branching fraction is measured to be Rηc(2S)=(1.58 ±0.33 ±0.09)×10−2, where the first uncertainty is statistical and the second systematic. For the B+→X(3872)(→p¯ p)K+and the B+→ψ(3770)(→ p¯ p)K+decays, the upper limits at 90 (95)% confidence level are Rψ(3770)<9(10)×10−2, RX(3872)<0.20(0.25)×10−2. The visible branching fraction calculated using the value of B(B+→J/ψ K+) ×B(J/ψ →p¯ p) =(2.2 ±0.1) ×10−6[8] is determined to be B(B+→ηc(2S)K+)×B(ηc(2S)→p¯ p) =(3.47 ±0.72 ±0.20 ±0.16)×10−8, where the last uncertainty is due to the uncertainty on B(B+→ J/ψ K+) ×B(J/ψ →p¯ p). The differences between MJ/ψ and Mηc(1S)and between Mψ(2S)and Mηc(2S)are measured to be MJ/ψ −Mηc(1S)=110.2±0.5±0.9MeV, Mψ(2S)−Mηc(2S)=52.5±1.7±0.6MeV. The natural width of the ηc(1S)is found to be ηc(1S)=34.0±1.9±1.3MeV. In contrast to the determinations using radiative decays, these mass and width determinations do not depend on the knowledge of the line shapes of the magnetic dipole transition. Acknowledgements We express our gratitude to our colleagues in the CERN accelerator departments for the excellent performance of the LHC. We thank the technical and administrative staff at the LHCb institutes. We acknowledge support from CERN and from the national agencies: CAPES, CNPq, FAPERJ and FINEP (Brazil); NSFC (China); CNRS/IN2P3 (France); BMBF, DFG and MPG (Germany); INFN (Italy); FOM and NWO (The Netherlands); MNiSW and NCN (Poland); MEN/IFA (Romania); MinES and FANO (Russia); MinECo (Spain); SNSF and SER (Switzerland); NASU (Ukraine); STFC (United Kingdom); NSF (USA). We acknowledge the computing resources that are provided by CERN, IN2P3 (France), KIT and DESY (Germany), INFN (Italy), SURF (The Netherlands), PIC (Spain), GridPP (United Kingdom), RRCKI and Yandex LLC (Russia), CSCS (Switzerland), IFIN-HH (Romania), CBPF (Brazil), PL-GRID (Poland) and OSC (USA). We are indebted to the communities behind the multiple open source software packages on which we depend. Individual groups or members have received support from AvH Foundation (Germany), EPLANET, Marie Skłodowska-Curie Actions and ERC (European Union), Conseil Général de Haute-Savoie, Labex ENIGMASS and OCEVU, Région Auvergne (France), RFBR and Yandex LLC (Russia), GVA, XuntaGal and GENCAT (Spain), Herchel Smith Fund, The Royal Society, Royal Commission for the Exhibition of 1851 and the Leverhulme Trust (United Kingdom). References [1] N. Brambilla, et al., Heavy quarkonium: progress, puzzles, and opportunities, Eur. Phys. J. C 71 (2011) 1534, arXiv:1010.5827. [2] Particle Data Group, K.A. Olive, et al., Review of particle properties, Developments in heavy quarkonium spectroscopy (pages 1240–1247), Chin. Phys. C 38 (2014) 090001. [3] Belle Collaboration, S.K. Choi, et al., Observation of the ηc(2S)in exclusive B → KKsK−π+decays, Phys. Rev. Lett. 89 (2002) 102001, arXiv:hep-ex/0206002; Belle Collaboration, S.K. Choi, et al., Phys. Rev. Lett. 89 (2002) 129901 (Erratum). [4] BaBar Collaboration, B. Aubert, et al., Measurements of the mass and width of the ηcmeson and of an ηc(2S)candidate, Phys. Rev. Lett. 92 (2004) 142002, arXiv:hep-ex/0311038. [5] CLEO Collaboration, D.M. Asner, et