EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)
CERN-EP-2020-146 2020/11/18
CMS-BPH-19-001
Measurement of B
c(
2S
)
+
and B
c∗
(
2S
)
+
cross section ratios
in proton-proton collisions at
√
s
=
13 TeV
The CMS Collaboration
*Abstract
The ratios of the Bc(2S)+ to Bc+, Bc∗(2S)+ to Bc+, and Bc∗(2S)+ to Bc(2S)+ production cross sections are measured in proton-proton collisions at √s = 13 TeV, using a data sample collected by the CMS experiment at the LHC, corresponding to an in-tegrated luminosity of 143 fb−1. The three measurements are made in the Bc+ me-son phase space region defined by the transverse momentum pT > 15 GeV and ab-solute rapidity |y| < 2.4, with the excited Bc(∗)(2S)+ states reconstructed through the Bc(∗)+π+π−, followed by the Bc+ → J/ψ π+ and J/ψ → µ+µ− decays. The Bc(2S)+ to Bc+, Bc∗(2S)+to Bc+, and Bc∗(2S)+to Bc(2S)+cross section ratios, including the unknown Bc(∗)(2S)+ →Bc(∗)+π+π− branching fractions, are (3.47±0.63 (stat)± 0.33 (syst))%,(4.69±0.71 (stat)±0.56 (syst))%, and 1.35±0.32 (stat)±0.09 (syst), re-spectively. None of these ratios shows a significant dependence on the pT or |y|of the Bc+meson. The normalized dipion invariant mass distributions from the decays Bc(∗)(2S)+→Bc(∗)+π+π−are also reported.
”Published in Physical Review D as doi:10.1103/PhysRevD.102.092007.”
© 2020 CERN for the benefit of the CMS Collaboration. CC-BY-4.0 license *See Appendix A for the list of collaboration members
1
1
Introduction
The production cross sections of the Bc+family of mesons, quark-antiquark bound states of two different flavors, charm and beauty, are significantly smaller than those of the charmonium and bottomonium states. The unprecedented collision energies and integrated luminosities of the proton-proton (pp) data samples collected at the CERN LHC allow, for the first time, detailed studies regarding the production and properties of Bc+quarkonia. The observation of the Bc(2S)+and Bc∗(2S)+ states was recently reported by the CMS experiment [1], using a pp data sample collected at √s = 13 TeV between 2015 and 2018, on the basis of well-resolved peaks in the Bc+
π+π− invariant mass distribution, with the Bc+ meson reconstructed in the Bc+ → J/ψ π+ decay channel, and J/ψ → µ+µ−. The LHCb Collaboration also reported the observation of the Bc∗(2S)+state, using a pp data sample collected at 7, 8, and 13 TeV [2]. Masses of the Bc(2S)+and Bc∗(2S)+states are found to be consistent with theoretical predictions [3–5]. These results stimulated new theoretical studies aimed at reaching a better understanding of the Bc+quarkonium family, such as those reported in Refs. [6, 7].
The present paper reports an analysis that complements the previous observation of the Bc(2S)+
and Bc∗(2S)+states [1] with the measurement of the Bc(2S)+to Bc+, B
c
∗(2S)+
to Bc+, and B
c∗(2S)
+ to Bc(2S)+cross section ratios, an important step in making further progress on understand-ing these two excited Bc+states. The invariant mass distributions of the pair of pions emitted in the Bc(∗)(2S)+ → Bc(∗)+π+π− decays are also presented, to probe the existence of possible intermediate structure analogous to the ones observed in decays between the 2S and 1S states of charmonium and bottomonium [6, 7]. Throughout this paper, Bc(∗)+ denotes Bc+or Bc∗+, and Bc(∗)(2S)+denotes Bc(2S)+or Bc∗(2S)+. Charge-conjugate states are also implied, unless stated otherwise. The data sample of 13 TeV pp collisions used in this analysis corresponds to an inte-grated luminosity of 143 fb−1and was collected by CMS between 2015 and 2018. The measure-ments are performed in a phase space region defined by the Bc+meson transverse momentum pT >15 GeV and rapidity|y| <2.4.
2
Experimental apparatus, data sample, and event selection
The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diam-eter, providing a magnetic field of 3.8 T. Within the solenoid volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter, and a brass and scintillator hadron calorimeter, each composed of a barrel and two endcap sections. Muons are measured in the pseudorapidity range |η| < 2.4, with detection planes made using three technologies: drift tubes, cathode strip chambers, and resistive plate chambers. Matching muons to tracks measured in the silicon tracker results in a relative transverse momentum resolution, for muons with pT up to 100 GeV, of 1% in the barrel and 3% in the endcaps [8]. The single-muon trig-ger efficiency exceeds 90% over the full η range, and the efficiency to reconstruct and identify muons is greater than 96%. A more detailed description of the CMS detector, together with a definition of the coordinate system used and relevant kinematic variables, can be found in Ref. [9].
The event sample was collected with a two-level trigger system [10]. At level 1, custom hard-ware processors select events with two muons. The high-level trigger requires an opposite-sign muon pair of invariant mass in the range 2.9–3.3 GeV, a dimuon vertex fit χ2probability larger than 10%, a distance of closest approach between the two muons smaller than 0.5 cm, and a distance between the dimuon vertex and the beam axis, Lxy, larger than three times its uncertainty. Both muons must have pT > 4 GeV and |η| < 2.5. In addition p~T must be
aligned with the dimuon transverse decay displacement vector~Lxy by requiring cos θ > 0.9, where cos θ = ~Lxy· ~pT/(LxypT). The trigger also requires a third track in the event, compatible with being produced at the dimuon vertex (normalized χ2 < 10), and having pT > 1.2 GeV,
|η| <2.5, and a significance on the track impact parameter of at least 2. The offline reconstruc-tion requires two opposite-sign muons matching those that triggered the detector readout, with some requirements being stricter than at the trigger level, such as|η| < 2.4 and cos θ > 0.98. The muon candidates must pass high-purity track quality requirements [11], and fulfill the soft-muon identification requirements [8], which imply, in particular, that there are more than five hits in the silicon tracker, with at least one in the pixel layers. The two muons must also be close to each other in angular space:
√
(∆η)2+ (∆φ)2 <1.2, where∆η and ∆φ are the differences in pseudorapidity and azimuthal angle, respectively, between their momenta.
3
Measurement of the cross section ratios
3.1 Introduction
The ratios of the Bc(∗)(2S)+to Bc+and Bc∗(2S)+to Bc(2S)+cross sections, R∗+, R+, and R∗+/R+, respectively, reported in this paper are derived from the ratios of the measured yields, corrected by the detection efficiencies, e:
R+≡σ(Bc(2S) + ) σ(Bc+) B(Bc(2S) + →Bc+π+π−) = N(Bc(2S) + ) N(Bc+) e(Bc+) e(Bc(2S)+) , R∗+ ≡σ(Bc ∗(2S)+ ) σ(Bc+) B(Bc ∗( 2S)+→Bc∗+π+π−) = N(Bc ∗(2S)+ ) N(Bc+) e(Bc+) e(Bc∗(2S)+) , R∗+/R+=σ(Bc ∗(2S)+ ) σ(Bc(2S)+) B(Bc∗(2S)+→Bc∗+π+π−) B(Bc(2S)+→Bc+π+π−) = N(Bc∗(2S)+) N(Bc(2S)+) e(Bc(2S)+) e(Bc∗(2S)+) . (1)
TheBparameters are the unknown branching fractions of the Bc(∗)(2S)+→Bc(∗)+π+π−decays. The Bc∗+ meson is assumed to decay to the Bc+ ground state and a low-energy photon with a branching fraction of 100%, where the photon is not reconstructed.
3.2 Measurement of the Bc+yield
The Bc+→J/ψ π+ candidates are reconstructed through a kinematic vertex fit, combining the dimuon with another track. The dimuon invariant mass is constrained to the world-average J/ψ mass [12] and the other track, assumed to be a pion, must fulfil|η| <2.4 and pT >3.5 GeV. The primary vertex (PV) associated with the Bc+ candidate is selected among all the reconstructed vertices [13] as the one with the smallest angle between the reconstructed Bc+momentum and the vector joining the PV with the Bc+ decay vertex. To avoid biases, this PV is then refitted without the tracks associated with the muons and the pion. The Bc+ candidates are required to have pT > 15 GeV, |y| < 2.4, a kinematic vertex fit χ2 probability larger than 10%, and a decay length (distance between the J/ψ π+vertex and the PV) larger than 100 µm. If several Bc+ candidates are found in the same event, which happens in 1.6% of the events, only the one with the highest pT is kept. Simulation studies show that this choice identifies the correct candidate with 99% probability. These selection criteria were defined through studies of simulated signal samples and measured sideband events [1].
