Measurement of the B − c meson production fraction and asymmetry in 7 and 13 TeV pp collisions
LHCb collaboration, R. Aaij, C. Abellán Beteta, T. Ackernley, B. Adeva, M. Adinolfi, H. Afsharnia, C.A. Aidala, S. Aiola, Z. Ajaltouni, S. Akar, P. Albicocco, J. Albrecht, F. Alessio, M. Alexander, A. Alfonso Albero, G. Alkhazov, P. Alvarez Cartelle, A.A. Alves Jr, S. Amato, Y. Amhis, L. An, L. Anderlini, G. Andreassi, M. Andreotti, F. Archilli, J. Arnau Romeu, A. Artamonov, M. Artuso, K. Arzymatov, E. Aslanides, M. Atzeni, B. Audurier, S. Bachmann, J.J. Back, S. Baker, V. Balagura, W. Baldini, A. Baranov, R.J. Barlow, S. Barsuk, W. Barter, M. Bartolini, F. Baryshnikov, G. Bassi, V. Batozskaya, B. Batsukh, A. Battig, A. Bay, M. Becker, F. Bedeschi, I. Bediaga, A. Beiter, L.J. Bel, V. Belavin, S. Belin, N. Beliy, V. Bellee, K. Belous, I. Belyaev, G. Bencivenni, E. Ben-Haim, S. Benson, S. Beranek, A. Berezhnoy, R. Bernet, D. Berninghoff, H.C. Bernstein, E. Bertholet, A. Bertolin, C. Betancourt, F. Betti, M.O. Bettler, Ia. Bezshyiko, S. Bhasin, J. Bhom, M.S. Bieker, S. Bifani, P. Billoir, A. Bizzeti, M. Bjørn, M.P. Blago, T. Blake, F. Blanc, S. Blusk, D. Bobulska, V. Bocci, O. Boente Garcia, T. Boettcher, A. Boldyrev, A. Bondar, N. Bondar, S. Borghi, M. Borisyak, M. Borsato, J.T. Borsuk, T.J.V. Bowcock, C. Bozzi, M.J. Bradley, S. Braun, et al. (807 additional authors not shown)
EEUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)
CERN-EP-2019-216LHCb-PAPER-2019-033December 19, 2019
Measurement of the B − c mesonproduction fraction and asymmetryin 7 and 13 TeV pp collisions LHCb collaboration † Abstract
The production fraction of the B − c meson with respect to the sum of B − and B mesons is measured in both 7 and 13 TeV center-of-mass energy pp collisionsproduced by the Large Hadron Collider (LHC), using the LHCb detector. The rate,approximately 3.7 per mille, does not change with energy, but shows a transversemomentum dependence. The B − c − B + c production asymmetry is also measured, andis consistent with zero within the determined statistical and systematic uncertaintiesof a few percent. Published in Phys. Rev. D100 (2019) 112006 c (cid:13) † Authors are listed at the end of this paper. a r X i v : . [ h e p - e x ] D ec i Introduction
The B − c meson is a bound state containing a b quark with a c quark. It has the largestmass of any two differently flavored quarks in a mesonic ground state. Studies of itsproduction or determination of individual decay widths require measurements of itsbranching fractions to exclusive final states. Since the branching fractions of some decaymodes of B − and B mesons are accurately known, we determine the ratio of B − c mesonproduction relative to the sum of B − and B mesons. Here we use techniques similar tothose employed for the measurement of B s meson and Λ b baryon fractions [1]. In thatpaper use is made of the fact that the semileptonic widths of all b -flavored hadrons withlight and strange quarks are equal. However, both the b and c quarks can decay, renderingthat concept inapplicable. Instead we rely on theoretical predictions of the semileptonicdecay branching fraction B ( B − c → J/ψ µ − ν ). Currently, only the relative productioncross-section times the branching fraction of either the B − c → J/ψ µ − ν or B − c → J/ψ π − modes have been measured by the CDF [2, 3], LHCb [4, 5] and CMS [6, 7] experiments.The B − c meson production fraction ( f c ) relative to the sum of B ( f d ) and B − ( f u )mesons is defined as R c = f c f u + f d ≡ n cor ( B − c → J/ψ µ − ν ) n cor ( B → D Xµ − ν ) + n cor ( B → D + Xµ − ν ) · (cid:104)B sl (cid:105)B ( B − c → J/ψ µ − ν ) , (1)where n cor refers to the efficiency and branching fraction corrected number of signal events.The modes containing D and D + mesons are also corrected for cross-feeds with B s and Λ b decays. The determination of the corrected yields of the B → DXµ − ν decays followsour previous measurement strategy in Ref. [1] where the equations relating the fractionsto the corrected yields, including cross-feed contributions, are given. We also correctfor the 0.4% effect of doubly-Cabibbo-suppressed decays and D mixing. The relevanthadron branching fractions are listed in Table 1. The average semileptonic branchingfractions of B and B − , (cid:104)B sl (cid:105) = (10 . ± . b → cµ − ν µ modes are detected in this analysis, a correction for the small b → uµ − ν µ rateof 1% is applied to the denominator of Eq. 1. Table 1: Charm and charmonium branching fractions for the decay modes used in this analysis.
Particle and decay B (%) Source D → K − π + . ± .
03 PDG average [12] D + → K − π + π + . ± .
17 CLEO III [13]
J/ψ → µ + µ − . ± .
03 PDG average [12]The dominant production mechanism for B − c mesons is gluon-gluon fusion, gg → B − c +¯ b + c . Non-relativistic quantum chromodynamics is used along with fragmentation functionsto predict cross-sections as functions of transverse momentum ( p T ) and pseudorapidity( η ). The literature is nicely summarized in Ref. [14]. We define H b to refer to B c , B , and B − mesons, while H c refers to D and D + mesons. The mention of a particular state implies the use of the charge-conjugate state as well, except whendiscussing production asymmetries.