al., Observation of η cproduction in γγ fusion at CLEO, Phys. Rev. Lett. 92 (2004) 142001, arXiv:hep-ex/0312058. [6] LHCb Collaboration, R. Aaij, et al., Measurements of the branching fractions of B+→p¯ pK+decays, Eur. Phys. J. C 73 (6) (2013) 2462, arXiv:1303.7133. [7] BESIII Collaboration, M. Ablikim, et al., Search for ηc(2S)/hc→p¯ pdecays and measurements of the χcJ →pp branching fractions, Phys. Rev. D 88 (2013) 112001, arXiv:1310.6099. [8] Particle Data Group, K.A. Olive, et al., Review of particle physics, Chin. Phys. C 38 (2014) 090001, and 2015 update. [9] V.V. Anashin, et al., Measurement of J/ψ →γη cdecay rate and ηcparameters at KEDR, Phys. Lett. B 738 (2014) 391, arXiv:1406.7644. [10] CLEO Collaboration, R.E. Mitchell, et al., J/ψ and ψ(2S)radiative decays to ηc, Phys. Rev. Lett. 102 (2009) 011801, arXiv:0805.0252; CLEO Collaboration, R.E. Mitchell, et al., Phys. Rev. Lett. 106 (2011) 159903 (Erratum). [11] LHCb Collaboration, A.A. Alves Jr., et al., The LHCb detector at the LHC, J. Instrum. 3 (2008) S08005. [12] LHCb Collaboration, R. Aaij, et al., LHCb detector performance, Int. J. Mod. Phys. A 30 (2015) 1530022, arXiv:1412.6352. [13] V.V. Gligorov, M. Williams, Efficient, reliable and fast high-level triggering using a bonsai boosted decision tree, J. Instrum. 8 (2013) P02013, arXiv:1210.6861. [14] T. Sjöstrand, S. Mrenna, P. Skands, A brief introduction to PYTHIA 8.1, Comput. Phys. Commun. 178 (2008) 852, arXiv:0710.3820; T. Sjöstrand, S. Mrenna, P. Skands, PYTHIA 6.4 physics and manual, J. High Energy Phys. 05 (2006) 026, arXiv:hep-ph/0603175. [15] I. Belyaev, et al., Handling of the generation of primary events in Gauss, the LHCb simulation framework, J. Phys. Conf. Ser. 331 (2011) 032047. [16] D.J. Lange, The EvtGen particle decay simulation package, Nucl. Instrum. Methods A 462 (2001) 152. [17] P. Golonka, Z. Was, PHOTOS Monte Carlo: a precision tool for QED corrections in Zand Wdecays, Eur. Phys. J. C 45 (2006) 97, arXiv:hep-ph/0506026. [18] Geant4 Collaboration, J. Allison, et al., Geant4 developments and applications, IEEE Trans. Nucl. Sci. 53 (2006) 270; Geant4 Collaboration, S. Agostinelli, et al., Geant4: a simulation toolkit, Nucl. Instrum. Methods A 506 (2003) 250. [19] M. Clemencic, et al., The LHCb simulation application, Gauss: design, evolution and experience, J. Phys. Conf. Ser. 331 (2011) 032023. [20] L. Breiman, J.H. Friedman, R.A. Olshen, C.J. Stone, Classification and Regression Trees, Wadsworth International Group, Belmont, California, USA, 1984. [21] B.P. Roe, et al., Boosted decision trees as an alternative to artificial neural networks for particle identification, Nucl. Instrum. Methods A 543 (2005) 577, arXiv:physics/0408124. [22] D. Martínez Santos, F. Dupertuis, Mass distributions marginalized over perevent errors, Nucl. Instrum. Methods A 764 (2014) 150, arXiv:1312.5000. [23] ARGUS Collaboration, H. Albrecht, et al., Measurement of the polarization in the decay B →J/ψ K∗, Phys. Lett. B 340 (1994) 217. [24] BaBar Collaboration, P. del Amo Sanchez, et al., Study of B →Xγdecays and determination of |Vtd/Vts|, Phys. Rev. D 82 (2010) 