Figure 1 shows the invariant mass distribution of the reconstructed and selected Bc+→J/ψ π+ candidates, where the Bc+ signal is clearly seen as a prominent peak [1]. The result of an
un-3.3 Measurement of the Bc(2S)+and Bc∗(2S)+yields 3 6.0 6.1 6.2 6.3 6.4 6.5 ) (GeV) + π ψ (J/ M 500 1000 1500 2000 Events / 15 MeV Data Fit result signal + π ψ J/ → + c B + K ψ J/ → + c B + X + π ψ J/ → + c B Comb. backg. = 13 TeV s -1 L = 143 fb CMS
Figure 1: Invariant mass distribution of the Bc+→J/ψ π+candidates, after applying all event selection criteria [1]. The fitted contributions are shown by the stacked distributions, the solid line representing their sum. The vertical dashed lines indicate the mass window used to select the Bc+candidates for the Bc(∗)(2S)+reconstruction.
binned maximum-likelihood fit is also shown, together with the signal and background con-tributions. The underlying background is modeled as the sum of three terms: (a) uncorrelated J/ψ-track combinations (combinatorial background), parametrized by a first-order polynomial; (b) partially reconstructed Bc+→J/ψ π+X decays, only relevant for invariant mass values be-low 6.2 GeV and parametrized by a generalized ARGUS function [14] convolved with a Gaus-sian resolution; and (c) a small contribution from Bc+→J/ψ K+decays, with a shape fixed from simulation studies (described later) and a normalization fixed by the Bc+→J/ψ π+yield, scaled by the ratio of the corresponding branching fractions [15] and reconstruction efficiencies. The Bc+signal peak is modeled by a double-Gaussian function,
wG(µ, σ1) + (1−w)G(µ, σ2), (2)
where G(µ, σ)represents a Gaussian function with mean µ and standard deviation σ, and w is the relative fraction of the narrower Gaussian in the fit. The single mean µ corresponds to the average reconstructed Bc+ mass. The fit gives w = 47%, σ1 = 21 MeV, and σ2 = 42 MeV, the very different Gaussian widths reflecting the fact that the Bc+mass resolution depends on rapidity, degrading from the barrel to the endcap regions. The Bc+mass resolution [1] agrees with expectations from simulation studies, of approximately 34 MeV.
The fitted Bc+mass is M(B
c+) = 6271.1±0.5 MeV and the Bc+signal yield is 7629±225 events,
where the uncertainties are statistical only. The measured invariant mass distribution is well reproduced by the sum of the fitted contributions, reflected in the χ2 between the binned dis-tribution and the fit function of 35 for 30 degrees of freedom.
3.3 Measurement of the Bc
(2S)
+and Bc∗(2S)
+yieldsThe Bc(2S)+and Bc∗(2S)+candidates are also reconstructed through vertex kinematic fits, com-bining a Bc+candidate with two opposite-sign, high-purity tracks, assumed to be pions. The selected Bc+ candidates must have invariant mass in the 6.2–6.355 GeV range, where the low-mass edge is selected so as to avoid the background caused by partially reconstructed decays (represented by the gray area below 6.2 GeV in Fig. 1). The lifetimes of the Bc(2S)+and Bc∗(2S)+
are assumed to be negligible with respect to the measurement resolution, so that the produc-tion and decay vertices essentially coincide. Therefore, the daughter pions are among the tracks used in the refitted PV. Furthermore, one of the pions must have pT > 0.8 GeV and the other pT >0.6 GeV. The Bc+
π+π−candidates must have|y| <2.4 and a vertex kinematic fit χ2 prob-ability larger than 10%. As before, if several Bc+π+π−candidates are found in the same event, only the one with the highest pTis kept.
Figure 2 shows the M(Bc+π+π−) −M(Bc+) +mBc+distribution, where M(Bc+π+π−)and M(Bc+) are the reconstructed invariant masses of the Bc+π+π− and Bc+ candidates, respectively, and mBc+ is the world-average Bc+ mass [12]. This variable is used in the analysis because it is measured with a better resolution than M(Bc+π+π−), given that some of the measurement uncertainties cancel in the difference. The measured distribution is fitted to a superposition of two signal peaks using the same parametrization as in Eq. 2, plus a third-order Chebyshev polynomial, modeling the nonpeaking, combinatorial background. Two background contribu-tions arising from Bc+→J/ψ K+ decays are also considered, with shapes identical to those of the signal peaks, ignoring a negligible shift (less than 1 MeV) to lower mass values, and nor-malizations fixed by the ratio of the Bc+→J/ψ K+to Bc+→J/ψ π+signal yields.
6.7 6.8 6.9 7.0 7.1 (GeV) + c B m ) + + c (B M − ) -π + π + c (B M 0 10 20 30 40 50 60 Events / 10 MeV Data Fit result Signal − π + π ) + K ψ (J/ + c B Comb. backg. (13 TeV) -1 143 fb CMS
Figure 2: Invariant mass distribution of the Bc(∗)(2S)+ → Bc(∗)+π+π− candidates [1]. The Bc∗(2S)+ corresponds to the lower-mass peak, the Bc(2S)+ to the higher. The fitted contribu-tions are shown by the stacked distribucontribu-tions, the solid line representing their sum.
Given the small number of events in the two signal peaks, the w and σ2double-Gaussian pa-rameters are fixed to values determined in simulation studies: w=92% and σ2=3.1 σ1for the lower-mass peak; and w =86% and σ2 =2.8 σ1for the higher-mass peak. The two resonances are well resolved, with a mass difference of 28.9±1.5 MeV, where the uncertainty is statisti-cal only. The widths of the peaks are consistent with the measurement resolution evaluated through simulation studies, which is approximately σ = 6 MeV [1]. The unbinned extended maximum-likelihood fit gives 67±10 and 52±9 events for the lower- and higher-mass peaks, respectively. The quality of the fit can be quantified through the χ2 per degrees of freedom ratio, 41/35.
As explained in Ref. [1], the Bc∗(2S)+peak is seen in the Bc+π+π−invariant mass distribution at a mass value lower than that of the Bc(2S)+peak. The reason is that, contrary to what happens to the Bc(2S)+, which decays directly to Bc+
π+π−, the Bc∗(2S)+ meson decays to Bc∗+π+π− where the photon emitted in the subsequent Bc∗+→Bc+γ decay has too low energy to be
re-3.4 Reconstruction efficiencies 5
constructed. Therefore, the Bc∗(2S)+peak is seen in the Bc+π+π− mass spectrum at the mass M(Bc(2S)+) −∆M, where ∆M ≡ [M(Bc∗+) −M(B+c )] − [M(Bc∗(2S)+) −M(Bc(2S)+)]. Since M(Bc∗+) −M(Bc+)is expected to be larger than M(Bc∗(2S)+) −M(Bc(2S)+), the Bc∗(2S)+ state corresponds to the lower-mass peak [3–5].
3.4 Reconstruction efficiencies
With respect to the observation analysis reported in Ref. [1], the main challenge in the de-termination of the Bc(∗)(2S)+ to Bc+ cross section ratios is the evaluation of the corresponding (relative) detection efficiencies. Since the trigger requires J/ψ→µ+µ−from the Bc+→J/ψ π+ decay, the trigger efficiencies for the Bc+and Bc+π+π−candidates are essentially the same and cancel in the cross section ratios. So only the reconstruction efficiencies need to be evaluated, which is done using simulated event samples. All three mesons (Bc+, Bc(2S)+, and Bc∗(2S)+) are generated using theBCVEGPY2.2 [16] Monte Carlo event generator. The events are then passed to PYTHIA8.230 [17] to simulate the hadronization process. The decays are performed by the EVTGEN 1.6.0 package [18] and the quantum electrodynamic final-state radiation is modeled withPHOTOS3.61 [19]. The simulated events are then processed through a detailed simulation of the CMS detector, based on the GEANT4 package [20], using the same trigger and reconstruc-tion algorithms used to collect and process the data. The simulated events include multiple pp interactions in the same or nearby beam crossings (pileup), with a distribution matching the one observed in data. Monte Carlo samples were extensive validated using control regions in data.