1n this analysis η is determined by measuring the angle of the B meson with respect tothe beam direction by using the positions of the primary pp interaction vertex (PV) andthe B meson decay point into either J/ψ µ − , D µ − , or D + µ − . The transverse momentuminitially refers to the vector sum of the charmed-hadron and µ − momentum transverseto the proton beams. However, the results are re-interpreted in terms of the H b meson p T ( H b ) by simulating and correcting the effects of the missing momenta.The production asymmetry between B − c and B + c mesons, which should be small, isdefined as a prod ≡ σ ( B − c ) − σ ( B + c ) σ ( B − c ) + σ ( B + c ) = a raw − a det , (2)where a raw and a det are the asymmetries in the signal yields and the efficiencies of B − c and B + c detection, respectively. The CP asymmetry in the B − c → J/ψ µ − ν decay is assumedto be zero in this analysis.The branching fraction predictions from various models of semileptonic B − c decays arelisted in Table 2. For B ( B − c → J/ψ µ − ν ) they range from 1.4 to 7.5%, which is quite alarge interval. Branching fractions for other modes are also listed where available. We usethe Z expansion fit results from Ref. [32], and the method II results for Ref. [33]. Table 2: Branching fractions predictions (%). The B − c lifetime is taken as 0.507 ps [12]. Thevalue for the semileptonic decays of the B − c meson, B c sl , is derived by summing the J/ψ µ − ν and η c µ − ν individual predictions with the average predictions of 0.1% for ψ (2 S ) µ − ν , the sumof χ c , , µ − ν as 0.6%, and 0.3% for h c µ − ν . In the one case where η c µ − ν was not predictedaverages from other measurements are used. Ref. \ Mode
J/ψ µ − ν η c µ − ν ψ (2 S ) µ − ν χ c , , µ − ν h c µ − ν B c sl [15] 6.4 5.0 1.3 13.6[16] 0.5[17] 1.4 0.5 2.9[18] 7.5 2.4 10.9[19] 1.9 0.6 0.1 3.5[20] 2.3 0.9 0.8 4.2[21] 2.7 1.8 5.5[22] 1.6 0.8 3.4[23] 1.7 0.5 0.6 3.3[24] 1.7 0.2 2.9[25] 1.9 0.8 0.1 3.7[26] 2.3 0.9 4.2[27] 2.2 0.8 0.1 4.0[28] 2.6 0.1 1.1 4.2[29] 2.5 1.1 4.6[30] 1.3 0.8 0.2 3.1[31] 1.4 0.7 3.1[32] 1.5 0.7 0.5 0.3 3.2[33] 1.9 0.6 0.1 0.3 0.3 3.5[34] 2.2 0.8 4.02ome restrictions on models are possible by comparing to lighter B meson decays.Since the inclusive semileptonic branching fraction for these decays, B sl , is about 10.5%and the B − c lifetime, τ B c , is 1/3 that of the B , we disregard models that predict 10% orlarger values for B c sl of the B − c . This excludes from consideration the models of Refs. [15]and [18]. The average model prediction is then B ( B − c → J/ψ µ − ν ) = 1 . The LHCb detector [35,36] is a single-arm forward spectrometer covering the pseudorapidityrange 2 < η <
5, designed for the study of particles containing b or c quarks. The detectorelements that are particularly relevant to this analysis are: a silicon-strip vertex detectorsurrounding the pp interaction region that allows c and b hadrons to be identified fromtheir characteristically long flight distance; a tracking system that provides a measurementof the momentum, p , of charged particles; two ring-imaging Cherenkov detectors thatare able to discriminate between different species of charged hadrons; and a downstreamsystem of iron interspersed with chambers is used to identify muons.The magnetic field deflects positively and negatively charged particles in oppositedirections and this can lead to detection asymmetries. Periodically reversing the magneticfield polarity throughout the data taking almost cancels the effect. The configuration withthe magnetic field pointing upwards (downwards) bends positively (negatively) chargedparticles in the horizontal plane towards the centre of the LHC ring. This analysis usesdata collected in 2011 (7 TeV) and 2016 (13 TeV) where appropriate triggers are available.The data taking was split between magnetic field up and down configurations. In the 2011data 0.6 fb − (0.4 fb − ) were collected with the field pointing up (down), while in 2016the split was 0.9 fb − with field up and 0.8 fb − with field down.The trigger [37] consists of a hardware stage, based on information from the calorimeterand muon systems, followed by a software stage, in which all charged particles with p T >
500 (300) MeV are reconstructed for 2011 (2016) data.Separate hardware triggers are used for the
J/ψ µ − and H c samples. For the former werequire a µ + µ − pair. For the latter, we require a single muon with large p T for the 7 TeVdata as used in Ref. [38]. For the 13 TeV data, the single muon trigger was not available,therefore at the hardware trigger stage, events are required to have a hadron, photon orelectron transverse energy greater than approximately 3.5 GeV in the calorimeters. Thesoftware trigger requires a two-, three- or four-track secondary vertex with a significantdisplacement from any primary pp interaction vertex as described in Ref. [1]. At least onecharged particle must have p T > . b hadron.Simulation is required to model the effects of the detector acceptance and the imposedselection requirements. In the simulation, pp collisions are generated using Pythia [40]with a specific LHCb configuration [41]. Decays of unstable particles are described This is evident since B c sl = Γ sl · τ B c , and Γ sl is approximately the same for all b -hadron species. We usenatural units where c = (cid:126) = 1 . EvtGen [42], in which final-state radiation is generated using
Photos [43]. Theinteraction of the generated particles with the detector, and its response, are implementedusing the
Geant4 toolkit [44] as described in Ref. [45]. B − c → J/ψ µ − ν candidates The analysis is done separately for the light B meson modes and the B − c → J/ψ µ − ν decay. In each case the triggered events are subject to further filtering requirements. Inaddition, the J/ψ µ − sample is subjected to a boosted decision tree (BDT), a multivariateclassification method, using the TMVA toolkit [46]. This is not necessary for the D or D + modes because they have large signals and are relatively free from backgrounds [1].For the J/ψ µ − ν final state the initial selection requires that muons that satisfy the J/ψ candidate trigger each have minimum p T >
550 MeV, have large impact parameterswith the PV, form a good quality vertex, have a reasonable flight distance significancefrom the PV, and have a summed p T > J/ψ decay must be well identified and form a good quality vertex with the
J/ψ candidate, which must be downstream of the PV.To suppress muon tracks that are reconstructed more than once, we require a smallminimum opening angle between the muons from the
J/ψ decay and the companion muonmomentum measured in the plane transverse to the beam line. Specifically, this openingangle must be greater than 0.8 ◦ . The invariant mass of the companion muon and theoppositely charged muon from J/ψ must differ from the known value of the
J/ψ mass bymore than 50 MeV [12], while the invariant mass with the same charged muon is requiredto be larger than 400 MeV.Since we are dealing with an exclusive final state, we define m cor ≡ (cid:113) m ( J/ψ µ − ) + p ⊥ + p ⊥ , (3)where p ⊥ is the magnitude of the combination’s momentum component transverse to the b -hadron flight direction. Figure 1 shows the distributions of m cor versus the invariant J/ψ µ − mass, m ( J/ψ µ − ), for both data and simulation. To remove background, a requirement of m ( J/ψ µ − ) > . B + c and B − c mesons, werestrict the angular acceptance of the companion muon to make it more uniform byremoving muons close to the edge of the detector, in the bending direction ( x -direction),where large acceptance-induced asymmetries can occur. Thus, we require that the x -component of the momentum satisfies | p x | ≤ . p z − , (4)where p z is the muon momentum along the direction of the proton beam downstream ofthe PV, as is done in Refs. [47, 48].After these initial restrictions, we turn to the multivariate selection, forming theclassifier denoted BDT in the following. The discriminating variables used are: (a) the χ of the vertex fit of the J/ψ with the µ − ; (b) the ln χ , where χ is defined as the χ [GeV] cor m [ G e V ] ) - my m ( J / (a) LHCb [GeV] cor m [ G e V ] ) - my m ( J / (b) LHCb simulation [GeV] cor m [ G e V ] ) - my m ( J / (c) LHCb [GeV] cor m [ G e V ] ) - my m ( J / (d) LHCb simulation Figure 1: Distributions of corrected mass m cor and m ( J/ψ µ − ) for (top) 7 TeV and (bottom)13 TeV data, where (a) and (c) are data and (b) and (d) simulated signal. The (red) dashed lineindicates the m ( J/ψ µ − ) > . of the impact parameter with respect to the PV, of the J/ψ , µ − and their combination;(c) the p T of the J/ψ and the µ − ; and (d) the cosine of the angle between the µ − andthe J/ψ meson in the plane perpendicular to the beam direction. The training samplefor signal is simulated B − c → J/ψ µ − ν events, and for background is inclusive b → J/ψ X simulated events.We then optimize the BDT output threshold by maximizing S/ √ S + B , where S and B are the number of the signal and background yields in the signal region definedas m cor ∈ (4 . , .