051101, arXiv:1005.4087. [25] M. Pivk, F. Le Diberder, sPlot: a statistical tool to unfold data distributions, Nucl. Instrum. Methods A 555 (2005) 356, arXiv:physics/0402083. [26] W.D. Hulsbergen, Decay chain fitting with a Kalman filter, Nucl. Instrum. Methods A 552 (2005) 566, arXiv:physics/0503191. [27] LHCb Collaboration, R. Aaij, et al., Measurements of the 0 b, − b, and − b baryon masses, Phys. Rev. Lett. 110 (2013) 182001, arXiv:1302.1072. [28] S.S. Wilks, The large-sample distribution of the likelihood ratio for testing composite hypotheses, Ann. Math. Stat. 9 (1938) 60. LHCb Collaboration R. Aaij 39, B. Adeva 38, M. Adinolfi 47, Z. Ajaltouni 5, S. Akar 6, J. Albrecht 10, F. Alessio 39, M. Alexander 52, S. Ali 42, G. Alkhazov 31, P. Alvarez Cartelle 54, A.A. Alves Jr. 58, S. Amato 2, S. Amerio 23, Y. Amhis 7, 310 LHCb Collaboration / Physics Letters B 769 (2017) 305–313 L. An 40, L. Anderlini 18, G. Andreassi 40, M. Andreotti 17,g, J.E. Andrews 59, R.B. Appleby 55, O. Aquines Gutierrez 11, F. Archilli 1, P. d’Argent 12, J. Arnau Romeu 6, A. Artamonov36, M. Artuso 60, E. Aslanides 6, G. Auriemma 26, M. Baalouch 5, I. Babuschkin 55, S. Bachmann 12, J.J. Back 49, A. Badalov 37, C. Baesso 61, W. Baldini 17, R.J. Barlow 55, C. Barschel 39, S. Barsuk 7, W. Barter 39, V. Batozskaya 29, B. Batsukh 60, V. Battista 40, A. Bay40, L. Beaucourt 4, J. Beddow 52, F. Bedeschi 24, I. Bediaga 1, L.J. Bel 42, V. Bellee 40, N. Belloli 21,i, K. Belous 36, I. Belyaev 32, E. Ben-Haim 8, G. Bencivenni 19, S. Benson 39, J. Benton 47, A. Berezhnoy 33, R. Bernet 41, A. Bertolin23, F. Betti 15, M.-O. Bettler 39, M. van Beuzekom 42, S. Bifani 46, P. Billoir 8, T. Bird 55, A. Birnkraut 10, A. Bitadze 55, A. Bizzeti 18,u, T. Blake 49, F. Blanc 40, J. Blouw 11, S. Blusk 60, V. Bocci 26, T. Boettcher 57, A. Bondar35, N. Bondar 31,39, W. Bonivento 16, A. Borgheresi 21,i, S. Borghi 55, M. Borisyak 67, M. Borsato 38, F. Bossu 7, M. Boubdir 9, T.J.V. Bowcock 53, E. Bowen 41, C. Bozzi 17,39, S. Braun 12, M. Britsch 12, T. Britton 60, J. Brodzicka 55, E. Buchanan 47, C. Burr 55, A. Bursche2, J. Buytaert 39, S. Cadeddu 16, R. Calabrese 17,g, M. Calvi 21,i, M. Calvo Gomez 37,m, P. Campana 19, D. Campora Perez 39, L. Capriotti 55, A. Carbone15,e, G. Carboni 25,j, R. Cardinale 20,∗,h, A. Cardini 16, P. Carniti 21,i, L. Carson 51, K. Carvalho Akiba 2, G. Casse 53, L. Cassina 21,i, L. Castillo Garcia 40, M. Cattaneo 39, Ch. Cauet 10, G. Cavallero 20, R. Cenci 24,t, M. Charles 8, Ph. Charpentier 39, G. Chatzikonstantinidis 46, M. Chefdeville 4, S. Chen 55, S.-F. Cheung 56, V. Chobanova 38, M. Chrzaszcz 41,27, X. Cid Vidal 38, G. Ciezarek 42, P.E.L. Clarke 51, M. Clemencic 39, H.V. Cliff 48, J. Closier 39, V. Coco 58, J. Cogan 6, E. Cogneras 5, V. Cogoni 16,39,f, L. Cojocariu 30, G. Collazuol 23,o, P. Collins 39, A. Comerma-Montells 12, A. Contu 39, A. Cook 47, S. Coquereau 8, G. Corti 39, M. Corvo 17,g, C.M. Costa Sobral 49, B. Couturier 39, G.A. Cowan 51, D.C. Craik 51, A. Crocombe 49, M. Cruz Torres 61, S. Cunliffe 54, R. Currie 54, C. D’Ambrosio 39, E. Dall’Occo 42, J. Dalseno 47, P.N.Y. David 42, A. Davis 58, O. De Aguiar Francisco 2, K. De Bruyn 6, S. De Capua 55, M. De Cian 12, J.M. De Miranda 1, L. De Paula 2, P. De Simone 19, C.