The Bc(2S)+and Bc∗(2S)+efficiencies are computed as Nrec(Bc(∗)(2S)+)/Ngen(Bc(∗)(2S)+), where Ngen(Bc(∗)(2S)+)are the numbers of Bc(∗)(2S)+events generated in the Bc(∗)+π+π−channel, in the phase space region of the analysis, pT(Bc+) >15 GeV and|y(B+c )| <2.4, and Nrec(Bc(∗)(2S)+)
are the numbers of events that survive all the reconstruction steps and event selection criteria. The Bc+ efficiency is computed in a completely analogous way, except that it uses Bc+ events generated in the Bc+→J/ψ π+decay channel. These evaluations are independently made for the 2016, 2017, and 2018 running periods. The events collected in 2015, corresponding to 2% of the total sample, are treated the same as the 2016 sample for the purpose of efficiency de-termination. It was checked that the 2016 Monte Carlo simulation describes the 2015 data well enough so that no residual systematic uncertainty is required. The final efficiencies are obtained as weighted averages, using the integrated luminosities as weights: 2.8+36.1, 42.1, and 61.6 fb−1, respectively, for the 2015+2016, 2017, and 2018 periods [21–24]. The results are e(Bc+) =1.31%, e(Bc(2S)+) =0.26%, and e(Bc∗(2S)+) =0.24%. The Bc(2S)+and Bc∗(2S)+ recon-struction efficiencies are very similar, the slightly smaller Bc∗(2S)+value reflecting the (missed) low-energy photon, which implies a small reduction of the Bc+π+π−phase space.
Table 1 lists the efficiency ratios relevant for the determination of the cross section ratios. The first uncertainty (“Stat.”) shown reflects the finite size of the three simulated samples. The sec-ond (“Spread”) reflects the standard deviation of the computed values around their average and is used to conservatively cover potential residual mismatches between the running con-ditions and the settings used in simulation. For example, it could be that the simulated sam-ples do not accurately reproduce the time evolution of the instantaneous luminosity within each data-taking period, which would create differences in the measured and simulated pileup distributions. The last column (“Pions”) reflects the uncertainty in the reconstruction effi-ciency [25] of the two pions emitted in the Bc(∗)(2S)+ → Bc(∗)+π+π− decays. This uncertainty is relevant for the R∗+and R+ratios, but cancels in the R∗+/R+ratio.
Table 1: Ratios of the reconstruction efficiencies relevant for the determination of the R+, R∗+, and R∗+/R+ cross section ratios. The central values are followed by the several uncertainties presented in the text.
Central Stat. Spread Pions e(Bc(2S)+)/e(Bc+) 0.196 1.1% 1.8% 4.2% e(Bc∗(2S)+)/e(Bc+) 0.187 1.0% 1.6% 4.2% e(Bc∗(2S)+)/e(Bc(2S)+) 0.955 1.4% 0.9% —
3.5 Determination of the cross section ratios
Correcting the yield ratios by the corresponding efficiency ratios leads to the following Bc(2S)+
to Bc+, Bc∗(2S)+to Bc+, and Bc∗(2S)+to Bc(2S)+cross section ratios, always including the Bc(∗)(2S)+→
Bc(∗)+π+π−branching fractions, and always for pT(Bc+) >15 GeV and|y(Bc+)| <2.4: R+= (3.47±0.63)%,
R∗+ = (4.69±0.71)%, and R∗+/R+=1.35±0.32.
(3)
The quoted uncertainties are statistical only. The fact that the Bc(∗)(2S)+ events are a subset of the Bc+events has a negligible effect (less than 1%) on the uncertainties. The correlation between Bc∗(2S)+and Bc(2S)+yields, used in the double cross section ratio, is taken into account using an alternative fit to the M(Bc+π+π−) − M(Bc+) +mBc+ distribution, which directly provides the ratio of these yields. It is worth noting again that these ratios include branching fractions (shown in Eq. (1)) that have not yet been measured.
3.6 Dependence on the Bc+kinematics
In order to probe if these cross section ratios show a dependence on the kinematics of the Bc+ meson, the analysis is redone after splitting the events into three Bc+ meson pT bins and (independently) into three|y|bins. The bin edges are chosen so as to have similar uncertainties in the three bins: 15, 22.5, 30, and 60 GeV for pT, and 0, 0.4, 0.8, and 2.4 for|y|. The amount of events with pT > 60 GeV corresponds to 3.4% of the total sample and they are excluded from these kinematical distributions.
As shown in Fig. 3, none of the measured ratios shows significant variations with the pTor|y|of the Bc+meson, within the probed kinematical regions. The markers are shown at the average Bc+ pT or|y|values of the events contributing to each bin. The horizontal displacements between the markers seen in the top panels reflect the differences between the Bc(2S)+ and Bc∗(2S)+
kinematic distributions.
Reporting the cross section ratios as a function of the Bc+kinematics and in a phase space do-main defined by the Bc+ is the choice that best reflects the data analysis procedure and that cancels to the largest extent the systematic uncertainties related to the Bc+detection. Given the relatively small mass difference between the mother Bc(∗)(2S)+and the daughter Bc+states, the ratio of laboratory momentum to mass remains practically unchanged in the decays, on aver-age, so that the following kinematical relations hold to a very good approximation: yM = yd and pTM = (M/m)pdT, where yM, pMT, and M (respectively yd, pdT, and m) are the rapidity, pT, and mass of the mother (respectively daughter) [26].
3.7 Systematic uncertainties 7 20 30 40 50 60 ) (GeV) + c (B T p 2 4 6 8 10 (%) R + R + * R 20 30 40 50 60 ) (GeV) + c (B T p 1 2 + R / + * R (13 TeV) -1 143 fb CMS 0.0 0.5 1.0 1.5 2.0 ) + c |y|(B 2 4 6 8 10 (%) R + R + * R 0.0 0.5 1.0 1.5 2.0 ) + c |(B y | 1 2 + R / + * R (13 TeV) -1 143 fb CMS
Figure 3: The R+ and R∗+ (upper), and R∗+/R+ (lower) cross section ratios, including the Bc(∗)(2S)+ →Bc(∗)+π+π− branching fractions, as functions of the Bc+ pT (left) and |y| (right). The horizontal bars show the bin widths. The markers are shown at the average Bc+ pT or |y|
values of the events contributing to each bin, in the background-subtracted distributions, and the vertical bars represent the statistical uncertainties only. The systematic uncertainties are essentially independent of the Bc+kinematics.
3.7 Systematic uncertainties
Several sources of systematic effects that could potentially affect the measurement of the cross section ratios have been considered. For each of those effects, the analysis has been redone using an alternative option and the resulting cross section ratios are compared to those ob-tained in the baseline analysis. The observed difference between the two results is taken as the systematic uncertainty associated with that specific effect.
Naturally, no uncertainties are considered in factors that affect identically the numerator and denominator values that provide the cross section ratios, such as the efficiency of the J/ψ trig-ger used to collect the event sample or the efficiency of the event selections that determine the total number of Bc+ →J/ψ π+ candidates contributing to Fig. 1. But even if the integral of the measured J/ψ π+invariant mass distribution does not change, it is possible to vary the extracted Bc+yield by changing the functions used in the fit to describe the shapes of the sig-nal and background contributions, given that such variations might change the assignment of some events from the Bc+yield to the background yield, or vice versa. The importance of this effect is evaluated by independently varying the signal and background models used in the fit. The background model is varied by using an exponential function, instead of a first-order polynomial, to describe the uncorrelated J/ψ π+ pairs. The varied scenario for the Bc+ signal line shape consisted in replacing the double-Gaussian function by a Student’s t function [27]. Since these two variations only change the fitted Bc+yield, having no effect on the number of Bc+ →J/ψ π+ candidates used in the search for the Bc(∗)(2S)+ excited states, the correspond-ing (relative) systematic uncertainties, 4.3% for the signal model and 3.5% for the background model, are identical for the R+and R∗+ratios, and cancel in the R∗+/R+double ratio.
The measurement of the Bc(2S)+ and Bc∗(2S)+ yields is also affected by the choices made to model the shapes of the signal peaks and the underlying combinatorial background seen in Fig. 2. The effect of the signal modeling is evaluated with two independent approaches. First,
the default double-Gaussian function, having a common mean and fixing the relative widths and amplitudes from fits to the simulated distributions, is replaced by a single-Gaussian func-tion. The number of free parameters for each signal peak remains at three, but this simpler model is unable to describe the non-Gaussian tails of the peaks. Second, the signal yields are evaluated with a simple procedure that avoids fitting the mass region of the two signal peaks, thereby being insensitive to specific signal shape models. It starts by fitting the signal-free mass sidebands with the background function and then integrating that function within the two sig-nal regions to evaluate the background yields under the peaks, which are then subtracted from the total number of events in those two regions. To evaluate the impact of the background model, these alternative fits have been made with the third-order Chebyshev polynomial used in the baseline analysis and also with the function δλexp(
ν δ), where δ ≡ M(Bc+π+π−) −q0, and λ, ν, and q0 are free parameters. Comparing the cross section ratios obtained using the alternative fits with those of the baseline fit leads to fit modeling systematic uncertainties of 5.9, 2.9, and 2.9%, respectively for the R+, R∗+, and R∗+/R+ratios.