8) GeV. The sum, S + B , is the total number of events within theselimits, and S is taken from a fit to the m cor distribution. The optimal BDT outputthreshold results in a BDT signal efficiency of 89% with a background rejection of 63%,as determined by observing the resulting samples of input signal simulation events andbackground candidates.The m cor distribution is shown in Fig. 2. It consists not only of signal B − c events,but also of B − c → J/ψ τ − ν decays, where τ − → µ − νν , and other cc final states, mostimportantly B − c → ψ (2 S ) µ − ν and B − c → χ c µ − ν . We find shapes for these final statesusing simulation. The signal shape is a sum of a double Crystal Ball and a bifurcatedGaussian functions. The sum of the combinatorial and misidentification backgrounds arerepresented by a Gaussian kernel shape [49]. For the other background modes, we usehistograms directly. These shapes are fitted to the m cor distributions in Fig. 2 in orderto determine the B − c → J/ψ µ − ν yields. The ratio of the J/ψ τ − ν yield to the J/ψ µ − ν yield is fixed, after accounting for the relative detection efficiencies, from the LHCbmeasurement of 0 . ± . ± .
18, where the first uncertainty is statistical and the second5 [GeV] cor m C a nd i d a t e s / ( . G e V ) n - m c cfi - c B n - ty / J fi - c B n - my / J fi - c B (a) LHCb 7 TeV [GeV] cor m C a nd i d a t e s / ( . G e V ) n - m c cfi - c B n - ty / J fi - c B n - my / J fi - c B (b) LHCb 13 TeV Figure 2: Fitted m cor distributions in (a) 7 TeV and (b) 13 TeV samples. The signal and thebackgrounds are shown as the dark (orange) and lighter (gray) areas. The dashed (cyan) curvesshow the B − c → J/ψ τ − ν τ components, while the dotted (blue) curves show the B − c → χ c , , µ − ν components. The B − c → ψ (2 S ) µ − ν contribution is also in the fit but is too small to be seen.The total fit is shown by the solid (red) curve. systematic [50]; this convention is used throughout this paper. The other components ofthe fit are allowed to vary. We find 4010 ±
200 and 15 170 ±
710 signal B − c → J/ψ µ − ν events at 7 and 13 TeV, respectively, while the backgrounds sum to 950 and 5170 eventsat the same energies. These signal yields need to be corrected for the small backgroundfrom candidates with a correctly reconstructed J/ψ meson that is paired with a hadronmis-identified as a muon. B − c → J/ψ µ − ν Efficiencies are determined using both data [51, 52] and simulation of B − c → J/ψ µ − ν , withthe generated events weighted to match the p T ( H b ), and η distributions observed in data.In addition, we weight accordingly the χ distribution of the muon associated with the J/ψ . Weighting the simulation is important since the total efficiencies are functions ofthese variables. Efficiencies using data include trigger, and muon identification. Efficienciesusing simulation include detector acceptance, reconstruction and event selection, andremoval of beam crossings with an excess number of hits in the detector. Total efficienciesas a function of p T ( B − c ) for different η intervals are shown in Fig. 3. H c X µ − ν selection criteria Selection criteria for H b → H c Xµ − ν final states differ from those containing a J/ψ . Thetransverse momentum of each hadron must be greater than 0.3 GeV, and that of the muonlarger than 1.3 GeV. We require χ > pp interactions. All final state particles are required to bepositively identified using information from the RICH detectors. Particles from H c decaycandidates must have a good fit to a common vertex with χ /ndof <
9, where ndof is thenumber of degrees of freedom. They must also be well separated from the nearest PV,with the flight distance divided by its uncertainty greater than 5.Candidate b hadrons are formed by combining H c and muon candidates originatingfrom a common vertex with χ /ndof < H c µ − invariant mass in the range6 able 3: Yields of B → DXµ − ν decays. Mode 7 TeV Yields 13 TeV yieldsSignal fake muons Signal fake muons D Xµν
789 800 ±
940 5500 ±
160 12 285 000 ± ± D + Xµν
263 190 ±
570 990 ±
70 3 686 240 ± ± H c production at the PV needs to be considered. We usethe natural logarithm of the H c impact parameter, IP, with respect to the PV in units ofmm. Requiring ln(IP/mm) > − H c candidate mass spectra to find the b -hadron decay yields.The H c candidate mass distributions integrated over p T ( H b ) and η are shown inFig. 4 and consist of a prominent peak resulting from signal, and a small contributiondue to combinatorial background from random combinations of particles that pass theselection. They are fit with a signal component comprised of two Gaussian functions, anda combinatorial background component modeled as a linear function. The fitted yieldsare listed in Table 3. These numbers must be corrected for hadrons that are mis-identifiedas muons, and for semileptonic decays of B s and Λ b hadrons that produce D and D + mesons.In Table 3 the column labeled “fake muons” shows the yields of wrong-sign D Xµ + and D + Xµ + combinations that pass the selections. These yields provide good estimatesof the fake muon contributions in the signal samples, which are very small. Following theprocedure in Ref. [1], we find the cross-feed corrections of B s → ( D + D + ) Xµ − ν and Λ b → ( D + D + ) Xµ − ν to be twice the measured yields for B s → D K + Xµ − ν , whichare 8500 ±
340 (7 TeV) and 69 390 ± Λ b → D pXµ − ν , which are2330 ±
140 (7 TeV) and 33 050 ±