-T. Dean 52, D. Decamp 4, M. Deckenhoff 10, L. Del Buono 8, M. Demmer 10, D. Derkach 67, O. Deschamps 5, F. Dettori 39, B. Dey 22, A. Di Canto 39, H. Dijkstra 39, F. Dordei 39, M. Dorigo 40, A. Dosil Suárez 38, A. Dovbnya 44, K. Dreimanis 53, L. Dufour 42, G. Dujany 55, K. Dungs 39, P. Durante 39, R. Dzhelyadin 36, A. Dziurda 39, A. Dzyuba31, N. Déléage 4, S. Easo 50, U. Egede 54, V. Egorychev 32, S. Eidelman 35, S. Eisenhardt 51, U. Eitschberger 10, R. Ekelhof 10, L. Eklund 52, Ch. Elsasser 41, S. Ely 60, S. Esen 12, H.M. Evans 48, T. Evans 56, A. Falabella 15, N. Farley 46, S. Farry 53, R. Fay 53, D. Fazzini 21,i, D. Ferguson 51, V. Fernandez Albor 38, F. Ferrari 15,39, F. Ferreira Rodrigues 1, M. Ferro-Luzzi 39, S. Filippov 34, M. Fiore 17,g, M. Fiorini 17,g, M. Firlej 28, C. Fitzpatrick 40, T. Fiutowski 28, F. Fleuret 7,b, K. Fohl 39, M. Fontana 16, F. Fontanelli 20,h, D.C. Forshaw 60, R. Forty 39, V. Franco Lima 53, M. Frank 39, C. Frei 39, J. Fu 22,q, E. Furfaro 25,j, C. Färber 39, A. Gallas Torreira 38, D. Galli 15,e, S. Gallorini 23, S. Gambetta 51, M. Gandelman 2, P. Gandini 56, Y. Gao 3, J. García Pardiñas 38, J. Garra Tico 48, L. Garrido 37, P.J. Garsed 48, D. Gascon 37, C. Gaspar 39, L. Gavardi 10, G. Gazzoni 5, D. Gerick 12, E. Gersabeck 12, M. Gersabeck 55, T. Gershon 49, Ph. Ghez 4, S. Gianì 40, V. Gibson 48, O.G. Girard 40, L. Giubega 30, K. Gizdov 51, V.V. Gligorov 8, D. Golubkov 32, A. Golutvin 54,39, A. Gomes1,a, I.V. Gorelov 33, C. Gotti 21,i, M. Grabalosa Gándara 5, R. Graciani Diaz 37, L.A. Granado Cardoso 39, E. Graugés 37, E. Graverini 41, G. Graziani 18, A. Grecu30, P. Griffith 46, L. Grillo 21, B.R. Gruberg Cazon 56, O. Grünberg 65, E. Gushchin 34, Yu. Guz 36, T. Gys 39, C. Göbel 61, T. Hadavizadeh 56, C. Hadjivasiliou 5, G. Haefeli 40, C. Haen 39, S.C. Haines 48, S. Hall 54, B. Hamilton 59, X. Han 12, S. Hansmann-Menzemer 12, N. Harnew 56, S.T. Harnew 47, J. Harrison 55, M. Hatch 39, J. He 62, T. Head 40, A. Heister 9, K. Hennessy 53, P. Henrard 5, L. Henry 8, J.A. Hernando Morata 38, E. van Herwijnen 39, M. Heß 65, A. Hicheur 2, D. Hill 56, C. Hombach 55, W. Hulsbergen 42, T. Humair 54, M. Hushchyn 67, N. Hussain 56, D. Hutchcroft 53, M. Idzik 28, P. Ilten 57, R. Jacobsson 39, A. Jaeger 12, J. Jalocha 56, E. Jans 42, A. Jawahery59, M. John 56, D. Johnson 39, C.R. Jones 48, C. Joram 39, B. Jost 39, N. Jurik 60, S. Kandybei 44, W. Kanso 6, M. Karacson 39, J.M. Kariuki 47, S. Karodia 52, M. Kecke 12, M. Kelsey 60, I.R. Kenyon 46, M. Kenzie 39, T. Ketel 43, E. Khairullin 67, B. Khanji 21,39,i, C. Khurewathanakul 40, T. Kirn 9, S. Klaver 55, K. Klimaszewski 29, S. Koliiev 45, M. Kolpin 12, I. Komarov 40, R.F. Koopman 43, P. Koppenburg 42, A. Kozachuk 33, M. Kozeiha 5, L. Kravchuk 34, K. Kreplin 12, M. Kreps 49, P. Krokovny 35, F. Kruse 10, W. Krzemien 29, W. Kucewicz 27,l, M. Kucharczyk 27, V. Kudryavtsev 35, A.K. Kuonen40, K. Kurek 29, T. Kvaratskheliya 32,39, D. Lacarrere 39, G. Lafferty 55,39, A. Lai16, D. Lambert 51, G. Lanfranchi 19, C. Langenbruch 9, B. Langhans 39, T. Latham 49, C. Lazzeroni 46, R. Le Gac 6, J. van Leerdam 42, J.