The fit of the Bc+π+π−invariant mass distribution also includes two small contributions rep-resenting the cases where the Bc+meson decays through the Bc+→J/ψ K+channel rather than through the Bc+→J/ψ π+channel assumed in the reconstruction. In the baseline analysis, these terms are modeled using the same shapes as the Bc(∗)(2S)+signal shapes and yields fixed to the yields of those resonances, scaled by the ratio of the two branching fractions, 0.079±0.008 [15], and by the ratio of the two reconstruction efficiencies, 1.06±0.01, in the signal region defined above. To evaluate the influence of these terms on the measured cross section ratios, the anal-ysis is redone varying those two scale factors by their uncertainties. The results are insensitive to those variations, so no systematic uncertainty is assigned to this source.
When searching for Bc(∗)(2S)+ candidates, the baseline analysis starts from an event sample composed of Bc+→J/ψ π+ events with invariant mass in the 6.2–6.355 GeV range. In order to probe if a potential residual contribution of the partially reconstructed Bc+decays could have a significant effect on the determination of the cross section ratios, the analysis is repeated with the lowest allowed invariant mass value changed from 6.2 to 6.1 GeV. The results remain essentially identical, the variations being smaller than their statistical uncertainties, evaluated taking into account that one event sample is a subset of the other, so that the results are fully correlated. Therefore, no systematic uncertainty is assigned to this potential effect.
The uncertainties affecting the ratios of reconstruction efficiencies already presented in Table 1 translate directly into corresponding systematic uncertainties in the cross section ratios. In the evaluation of the Bc(∗)(2S)+reconstruction efficiencies, it is assumed that the two pions emitted in the Bc+π+π−decay have no kinematical correlations between them, besides the constraint of being decay products of the same mother particle. To evaluate the sensitivity of the measured cross section ratios to this assumption, the reconstruction efficiencies are recomputed under two other scenarios. These assume that the π+π− kinematic distributions (a) reflect the exis-tence of an intermediate resonance, or (b) are dependent on the (different) spins of the Bc(2S)+
and Bc∗(2S)+states. The first scenario is simulated by independently reweighting the generated Bc(∗)(2S)+event samples, which previously reflected a simple phase space model, so that their π+π− invariant mass distributions (“decay kinematics”) match that in the data (presented in Section 4). The second scenario follows an analogous procedure using the helicity angle distri-bution (“helicity angle”), where the helicity angle is the angle between the directions of the π+ and Bc+in the dipion rest frame. The differences between the resulting ratios of reconstruction efficiencies and those obtained in the baseline scenario are considered as systematic uncertain-ties: 1.5, 6.9, and 4.2% for the decay kinematics, and 1.0, 6.0, and 3.5% for the helicity angle, respectively, for the R+, R∗+, and R∗+/R+ratios.
9
Several studies have been performed to verify the stability of the results with respect to the selection criteria, including the threshold values used to select the daughter particles. The variations in the reported ratios were smaller than the respective uncertainties, computed ac-counting for the correlation induced by the overlap of the baseline and varied event samples, so that no corresponding systematic uncertainty has been considered.
All the values mentioned above are listed in Table 2, which also shows the total systematic uncertainties, computed as the sum in quadrature of the individual terms.
Table 2: Relative systematic uncertainties (in %) in the cross section ratios, including the Bc(∗)(2S)+ → Bc(∗)+π+π− branching fractions, corresponding to the sources described in the text. The total uncertainty is the sum in quadrature of the individual terms.
R+ R∗+ R∗+/R+
J/ψ π+fit model 5.5 5.5 —
Bc+π+π−fit model 5.9 2.9 2.9
Efficiencies: statistical uncertainty 1.1 1.0 1.4 Efficiencies: spread among years 1.8 1.6 0.9 Efficiencies: pion tracking 4.2 4.2 —
Decay kinematics 1.5 6.9 4.2
Helicity angle 1.0 6.0 3.5
Total 9.5 12.0 6.4
4
Invariant mass distribution of the dipion system
As a complement to the measurement of the cross section ratios, it is also interesting to mea-sure the invariant mass distributions of the dipions emitted in the Bc+π+π−decays of the two Bc(∗)(2S)+ states. In particular, comparing these distributions to those seen in the analogous ψ(2S) →J/ψ π+π−andΥ(2S) →Υ(1S)π+π−decays should provide relevant information to characterize the excited Bc+states and their production processes [6, 7].
Figure 4 compares the invariant mass distributions, normalized to unity, of the dipions emitted in the Bc(2S)+(closed red circles) and Bc∗(2S)+(open blue squares) decays between themselves and with the two corresponding simulated phase space distributions (lines). The Bc(∗)(2S)+
data distributions are derived from the Bc+π+π−invariant mass distribution shown in Fig. 2. The contribution of the background events under the peaks is subtracted using the shape of the measured same-sign dipion invariant mass spectrum and normalizing the sum of the Bc+π+π+ and Bc+π−π−events to the Bc+π+π−spectrum in the invariant mass sideband regions. The di-pion invariant mass distributions have also been obtained using the sPlot technique [28] to sub-tract the background, which resulted in distributions consistent with those reported in Fig. 4. Simulation studies show no dependence of the reconstruction efficiencies on the π+π− in-variant mass, so no correction is applied to these normalized distributions, where only the shapes are informative. For the same reason, systematic uncertainties that affect the distribu-tions globally are not relevant, as they have no impact on the shapes and are canceled by the normalizations.
The dipion mass-dependent systematic uncertainties have been evaluated by comparing, bin by bin, the baseline distributions with those obtained in alternative analyses, where variations are made, as mentioned above, on the models used to fit the signal and background
compo-300 400 500 600 ) (MeV) − π + π ( M 0 0.2 0.4
Normalized mass distribution
data + (2S) c B data + (2S) * c B phase space + (2S) c B phase space + (2S) * c B (13 TeV) -1 143 fb CMS
Figure 4: The dipion invariant mass distributions from Bc(∗)(2S)+→Bc(∗)+π+π−decays in data, normalized to unity. The inner and outer tick marks designate the statistical and total uncer-tainties, respectively. The lines show the corresponding predictions from phase space simula-tions.
nents of the Bc+π+π−mass distribution and on the small contributions from the Bc+→J/ψ K+ and partially reconstructed Bc+decays.
As seen in Fig. 4, the Bc(∗)(2S)+dipion invariant mass distributions are compatible with each other within the uncertainties, and have shapes different from the rather flat distributions pre-dicted from the phase space simulations.
5
Summary
The ratios of the Bc(2S)+ to Bc+, Bc∗(2S)+ to Bc+, and Bc∗(2S)+ to Bc(2S)+production cross sec-tions, R+, R∗+, and R∗+/R+, respectively, have been measured in proton-proton collisions at
√
s=13 TeV. Data set used in the analysis corresponds to an integrated luminosity of 143 fb−1 collected by the CMS experiment at the LHC between 2015 and 2018.
The Bc(∗)(2S)+ mesons were reconstructed through the decays Bc(∗)(2S)+ → Bc(∗)+π+π−, fol-lowed by the Bc+→J/ψ π+and J/ψ→
µ+µ−. The measured cross section ratios, including the (unknown) Bc(∗)(2S)+→Bc(∗)+π+π−branching fractions, are
R+= (3.47±0.63 (stat)±0.33 (syst))%, R∗+ = (4.69±0.71 (stat)±0.56 (syst))%, and R∗+/R+=1.35±0.32 (stat)±0.09 (syst).
(4)
No significant dependences on the transverse momentum pTor rapidity |y|of the Bc+mesons have been observed for any of these three ratios. The normalized dipion invariant mass distri-butions for the Bc(∗)(2S)+→Bc(∗)+π+π−decays are also reported. These results, obtained in the phase space region defined by Bc+meson pT >15 GeV and|y| < 2.4, may provide new impor-tant input to improve the theoretical understanding of the nature of the bc heavy-quarkonium states and their production processes.
11
Acknowledgments
We congratulate our colleagues in the CERN accelerator departments for the excellent perfor-mance of the LHC and thank the technical and administrative staffs at CERN and at other CMS institutes for their contributions to the success of the CMS effort. In addition, we gratefully acknowledge the computing centers and personnel of the Worldwide LHC Computing Grid for delivering so effectively the computing infrastructure essential to our analyses. Finally, we acknowledge the enduring support for the construction and operation of the LHC and the CMS detector provided by the following funding agencies: BMBWF and FWF (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, FAPERGS, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES and CSF (Croatia); RIF (Cyprus); SENESCYT (Ecuador); MoER, ERC IUT, PUT and ERDF (Estonia); Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); NKFIA (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); MSIP and NRF (Republic of Korea); MES (Latvia); LAS (Lithuania); MOE and UM (Malaysia); BUAP, CINVESTAV, CONACYT, LNS, SEP, and UASLP-FAI (Mexico); MOS (Mon-tenegro); MBIE (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Dubna); MON, RosAtom, RAS, RFBR, and NRC KI (Russia); MESTD (Serbia); SEIDI, CPAN, PCTI, and FEDER (Spain); MOSTR (Sri Lanka); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST, STAR, and NSTDA (Thailand); TUBITAK and TAEK (Turkey); NASU (Ukraine); STFC (United Kingdom); DOE and NSF (USA).