460 (13 TeV). Relative efficiencies for detecting finalstates with a single extra hadron are taken into account when subtracting these yields. ) [GeV] - c B ( T p T o t a l e ff i c i e n c y < 3 h h h h n - my / J fi - c B (a) LHCb 7 TeV ) [GeV] - c B ( T p T o t a l e ff i c i e n c y < 3 h h h h n - my / J fi - c B (b) LHCb 13 TeV Figure 3: The total efficiency for B − c → J/ψ µ − ν , as a function of p T ( B − c ) in different intervalsof η in (a) 7 TeV and (b) 13 TeV samples. .4 Efficiencies for B → D X µ − ν and B → D + X µ − ν Similar methods based on data, as implemented for the B − c decay, are used to evaluatethe efficiencies for trigger and particle identification. Simulation is also used to determinethe efficiencies of event selection and reconstruction of these modes. The total efficienciesfor B meson decays into D Xµ − ν and D + Xµ − ν are shown in Fig. 5. p T ( H b ) distributions due to the missingneutrino Since the production kinematics of B and B − c mesons can differ as functions of p T ( H b )and η , we need to measure f c / ( f u + f d ) as functions of these variables. The measurementof η is straightforward, however, we do not measure directly the p T ( H b ) of the b -flavoredhadron because of the missing neutrino, and in the case of the B meson possible missingextra particles. Following a procedure similar to the one used in Ref. [1], we determinea correction factor, k , that is the ratio of the average reconstructed to true p T ( H b ) as afunction of the invariant mass of the charmed hadron plus muon. The ratio distributionas a function of hadron-muon invariant mass are shown in Fig. 6. The average correction,the k –factor, is shown on the figure. For the B meson it varies from 0.75 to unity over [MeV] ) + p - m(K C a nd i d a t e s / ( G e V ) n - m X D fi B (a) LHCb 7 TeV [MeV] ) + p + p - m(K C a nd i d a t e s / ( G e V ) n - m X + D fi B (b) LHCb 7 TeV [MeV] ) + p - m(K C a nd i d a t e s / ( G e V ) · DataTotal fitSignalBackground n - m X D fi B (c) LHCb 13 TeV [MeV] ) + p + p - m(K C a nd i d a t e s / ( G e V ) · DataTotal fitSignalBackground n - m X + D fi B (d) LHCb 13 TeV Figure 4: Invariant-mass distributions of (a) K − π + and (b) K − π + π + for 7 TeV, and (c) and (d)for 13 TeV collisions. The data are shown by solid points. The (red) dashed lines represent thesignal components. The combinatorial backgrounds are shown as the dotted (magenta) line, andthe solid (blue) line shows the total fit. [GeV] b H ( T p T o t a l e ff i c i e n c y < 3 h h h h n - m X D fi B (a) LHCb 7 TeV ) [GeV] b H ( T p T o t a l e ff i c i e n c y < 3 h h h h n - m X + D fi B (b) LHCb 7 TeV ) [GeV] b H ( T p T o t a l e ff i c i e n c y < 3 h h h h n - m X D fi B (c) LHCb 13 TeV ) [GeV] b H ( T p T o t a l e ff i c i e n c y < 3 h h h h n - m X + D fi B (d) LHCb 13 TeV Figure 5: Total efficiencies for the (a) D Xµ − ν and (b) D + Xµ − ν signals in 7 TeV and (c) and(d) in 13 TeV samples as functions of p T in η intervals.Table 4: Results of the fits to Eq. 5 . Energy p p · − (GeV − )7 TeV 3 . ± . ± . − . ± . ± .
113 TeV 4 . ± . ± . − . ± . ± . B mass, and for the B − c meson it varies from 0.85 to unityover the interval from 4 GeV to the B − c mass. B − c fraction results The ratio of production fractions, f c / ( f u + f d ), are shown as functions of p T ( H b ) and η in Fig. 7. There is little dependence on η , but the decrease as a function of p T ( H b ) isnoticeable.To describe the p T ( H b ) dependence we use an equation of the form f c f u + f d ( p T ) = A [ p + p ( p T ( H b ) − (cid:104) p T (cid:105) )] , (5)where A represents the overall normalization and contains the total global systematicuncertainty, thus, A = 1 ± . (cid:104) p T (cid:105) is taken as 7.2 GeV, close to the average p T of the B − c . The slopes, p , are similar in size to those measured for the B s meson fraction ratioas a function of p T [1, 53]. Results of fits to the data using Eq. 5 are listed in Table 4. See Section 5 for the discussion of the systematic uncertainties. < p T ( H b ) <
25 GeV are found by integrating over p T ( H b ). To allow for facile changes to our results due to improved theoretical predictions,we provide the results for f c f u + f d · B ( B − c → J/ψ µ − ν ) = (7 . ± . ± . · − for 7 TeV ,f c f u + f d · B ( B − c → J/ψ µ − ν ) = (7 . ± . ± . · − for 13 TeV . Next we give the result on the fractions ratio f c f u + f d = (3 . ± . ± . ± . · − for 7 TeV ,f c f u + f d = (3 . ± . ± . ± . · − for 13 TeV , where the third uncertainty is due to the theoretical prediction of B ( B − c → J/ψ µ − ν ) . Tofind f c /f u just double these numbers.We also measure the ratio of the B − c production fraction at 7 TeV to that at 13 TeV.Figure 8 shows the ratio as functions of p T and η . Here most of the systematic uncertaintiescancel. The integrated value of the ratio of 13 TeV and 7 TeV is measured as 1 . ± . ± ) [MeV] - my / J ( m ( t r u e ) T p ⁄ (r ec on s t r u c t e d ) T p n - my / J fi - c B
13 TeV (a) LHCb simulation 020406080100120140 ) [MeV] - m D ( m ( t r u e ) T p ⁄ (r ec on s t r u c t e d ) T p n - m X D fi B
13 TeV (b) LHCb simulation0102030405060 ) [MeV] - m + D ( m ( t r u e ) T p ⁄ (r ec on s t r u c t e d ) T p n - m X + D fi B
13 TeV (c) LHCb simulation
Figure 6: The k -factor corrections as a function of invariant mass of (a) m ( J/ψ µ − ), (b) m ( D µ − ),and (c) m ( D + µ − ) for the 13 TeV simulation samples. (The 7 TeV results are almost identical.)The points (magenta) are the average k -factor corrections, and the (green) dashed line shows asecond-order polynomial fit to the average data. .
04, consistent with no increase in the B − c fraction ratio as a function of center-of-massenergy.The B − c fraction with respect to inclusive b –hadron production can be derived fromthe information in previous LHCb b –hadron fraction papers Ref. [1, 38, 53]. There themeasured values of the ratios of b –hadron fractions over the same p T range in terms ofthe b –hadron p T are for B s mesons ( f s ) and Λ b baryons f s f u + f d = (cid:40) . ± .
010 (7 TeV) [53]0 . ± .
006 (13 TeV) [1] , (6) f Λ b f u + f d = (cid:40) . ± .
036 (7 TeV) [38]0 . ± .
018 (13 TeV) [1] , (7)where the uncertainties contain both statistical and systematic components added inquadrature. For the measurement of the f Λ b fraction at 7 TeV, the dominant systematicuncertainty is from the lack of the knowledge of B ( Λ + c → pK − π + ) at that time [38];here the value and uncertainty have been recalculated according to the latest value of B ( Λ + c → pK − π + ) from the PDG [12].Taking the sum of all the b -hadron fractions to be unity, and ignoring f c here becauseit is so small, f u + f d + f s + f Λ b (1 + δ ) = 1 , (8) ) [GeV] b H ( T p ) - · ( d f + u f c f (a) LHCb 7 TeVDataFitAverage ) [GeV] b H ( T p ) - · ( d f + u f c f (b) LHCb 13 TeVDataFitAverage h ) - · ( d f + u f c f (c) LHCb 7 TeVDataAverage h ) - · ( d f + u f c f (d) LHCb 13 TeVDataAverage Figure 7: Ratio of production fractions after the k -factor correction as a function of (a) p T ( H b )and (c) η in 7 TeV data and (b) and (d) in 13 TeV data. The smaller error bars show thestatistical uncertainties and the larger ones include the statistical and systematic uncertainties.The horizontal (green) dashed-lines show the average values. δ = 0 . ± .