-P. Lees 4, A. Leflat33,39, J. Lefrançois 7, R. Lefèvre 5, LHCb Collaboration / Physics Letters B 769 (2017) 305–313 311 F. Lemaitre 39, E. Lemos Cid 38, O. Leroy 6, T. Lesiak 27, B. Leverington 12, Y. Li 7, T. Likhomanenko 67,66, R. Lindner 39, C. Linn 39, F. Lionetto 41, B. Liu 16, X. Liu 3, D. Loh 49, I. Longstaff 52, J.H. Lopes 2, D. Lucchesi 23,o, M. Lucio Martinez 38, H. Luo 51, A. Lupato 23, E. Luppi 17,g, O. Lupton 56, A. Lusiani24, X. Lyu 62, F. Machefert 7, F. Maciuc 30, O. Maev 31, K. Maguire 55, S. Malde 56, A. Malinin 66, T. Maltsev 35, G. Manca 7, G. Mancinelli 6, P. Manning 60, J. Maratas 5,v, J.F. Marchand 4, U. Marconi 15, C. Marin Benito 37, P. Marino 24,t, J. Marks 12, G. Martellotti 26, M. Martin 6, M. Martinelli 40, D. Martinez Santos 38, F. Martinez Vidal 68, D. Martins Tostes 2, L.M. Massacrier 7, A. Massafferri 1, R. Matev 39, A. Mathad49, Z. Mathe 39, C. Matteuzzi 21, A. Mauri 41, B. Maurin 40, A. Mazurov 46, M. McCann 54, J. McCarthy 46, A. McNab 55, R. McNulty 13, B. Meadows 58, F. Meier 10, M. Meissner 12, D. Melnychuk 29, M. Merk 42, A. Merli 22,q, E. Michielin 23, D.A. Milanes 64, M.-N. Minard 4, D.S. Mitzel 12, J. Molina Rodriguez 61, I.A. Monroy 64, S. Monteil 5, M. Morandin 23, P. Morawski 28, A. Mordà 6, M.J. Morello 24,t, J. Moron 28, A.B. Morris 51, R. Mountain 60, F. Muheim 51, M. Mulder 42, M. Mussini 15, D. Müller 55, J. Müller 10, K. Müller 41, V. Müller 10, P. Naik 47, T. Nakada 40, R. Nandakumar 50, A. Nandi56, I. Nasteva 2, M. Needham 51, N. Neri 22, S. Neubert 12, N. Neufeld 39, M. Neuner 12, A.D. Nguyen 40, C. Nguyen-Mau 40,n, S. Nieswand 9, R. Niet 10, N. Nikitin 33, T. Nikodem 12, A. Novoselov 36, D.P. O’Hanlon 49, A. Oblakowska-Mucha 28, V. Obraztsov 36, S. Ogilvy 19, R. Oldeman 48, C.J.G. Onderwater 69, J.M. Otalora Goicochea 2, A. Otto 39, P. Owen 41, A. Oyanguren 68, P.R. Pais 40, A. Palano14,d, F. Palombo 22,q, M. Palutan 19, J. Panman 39, A. Papanestis 50, M. Pappagallo 52, L.L. Pappalardo 17,g, C. Pappenheimer 58, W. Parker 59, C. Parkes 55, G. Passaleva 18, G.D. Patel 53, M. Patel 54, C. Patrignani 15,∗,e, A. Pearce55,50, A. Pellegrino 42, G. Penso 26,k, M. Pepe Altarelli 39, S. Perazzini 39, P. Perret 5, L. Pescatore 46, K. Petridis 47, A. Petrolini 20,h, A. Petrov 66, M. Petruzzo 22,q, E. Picatoste Olloqui 37, B. Pietrzyk 4, M. Pikies 27, D. Pinci 26, A. Pistone20, A. Piucci 12, S. Playfer 51, M. Plo Casasus 38, T. Poikela 39, F. Polci 8, A. Poluektov 49,35, I. Polyakov 60, E. Polycarpo 2, G.J. Pomery 47, A. Popov36, D. Popov 11,39, B. Popovici 30, C. Potterat 2, E. Price 47, J.D. Price 53, J. Prisciandaro 38, A. Pritchard 53, C. Prouve 47, V. Pugatch 45, A. Puig Navarro 40, G. Punzi 24,p, W. Qian 56, R. Quagliani 7,47, B. Rachwal 27, J.H. Rademacker 47, M. Rama 24, M. Ramos Pernas 38, M.S. Rangel 2, I. Raniuk 44, G. Raven 43, F. Redi 54, S. Reichert 10, A.C. dos Reis1, C. Remon Alepuz 68, V. Renaudin 7, S. Ricciardi 50, S. Richards 47, M. Rihl 39, K. Rinnert 53,39, V. Rives Molina 37, P. Robbe 7,39, A.B. Rodrigues 1, E. Rodrigues 58, J.A. Rodriguez Lopez 64, P. Rodriguez