Individuals have received support from the Marie-Curie program and the European Research Council and Horizon 2020 Grant, contract Nos. 675440, 752730, and 765710 (European Union); the Leventis Foundation; the A.P. Sloan Foundation; the Alexander von Humboldt Foundation; the Belgian Federal Science Policy Office; the Fonds pour la Formation `a la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Weten-schap en Technologie (IWT-Belgium); the F.R.S.-FNRS and FWO (Belgium) under the “Excel-lence of Science – EOS” – be.h project n. 30820817; the Beijing Municipal Science & Technology Commission, No. Z191100007219010; the Ministry of Education, Youth and Sports (MEYS) of the Czech Republic; the Deutsche Forschungsgemeinschaft (DFG) under Germany’s Excellence Strategy – EXC 2121 “Quantum Universe” – 390833306; the Lend ¨ulet (“Momentum”) Program and the J´anos Bolyai Research Scholarship of the Hungarian Academy of Sciences, the New Na-tional Excellence Program ´UNKP, the NKFIA research grants 123842, 123959, 124845, 124850, 125105, 128713, 128786, and 129058 (Hungary); the Council of Science and Industrial Research, India; the Bilateral Scientific and Technological Cooperation Program between Italy and Mex-ico 2018-2020 (project MX18MO11 and additional MAECI project PGR 00783/2019); the HOM-ING PLUS program of the Foundation for Polish Science, cofinanced from European Union, Regional Development Fund, the Mobility Plus program of the Ministry of Science and Higher Education, the National Science Center (Poland), contracts Harmonia 2014/14/M/ST2/00428, Opus 2014/13/B/ST2/02543, 2014/15/B/ST2/03998, and 2015/19/B/ST2/02861, Sonata-bis 2012/07/E/ST2/01406; the National Priorities Research Program by Qatar National Research Fund; the Ministry of Science and Higher Education, project no. 02.a03.21.0005 (Russia); the Programa Estatal de Fomento de la Investigaci ´on Cient´ıfica y T´ecnica de Excelencia Mar´ıa de Maeztu, grant MDM-2015-0509 and the Programa Severo Ochoa del Principado de Asturias; the Thalis and Aristeia programs cofinanced by EU-ESF and the Greek NSRF; the Rachadapisek Sompot Fund for Postdoctoral Fellowship, Chulalongkorn University and the Chulalongkorn Academic into Its 2nd Century Project Advancement Project (Thailand); the Kavli Foundation; the Nvidia Corporation; the SuperMicro Corporation; the Welch Foundation, contract C-1845; and the Weston Havens Foundation (USA).
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15
A
The CMS Collaboration
Yerevan Physics Institute, Yerevan, Armenia
A.M. Sirunyan†, A. Tumasyan
Institut f ¨ur Hochenergiephysik, Wien, Austria
W. Adam, F. Ambrogi, T. Bergauer, M. Dragicevic, J. Er ¨o, A. Escalante Del Valle, R. Fr ¨uhwirth1, M. Jeitler1, N. Krammer, L. Lechner, D. Liko, T. Madlener, I. Mikulec, F.M. Pitters, N. Rad, J. Schieck1, R. Sch ¨ofbeck, M. Spanring, S. Templ, W. Waltenberger, C.-E. Wulz1, M. Zarucki Institute for Nuclear Problems, Minsk, Belarus
V. Chekhovsky, A. Litomin, V. Makarenko, J. Suarez Gonzalez
Universiteit Antwerpen, Antwerpen, Belgium
M.R. Darwish2, E.A. De Wolf, D. Di Croce, X. Janssen, T. Kello3, A. Lelek, M. Pieters, H. Rejeb Sfar, H. Van Haevermaet, P. Van Mechelen, S. Van Putte, N. Van Remortel
Vrije Universiteit Brussel, Brussel, Belgium
F. Blekman, E.S. Bols, S.S. Chhibra, J. D’Hondt, J. De Clercq, D. Lontkovskyi, S. Lowette, I. Marchesini, S. Moortgat, A. Morton, Q. Python, S. Tavernier, W. Van Doninck, P. Van Mulders
Universit´e Libre de Bruxelles, Bruxelles, Belgium
D. Beghin, B. Bilin, B. Clerbaux, G. De Lentdecker, B. Dorney, L. Favart, A. Grebenyuk, A.K. Kalsi, I. Makarenko, L. Moureaux, L. P´etr´e, A. Popov, N. Postiau, E. Starling, L. Thomas, C. Vander Velde, P. Vanlaer, D. Vannerom, L. Wezenbeek
Ghent University, Ghent, Belgium
T. Cornelis, D. Dobur, M. Gruchala, I. Khvastunov4, M. Niedziela, C. Roskas, K. Skovpen, M. Tytgat, W. Verbeke, B. Vermassen, M. Vit
Universit´e Catholique de Louvain, Louvain-la-Neuve, Belgium
G. Bruno, F. Bury, C. Caputo, P. David, C. Delaere, M. Delcourt, I.S. Donertas, A. Giammanco, V. Lemaitre, K. Mondal, J. Prisciandaro, A. Taliercio, M. Teklishyn, P. Vischia, S. Wuyckens, J. Zobec
Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro, Brazil
G.A. Alves, G. Correia Silva, C. Hensel, A. Moraes
Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil
W.L. Ald´a J ´unior, E. Belchior Batista Das Chagas, H. BRANDAO MALBOUISSON, W. Carvalho, J. Chinellato5, E. Coelho, E.M. Da Costa, G.G. Da Silveira6, D. De Jesus Damiao, S. Fonseca De Souza, J. Martins7, D. Matos Figueiredo, M. Medina Jaime8, M. Melo De Almeida, C. Mora Herrera, L. Mundim, H. Nogima, P. Rebello Teles, L.J. Sanchez Rosas, A. Santoro, S.M. Silva Do Amaral, A. Sznajder, M. Thiel, E.J. Tonelli Manganote5, F. Torres Da Silva De Araujo, A. Vilela Pereira
Universidade Estadual Paulistaa, Universidade Federal do ABCb, S˜ao Paulo, Brazil
C.A. Bernardesa, L. Calligarisa, T.R. Fernandez Perez Tomeia, E.M. Gregoresb, D.S. Lemosa,
P.G. Mercadanteb, S.F. Novaesa, Sandra S. Padulaa
Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Sofia, Bulgaria
A. Aleksandrov, G. Antchev, I. Atanasov, R. Hadjiiska, P. Iaydjiev, M. Misheva, M. Rodozov, M. Shopova, G. Sultanov
University of Sofia, Sofia, Bulgaria
M. Bonchev, A. Dimitrov, T. Ivanov, L. Litov, B. Pavlov, P. Petkov, A. Petrov
Beihang University, Beijing, China
W. Fang3, Q. Guo, H. Wang, L. Yuan
Department of Physics, Tsinghua University, Beijing, China
M. Ahmad, Z. Hu, Y. Wang
Institute of High Energy Physics, Beijing, China
E. Chapon, G.M. Chen9, H.S. Chen9, M. Chen, A. Kapoor, D. Leggat, H. Liao, Z. Liu, R. Sharma,
A. Spiezia, J. Tao, J. Thomas-wilsker, J. Wang, H. Zhang, S. Zhang9, J. Zhao
State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing, China
A. Agapitos, Y. Ban, C. Chen, A. Levin, Q. Li, M. Lu, X. Lyu, Y. Mao, S.J. Qian, D. Wang, Q. Wang, J. Xiao
Sun Yat-Sen University, Guangzhou, China
Z. You
Institute of Modern Physics and Key Laboratory of Nuclear Physics and Ion-beam Application (MOE) - Fudan University, Shanghai, China