10 is a correction factor derived in Ref. [11] that accounts for heavier b –baryons, mainly the Ξ b . Solving for f u + f d yields f u + f d = (cid:18) f s f u + f d + f Λ b f u + f d (1 + δ ) (cid:19) − , = (cid:40) . ± .
026 (7 TeV)0 . ± .
015 (13 TeV) . (9)We find that f c · B ( B − c → J/ψ µ − ν ) = (cid:40) (5 . ± . ± . ± . · − (7 TeV)(5 . ± . ± . ± . · − (13 TeV) , where the first uncertainty is statistical, the second is systematic, and the third is fromthe fractions of the B s and Λ b given in Eq. 9. We also provide the result for f c , f c = (cid:40) (2 . ± . ± . ± . · − (7 TeV)(2 . ± . ± . ± . · − (13 TeV) , where the first uncertainty is statistical, the second is systematic including that from B ( B − c → J/ψ µ − ν ) and the third is from the fractions of the B s and Λ b given in Eq. 9. B − c − B + c production asymmetry The production asymmetries are measured in two different magnetic field configurationsand then averaged. No significant asymmetry is observed in any intervals of p T ( H b ) or η .The results are summarized in Table 5.Averaging the B − c − B + c production asymmetries over p T ( H b ) and η , we find( − . ± . ± . − . ± . ± . ) [GeV] b H ( T p R a ti o (a)LHCb h R a ti o (b)LHCb Figure 8: Ratio of the B − c production fractions at 13 TeV to 7 TeV as a function of (a) p T ( H b )and (b) η . The smaller error bars show the statistical uncertainties and the larger ones includethe statistical and systematic uncertainties added in quadrature. able 5: The B − c − B + c production asymmetry ( × − ) as a function of p T ( H b ) and η at 7 TeVand 13 TeV. p T (GeV) \ η . − . . − . − . ± . ± . − . ± . ± . − − . ± . ± . − . ± . ± . − − . ± . ± . − . ± . ± . −
25 0 . ± . ± . − . ± . ± . p T (GeV) \ η . − . . − . − . ± . ± .
16 1 . ± . ± . − − . ± . ± . − . ± . ± . −
10 2 . ± . ± . − . ± . ± . −
25 1 . ± . ± . − . ± . ± . Systematic uncertainties are separated into two categories: “global”, which apply acrossthe phase space, and “local”, which are calculated in each two-dimensional p T ( H b ) − η bin. These uncertainties are listed in Table 6.First let us consider the B − c → J/ψ µ − ν decay. The uncertainty due to the signalshape used to fit the m cor distribution is determined by changing the baseline signal shape,the sum of a double sided Crystal Ball function and a bifurcated Gaussian, to a kernelestimation. To find the shape of the combinatorial and misidentification backgroundswe use simulated inclusive samples of b → J/ψ X events not including B − c decays. Atotal of 500 samples are generated and different fits to the samples are performed todetermine the possible uncertainty. This procedure is also used for the a prod measurement.We call contributions to the J/ψ µ − mass spectrum “feed-down” contributions, occurringfrom other B − c decay channels including J/ψ τ ν , ψ (2 S ) µ − ν , and χ c µ − ν . The systematicuncertainty results from the uncertainties in their branching fractions. Different decaymodels for B − c → J/ψ µ − ν decays can change the m cor shape. We use the model of Ebert et al. [16] for our baseline prediction. Then we also use the model by Kiselev [27] to findthe efficiencies and take half the difference as the systematic uncertainty. We also estimatethe uncertainty due to the sensitivity to various selection requirements and simulationstatistics. The muon identification efficiencies are determined from data using inclusivesamples of J/ψ decay where one of the muon candidates is not identified. The triggerefficiency is determined by using three independent samples of events, those that triggeron a
J/ψ , those that triggered on something else in the event, and those that trigger onboth the
J/ψ and something else. These samples are then used to compute the triggerefficiencies in two-dimensional p T ( H b ) and η bins.Next, we turn to the B → DXµν modes. The efficiencies and their uncertainties foridentifying pions and kaons are determined by using almost background free samples of D ∗ + → π + D , D → K − π + decays. The trigger and muon identification efficiencies, and13 able 6: Summary of the relative systematic uncertainties for f c / ( f u + f d )(%) and the absoluteproduction asymmetries a prod (%). For local uncertainties, the ranges correspond to the minimumand maximum uncertainties evaluated in the p T ( H b ) and η ranges. f c / ( f u + f d ) a prod Local uncertainties
Signal shape 0.12–9.56 0.14–2.80 0.04–1.80 0.01–0.78Background shape 0.34–6.16 0.02–5.80 0.06–3.05 0.05–2.45Feed-down channels 0.12–5.00 0.43–2.27 0.01–1.11 0.03–0.65Decay models 0.00–2.00 0.01–3.84 0.02–0.28 0.02–0.61Muon ID in
J/ψ µ − J/ψ
DXµ − ν DXµ − ν k -factor 0.02–0.95 0.05–0.70 0.01–0.10 0.00–0.10Tracking asymmetry – – 0.00–0.28 0.00–0.09 Global uncertainties B ( J/ψ → µ + µ − ) 0 .
55 0 . − −B ( D + → K − π + π + ) or B ( D → K − π + ) 1 . . − −B ( B → H c Xµ − ν ) 1 . . − − Cross-feed contribution 0 . . − − Multiplicity cut 1.2 2.7 − −
Tracking efficiency 1 . . − − Uncertainty sum B ( B − c → J/ψ µ − ν ) 23.6 23.6 – – Overall uncertainty B − c → J/ψ µ − ν mode.There are small systematic uncertainties related to efficiency estimates and the assumed D ∗ to D mixtures, as well as simulation statistics. Global systematic uncertainties includethe hadron branching fractions listed in Table 1, cross-feed corrections arising from B s and Λ b decays into DXµ − ν events, and a global hadron plus photon multiplicity requirement.The latter is evaluated with data. In 7 and 13 TeV pp collisions the product of B ( B − c → J/ψ µ − ν ) with the relative fractionof B − c mesons with respect to the sum of B and B + mesons in the ranges 2 . < η < . < p T ( H b ) <
25 GeV is found to be f c f u + f d · B ( B − c → J/ψ µ − ν ) = (7 . ± . ± . · − for 7 TeV ,f c f u + f d · B ( B − c → J/ψ µ − ν ) = (7 . ± . ± . · − for 13 TeV . We derive the product of f c · B ( B − c → J/ψ µ − ν ) at the two energies as f c · B ( B − c → J/ψ µ − ν ) = (cid:40) (5 . ± . ± . ± . · − (7 TeV)(5 . ± . ± . ± . · − (13 TeV)Using the average of the theoretical prediction B ( B − c → J/ψ µ − ν ) = (1 . ± . f c f u + f d = (3 . ± . ± . ± . · − for 7 TeV ,f c f u + f d = (3 . ± . ± . ± . · − for 13 TeV , where the first uncertainties are statistical, the second systematic, and the third due to thetheoretical prediction of B ( B − c → J/ψ µ − ν ) . There is a small dependence on the transversemomentum of the B + c meson, but no dependence on its pseudorapidity is observed. Wealso report f c = (cid:40) (2 . ± . ± . ± . · − (7 TeV)(2 . ± . ± . ± . · − (13 TeV) , where the first uncertainty is statistical, the second is systematic including that from B ( B − c → J/ψ µ − ν ) and the third is from the fractions of the B s and Λ b given in Eq. 9.The ratio of fractions, 1 . ± . ± .