Perez 55, A. Rogozhnikov 67, S. Roiser 39, V. Romanovskiy 36, A. Romero Vidal 38, J.W. Ronayne 13, M. Rotondo 23, M.S. Rudolph 60, T. Ruf 39, P. Ruiz Valls 68, J.J. Saborido Silva 38, E. Sadykhov 32, N. Sagidova 31, B. Saitta 16,f, V. Salustino Guimaraes 2, C. Sanchez Mayordomo 68, B. Sanmartin Sedes 38, R. Santacesaria 26, C. Santamarina Rios 38, M. Santimaria 19, E. Santovetti 25,j, A. Sarti19,k, C. Satriano 26,s, A. Satta25, D.M. Saunders 47, D. Savrina 32,33, S. Schael 9, M. Schellenberg 10, M. Schiller 39, H. Schindler 39, M. Schlupp 10, M. Schmelling 11, T. Schmelzer 10, B. Schmidt 39, O. Schneider 40, A. Schopper 39, K. Schubert 10, M. Schubiger 40, M.-H. Schune 7, R. Schwemmer 39, B. Sciascia 19, A. Sciubba 26,k, A. Semennikov 32, A. Sergi 46, N. Serra 41, J. Serrano 6, L. Sestini 23, P. Seyfert 21, M. Shapkin 36, I. Shapoval 17,44,g, Y. Shcheglov 31, T. Shears 53, L. Shekhtman 35, V. Shevchenko 66, A. Shires 10, B.G. Siddi 17, R. Silva Coutinho 41, L. Silva de Oliveira 2, G. Simi 23,o, M. Sirendi 48, N. Skidmore 47, T. Skwarnicki 60, E. Smith 54, I.T. Smith 51, J. Smith 48, M. Smith 55, H. Snoek 42, M.D. Sokoloff 58, F.J.P. Soler 52, D. Souza 47, B. Souza De Paula 2, B. Spaan 10, P. Spradlin 52, S. Sridharan 39, F. Stagni 39, M. Stahl 12, S. Stahl 39, P. Stefko 40, S. Stefkova 54, O. Steinkamp 41, S. Stemmle 12, O. Stenyakin 36, S. Stevenson 56, S. Stoica 30, S. Stone 60, B. Storaci 41, S. Stracka 24,t, M. Straticiuc 30, U. Straumann 41, L. Sun 58, W. Sutcliffe 54, K. Swientek 28, V. Syropoulos 43, M. Szczekowski 29, T. Szumlak 28, S. T’Jampens 4, A. Tayduganov6, T. Tekampe 10, G. Tellarini 17,g, F. Teubert 39, C. Thomas 56, E. Thomas 39, J. van Tilburg 42, V. Tisserand 4, M. Tobin 40, S. Tolk 48, L. Tomassetti 17,g, D. Tonelli 39, S. Topp-Joergensen 56, F. Toriello 60, E. Tournefier 4, S. Tourneur 40, K. Trabelsi 40, M. Traill 52, M.T. Tran 40, M. Tresch 41, A. Trisovic 39, A. Tsaregorodtsev 6, P. Tsopelas 42, A. Tully 48, N. Tuning 42, A. Ukleja29, A. Ustyuzhanin 67,66, U. Uwer 12, C. Vacca 16,39,f, V. Vagnoni 15,39, S. Valat 39, G. Valenti 15, A. Vallier 7, R. Vazquez Gomez 19, P. Vazquez Regueiro 38, S. Vecchi 17, M. van Veghel 42, J.J. Velthuis 47, M. Veltri 18,r, G. Veneziano 40, A. Venkateswaran 60, M. Vernet 5, M. Vesterinen 12, B. Viaud 7, D. Vieira 1, M. Vieites Diaz 38, X. Vilasis-Cardona 37,m, V. Volkov 33, A. Vollhardt 41, B. Voneki 39, D. Voong 47, A. Vorobyev31, 312 LHCb Collaboration / Physics Letters B 769 (2017) 305–313 V. Vorobyev 35, C. Voß 65, J.A. de Vries 42, C. Vázquez Sierra 38, R. Waldi 65, C. Wallace 49, R. Wallace 13, J. Walsh 24, J. Wang 60, D.R. Ward 48, H.M. Wark 53, N.K. Watson 46, D. Websdale 54, A. Weiden41, M. Whitehead 39, J. Wicht 49, G. Wilkinson 56,39, M. Wilkinson 60, M. Williams 39, M.P. Williams 46, M. Williams 57, T. Williams 46, F.F. Wilson 50, J. Wimberley 59, M. Winn 4, J. Wishahi 10, W. Wislicki 29, M. Witek 27, G. Wormser 7, S.A. Wotton 48, K. Wraight 52, S. Wright 48, K. Wyllie 39, Y. Xie 63, Z. Xing 60, Z. Xu 40, Z. Yang 3, H. Yin 63, J. Yu 63, X. Yuan 35, O. Yushchenko 36, M. Zangoli 15, K.A. Zarebski 46, M. Zavertyaev 11,c, L. Zhang 