X. Gao3
Zhejiang University, Hangzhou, China
M. Xiao
Universidad de Los Andes, Bogota, Colombia
C. Avila, A. Cabrera, C. Florez, J. Fraga, A. Sarkar, M.A. Segura Delgado
Universidad de Antioquia, Medellin, Colombia
J. Jaramillo, J. Mejia Guisao, F. Ramirez, M. Rodriguez, J.D. Ruiz Alvarez, C.A. Salazar Gonz´alez, N. Vanegas Arbelaez
University of Split, Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, Split, Croatia
D. Giljanovic, N. Godinovic, D. Lelas, I. Puljak, T. Sculac
University of Split, Faculty of Science, Split, Croatia
Z. Antunovic, M. Kovac
Institute Rudjer Boskovic, Zagreb, Croatia
V. Brigljevic, D. Ferencek, D. Majumder, M. Roguljic, A. Starodumov10, T. Susa
University of Cyprus, Nicosia, Cyprus
M.W. Ather, A. Attikis, E. Erodotou, A. Ioannou, G. Kole, M. Kolosova, S. Konstantinou, G. Mavromanolakis, J. Mousa, C. Nicolaou, F. Ptochos, P.A. Razis, H. Rykaczewski, H. Saka, D. Tsiakkouri
Charles University, Prague, Czech Republic
M. Finger11, M. Finger Jr.11, A. Kveton, J. Tomsa
Escuela Politecnica Nacional, Quito, Ecuador
E. Ayala
Universidad San Francisco de Quito, Quito, Ecuador
17
Academy of Scientific Research and Technology of the Arab Republic of Egypt, Egyptian Network of High Energy Physics, Cairo, Egypt
H. Abdalla12, S. Elgammal13, A. Mohamed14
Center for High Energy Physics (CHEP-FU), Fayoum University, El-Fayoum, Egypt
A. Lotfy, M.A. Mahmoud
National Institute of Chemical Physics and Biophysics, Tallinn, Estonia
S. Bhowmik, A. Carvalho Antunes De Oliveira, R.K. Dewanjee, K. Ehataht, M. Kadastik, M. Raidal, C. Veelken
Department of Physics, University of Helsinki, Helsinki, Finland
P. Eerola, L. Forthomme, H. Kirschenmann, K. Osterberg, M. Voutilainen
Helsinki Institute of Physics, Helsinki, Finland
E. Br ¨ucken, F. Garcia, J. Havukainen, V. Karim¨aki, M.S. Kim, R. Kinnunen, T. Lamp´en, K. Lassila-Perini, S. Laurila, S. Lehti, T. Lind´en, H. Siikonen, E. Tuominen, J. Tuominiemi
Lappeenranta University of Technology, Lappeenranta, Finland
P. Luukka, T. Tuuva
IRFU, CEA, Universit´e Paris-Saclay, Gif-sur-Yvette, France
C. Amendola, M. Besancon, F. Couderc, M. Dejardin, D. Denegri, J.L. Faure, F. Ferri, S. Ganjour, A. Givernaud, P. Gras, G. Hamel de Monchenault, P. Jarry, B. Lenzi, E. Locci, J. Malcles, J. Rander, A. Rosowsky, M. ¨O. Sahin, A. Savoy-Navarro15, M. Titov, G.B. Yu
Laboratoire Leprince-Ringuet, CNRS/IN2P3, Ecole Polytechnique, Institut Polytechnique de Paris, Paris, France
S. Ahuja, F. Beaudette, M. Bonanomi, A. Buchot Perraguin, P. Busson, C. Charlot, O. Davignon, B. Diab, G. Falmagne, R. Granier de Cassagnac, A. Hakimi, I. Kucher, A. Lobanov, C. Martin Perez, M. Nguyen, C. Ochando, P. Paganini, J. Rembser, R. Salerno, J.B. Sauvan, Y. Sirois, A. Zabi, A. Zghiche
Universit´e de Strasbourg, CNRS, IPHC UMR 7178, Strasbourg, France
J.-L. Agram16, J. Andrea, D. Bloch, G. Bourgatte, M. Brom, E.C. Chabert, C. Collard,
J.-C. Fontaine16, D. Gel´e, U. Goerlach, C. Grimault, A.-C. Le Bihan, P. Van Hove
Universit´e de Lyon, Universit´e Claude Bernard Lyon 1, CNRS-IN2P3, Institut de Physique Nucl´eaire de Lyon, Villeurbanne, France
E. Asilar, S. Beauceron, C. Bernet, G. Boudoul, C. Camen, A. Carle, N. Chanon, D. Contardo, P. Depasse, H. El Mamouni, J. Fay, S. Gascon, M. Gouzevitch, B. Ille, Sa. Jain, I.B. Laktineh, H. Lattaud, A. Lesauvage, M. Lethuillier, L. Mirabito, L. Torterotot, G. Touquet, M. Vander Donckt, S. Viret
Georgian Technical University, Tbilisi, Georgia
D. Lomidze, Z. Tsamalaidze11
RWTH Aachen University, I. Physikalisches Institut, Aachen, Germany
L. Feld, K. Klein, M. Lipinski, D. Meuser, A. Pauls, M. Preuten, M.P. Rauch, J. Schulz, M. Teroerde
RWTH Aachen University, III. Physikalisches Institut A, Aachen, Germany
D. Eliseev, M. Erdmann, P. Fackeldey, B. Fischer, S. Ghosh, T. Hebbeker, K. Hoepfner, H. Keller, L. Mastrolorenzo, M. Merschmeyer, A. Meyer, P. Millet, G. Mocellin, S. Mondal, S. Mukherjee,
D. Noll, A. Novak, T. Pook, A. Pozdnyakov, T. Quast, M. Radziej, Y. Rath, H. Reithler, J. Roemer, A. Schmidt, S.C. Schuler, A. Sharma, S. Wiedenbeck, S. Zaleski
RWTH Aachen University, III. Physikalisches Institut B, Aachen, Germany
C. Dziwok, G. Fl ¨ugge, W. Haj Ahmad17, O. Hlushchenko, T. Kress, A. Nowack, C. Pistone, O. Pooth, D. Roy, H. Sert, A. Stahl18, T. Ziemons
Deutsches Elektronen-Synchrotron, Hamburg, Germany
H. Aarup Petersen, M. Aldaya Martin, P. Asmuss, I. Babounikau, S. Baxter, O. Behnke, A. Berm ´udez Mart´ınez, A.A. Bin Anuar, K. Borras19, V. Botta, D. Brunner, A. Campbell, A. Cardini, P. Connor, S. Consuegra Rodr´ıguez, V. Danilov, A. De Wit, M.M. Defranchis, L. Didukh, D. Dom´ınguez Damiani, G. Eckerlin, D. Eckstein, T. Eichhorn, L.I. Estevez Banos, E. Gallo20, A. Geiser, A. Giraldi, A. Grohsjean, M. Guthoff, A. Harb, A. Jafari21, N.Z. Jomhari, H. Jung, A. Kasem19, M. Kasemann, H. Kaveh, C. Kleinwort, J. Knolle, D. Kr ¨ucker, W. Lange, T. Lenz, J. Lidrych, K. Lipka, W. Lohmann22, R. Mankel, I.-A. Melzer-Pellmann, J. Metwally, A.B. Meyer, M. Meyer, M. Missiroli, J. Mnich, A. Mussgiller, V. Myronenko, Y. Otarid, D. P´erez Ad´an, S.K. Pflitsch, D. Pitzl, A. Raspereza, A. Saggio, A. Saibel, M. Savitskyi, V. Scheurer, P. Sch ¨utze, C. Schwanenberger, A. Singh, R.E. Sosa Ricardo, N. Tonon, O. Turkot, A. Vagnerini, M. Van De Klundert, R. Walsh, D. Walter, Y. Wen, K. Wichmann, C. Wissing, S. Wuchterl, O. Zenaiev, R. Zlebcik
University of Hamburg, Hamburg, Germany
R. Aggleton, S. Bein, L. Benato, A. Benecke, K. De Leo, T. Dreyer, A. Ebrahimi, M. Eich, F. Feindt, A. Fr ¨ohlich, C. Garbers, E. Garutti, P. Gunnellini, J. Haller, A. Hinzmann, A. Karavdina, G. Kasieczka, R. Klanner, R. Kogler, V. Kutzner, J. Lange, T. Lange, A. Malara, C.E.N. Niemeyer, A. Nigamova, K.J. Pena Rodriguez, O. Rieger, P. Schleper, S. Schumann, J. Schwandt, D. Schwarz, J. Sonneveld, H. Stadie, G. Steinbr ¨uck, B. Vormwald, I. Zoi
Karlsruher Institut fuer Technologie, Karlsruhe, Germany