04, for 13 TeV/7 TeV is consistent with noincrease in the B − c fraction. Furthermore, using the assumption of no CP violation inthe B − c → J/ψ µ − ν decay, we find that the average asymmetry in B − c − B + c production isconsistent with zero. The measurements are ( − . ± . ± . − . ± . ± . B − c measurements,albeit with a relatively large uncertainty. They also challenge QCD calculations to predictthe measured B − c fractions and explain the consistency between the fractions measured at7 and 13 TeV [14, 54]. Acknowledgements
We express our gratitude to our colleagues in the CERN accelerator departments for theexcellent performance of the LHC. We thank the technical and administrative staff at theLHCb institutes. We acknowledge support from CERN and from the national agencies:CAPES, CNPq, FAPERJ and FINEP (Brazil); MOST and NSFC (China); CNRS/IN2P315France); BMBF, DFG and MPG (Germany); INFN (Italy); NWO (Netherlands); MNiSWand NCN (Poland); MEN/IFA (Romania); MSHE (Russia); MinECo (Spain); SNSF andSER (Switzerland); NASU (Ukraine); STFC (United Kingdom); DOE NP and NSF (USA).We acknowledge the computing resources that are provided by CERN, IN2P3 (France),KIT and DESY (Germany), INFN (Italy), SURF (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 tothe 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 Sk(cid:32)lodowska-Curie Actions and ERC (European Union); ANR, LabexP2IO and OCEVU, and R´egion Auvergne-Rhˆone-Alpes (France); Key Research Programof Frontier Sciences of CAS, CAS PIFI, and the Thousand Talents Program (China);RFBR, RSF and Yandex LLC (Russia); GVA, XuntaGal and GENCAT (Spain); theRoyal Society and the Leverhulme Trust (United Kingdom).
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Dordei , M. Dorigo ,y , A.C. dos Reis , L. Douglas , A. Dovbnya ,K. Dreimanis , M.W. Dudek , L. Dufour , G. Dujany , P. Durante , J.M. Durham ,D. Dutta , R. Dzhelyadin , † , M. Dziewiecki , A. Dziurda , A. Dzyuba , S. Easo ,U. Egede , V. Egorychev , S. Eidelman ,x , S. Eisenhardt , R. Ekelhof , S. Ek-In ,L. Eklund , S. Ely , A. Ene , S. Escher , S. Esen , T. Evans , A. Falabella , J. Fan ,N. Farley , S. Farry , D. Fazzini , M. F´eo , P. Fernandez Declara , A. Fernandez Prieto ,F. Ferrari ,e , L. Ferreira Lopes , F. Ferreira Rodrigues , S. Ferreres Sole , M. Ferrillo ,M. Ferro-Luzzi , S. Filippov , R.A. Fini , M. Fiorini ,g , M. Firlej , K.M. Fischer ,C. Fitzpatrick , T. Fiutowski , F. Fleuret ,b , M. Fontana , F. Fontanelli ,h , R. Forty ,V. Franco Lima , M. Franco Sevilla , M. Frank , C. Frei , D.A. Friday , J. Fu ,q ,M. Fuehring , W. Funk , E. Gabriel , A. Gallas Torreira , D. Galli ,e , S. Gallorini ,S. Gambetta , Y. Gan , M. Gandelman , P. Gandini , Y. Gao , L.M. Garcia Martin ,J. Garc´ıa Pardi˜nas , B. Garcia Plana , F.A. Garcia Rosales , J. Garra Tico , L. Garrido , . Gascon , C. Gaspar , D. Gerick , E. Gersabeck , M. Gersabeck , T. Gershon ,D. Gerstel , Ph. Ghez , V. Gibson , A. Giovent`u , O.G. Girard , P. Gironella Gironell ,L. Giubega , C. Giugliano , K. Gizdov , V.V. Gligorov , C. G¨obel , D. Golubkov ,A. Golutvin , , A. Gomes ,a , P. Gorbounov , , I.V. Gorelov , C. Gotti ,i , E. Govorkova ,J.P. Grabowski , R. Graciani Diaz , T. Grammatico , L.A. Granado Cardoso ,E. Graug´es , E. Graverini , G. Graziani , A. Grecu , R. Greim , P. Griffith , L. Grillo ,L. Gruber , B.R. Gruberg Cazon , C. Gu , E. Gushchin , A. Guth , Yu. Guz , , T. Gys ,T. Hadavizadeh , G. Haefeli , C. Haen , S.C. Haines , P.M. Hamilton , Q. Han , X. Han ,T.H. Hancock , S. Hansmann-Menzemer , N. Harnew , T. Harrison , R. Hart , C. Hasse ,M. Hatch , J. He , M. Hecker , K. Heijhoff , K. Heinicke , A. Heister , A.M. Hennequin ,K. Hennessy , L. Henry , J. Heuel , A. Hicheur , R. Hidalgo Charman , D. Hill ,M. Hilton , P.H. Hopchev , J. Hu , W. Hu , W. Huang , W. Hulsbergen , T. Humair ,R.J. Hunter , M. Hushchyn , D. Hutchcroft , D. Hynds , P. Ibis , M. Idzik , P. Ilten ,A. Inglessi , A. Inyakin , K. Ivshin , R. Jacobsson , S. Jakobsen , J. Jalocha , E. Jans ,B.K. Jashal , A. Jawahery , V. Jevtic , F. Jiang , M. John , D. Johnson , C.R. Jones ,B. Jost , N. Jurik , S. Kandybei , M. Karacson , J.M. Kariuki , N. Kazeev , M. Kecke ,F. Keizer , , M. Kelsey , M. Kenzie , T. Ketel , B. Khanji , A. Kharisova , K.E. Kim ,T. Kirn , V.S. Kirsebom , S. Klaver , K. Klimaszewski , S. Koliiev , A. Kondybayeva ,A. Konoplyannikov , P. Kopciewicz , R. Kopecna , P. Koppenburg , I. Kostiuk , ,O. Kot , S. Kotriakhova , L. Kravchuk , R.D. Krawczyk , M. Kreps , F. Kress ,S. Kretzschmar , P. Krokovny ,x , W. Krupa , W. Krzemien , W. Kucewicz ,l ,M. Kucharczyk , V. Kudryavtsev ,x , H.S. Kuindersma , G.J. Kunde , T. Kvaratskheliya ,D. Lacarrere , G. Lafferty , A. Lai , D. Lancierini , J.J. Lane , G. Lanfranchi ,C. Langenbruch , T. Latham , F. Lazzari ,v , C. Lazzeroni , R. Le Gac , R. Lef`evre ,A. Leflat , F. Lemaitre , O. Leroy , T. Lesiak , B. Leverington , H. Li , X. Li , Y. Li ,Z. Li , X. Liang , R. Lindner , V. Lisovskyi , G. Liu , X. Liu , D. Loh , A. Loi ,J. Lomba Castro , I. Longstaff , J.H. Lopes , G. Loustau , G.H. Lovell , Y. Lu ,D. Lucchesi ,o , M. Lucio Martinez , Y. Luo , A. Lupato , E. Luppi ,g , O. Lupton ,A. Lusiani , X. Lyu , S. Maccolini ,e , F. Machefert , F. Maciuc , V. Macko ,P. Mackowiak , S. Maddrell-Mander , L.R. Madhan Mohan , O. Maev , , A. Maevskiy ,D. Maisuzenko , M.W. Majewski , S. Malde , B. Malecki , A. Malinin , T. Maltsev ,x ,H. Malygina , G. Manca ,f , G. Mancinelli , R. Manera Escalero , D. Manuzzi ,e ,D. Marangotto ,q , J. Maratas ,w , J.F. Marchand , U. Marconi , S. Mariani ,C. Marin Benito , M. Marinangeli , P. Marino , J. Marks , P.J. Marshall , G. Martellotti ,L. Martinazzoli , M. Martinelli , D. Martinez Santos , F. Martinez Vidal , A. Massafferri ,M. Materok , R. Matev , A. Mathad , Z. Mathe , V. Matiunin , C. Matteuzzi ,K.R. Mattioli , A. Mauri , E. Maurice ,b , M. McCann , , L. Mcconnell , A. McNab ,R. McNulty , J.V. Mead , B. Meadows , C. Meaux , G. Meier , N. Meinert ,D. Melnychuk , S. Meloni ,i , M. Merk , A. Merli , M. Mikhasenko , D.A. Milanes ,E. Millard , M.