3, Y. Zhang 7, Y. Zhang 62, A. Zhelezov 12, Y. Zheng 62, A. Zhokhov32, V. Zhukov 9, S. Zucchelli 15 1Centro Brasileiro de Pesquisas Físicas (CBPF), Rio de Janeiro, Brazil 2Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil 3Center for High Energy Physics, Tsinghua University, Beijing, China 4LAPP, Université Savoie Mont-Blanc, CNRS/IN2P3, Annecy-Le-Vieux, France 5Clermont Université, Université Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France 6CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille, France 7LAL, Université Paris-Sud, CNRS/IN2P3, Orsay, France 8LPNHE, Université Pierre et Marie Curie, Université Paris Diderot, CNRS/IN2P3, Paris, France 9I. Physikalisches Institut, RWTH Aachen University, Aachen, Germany 10 Fakultät Physik, Technische Universität Dortmund, Dortmund, Germany 11 Max-Planck-Institut für Kernphysik (MPIK), Heidelberg, Germany 12 Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany 13 School of Physics, University College Dublin, Dublin, Ireland 14 Sezione INFN di Bari, Bari, Italy 15 Sezione INFN di Bologna, Bologna, Italy 16 Sezione INFN di Cagliari, Cagliari, Italy 17 Sezione INFN di Ferrara, Ferrara, Italy 18 Sezione INFN di Firenze, Firenze, Italy 19 Laboratori Nazionali dell’INFN di Frascati, Frascati, Italy 20 Sezione INFN di Genova, Genova, Italy 21 Sezione INFN di Milano Bicocca, Milano, Italy 22 Sezione INFN di Milano, Milano, Italy 23 Sezione INFN di Padova, Padova, Italy 24 Sezione INFN di Pisa, Pisa, Italy 25 Sezione INFN di Roma Tor Vergata, Roma, Italy 26 Sezione INFN di Roma La Sapienza, Roma, Italy 27 Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Kraków, Poland 28 AGH – University of Science and Technology, Faculty of Physics and Applied Computer Science, Kraków, Poland 29 National Center for Nuclear Research (NCBJ), Warsaw, Poland 30 Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania 31 Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia 32 Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia 33 Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia 34 Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia 35 Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State University, Novosibirsk, Russia 36 Institute for High Energy Physics (IHEP), Protvino, Russia 37 ICCUB, Universitat de Barcelona, Barcelona, Spain 38 Universidad de Santiago de Compostela, Santiago de Compostela, Spain 39 European Organization for Nuclear Research (CERN), Geneva, Switzerland 40 Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland 41 Physik-Institut, Universität Zürich, Zürich, Switzerland 42 Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands 43 Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam, The Netherlands 44 NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine 45 Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine 46 University of Birmingham, Birmingham, United Kingdom 47 H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom 48 Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom 49 Department of Physics, University of Warwick, Coventry, United Kingdom 50 STFC Rutherford Appleton