M. Baselga, S. Baur, J. Bechtel, T. Berger, E. Butz, R. Caspart, T. Chwalek, W. De Boer, A. Dierlamm, A. Droll, K. El Morabit, N. Faltermann, K. Fl ¨oh, M. Giffels, A. Gottmann, F. Hartmann18, C. Heidecker, U. Husemann, M.A. Iqbal, I. Katkov23, P. Keicher, R. Koppenh ¨ofer, S. Maier, M. Metzler, S. Mitra, D. M ¨uller, Th. M ¨uller, M. Musich, G. Quast, K. Rabbertz, J. Rauser, D. Savoiu, D. Sch¨afer, M. Schnepf, M. Schr ¨oder, D. Seith, I. Shvetsov, H.J. Simonis, R. Ulrich, M. Wassmer, M. Weber, R. Wolf, S. Wozniewski
Institute of Nuclear and Particle Physics (INPP), NCSR Demokritos, Aghia Paraskevi, Greece
G. Anagnostou, P. Asenov, G. Daskalakis, T. Geralis, A. Kyriakis, D. Loukas, G. Paspalaki, A. Stakia
National and Kapodistrian University of Athens, Athens, Greece
M. Diamantopoulou, D. Karasavvas, G. Karathanasis, P. Kontaxakis, C.K. Koraka, A. Manousakis-katsikakis, A. Panagiotou, I. Papavergou, N. Saoulidou, K. Theofilatos, K. Vellidis, E. Vourliotis
National Technical University of Athens, Athens, Greece
G. Bakas, K. Kousouris, I. Papakrivopoulos, G. Tsipolitis, A. Zacharopoulou
University of Io´annina, Io´annina, Greece
I. Evangelou, C. Foudas, P. Gianneios, P. Katsoulis, P. Kokkas, S. Mallios, K. Manitara, N. Manthos, I. Papadopoulos, J. Strologas
19
MTA-ELTE Lend ¨ulet CMS Particle and Nuclear Physics Group, E ¨otv ¨os Lor´and University, Budapest, Hungary
M. Bart ´ok24, R. Chudasama, M. Csanad, M.M.A. Gadallah25, S. L ¨ok ¨os26, P. Major, K. Mandal, A. Mehta, G. Pasztor, O. Sur´anyi, G.I. Veres
Wigner Research Centre for Physics, Budapest, Hungary
G. Bencze, C. Hajdu, D. Horvath27, F. Sikler, V. Veszpremi, G. Vesztergombi†
Institute of Nuclear Research ATOMKI, Debrecen, Hungary
S. Czellar, J. Karancsi24, J. Molnar, Z. Szillasi, D. Teyssier
Institute of Physics, University of Debrecen, Debrecen, Hungary
P. Raics, Z.L. Trocsanyi, B. Ujvari
Eszterhazy Karoly University, Karoly Robert Campus, Gyongyos, Hungary
T. Csorgo, F. Nemes, T. Novak
Indian Institute of Science (IISc), Bangalore, India
S. Choudhury, J.R. Komaragiri, D. Kumar, L. Panwar, P.C. Tiwari
National Institute of Science Education and Research, HBNI, Bhubaneswar, India
S. Bahinipati28, D. Dash, C. Kar, P. Mal, T. Mishra, V.K. Muraleedharan Nair Bindhu, A. Nayak29, D.K. Sahoo28, N. Sur, S.K. Swain
Panjab University, Chandigarh, India
S. Bansal, S.B. Beri, V. Bhatnagar, S. Chauhan, N. Dhingra30, R. Gupta, A. Kaur, S. Kaur,
P. Kumari, M. Lohan, M. Meena, K. Sandeep, S. Sharma, J.B. Singh, A.K. Virdi
University of Delhi, Delhi, India
A. Ahmed, A. Bhardwaj, B.C. Choudhary, R.B. Garg, M. Gola, S. Keshri, A. Kumar, M. Naimuddin, P. Priyanka, K. Ranjan, A. Shah
Saha Institute of Nuclear Physics, HBNI, Kolkata, India
M. Bharti31, R. Bhattacharya, S. Bhattacharya, D. Bhowmik, S. Dutta, S. Ghosh, B. Gomber32,
M. Maity33, S. Nandan, P. Palit, A. Purohit, P.K. Rout, G. Saha, S. Sarkar, M. Sharan, B. Singh31, S. Thakur31
Indian Institute of Technology Madras, Madras, India
P.K. Behera, S.C. Behera, P. Kalbhor, A. Muhammad, R. Pradhan, P.R. Pujahari, A. Sharma, A.K. Sikdar
Bhabha Atomic Research Centre, Mumbai, India
D. Dutta, V. Kumar, K. Naskar34, P.K. Netrakanti, L.M. Pant, P. Shukla
Tata Institute of Fundamental Research-A, Mumbai, India
T. Aziz, M.A. Bhat, S. Dugad, R. Kumar Verma, G.B. Mohanty, U. Sarkar
Tata Institute of Fundamental Research-B, Mumbai, India
S. Banerjee, S. Bhattacharya, S. Chatterjee, M. Guchait, S. Karmakar, S. Kumar, G. Majumder, K. Mazumdar, S. Mukherjee, D. Roy, N. Sahoo
Indian Institute of Science Education and Research (IISER), Pune, India
S. Dube, B. Kansal, K. Kothekar, S. Pandey, A. Rane, A. Rastogi, S. Sharma
Department of Physics, Isfahan University of Technology, Isfahan, Iran
Institute for Research in Fundamental Sciences (IPM), Tehran, Iran
S. Chenarani36, S.M. Etesami, M. Khakzad, M. Mohammadi Najafabadi
University College Dublin, Dublin, Ireland
M. Felcini, M. Grunewald
INFN Sezione di Baria, Universit`a di Barib, Politecnico di Baric, Bari, Italy
M. Abbresciaa,b, R. Alya,b,37, C. Arutaa,b, A. Colaleoa, D. Creanzaa,c, N. De Filippisa,c, M. De Palmaa,b, A. Di Florioa,b, A. Di Pilatoa,b, W. Elmetenaweea,b, L. Fiorea, A. Gelmia,b, M. Gula, G. Iasellia,c, M. Incea,b, S. Lezkia,b, G. Maggia,c, M. Maggia, I. Margjekaa,b, V. Mastrapasquaa,b, J.A. Merlina, S. Mya,b, S. Nuzzoa,b, A. Pompilia,b, G. Pugliesea,c, A. Ranieria, G. Selvaggia,b, L. Silvestrisa, F.M. Simonea,b, R. Vendittia, P. Verwilligena
INFN Sezione di Bolognaa, Universit`a di Bolognab, Bologna, Italy
G. Abbiendia, C. Battilanaa,b, D. Bonacorsia,b, L. Borgonovia,b, S. Braibant-Giacomellia,b, R. Campaninia,b, P. Capiluppia,b, A. Castroa,b, F.R. Cavalloa, C. Cioccaa, M. Cuffiania,b, G.M. Dallavallea, T. Diotalevia,b, F. Fabbria, A. Fanfania,b, E. Fontanesia,b, P. Giacomellia, L. Giommia,b, C. Grandia, L. Guiduccia,b, F. Iemmia,b, S. Lo Meoa,38, S. Marcellinia, G. Masettia, F.L. Navarriaa,b, A. Perrottaa, F. Primaveraa,b, T. Rovellia,b, G.P. Sirolia,b, N. Tosia
INFN Sezione di Cataniaa, Universit`a di Cataniab, Catania, Italy
S. Albergoa,b,39, S. Costaa,b, A. Di Mattiaa, R. Potenzaa,b, A. Tricomia,b,39, C. Tuvea,b
INFN Sezione di Firenzea, Universit`a di Firenzeb, Firenze, Italy
G. Barbaglia, A. Cassesea, R. Ceccarellia,b, V. Ciullia,b, C. Civininia, R. D’Alessandroa,b, F. Fioria, E. Focardia,b, G. Latinoa,b, P. Lenzia,b, M. Lizzoa,b, M. Meschinia, S. Paolettia, R. Seiditaa,b, G. Sguazzonia, L. Viliania
INFN Laboratori Nazionali di Frascati, Frascati, Italy
L. Benussi, S. Bianco, D. Piccolo
INFN Sezione di Genovaa, Universit`a di Genovab, Genova, Italy
M. Bozzoa,b, F. Ferroa, R. Mulargiaa,b, E. Robuttia, S. Tosia,b
INFN Sezione di Milano-Bicoccaa, Universit`a di Milano-Bicoccab, Milano, Italy
A. Benagliaa, A. Beschia,b, F. Brivioa,b, F. Cetorellia,b, V. Cirioloa,b,18, F. De Guioa,b, M.E. Dinardoa,b, P. Dinia, S. Gennaia, A. Ghezzia,b, P. Govonia,b, L. Guzzia,b, M. Malbertia, S. Malvezzia, D. Menascea, F. Montia,b, L. Moronia, M. Paganonia,b, D. Pedrinia, S. Ragazzia,b, T. Tabarelli de Fatisa,b, D. Valsecchia,b,18, D. Zuoloa,b
INFN Sezione di Napolia, Universit`a di Napoli ’Federico II’b, Napoli, Italy, Universit`a della Basilicatac, Potenza, Italy, Universit`a G. Marconid, Roma, Italy
S. Buontempoa, N. Cavalloa,c, A. De Iorioa,b, F. Fabozzia,c, F. Fiengaa, A.O.M. Iorioa,b, L. Listaa,b,
S. Meolaa,d,18, P. Paoluccia,18, B. Rossia, C. Sciaccaa,b, E. Voevodinaa,b
INFN Sezione di Padova a, Universit`a di Padova b, Padova, Italy, Universit`a di Trento c, Trento, Italy
P. Azzia, N. Bacchettaa, D. Biselloa,b, A. Bolettia,b, A. Bragagnoloa,b, R. Carlina,b, P. Checchiaa, P. De Castro Manzanoa, T. Dorigoa, F. Gasparinia,b, U. Gasparinia,b, S.Y. Hoha,b, L. Layera,40, M. Margonia,b, A.T. Meneguzzoa,b, M. Presillab, P. Ronchesea,b, R. Rossina,b, F. Simonettoa,b, G. Strong, A. Tikoa, M. Tosia,b, H. YARARa,b, M. Zanettia,b, P. Zottoa,b, A. Zucchettaa,b,
21
INFN Sezione di Paviaa, Universit`a di Paviab, Pavia, Italy
C. Aime‘a,b, A. Braghieria, S. Calzaferria,b, D. Fiorinaa,b, P. Montagnaa,b, S.P. Rattia,b, V. Rea, M. Ressegottia,b, C. Riccardia,b, P. Salvinia, I. Vaia, P. Vituloa,b
INFN Sezione di Perugiaa, Universit`a di Perugiab, Perugia, Italy
M. Biasinia,b, G.M. Bileia, D. Ciangottinia,b, L. Fan `oa,b, P. Laricciaa,b, G. Mantovania,b, V. Mariania,b, M. Menichellia, F. Moscatellia, A. Piccinellia,b, A. Rossia,b, A. Santocchiaa,b, D. Spigaa, T. Tedeschia,b
INFN Sezione di Pisaa, Universit`a di Pisab, Scuola Normale Superiore di Pisac, Pisa, Italy
K. Androsova, P. Azzurria, G. Bagliesia, V. Bertacchia,c, L. Bianchinia, T. Boccalia, R. Castaldia, M.A. Cioccia,b, R. Dell’Orsoa, M.R. Di Domenicoa,b, S. Donatoa, L. Gianninia,c, A. Giassia,
M.T. Grippoa, F. Ligabuea,c, E. Mancaa,c, G. Mandorlia,c, A. Messineoa,b, F. Pallaa, G. Ramirez-Sancheza,c, A. Rizzia,b, G. Rolandia,c, S. Roy Chowdhurya,c, A. Scribanoa, N. Shafieia,b, P. Spagnoloa, R. Tenchinia, G. Tonellia,b, N. Turinia, A. Venturia, P.G. Verdinia
INFN Sezione di Romaa, Sapienza Universit`a di Romab, Rome, Italy
F. Cavallaria, M. Cipriania,b, D. Del Rea,b, E. Di Marcoa, M. Diemoza, E. Longoa,b, P. Meridiania, G. Organtinia,b, F. Pandolfia, R. Paramattia,b, C. Quarantaa,b, S. Rahatloua,b, C. Rovellia, F. Santanastasioa,b, L. Soffia,b, R. Tramontanoa,b
INFN Sezione di Torino a, Universit`a di Torino b, Torino, Italy, Universit`a del Piemonte Orientalec, Novara, Italy
N. Amapanea,b, R. Arcidiaconoa,c, S. Argiroa,b, M. Arneodoa,c, N. Bartosika, R. Bellana,b, A. Belloraa,b, C. Biinoa, A. Cappatia,b, N. Cartigliaa, S. Comettia, M. Costaa,b, R. Covarellia,b, N. Demariaa, B. Kiania,b, F. Leggera, C. Mariottia, S. Masellia, E. Migliorea,b, V. Monacoa,b, E. Monteila,b, M. Montenoa, M.M. Obertinoa,b, G. Ortonaa, L. Pachera,b, N. Pastronea, M. Pelliccionia, G.L. Pinna Angionia,b, M. Ruspaa,c, R. Salvaticoa,b, F. Sivieroa,b, V. Solaa,
A. Solanoa,b, D. Soldia,b, A. Staianoa, D. Trocinoa,b
INFN Sezione di Triestea, Universit`a di Triesteb, Trieste, Italy
S. Belfortea, V. Candelisea,b, M. Casarsaa, F. Cossuttia, A. Da Rolda,b, G. Della Riccaa,b, F. Vazzolera,b
Kyungpook National University, Daegu, Korea
S. Dogra, C. Huh, B. Kim, D.H. Kim, G.N. Kim, J. Lee, S.W. Lee, C.S. Moon, Y.D. Oh, S.I. Pak, B.C. Radburn-Smith, S. Sekmen, Y.C. Yang
Chonnam National University, Institute for Universe and Elementary Particles, Kwangju, Korea
H. Kim, D.H. Moon
Hanyang University, Seoul, Korea
B. Francois, T.J. Kim, J. Park
Korea University, Seoul, Korea
S. Cho, S. Choi, Y. Go, S. Ha, B. Hong, K. Lee, K.S. Lee, J. Lim, J. Park, S.K. Park, J. Yoo
Kyung Hee University, Department of Physics, Seoul, Republic of Korea
J. Goh, A. Gurtu
Sejong University, Seoul, Korea
Seoul National University, Seoul, Korea
J. Almond, J.H. Bhyun, J. Choi, S. Jeon, J. Kim, J.S. Kim, S. Ko, H. Kwon, H. Lee, K. Lee, S. Lee, K. Nam, B.H. Oh, M. Oh, S.B. Oh, H. Seo, U.K. Yang, I. Yoon
University of Seoul, Seoul, Korea
D. Jeon, J.H. Kim, B. Ko, J.S.H. Lee, I.C. Park, Y. Roh, D. Song, I.J. Watson
Yonsei University, Department of Physics, Seoul, Korea
H.D. Yoo
Sungkyunkwan University, Suwon, Korea
Y. Choi, C. Hwang, Y. Jeong, H. Lee, Y. Lee, I. Yu
Riga Technical University, Riga, Latvia
V. Veckalns41
Vilnius University, Vilnius, Lithuania
A. Juodagalvis, A. Rinkevicius, G. Tamulaitis
National Centre for Particle Physics, Universiti Malaya, Kuala Lumpur, Malaysia
W.A.T. Wan Abdullah, M.N. Yusli, Z. Zolkapli
Universidad de Sonora (UNISON), Hermosillo, Mexico
J.F. Benitez, A. Castaneda Hernandez, J.A. Murillo Quijada, L. Valencia Palomo
Centro de Investigacion y de Estudios Avanzados del IPN, Mexico City, Mexico
H. Castilla-Valdez, E. De La Cruz-Burelo, I. Heredia-De La Cruz42, R. Lopez-Fernandez,
C.A. Mondragon Herrera, D.A. Perez Navarro, A. Sanchez-Hernandez
Universidad Iberoamericana, Mexico City, Mexico
S. Carrillo Moreno, C. Oropeza Barrera, M. Ramirez-Garcia, F. Vazquez Valencia
Benemerita Universidad Autonoma de Puebla, Puebla, Mexico
J. Eysermans, I. Pedraza, H.A. Salazar Ibarguen, C. Uribe Estrada
Universidad Aut ´onoma de San Luis Potos´ı, San Luis Potos´ı, Mexico
A. Morelos Pineda
University of Montenegro, Podgorica, Montenegro
J. Mijuskovic4, N. Raicevic
University of Auckland, Auckland, New Zealand
D. Krofcheck
University of Canterbury, Christchurch, New Zealand
S. Bheesette, P.H. Butler
National Centre for Physics, Quaid-I-Azam University, Islamabad, Pakistan
A. Ahmad, M.I. Asghar, M.I.M. Awan, H.R. Hoorani, W.A. Khan, M.A. Shah, M. Shoaib, M. Waqas
AGH University of Science and Technology Faculty of Computer Science, Electronics and Telecommunications, Krakow, Poland
V. Avati, L. Grzanka, M. Malawski
National Centre for Nuclear Research, Swierk, Poland
H. Bialkowska, M. Bluj, B. Boimska, T. Frueboes, M. G ´orski, M. Kazana, M. Szleper, P. Traczyk, P. Zalewski
![Figure 1: Invariant mass distribution of the B c + → J/ψ π + candidates, after applying all event selection criteria [1]](https://thumb-eu.123doks.com/thumbv2/9libnet/3902396.44162/5.892.243.646.165.453/figure-invariant-distribution-candidates-applying-event-selection-criteria.webp)