-N. Minard , O. Mineev , L. Minzoni ,g , S.E. Mitchell , B. Mitreska ,D.S. Mitzel , A. M¨odden , A. Mogini , R.D. Moise , T. Momb¨acher , I.A. Monroy ,S. Monteil , M. Morandin , G. Morello , M.J. Morello ,t , J. Moron , A.B. Morris ,A.G. Morris , R. Mountain , H. Mu , F. Muheim , M. Mukherjee , M. Mulder ,D. M¨uller , K. M¨uller , V. M¨uller , C.H. Murphy , D. Murray , P. Muzzetto , P. Naik ,T. Nakada , R. Nandakumar , A. Nandi , T. Nanut , I. Nasteva , M. Needham ,N. Neri ,q , S. Neubert , N. Neufeld , R. Newcombe , T.D. Nguyen , C. Nguyen-Mau ,n ,E.M. Niel , S. Nieswand , N. Nikitin , N.S. Nolte , C. Nunez , A. Oblakowska-Mucha ,V. Obraztsov , S. Ogilvy , D.P. O’Hanlon , R. Oldeman ,f , C.J.G. Onderwater , J.D. Osborn , A. Ossowska , J.M. Otalora Goicochea , T. Ovsiannikova , P. Owen ,A. Oyanguren , P.R. Pais , T. Pajero ,t , A. Palano , M. Palutan , G. Panshin , . Papanestis , M. Pappagallo , L.L. Pappalardo ,g , C. Pappenheimer , W. Parker ,C. Parkes , G. Passaleva , , A. Pastore , M. Patel , C. Patrignani ,e , A. Pearce ,A. Pellegrino , M. Pepe Altarelli , S. Perazzini , D. Pereima , P. Perret , L. Pescatore ,K. Petridis , A. Petrolini ,h , A. Petrov , S. Petrucci , M. Petruzzo ,q , B. Pietrzyk ,G. Pietrzyk , M. Pikies , M. Pili , D. Pinci , J. Pinzino , F. Pisani , A. Piucci ,V. Placinta , S. Playfer , J. Plews , M. Plo Casasus , F. Polci , M. Poli Lener ,M. Poliakova , A. Poluektov , N. Polukhina ,c , I. Polyakov , E. Polycarpo , G.J. Pomery ,S. Ponce , A. Popov , D. Popov , S. Poslavskii , K. Prasanth , L. Promberger ,C. Prouve , V. Pugatch , A. Puig Navarro , H. Pullen , G. Punzi ,p , W. Qian , J. Qin ,R. Quagliani , B. Quintana , N.V. Raab , R.I. Rabadan Trejo , B. Rachwal ,J.H. Rademacker , M. Rama , M. Ramos Pernas , M.S. Rangel , F. Ratnikov , ,G. Raven , M. Reboud , F. Redi , F. Reiss , C. Remon Alepuz , Z. Ren , V. Renaudin ,S. Ricciardi , S. Richards , K. Rinnert , P. Robbe , A. Robert , A.B. Rodrigues ,E. Rodrigues , J.A. Rodriguez Lopez , M. Roehrken , S. Roiser , A. Rollings ,V. Romanovskiy , M. Romero Lamas , A. Romero Vidal , J.D. Roth , M. Rotondo ,M.S. Rudolph , T. Ruf , J. Ruiz Vidal , J. Ryzka , J.J. Saborido Silva , N. Sagidova ,B. Saitta ,f , C. Sanchez Gras , C. Sanchez Mayordomo , B. Sanmartin Sedes ,R. Santacesaria , C. Santamarina Rios , M. Santimaria , E. Santovetti ,j , G. Sarpis ,A. Sarti , C. Satriano ,s , A. Satta , M. Saur , D. Savrina , , L.G. Scantlebury Smead ,S. Schael , M. Schellenberg , M. Schiller , H. Schindler , M. Schmelling , T. Schmelzer ,B. Schmidt , O. Schneider , A. Schopper , H.F. Schreiner , M. Schubiger , S. Schulte ,M.H. Schune , R. Schwemmer , B. Sciascia , A. Sciubba ,k , S. Sellam , A. Semennikov ,A. Sergi , , N. Serra , J. Serrano , L. Sestini , A. Seuthe , P. Seyfert , D.M. Shangase ,M. Shapkin , T. Shears , L. Shekhtman ,x , V. Shevchenko , , E. Shmanin ,J.D. Shupperd , B.G. Siddi , R. Silva Coutinho , L. Silva de Oliveira , G. Simi ,o ,S. Simone ,d , I. Skiba , N. Skidmore , T. Skwarnicki , M.W. Slater , J.G. Smeaton ,A. Smetkina , E. Smith , I.T. Smith , M. Smith , A. Snoch , M. Soares ,L. Soares Lavra , M.D. Sokoloff , F.J.P. Soler , B. Souza De Paula , B. Spaan ,E. Spadaro Norella ,q , P. Spradlin , F. Stagni , M. Stahl , S. Stahl , P. Stefko ,S. Stefkova , O. Steinkamp , S. Stemmle , O. Stenyakin , M. Stepanova , H. Stevens ,S. Stone , S. Stracka , M.E. Stramaglia , M. Straticiuc , S. Strokov , J. Sun , L. Sun ,Y. Sun , P. Svihra , K. Swientek , A. Szabelski , T. Szumlak , M. Szymanski , S. Taneja ,Z. Tang , T. Tekampe , G. Tellarini , F. Teubert , E. Thomas , K.A. Thomson ,M.J. Tilley , V. Tisserand , S. T’Jampens , M. Tobin , S. Tolk , L. Tomassetti ,g ,D. Tonelli , D.Y. Tou , E. Tournefier , M. Traill , M.T. Tran , C. Trippl , A. Trisovic ,A. Tsaregorodtsev , G. Tuci , ,p , A. Tully , N. Tuning , A. Ukleja , A. Usachov ,A. Ustyuzhanin , , U. Uwer , A. Vagner , V. Vagnoni , A. Valassi , G. Valenti ,M. van Beuzekom , H. Van Hecke , E. van Herwijnen , C.B. Van Hulse , M. van Veghel ,R. Vazquez Gomez , P. Vazquez Regueiro , C. V´azquez Sierra , S. Vecchi , J.J. Velthuis ,M. Veltri ,r , A. Venkateswaran , M. Vernet , M. Veronesi , M. Vesterinen ,J.V. Viana Barbosa , D. Vieira , M. Vieites Diaz , H. Viemann , X. Vilasis-Cardona ,m ,A. Vitkovskiy , V. Volkov , A. Vollhardt , D. Vom Bruch , A. Vorobyev , V. Vorobyev ,x ,N. Voropaev , R. Waldi , J. Walsh , J. Wang , J. Wang , J. Wang , M. Wang , Y. Wang ,Z. Wang , D.R. Ward , H.M. Wark , N.K. Watson , D. Websdale , A. Weiden ,C. Weisser , B.D.C. Westhenry , D.J. White , M. Whitehead , D. Wiedner ,G. Wilkinson , M. Wilkinson , I. Williams , M. Williams , M.R.J. Williams ,T. Williams , F.F. Wilson , M. Winn , W. Wislicki , M. Witek , G. Wormser ,S.A. Wotton , H. Wu , K. Wyllie , Z. Xiang , D. Xiao , Y. Xie , H. Xing , A. Xu , L. Xu ,M. Xu , Q. Xu , Z. Xu , Z. Xu , Z. Yang , Z. Yang , Y. Yao , L.E. Yeomans , H. Yin ,J. Yu ,aa , X. Yuan , O. Yushchenko , K.A. Zarebski , M. Zavertyaev ,c , M. Zdybal , . Zeng , D. Zhang , L. Zhang , S. Zhang , W.C. Zhang ,z , Y. Zhang , A. Zhelezov ,Y. Zheng , X. Zhou , Y. Zhou , X. Zhu , V. Zhukov , , J.B. Zonneveld , S. Zucchelli ,e . Centro Brasileiro de Pesquisas F´ısicas (CBPF), Rio de Janeiro, Brazil Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil Center for High Energy Physics, Tsinghua University, Beijing, China School of Physics State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing,China University of Chinese Academy of Sciences, Beijing, China Institute Of High Energy Physics (IHEP), Beijing, China Institute of Particle Physics, Central China Normal University, Wuhan, Hubei, China Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IN2P3-LAPP, Annecy, France Universit´e Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France Aix Marseille Univ, CNRS/IN2P3, CPPM, Marseille, France LAL, Univ. Paris-Sud, CNRS/IN2P3, Universit´e Paris-Saclay, Orsay, France LPNHE, Sorbonne Universit´e, Paris Diderot Sorbonne Paris Cit´e, CNRS/IN2P3, Paris, France I. Physikalisches Institut, RWTH Aachen University, Aachen, Germany Fakult¨at Physik, Technische Universit¨at Dortmund, Dortmund, Germany Max-Planck-Institut f¨ur Kernphysik (MPIK), Heidelberg, Germany Physikalisches Institut, Ruprecht-Karls-Universit¨at Heidelberg, Heidelberg, Germany School of Physics, University College Dublin, Dublin, Ireland INFN Sezione di Bari, Bari, Italy INFN Sezione di Bologna, Bologna, Italy INFN Sezione di Ferrara, Ferrara, Italy INFN Sezione di Firenze, Firenze, Italy INFN Laboratori Nazionali di Frascati, Frascati, Italy INFN Sezione di Genova, Genova, Italy INFN Sezione di Milano-Bicocca, Milano, Italy INFN Sezione di Milano, Milano, Italy INFN Sezione di Cagliari, Monserrato, Italy INFN Sezione di Padova, Padova, Italy INFN Sezione di Pisa, Pisa, Italy INFN Sezione di Roma Tor Vergata, Roma, Italy INFN Sezione di Roma La Sapienza, Roma, Italy Nikhef National Institute for Subatomic Physics, Amsterdam, Netherlands Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam,Netherlands Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Krak´ow, Poland AGH - University of Science and Technology, Faculty of Physics and Applied Computer Science,Krak´ow, Poland National Center for Nuclear Research (NCBJ), Warsaw, Poland Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania Petersburg Nuclear Physics Institute NRC Kurchatov Institute (PNPI NRC KI), Gatchina, Russia Institute of Theoretical and Experimental Physics NRC Kurchatov Institute (ITEP NRC KI), Moscow,Russia, Moscow, Russia Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia Institute for Nuclear Research of the Russian Academy of Sciences (INR RAS), Moscow, Russia Yandex School of Data Analysis, Moscow, Russia Budker Institute of Nuclear Physics (SB RAS), Novosibirsk, Russia Institute for High Energy Physics NRC Kurchatov Institute (IHEP NRC KI), Protvino, Russia,Protvino, Russia ICCUB, Universitat de Barcelona, Barcelona, Spain Instituto Galego de F´ısica de Altas Enerx´ıas (IGFAE), Universidade de Santiago de Compostela,Santiago de Compostela, Spain Instituto de Fisica Corpuscular, Centro Mixto Universidad de Valencia - CSIC, Valencia, Spain European Organization for Nuclear Research (CERN), Geneva, Switzerland Institute of Physics, Ecole Polytechnique F´ed´erale de Lausanne (EPFL), Lausanne, Switzerland Physik-Institut, Universit¨at Z¨urich, Z¨urich, Switzerland NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine University of Birmingham, Birmingham, United Kingdom H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom Department of Physics, University of Warwick, Coventry, United Kingdom STFC Rutherford Appleton Laboratory, Didcot, United Kingdom School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom Imperial College London, London, United Kingdom Department of Physics and Astronomy, University of Manchester, Manchester, United Kingdom Department of Physics, University of Oxford, Oxford, United Kingdom Massachusetts Institute of Technology, Cambridge, MA, United States University of Cincinnati, Cincinnati, OH, United States University of Maryland, College Park, MD, United States Los Alamos National Laboratory (LANL), Los Alamos, United States Syracuse University, Syracuse, NY, United States Laboratory of Mathematical and Subatomic Physics , Constantine, Algeria, associated to
Pontif´ıcia Universidade Cat´olica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil, associated to
South China Normal University, Guangzhou, China, associated to
School of Physics and Technology, Wuhan University, Wuhan, China, associated to
Departamento de Fisica , Universidad Nacional de Colombia, Bogota, Colombia, associated to
Institut f¨ur Physik, Universit¨at Rostock, Rostock, Germany, associated to
Van Swinderen Institute, University of Groningen, Groningen, Netherlands, associated to
National Research Centre Kurchatov Institute, Moscow, Russia, associated to
National University of Science and Technology “MISIS”, Moscow, Russia, associated to
National Research University Higher School of Economics, Moscow, Russia, associated to
National Research Tomsk Polytechnic University, Tomsk, Russia, associated to