Laboratory, Didcot, United Kingdom 51 School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom 52 School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom 53 Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom 54 Imperial College London, London, United Kingdom 55 School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom 56 Department of Physics, University of Oxford, Oxford, United Kingdom 57 Massachusetts Institute of Technology, Cambridge, MA, United States 58 University of Cincinnati, Cincinnati, OH, United States 59 University of Maryland, College Park, MD, United States 60 Syracuse University, Syracuse, NY, United States 61 Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil w 62 University of Chinese Academy of Sciences, Beijing, China x 63 Institute of Particle Physics, Central China Normal University, Wuhan, Hubei, China x 64 Departamento de Fisica, Universidad Nacional de Colombia, Bogota, Colombia y 65 Institut für Physik, Universität Rostock, Rostock, Germany z 66 National Research Centre Kurchatov Institute, Moscow, Russia aa LHCb Collaboration / Physics Letters B 769 (2017) 305–313 313 67 Yandex School of Data Analysis, Moscow, Russia aa 68 Instituto de Fisica Corpuscular (IFIC), Universitat de Valencia-CSIC, Valencia, Spain ab 69 Van Swinderen Institute, University of Groningen, Groningen, The Netherlands ac *Corresponding authors. E-mail addresses: roberta.car[email protected] (R. Cardinale), [email protected]h (C. Patrignani). aUniversidade Federal do Triângulo Mineiro (UFTM), Uberaba-MG, Brazil. bLaboratoire Leprince-Ringuet, Palaiseau, France. cP.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS), Moscow, Russia. dUniversità di Bari, Bari, Italy. eUniversità di Bologna, Bologna, Italy. fUniversità di Cagliari, Cagliari, Italy. gUniversità di Ferrara, Ferrara, Italy. hUniversità di Genova, Genova, Italy. iUniversità di Milano Bicocca, Milano, Italy. jUniversità di Roma Tor Vergata, Roma, Italy. kUniversità di Roma La Sapienza, Roma, Italy. lAGH – University of Science and Technology, Faculty of Computer Science, Electronics and Telecommunications, Kraków, Poland. mLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain. nHanoi University of Science, Hanoi, Viet Nam. oUniversità di Padova, Padova, Italy. pUniversità di Pisa, Pisa, Italy. qUniversità degli Studi di Milano, Milano, Italy. rUniversità di Urbino, Urbino, Italy. sUniversità della Basilicata, Potenza, Italy. tScuola Normale Superiore, Pisa, Italy. uUniversità di Modena e Reggio Emilia, Modena, Italy. vIligan Institute of Technology (IIT), Iligan, Philippines. wAssociated to Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil. xAssociated to Center for High Energy Physics, Tsinghua University, Beijing, China. yAssociated to LPNHE, Université Pierre et Marie Curie, Université Paris Diderot, CNRS/IN2P3, Paris, France. zAssociated to Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany. aa Associated to Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia. ab Associated to ICCUB, Universitat de Barcelona, Barcelona, Spain. ac Associated to Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands.