Measurement of beauty and charm production in pp collisions at \sqrt{s}=5.02 TeV via non-prompt and prompt D mesons
aa r X i v : . [ nu c l - e x ] F e b EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH
CERN-EP-2021-03423 February 2021© 2021 CERN for the benefit of the ALICE Collaboration.Reproduction of this article or parts of it is allowed as specified in the CC-BY-4.0 license.
Measurement of beauty and charm production in pp collisions at √ s = .
02 TeV √ s = .
02 TeV √ s = .
02 TeV via non-prompt and prompt D mesons
ALICE Collaboration * Abstract
The p T -differential production cross sections of prompt and non-prompt (produced in beauty-hadrondecays) D mesons were measured by the ALICE experiment at midrapidity ( | y | < .
5) in proton–proton collisions at √ s = .
02 TeV. The data sample used in the analysis corresponds to an integratedluminosity of ( . ± . ) nb − . D mesons were reconstructed from their decays D → K − π + ,D + → K − π + π + , and D + s → φπ + → K − K + π + and their charge conjugates. Compared to previousmeasurements in the same rapidity region, the cross sections of prompt D + and D + s mesons have anextended p T coverage and total uncertainties reduced by a factor ranging from 1.05 to 1.6, dependingon p T , allowing for a more precise determination of their p T -integrated cross sections. The resultsare well described by perturbative QCD calculations. The fragmentation fraction of heavy quarksto strange mesons divided by the one to non-strange mesons, f s / ( f u + f d ) , is compatible for charmand beauty quarks and with previous measurements at different centre-of-mass energies and collisionsystems. The bb production cross section per rapidity unit at midrapidity, estimated from non-promptD-meson measurements, is d σ bb / d y | | y | < . = . ± . ( stat ) + . − . ( tot . syst ) µ b. It is compatible withprevious measurements at the same centre-of-mass energy and with the cross section predicted byperturbative QCD calculations. * See Appendix A for the list of collaboration members on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration
Measurements of the production of hadrons containing charm or beauty quarks in proton–proton (pp)collisions provide an important test of Quantum Chromodynamics (QCD) calculations. They also setthe reference for the respective measurements in heavy-ion collisions, where the study of charm- andbeauty-quark interaction with the quark–gluon plasma (QGP) constituents is a rich source of informationabout the medium properties and its inner dynamics [1]. Several measurements of charm and beautyproduction were carried out in pp collisions at √ s = . , . , ,
8, and 13 TeV by the ALICE [2–16],ATLAS [17–21], CMS [22–31], and LHCb [32–46] experiments at the LHC. At lower collision energies,measurements were performed at √ s =
200 GeV at RHIC [47–50] and in pp collisions at √ s =
630 GeVat the SppS [51] and at √ s = .
96 TeV at the Tevatron [52–55]. The D- and B-meson data are generallydescribed within uncertainties by perturbative QCD calculations at Next-to-Leading-Order with Next-to-Leading Log resummation, like FONLL [56, 57] and GM-VFNS [58–63]. These calculations rely onthe factorisation of soft (non-perturbative) and hard (perturbative) processes and calculate the transverse-momentum ( p T ) differential cross sections of charm- or beauty-hadron production as a convolution of ahard-scattering cross section at the partonic level, parton distribution functions (PDFs) of the collidingprotons, and fragmentation functions (FF) modelling the transition from heavy quarks to heavy-flavourhadrons [64]. Recently, also calculations with next-to-next-to-leading-order (NNLO) QCD radiativecorrections became available for the beauty-quark production [65].In this paper we report an update of the measurement of prompt (i.e. produced in the charm quarkfragmentation, either directly or through decays of excited open charm and charmonium states) D + -and D + s -meson production performed with ALICE in the rapidity interval | y | < . √ s = .
02 TeV [3], obtained using an improved analysis technique. We also present a new measurementof the production of non-prompt D , D + , and D + s mesons from beauty-hadron decays. The analysisof prompt D + and D + s mesons is extended down to p T = / c , respectively. Non-prompt Dmesons are measured down to p T = / c (D meson) and 2 GeV / c (D + and D + s mesons). These newresults provide an improvement in terms of low- p T reach and particle species accessed with respect tothe previous measurement of non-prompt D production by CMS [30]. Such an extension is important totest perturbative QCD (pQCD) calculations over a wider p T interval and to better determine the heavy-quark production cross section. These measurements also provide a reference for Pb–Pb collisions inthe low- p T region, a relevant one to address nuclear effects like shadowing, heavy-quark diffusion in theQGP, and the expected enhancement of the production of hadrons with strange quarks [66].The paper is organised as follows. In Section 2 the ALICE apparatus and the analysed data sample aredescribed. In Section 3 the analysis procedure is explained. Machine-learning algorithms are used toclassify and separate the prompt and non-prompt D-meson signals and the combinatorial background.A data-driven procedure is used to calculate the fraction of prompt and non-prompt D mesons. Thesystematic uncertainties are discussed in Section 4. In Section 5 the results are presented. First, inSection 5.1, the p T -differential cross sections of prompt and non-prompt D mesons are reported andcompared to theoretical predictions. Then, in Section 5.2, the ratios of the measured cross sections of theD-meson species are computed. In theoretical calculations, these ratios are sensitive mainly to the FF orthe adopted hadronisation model. In particular, the comparison of the production rate of strange mesonswith that of non-strange ones allows the determination of the ratio f s / ( f u + f d ) , i.e. the fragmentationfraction of charm and beauty quarks to strange mesons divided by the one to non-strange mesons. InSection 5.3, by extrapolating down to p T = √ s = .
02 TeV. A summary concludes the paper.2on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration
The ALICE apparatus is composed of a central barrel, consisting of a set of detectors for particlereconstruction and identification at midrapidity, a forward muon spectrometer, and various forward andbackward detectors for triggering and event characterisation. A complete description and an overview oftheir typical performance are presented in Refs. [67, 68].The D-meson decay products were reconstructed at midrapidity exploiting the tracking and particle iden-tification capabilities of the central barrel detectors, which cover the full azimuth in the pseudorapidityinterval | η | < .
9. These detectors are embedded in a large solenoidal magnet that provides a magneticfield B = . E / d x . The particle identificationcapabilities of the TPC are extended by the Time-Of-Flight (TOF) detector, which is used to measurethe flight time of the charged particles from the interaction point. The event collision time is obtainedusing either the information from the T0 detector, the TOF detector, or a combination of the two. TheT0 detector consists of two arrays of ˇCerenkov counters, located on both sides of the nominal interactionpoint, covering the pseudorapidity intervals − . < η < − .
97 and 4 . < η < .
92. The V0 detectorwas used for triggering and event selection. It is composed of two scintillator arrays, located on bothsides of the nominal interaction point and covering the pseudorapidity intervals − . < η < − . . < η < . √ s = .
02 TeV collected in 2017. The events used in the analysis were recorded with a minimumbias (MB) trigger which required coincident signals in the two scintillator arrays of the V0 detector.Events were further selected offline in order to remove background due to the interaction betweenone of the beams and the residual gas present in the beam vacuum tube and other machine-inducedbackgrounds [68]. This selection was based on the timing information of the two V0 arrays and thecorrelation between the number of hits and track segments in the two innermost layers of the ITS,consisting of Silicon Pixel Detectors (SPD). In order to maintain a uniform acceptance in pseudorapidity,events were required to have a reconstructed collision vertex located within ±
10 cm from the centre ofthe detector along the beam-line direction. Events with multiple primary vertices reconstructed fromTPC and ITS tracks, due to pileup of several collisions, were rejected. The remaining undetectedpileup is negligible in the present analysis. After the aforementioned selections, the data sample usedfor the analysis consists of about 990 million MB events, corresponding to an integrated luminosity L int = ( . ± . ) nb − [69].The Monte Carlo samples utilised in the analysis were obtained simulating pp collisions with thePYTHIA 8.243 event generator [70, 71] (Monash-13 tune [72]), and propagating the generated particlesthrough the detector using the GEANT3 package [73]. A cc- or bb-quark pair was required in eachsimulated PYTHIA pp event and D mesons were forced to decay into the hadronic channels of interestfor the analysis. The luminous region distribution and the conditions of all the ALICE detectors in termsof active channels, gain, noise level, and alignment, and their evolution with time during the data taking,were taken into account in the simulations. D , D + , and D + s mesons and their charge conjugates were reconstructed through the decay channelsD → K − π + (with branching ratio BR = ( . ± . ) %), D + → K − π + π + (BR = ( . ± . ) %),3on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaborationand D + s → φπ + → K − K + π + (BR = ( . ± . ) %) [74]. The analysis was based on the reconstructionof decay-vertex topologies displaced from the interaction vertex. The separation induced by the weakdecays of prompt D , D + , and D + s is typically a few hundred of µ m ( c τ ≃ µ m,respectively [74]). Decay vertices of non-prompt D mesons, originating from beauty-hadron decays, onaverage are more displaced from the interaction vertex due to the larger mean proper decay lengths ofbeauty hadrons ( c τ ≃ µ m [74])]) as compared to charm hadrons. Therefore, exploiting the selectionof displaced decay-vertex topologies, it is possible not only to separate D mesons from the combinatorialbackground, but also non-prompt from prompt D mesons.D-meson candidates were built combining pairs or triplets of tracks with the proper charge signs, eachwith | η | < . p T > . / c , at least 70 (out of 159) associated space points in the TPC, a fitquality χ / ndf < | y | > . p T and for | y | > . p T > / c . Thus, only D-meson candidates within a fiducial acceptance region, | y | < y fid ( p T ) ,were selected. The y fid ( p T ) value was defined as a second-order polynomial function, increasing from0.5 to 0.8 in the transverse-momentum range 0 < p T < / c , and as a constant term, y fid = .
8, for p T > / c .To reduce the large combinatorial background and to separate the contribution of prompt and non-prompt D mesons, a machine-learning approach based on Boosted Decision Trees (BDT) was adopted.Two different implementations of the BDT algorithm, provided by the TMVA [75] and XGBoost [76]libraries, were considered. Signal samples of prompt and non-prompt D mesons for the BDT trainingwere obtained from simulations based on the PYTHIA 8 event generator as described in Section 2. Thebackground samples were obtained from the sidebands of the candidate invariant-mass distributions inthe data. Before the training, loose kinematic and topological selections were applied to the D-mesoncandidates together with the particle identification (PID) of decay-product tracks. Pions and kaonswere selected by requiring compatibility with the respective particle hypothesis within three standarddeviations (3 σ ) between the measured and the expected signals for both the TPC d E / d x and the timeof flight. Tracks without TOF hits were identified using only the TPC information. For D + s -mesoncandidates, an absolute difference of the reconstructed K + K − invariant mass with respect to the PDGworld average of the φ meson [74] ( ∆ M KK ) under 15 MeV / c was additionally required. The D-mesoncandidate information provided to the BDTs, as an input for the models to distinguish among promptand non-prompt D mesons and background candidates, was mainly based on the displacement of thetracks from the primary vertex ( d ), the distance between the D-meson decay vertex and the primaryvertex (decay length, L ), the D-meson impact parameter, and the cosine of the pointing angle betweenthe D-meson candidate line of flight (the vector connecting the primary and secondary vertices) and itsreconstructed momentum vector. Additional variables related to the PID of decay tracks were used forD + and D + s candidates. The value of ∆ M KK was also considered for D + s candidates. Independent BDTswere trained for the different D-meson species and in different p T intervals. Subsequently, they wereapplied to the real data sample in which the type of candidate is unknown. The BDT outputs are relatedto the candidate probability to be a non-prompt D meson or combinatorial background. Selections on theBDT outputs were optimised to obtain a high non-prompt D-meson fraction while maintaining a reliablesignal extraction in the case of the non-prompt analysis. For the prompt D + and D + s analysis, selectionswere tuned to provide a large statistical significance for the signal and a small contribution of non-promptcandidates. D , D + , and D + s mesons Samples enhanced with non-prompt candidates were selected by requiring a low candidate probabilityto be combinatorial background and a high probability to be non-prompt. The raw yields of D , D + , and4on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration ) c ) (GeV/ π (K M c C oun t s pe r M e V / ALICE = 5.02 TeV s pp, and charge conj. + π − K → D c < 2 GeV/ T p ± = 103 S ± ± = 0.95 non-prompt f ) c ) (GeV/ ππ (K M c C oun t s pe r M e V / ALICE = 5.02 TeV s pp, and charge conj. + π + π − K → + D c < 10 GeV/ T p ± = 178 S ± ± = 0.66 non-prompt f ) c ) (GeV/ π (KK M c C oun t s pe r M e V / ALICE = 5.02 TeV s pp, and charge conj. + π − K + K → + πφ → +s D c < 4 GeV/ T p ± = 137 S ± ± = 0.62 non-prompt f Figure 1:
Invariant-mass distributions of D , D + , and D + s candidates and charge conjugates in 1 < p T < / c ,8 < p T <
10 GeV / c , and 2 < p T < / c intervals, respectively. The blue solid lines show the total fit functionsas described in the text and the red dashed lines are the combinatorial background. In case of the D candidates, thegrey dashed line represents the combinatorial background with the contribution of the reflections. The raw-yield( S ) values are reported together with their statistical uncertainties resulting from the fit. The fraction of non-promptcandidates in the measured raw yield is reported with its statistical and systematic uncertainties. D + s mesons, including both particles and antiparticles, were extracted from binned maximum-likelihoodfits to the invariant-mass ( M ) distributions. The raw yields could be extracted in transverse-momentumintervals in the range 1 < p T <
24 GeV / c for D mesons, 2 < p T <
16 GeV / c for D + mesons, and2 < p T <
12 GeV / c for D + s mesons. The fit function was composed of a Gaussian for the descriptionof the signal and of an exponential term for the background. To improve the stability of the fits, thewidths of the D-meson signal peaks were fixed to the values extracted from data samples dominated byprompt candidates, given the naturally larger abundance of prompt compared to non-prompt D mesons.For the M ( KK π ) distribution, an additional Gaussian was used to describe the peak due to the decayD + → K − K + π + , with a branching ratio of (9 . ± . ) × − [74], present at a lower invariant-mass value than the D + s -meson signal peak. For the D meson, the contribution of signal candidatesto the invariant-mass distribution with the wrong mass assigned to the D -decay tracks (reflections) wasincluded in the fit. It was estimated based on the invariant-mass distributions of the reflected signal in thesimulation, which were described as the sum of two Gaussian functions. The contribution of reflectionsto the raw yield is about 0 . − p T . Examples of invariant-mass distributionstogether with the result of the fits and the estimated non-prompt fractions are reported in Fig. 1, forthe 1 < p T < / c , 8 < p T <
10 GeV / c , and 2 < p T < / c intervals of the D , D + , and D + s candidates, respectively. The procedure used to calculate the fraction of non-prompt candidates presentin the extracted raw yields is described in Section 3.2. The measured raw yields, although dominatedby non-prompt candidates, still contain a residual contribution of prompt D mesons which satisfy theBDT-based selections. The statistical significance of the observed signals, S / √ S + B , varies from 4 to10, depending on the D-meson species and on the p T interval.The p T -differential cross section of non-prompt D mesons was computed for each p T interval asd σ D d p T d y = c ∆ y ( p T ) ∆ p T × × f non-prompt ( p T ) × N D + D , raw ( p T ) (cid:12)(cid:12)(cid:12) | y | < y fid ( p T ) ( Acc × ε ) non-prompt ( p T ) L int . (1)The raw-yield values (sum of particles and antiparticles, N D + D , raw ) were divided by a factor of two andmultiplied by the non-prompt fraction f non-prompt to obtain the charged-averaged yields of non-prompt Dmesons. Furthermore, they were divided by the acceptance times efficiency of non-prompt D mesons ( Acc × ε ) non-prompt , the BR of the decay channel, the width of the p T interval ( ∆ p T ), the correction factorfor the rapidity coverage c ∆ y (see below), and the integrated luminosity L int = N ev / σ MB , where N ev √ s = .
02 TeV ALICE Collaboration − − − − −
10 1 e ff i c i en cy × A cc ep t an c e and charge conj. + π − K → D PromptNon-prompt
ALICE = 5.02 TeV s pp, ) c (GeV/ T p p r o m p t non - p r o m p t and charge conj. + π + π − K → + D PromptNon-prompt ) c (GeV/ T p and charge conj. + π − K + K → + πφ → +s D PromptNon-prompt ) c (GeV/ T p Figure 2:
Acceptance-times-efficiency factor for D , D + , and D + s mesons as a function of p T . The ( Acc × ε ) factors for non-prompt (blue) and prompt (red) D mesons are shown together with their ratio (bottom panels). is the number of analysed events and σ MB = ( . ± . ) mb is the cross section for the MB triggercondition [69].The ( Acc × ε ) correction was obtained from simulations, described in Section 2, using samples notemployed in the BDT training. The ( Acc × ε ) factors, computed for the selections used in the final result,as a function of p T for prompt and non-prompt D , D + , and D + s mesons within the fiducial acceptanceregion are shown in Fig. 2, along with the ratios of the non-prompt over prompt factors. The selectionapplied to obtain the non-prompt enhanced samples strongly suppresses the prompt D-meson efficiency,while the acceptance is the same between prompt and non-prompt D mesons. The prompt D-mesonacceptance times efficiency is smaller than the one of non-prompt D mesons by a factor varying from 5to 700, depending on the D-meson species and the p T interval. The difference between the ( Acc × ε ) factors of prompt and non-prompt mesons is less pronounced for D + than for D , due to the more similarlifetimes of D + and beauty hadrons. For D + s mesons, looser selections than those used for the other D-meson species were applied due to the lower yield of D + s mesons, leading to a smaller difference betweenthe ( Acc × ε ) factors of the prompt and non-prompt components.The correction factor for the rapidity acceptance c ∆ y was computed with the PYTHIA 8 event generator.It was defined as the ratio between the generated D-meson yield in ∆ y = y fid and that in | y | < . c ∆ y correction factor based on FONLLcalculations or on the assumption of uniform D-meson rapidity distributions in | y | < y fid give the sameresult. The f non-prompt fraction was calculated with a novel data-driven approach, which is described inSection 3.2. The fraction f non-prompt of non-prompt D mesons in the raw yield was estimated by sampling the rawyield at different values of the BDT output related to the candidate probability of being a non-promptD meson. In this way, a set of raw yields Y i with different contributions of prompt and non-prompt Dmesons was obtained. These raw yields can be related to the corrected yields of prompt ( N prompt ) andnon-prompt ( N non-prompt ) D mesons via the acceptance-times-efficiency factors as follows ( Acc × ε ) prompti × N prompt + ( Acc × ε ) non-prompti × N non-prompt − Y i = δ i . (2)In the above equation, δ i represents a residuum that accounts for the equation not holding exactly due tothe uncertainty on Y i , ( Acc × ε ) non-prompti , and ( Acc × ε ) prompti . The definition of n selections leads to the6on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaborationfollowing algebraic system ( Acc × ε ) prompt1 ( Acc × ε ) non-prompt1 ... ... ( Acc × ε ) prompt n ( Acc × ε ) non-prompt n × N prompt N non-prompt ! − Y ... Y n = δ ... δ n , (3)that can be exactly solved in case of two equations (assuming δ i = n selections, the N prompt and N non-prompt parameters are obtained by minimising the χ χ = δ T δ T δ T C − C − C − δδδ , (4)where δ T δ T δ T is the row vector of residuals and CCC the covariance matrix accounting for the uncertaintiesinherent to each equation. The variances σ were calculated from the statistical uncertainty on the rawyields and efficiencies as σ = σ Y i + N prompt × σ ( Acc × ε ) prompti + N non-prompt × σ ( Acc × ε ) non-prompti . (5)Given that the corrected yields are unknown variables, an iterative procedure was used to define the totaluncertainty: in the first step only the uncertainty on the raw yields was taken into account, while fromthe second iteration the corrected yields N prompt and N non-prompt obtained in the previous step were alsoused. In the covariance terms σ i , j the correlation coefficient was assumed to be ρ i , j = σ i σ j , with i ⊂ j . (6)This assumption is justified by the fact that the BDT response is sampled monotonically, so that the n selections are ordered in such a way that the i th selected sample is completely included in the ( i − ) th one.For D mesons, only the equation for the strictest set of selections was defined as in Eq. 2. All the otherswere expressed in terms of the difference between the ( i − ) th and the i th raw yields, ∆ Y i − , i = Y i − − Y i .In this case, the covariance terms were assumed to be zero, resulting in a diagonal covariance matrix.The fraction of non-prompt D mesons in the raw yield can be computed for any set of selections i fromthe corrected yields obtained from the χ minimisation as f inon-prompt = ( Acc × ε ) non-prompti × N non-prompt ( Acc × ε ) non-prompti × N non-prompt + ( Acc × ε ) prompti × N prompt . (7)Rather than from the N non-prompt parameter obtained from the minimisation of the χ in Eq. 4, the finalvalues of the non-prompt D-meson cross sections were determined by choosing a selection providing ahigh non-prompt component and a good signal extraction, as described in Section 3, and by calculatingits respective f non-prompt fraction according to Eq. 7. This approach facilitates the determination of thesystematic uncertainty.Figure 3 shows an example of raw-yield distribution as a function of the BDT-based selection employedin the minimisation procedure for D mesons with 1 < p T < / c (top left panel), D + mesonswith 8 < p T <
10 GeV / c (top right panel), and D + s mesons with 2 < p T < / c (bottom leftpanel). The leftmost data point of each distribution is the raw yield corresponding to the looser selectionon the BDT output related to the candidate’s probability of being a non-prompt D meson, while therightmost one corresponds to the strictest selection, which is expected to preferentially select non-promptD mesons. The prompt and non-prompt components, obtained for each BDT-based selection from theminimisation procedure as ( Acc × ε ) prompti N prompt and ( Acc × ε ) non-prompti N non-prompt , are represented bythe red and blue filled histograms, respectively, while their sum is reported by the green histograms. In7on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration
ML based selection R a w y i e l d c < 2 GeV/ T p Prompt D Non-prompt DTotal
ALICE = 5.02 TeV s pp, ML based selection R a w y i e l d c < 10 GeV/ T p + Prompt D + Non-prompt DTotal
ALICE = 5.02 TeV s pp, ML based selection R a w y i e l d c < 4 GeV/ T p +s Prompt D +s Non-prompt DTotal
ALICE = 5.02 TeV s pp, ) c (GeV/ T p non - p r o m p t f ALICE = 5.02 TeV s pp, D + D +s D Figure 3:
Examples of raw-yield distribution as a function of the BDT-based selection employed in the χ -minimisation procedure adopted for the determination of f non-prompt of D mesons (top left panel), D + mesons (topright panel), and D + s mesons (bottom left panel) for three different p T intervals. Bottom right panel, f non-prompt fraction as a function of p T obtained for the set of selection criteria adopted in the analysis of non-prompt Dmesons. the bottom right panel of Fig. 3, the f non-prompt fractions of D , D + , and D + s mesons, computed withthe formula in Eq. 7, corresponding to the samples enhanced with non-prompt candidates introduced inSection 3 are shown as a function of p T . The vertical bars represent the statistical uncertainty computedpropagating the uncertainties on the corrected yields obtained with the χ -minimisation procedure, wherethe correlation between N prompt and N non-prompt is also accounted for. The open boxes represent thesystematic uncertainty, which will be described in Section 4. The f non-prompt fractions range in the interval0 . − .
95 for D mesons, 0 . − .
75 for D + mesons, and 0 . − .
65 for D + s mesons. In general, the f non-prompt values decrease with p T , because at high p T a less stringent selection on the BDT probabilityof being non-prompt is needed to preserve a sufficient number of candidates to perform the invariant-mass analysis. D + and D + s mesons The measurement of prompt D + and D + s mesons follows the same procedure described in Section 3.1.The same machine-learning models trained for the non-prompt D + and D + s analysis were employed.8on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration ) c ) (GeV/ ππ (K M c C oun t s pe r M e V / ALICE = 5.02 TeV s pp, and charge conj. + π + π − K → + D c < 1 GeV/ T p ± = 114 S c
2) MeV/ ± = (1873 µ c
2) MeV/ ± = (6 σ ) c ) (GeV/ π (KK M c C oun t s pe r M e V / ALICE = 5.02 TeV s pp, and charge conj. + π − K + K → + πφ → +s D c < 2 GeV/ T p ± = 63 S c
2) MeV/ ± = (1972 µ c
2) MeV/ ± = (6 σ Figure 4:
Invariant-mass distributions of D + and D + s candidates and charge conjugates in the intervals 0 < p T < / c and 1 < p T < / c , respectively. The blue solid lines show the total fit functions as described in thetext and the red dashed lines are the combinatorial-background components. The values of the mean ( µ ) and thewidth ( σ ) of the signal peak are reported together with the raw yield ( S ). The reported uncertainties are only thestatistical uncertainties from the fit. Samples containing a small fraction of non-prompt candidates were obtained selecting on the BDToutputs and requiring a low candidate probability to be combinatorial background and non-prompt.The raw yields of D + and D + s mesons were extracted in the transverse-momentum intervals 0 < p T <
36 GeV / c and 1 < p T <
24 GeV / c , respectively, extending the measurement to lower p T with respect tothe previously published results [3]. The employed fit configurations were the same as for the non-promptanalysis, except that the widths of the D + - and D + s -meson signal peaks were unconstrained in the fit.Moreover, for D + mesons in 0 < p T < / c a third-order polynomial function was used to describethe combinatorial background, instead of an exponential function. Figure 4 shows the invariant-massdistributions, together with the result of the fits, in the 0 < p T < / c and 1 < p T < / c intervalsfor D + and D + s candidates, respectively. The statistical significance of the observed signals varies fromabout 3 to 40 for D + mesons and from 4 to 14 for D + s mesons, depending on the p T interval. The S / B values obtained are 0 . − . . − .
1) for D + (D + s ) mesons, depending on p T . The performanceof the adopted BDT-based selections was compared with that obtained in the previous study [3]. Animprovement of the statistical significance by a factor 1 . − . − .
7) for D + (D + s ) mesons in thecommon p T regions of the two measurements is observed, implying a reduction of statistical uncertaintiesby the same factor. Furthermore, the efficiency for prompt D + and D + s mesons is higher in the BDT-basedanalysis by a factor 1 . − . − .
2, respectively, depending on the p T interval.The data-driven method described in Section 3.2, which is based on the reliable extraction of raw yieldswith different fractions of prompt and non-prompt candidates, cannot be used for the estimation of the f prompt fraction in all the p T intervals of the prompt D + and D + s measurements, due to the limited size ofthe analysed data sample. Thus, the f prompt fraction was calculated similarly to previous measurements(see e.g. Refs. [4, 77]) using the beauty-hadron production cross sections from FONLL calculations, thebeauty hadron to D + X decay kinematics from the PYTHIA 8 decayer, and the measured acceptance-time-efficiency correction factors for non-prompt D + and D + s mesons. The values of f prompt rangebetween 0.86 and 0.96 depending on the D-meson species and p T interval. The procedure to estimate thesystematic uncertainty on f prompt will be described in Section 4. Figure 5 reports the D + - and D + s -meson f prompt fractions obtained with the FONLL-based approach compared with those resulting from the data-driven method, the latter were computed in the p T ranges of the non-prompt D + and D + s measurements9on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration ) c (GeV/ T p p r o m p t f ALICE = 5.02 TeV s pp, and charge conj. + π + π − K → + D Data-driven methodFONLL-based method ) c (GeV/ T p p r o m p t f ALICE = 5.02 TeV s pp, and charge conj. + π − K + K → + πφ → +s D Data-driven methodFONLL-based method
Figure 5:
Comparison of the fractions of prompt D + - and D + s -meson raw yields as a function of p T betweenthe FONLL-based and the data-driven approach. The results from the data-driven method are shown as diamondmarkers with the error bars (boxes) representing the statistical (systematic) uncertainty. The central values of f prompt from the FONLL-based approach are shown by the continuous line and their uncertainty by the shadedboxes. where a good reliability of the method can be granted. The fractions of prompt D-meson yields estimatedwith the two different strategies are well in agreement within the statistical and systematic uncertaintiesin the common p T intervals. The systematic uncertainties on the measurement of prompt and non-prompt D-meson cross sectionswere estimated with procedures similar to those described in Refs. [3, 77, 78], including the followingsources: (i) extraction of the raw yield from the invariant-mass distributions; (ii) non-prompt and promptfraction estimations; (iii) track reconstruction efficiency; (iv) D-meson selection efficiency; (v) PIDefficiency; (vi) generated D-meson p T shape in the simulation. In addition, an overall normalisationsystematic uncertainty induced by the branching ratios of the considered D-meson decays [74] and theintegrated luminosity [69] were considered. The estimated values of the systematic uncertainties forsome representative p T intervals of the different analyses are summarised in Table 1. The contributionsof the different sources were summed in quadrature to obtain the total systematic uncertainty. For non-prompt D mesons, the systematic uncertainties on the non-prompt fraction estimation and the raw-yieldextraction were treated as correlated and summed linearly.The systematic uncertainty on the raw-yield extraction was evaluated by repeating the fit of the invariant-mass distribution varying the lower and upper limits of the fit range and the functional form of thebackground fit function. In order to test the sensitivity to the line-shape of the signal, a bin-countingmethod was used, in which the signal yield was obtained by integrating the invariant-mass distributionafter subtracting the background estimated from the side-band fit. In addition, for the analysis of non-prompt D mesons the width of the Gaussian function used to model the signal peaks was varied withinthe uncertainty of the value obtained from the fits to the prompt-enhanced sample. The effect was foundto be negligible, hence no additional systematic uncertainty was assigned. For non-prompt D mesons,an additional contribution due to the description of signal reflections in the invariant-mass distributionwas estimated by varying the shape and the normalisation of the templates used for the reflections in theinvariant-mass fits. The systematic uncertainty was defined as the RMS of the distribution of the signal10on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration
Table 1:
Summary of the relative systematic uncertainties on non-prompt D , D + , and D + s cross sections andprompt D + and D + s cross sections in different p T intervals. Meson non-prompt D non-prompt D + non-prompt D + s prompt D + prompt D + s p T ( GeV / c ) − −
12 2 − −
12 2 − −
12 0 − −
12 1 − − p T shape in MC 1% 0 1% 1% 1% 1% 7% 0 1% 0Fraction estimation 3% 5% 2% 5% 2% 4% + − % + − % + − % + − %Branching ratio 1% 2% 4% 2% 4%Luminosity 2% yields obtained from all these variations and ranges from 1% to 11% depending on the D-meson speciesand the p T interval.The systematic uncertainty on the value of f non-prompt obtained with the data-driven approach wasestimated by changing the sets of selection criteria used for the procedure described in Section 3.2.A systematic uncertainty ranging from 2% to 10% was assigned. This source of systematic uncertaintywas found to be mostly correlated with the signal extraction procedure. The correlation was evaluated byrepeating the computation of f non-prompt varying the fit configurations used for the raw-yield extraction,as described above. For the analysis of prompt D + and D + s mesons, the systematic uncertainty on f prompt was estimated by varying the FONLL parameters (b-quark mass, factorisation, and renormalisationscales) as prescribed in [79]. It ranges between + − % and + − % depending on the D-meson species and p T interval.The systematic uncertainty on the track reconstruction efficiency was evaluated by varying the track-quality selection criteria and by comparing the prolongation probability of the TPC tracks to the ITShits in data and simulation. The comparison of the ITS-TPC prolongation efficiency in data andsimulations was performed after weighting the relative abundances of primary and secondary particlesin the simulation to match those observed in data, which were estimated via fits to the inclusive trackimpact-parameter distributions [80]. The estimated uncertainty depends on the D-meson p T and rangesfrom 3% to 5% for the two-body decay of D mesons and from 4% to 7% for the three-body decays ofD + and D + s mesons.The systematic uncertainty on the selection efficiency originates from imperfections in the description ofthe detector resolutions and alignments in the simulation. It was estimated by comparing the correctedyields obtained by repeating the analysis with different machine-learning selection criteria, i.e. varyingthe selections on the BDT outputs, resulting in a significant modification of the efficiencies, raw yieldand background values. The assigned systematic uncertainty ranges from 2% to 10%.To estimate the uncertainty on the PID selection efficiency, the pion and kaon PID selection efficiencieswere compared in data and in simulations. For this study, a pure sample of pions was selected from K S and Λ decays, while samples of kaons in the TPC (TOF) were obtained applying a strict PID selectionusing the TOF (TPC) information. Since no significant differences were observed, no systematicuncertainty was assigned. As an additional test, the analysis was repeated without PID selection. Theresulting D-meson cross sections were found to be compatible with those obtained with the PID selection.The systematic effect on the efficiency due to a possible difference between the real and simulated D-meson transverse-momentum distributions was estimated by evaluating the efficiency after reweighting11on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration ) c (GeV/ T p − − −
10 110 ) c − b G e V µ ) ( y d T p / ( d σ d ALICE = 5.02 TeV s pp, | < 0.5 y | ± BR syst. unc. not shown
Non-prompt D + D +s D Prompt D + D +s D ) c (GeV/ T p ( p r o m p t ) y d T p / d σ ( non - p r o m p t ) / d y d T p / d σ d ALICE = 5.02 TeV s pp, | < 0.5 y | D + D +s D Figure 6:
Left: p T -differential production cross sections of prompt and non-prompt D , D + , and D + s mesons inpp collisions at √ s = .
02 TeV. The measurement of prompt D mesons is the one reported in Ref. [3], withupdated decay BR as discussed in the text. Right: ratios of p T -differential production cross sections of non-promptand prompt D , D + , and D + s mesons. Statistical (vertical bars) and systematic uncertainties (boxes) are shown.The symbols are positioned horizontally at the centre of each p T interval, with the horizontal bars representing thewidth of the p T interval. the p T shape from the PYTHIA 8 generator to match the one from FONLL calculations. The weightswere applied to the p T distributions of prompt D mesons and to the decaying beauty hadrons in case ofnon-prompt D mesons. The assigned uncertainty is 7% in the p T interval 0 − / c of the prompt D + meson, where the selection criteria are strict, while for other p T intervals the uncertainty is less than 1%. The p T -differential production cross sections of prompt and non-prompt D , D + , and D + s mesonsmeasured in | y | < . p T -differential cross sections ofprompt D + and D + s mesons are compatible within uncertainties with the previous results [3], but haveextended p T coverage and total uncertainties reduced by a factor ranging from 1.05 to 1.6 dependingon p T and D-meson species due to the improved analysis technique described in Section 3.3. Themeasurement of prompt D mesons is the one reported previously in Ref. [3], scaled for the updatedBR = ( . ± . ) % of the D → K − π + decay reported in Ref. [74].The right panel of Fig. 6 shows the ratios of the p T -differential cross sections of non-prompt and promptD mesons. The statistical uncertainties assigned to each ratio were computed considering that those ofthe prompt and non-prompt measurements are uncorrelated. This assumption is valid since the fractionof D-meson candidates shared by the two samples is small. The systematic uncertainty related to thedetermination of the tracking efficiency and to the luminosity were propagated as correlated in theratios, while all the other sources of systematic uncertainties were considered as uncorrelated betweenthe measurements of prompt and non-prompt D mesons. The ratio increases with increasing p T for12on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration
Table 2:
Fragmentation fractions of b-quarks into beauty-hadron species in Z → bb decays, and in pp collisions at √ s = .
96 TeV [74]. b-hadron Fraction at Z (%) Fraction at pp (%)B , B + . ± . . ± . . ± . . ± . Λ . ± . . ± . p T =
12 GeV / c , as expected due to the harder p T distribution ofbeauty hadrons (H b ) compared to D mesons. The ratios for D + and D mesons are compatible withinuncertainties, while for the D + s meson the central points are systematically higher compared to the othertwo D-meson species, suggesting a larger contribution of beauty-hadron decays to D + s compared to non-strange D mesons, although no firm conclusion can be drawn given the current uncertainties.The p T -differential cross sections of prompt and non-prompt D mesons are compared to predictionsobtained with FONLL [56, 57, 79] and GM-VFNS [60, 61, 63] pQCD calculations in Fig. 7 andFig. 8, respectively. The FONLL uncertainty band includes the uncertainties due to the choice of therenormalisation ( µ R ) and factorisation ( µ F ) scales and of the c and b quark masses, as well as theuncertainties on the CTEQ6.6 PDFs [81]. In GM-VFNS, the uncertainty related to the choice of thescales is estimated by varying only µ R and the CTEQ14 PDFs [82] are employed. Within the FONLLframework, the fragmentation fractions f ( c → D ) from Ref. [83] were used to normalise the prompt D -and D + -meson cross sections, while a calculation of the prompt D + s -meson production cross section is notavailable. For non-prompt D mesons, FONLL calculations were used to compute the beauty-hadron crosssection, while PYTHIA 8 [70, 71] was used for the description of H b → D + X decay kinematics andbranching ratios. The contributions from the different beauty-hadron species were weighted according tofragmentation fractions of b quarks into b-hadron species f ( b → H b ) measured in the Z → bb decays [74]reported in Table 2, which provide a good normalisation for B-meson measurements performed by theATLAS, CMS, and LHCb Collaborations [19, 36, 84]. A different approach is instead used in the GM-VFNS framework, where the transition from the beauty quark to the charm hadron is described in a singlestep, exploiting a set of FFs for b → D + X obtained from measurements in e + e − collisions as describedin Refs. [85, 86].The measured p T -differential cross sections of prompt D , D + , and D + s mesons are described withinuncertainties by the FONLL and GM-VFNS predictions. In the case of FONLL, the data lie on theupper edge of the theory uncertainty band, while for the GM-VFNS calculation, the central values of thepredictions tend to underestimate the data at low and intermediate p T and to overestimate them at high p T .The measured non-prompt D-meson cross sections are instead in better agreement with the central valuesof the FONLL+PYTHIA 8 predictions, while they are underestimated by a factor ranging between 2 and10 depending on p T by the GM-VFNS calculations. However, a better description of the data would beobtained in the GM-VFNS framework using the b-quark cross section from the pQCD calculation alongwith the two-step approach for the b → D + X transition described in Ref [63] and consisting in separatesteps for the b → H b fragmentation and the H b → D + X decay kinematics, similarly to what performedin the FONLL+PYTHIA8 calculation. This confirms that all the different terms of the factorisationapproach play a crucial role in the description of the heavy-flavour hadron cross sections, indicating theimportance of setting stronger constraints on the fragmentation and decay kinematics.The visible cross sections of prompt and non-prompt D mesons were computed by integrating themeasured p T -differential cross sections in the measured p T range. The results are reported in Table 3,where the prompt D -meson cross section is the same as in Ref. [3], scaled for the updated BR of theD → K − π + decay channel reported in Ref. [74]. In the integration of the p T -differential cross sections,13on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration − − −
10 110 ) c − b G e V µ )( y d T p / ( d σ d Prompt DDataFONLL Non-prompt DDataFONLL + PYTHIA8 Decayer
ALICE = 5.02 TeV s pp, | < 0.5 y | ± ± ) c (GeV/ T p m ode l da t a ) c (GeV/ T p m ode l da t a − − −
10 110 ) c − b G e V µ )( y d T p / ( d σ d + Prompt DDataFONLL + Non-prompt DDataFONLL + PYTHIA8 Decayer
ALICE = 5.02 TeV s pp, | < 0.5 y | ± ± ) c (GeV/ T p m ode l da t a ) c (GeV/ T p m ode l da t a − − −
10 110 ) c − b G e V µ )( y d T p / ( d σ d +s Prompt DData +s Non-prompt DDataFONLL + PYTHIA8 Decayer
ALICE = 5.02 TeV s pp, | < 0.5 y | ± ± ) c (GeV/ T p m ode l da t a Figure 7: p T -differential production cross sections of prompt and non-prompt D (top left panel), D + (top rightpanel), and D + s (bottom panel) mesons compared to predictions obtained with FONLL calculations [56, 57]combined with PYTHIA 8 [70, 71] for the H b → D + X decay kinematics. The measurement of prompt D mesonsis the one reported in Ref. [3], with updated decay BR as discussed in the text. the systematic uncertainties were propagated as fully correlated among the measured p T intervals, exceptfor the raw-yield extraction uncertainty, which was treated as uncorrelated considering the variations ofthe signal-to-background ratio and the shape of the combinatorial-background distribution as a functionof p T . The p T -integrated production cross sections in | y | < . √ s = .
02 TeV ALICE Collaboration − − −
10 110 ) c - b G e V µ ) ( y d T p / ( d σ d Prompt DDataGM-VFNS Non-prompt DDataGM-VFNS
ALICE = 5.02 TeV s pp, | < 0.5 y | ± ± ) c (GeV/ T p m ode l da t a ) c (GeV/ T p m ode l da t a − − −
10 110 ) c - b G e V µ ) ( y d T p / ( d σ d + Prompt DDataGM-VFNS + Non-prompt DDataGM-VFNS
ALICE = 5.02 TeV s pp, | < 0.5 y | ± ± ) c (GeV/ T p m ode l da t a ) c (GeV/ T p m ode l da t a − − −
10 110 ) c - b G e V µ ) ( y d T p / ( d σ d +s Prompt DDataGM-VFNS +s Non-prompt DDataGM-VFNS
ALICE = 5.02 TeV s pp, | < 0.5 y | ± ± ) c (GeV/ T p m ode l da t a ) c (GeV/ T p m ode l da t a Figure 8: p T -differential production cross sections of prompt and non-prompt D (top left panel), D + (top rightpanel), and D + s (bottom panel) mesons compared to predictions obtained with GM-VFNS calculations [60, 61, 63].The measurement of prompt D mesons is the one reported in Ref. [3], with updated decay BR as discussed in thetext. cross sections by an extrapolation factor calculated as follows. For prompt D mesons, the extrapolationfactor for each D-meson species was computed using the FONLL central predictions to evaluate theratio between the production cross section in | y | < . p T interval. Thesystematic uncertainties on the extrapolation factor were estimated by considering (i) the variation of15on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration
Table 3: p T -integrated production cross sections in the measured p T range for prompt and non-prompt D mesonsin the range | y | < . √ s = .
02 TeV.
Meson Kinematic range ( GeV / c ) Visible cross section ( µ b)PromptD < p T <
36 440 ± ( stat ) ± ( syst ) ± ( lumi ) ± ( BR ) D + < p T <
36 195 ± ( stat ) ± ( syst ) ± ( lumi ) ± ( BR ) D + s < p T <
24 64 ± ( stat ) + − ( syst ) ± ( lumi ) ± ( BR ) Non-promptD < p T <
24 14 . ± . ( stat ) ± . ( syst ) ± . ( lumi ) ± . ( BR ) D + < p T <
16 4 . ± . ( stat ) ± . ( syst ) ± . ( lumi ) ± . ( BR ) D + s < p T <
12 3 . ± . ( stat ) ± . ( syst ) ± . ( lumi ) ± . ( BR ) the factorisation and renormalisation scales in the FONLL calculation, (ii) the uncertainty on the massof the charm quark, and (iii) the CTEQ6.6 PDFs uncertainties, as proposed in Ref. [79]. Since FONLLpredictions are not available for prompt D + s mesons, the central value of the extrapolation factor wascomputed as described in Ref. [3], using the prediction based on the p T -differential cross section ofcharm quarks from FONLL, the fragmentation fractions f ( c → D + s ) and f ( c → D ∗ + s ) from ALEPHmeasurements [87], and the charm fragmentation functions from Ref. [88]. The measurements of D and D + mesons extend from p T = p T =
36 GeV / c , leading to an extrapolation factor close tounity and a negligible associated uncertainty. In the case of non-prompt D mesons, the extrapolationfactor was evaluated using the FONLL predictions for the beauty-hadron production and PYTHIA 8 todescribe the H b → D + X decay kinematics. Besides the uncertainties of FONLL, for the non-promptD-meson extrapolation factors two additional sources of systematic uncertainties were considered, i.e.the uncertainty on (i) the beauty fragmentation fractions f ( b → H b ) and (ii) the branching ratios of theH b → D + X decays. The former was estimated considering an alternative set of beauty fragmentationfractions measured in pp collisions [74] reported in Table 2, while for the latter the branching ratiosimplemented in PYTHIA 8 were reweighted in order to reproduce the measured values reported inRef. [74]. In addition, it was verified that the extrapolation factors computed with the PYTHIA 8 decayerwere compatible with those resulting from the usage of the EvtGen package [89] for the description of thebeauty-hadron decays. The production cross sections for prompt and non-prompt D mesons in | y | < . + s and D + mesons are compatible with thosereported in Ref. [3], but their total uncertainties are reduced, owing to the improved precision of the p T -differential measurements and the extended p T range, which implies a smaller fraction of extrapolatedcross section. The p T -integrated cross sections were used to compute the ratios of production yields among the differentD-meson species reported in Table 5. In the computation of these ratios, the systematic uncertaintiesrelated to the tracking efficiency, luminosity, and, for the prompt D mesons, the contribution due tothe subtraction of the component from beauty-hadron decays, were considered as correlated among thedifferent D-meson species. The extrapolation uncertainties were also treated as correlated, except for thesource of uncertainty due to the branching ratios of the beauty-hadron decays used in the extrapolation ofthe p T -integrated cross section of non-prompt D mesons. All the other sources of systematic uncertaintieswere propagated as uncorrelated. The D + / D ratio is compatible between prompt and non-prompt D-meson production, while for the D + s over non-strange D meson ratios, the measured values are higher16on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration
Table 4:
Production cross sections of prompt and non-prompt D mesons in the range | y | < . √ s = .
02 TeV.
Meson Extr. factor to p T > σ / d y | | y | < . ( µ b)PromptD . + . − . ± ( stat ) ± ( syst ) ± ( lumi ) ± ( BR ) D + . + . − . ± ( stat ) ± ( syst ) ± ( lumi ) ± ( BR ) D + s . + . − . ± ( stat ) ± ( syst ) ± ( lumi ) ± ( BR ) + − ( extr ) Non-promptD . + . − . . ± . ( stat ) ± . ( syst ) ± . ( lumi ) ± . ( BR ) + . − . ( extr ) D + . + . − . . ± . ( stat ) ± . ( syst ) ± . ( lumi ) ± . ( BR ) + . − . ( extr ) D + s . + . − . . ± . ( stat ) ± . ( syst ) ± . ( lumi ) ± . ( BR ) + . − . ( extr ) Table 5:
Ratios of the measured production cross sections of prompt and non-prompt D mesons in the range | y | < . √ s = .
02 TeV.
PromptD + / D . ± . ( stat ) ± . ( syst ) ± . ( BR ) D + s / D . ± . ( stat ) ± . ( syst ) ± . ( BR ) + . − . ( extr ) D + s / D + . ± . ( stat ) ± . ( syst ) ± . ( BR ) + . − . ( extr ) D + s / ( D + D + ) . ± . ( stat ) ± . ( syst ) ± . ( BR ) + . − . ( extr ) Non-promptD + / D . ± . ( stat ) ± . ( syst ) ± . ( BR ) + . − . ( extr ) D + s / D . ± . ( stat ) ± . ( syst ) ± . ( BR ) + . − . ( extr ) D + s / D + . ± . ( stat ) ± . ( syst ) ± . ( BR ) + . − . ( extr ) D + s / ( D + D + ) . ± . ( stat ) ± . ( syst ) ± . ( BR ) + . − . ( extr ) for non-prompt D mesons than for prompt D mesons with a significance of about 2 . σ . This finding isconsistent with previous measurements at LEP [83].A possible p T dependence was investigated computing the p T -differential ratios. The ratios betweenthe p T -differential production cross sections of D + and D mesons and the ratios between the one ofD + s mesons and the sum of the D and D + mesons are reported in the left and right panels of Fig. 9,respectively. The measured ratios are independent of p T in the measured p T range within the currentexperimental precision. They are also compatible with the FONLL predictions in the case of promptD and D + mesons and FONLL+PYTHIA 8 in the case of non-prompt D mesons. In the right panelof Fig. 9, the contributions of D + s from B and non-strange B meson decays in the FONLL+PYTHIA 8calculation are depicted separately to highlight the substantial contribution of non-prompt D + s mesonsfrom the decay of non-strange B mesons.The prompt D + s / ( D + D + ) ratio represents the fragmentation fraction of charm quarks to charm-strangemesons f s divided by the one to non-strange charm mesons f u + f d , given that all D ∗ + and D ∗ mesons17on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration ) c (GeV/ T p / D + D PromptDataFONLL Non-promptDataFONLL + PYTHIA8 Dec.
ALICE = 5.02 TeV s pp, | < 0.5 y | ± ) c (GeV/ T p ) + + D / ( D + s D PromptData Non-promptDataFONLL + PYTHIA8 Dec. Λ + +B + +B B ← +s D + +B B ← +s D B ← +s D ALICE = 5.02 TeV s pp, | < 0.5 y | Figure 9:
Ratios between the p T -differential production cross sections of D + and D mesons (left panel) andbetween the one of D + s mesons and the sum of the D - and D + -meson cross sections (right panel) comparedwith predictions obtained with FONLL calculations [56, 57] and PYTHIA 8 [70, 71] for the H b → D + X decaykinematics. For the non-prompt D + s / ( D + D + ) ratio, the predictions for the D + s from B and from non-strange Bmeson decays are also displayed separately. decay to D and D + mesons, and all D ∗ + s mesons decay to D + s mesons. Considering that the uncertaintiesin the production ratios reported in Table 5 are dominated by the limited precision of the measurementsin the low p T region and that the p T -differential ratios are constant within uncertainties, the ratio ofcharm-quark fragmentation fractions was computed by fitting the data with a constant function, leadingto (cid:18) f s f u + f d (cid:19) charm = . ± . ( stat ) ± . ( syst ) ± . ( BR ) . (8)In addition to the degree of correlation among the D-meson species considered for the computation ofthe p T -differential ratios, all the sources of systematic uncertainties except for the one related to the raw-yield extraction were propagated as fully correlated among the different p T intervals. A similar strategywas adopted by the LHCb Collaboration for the beauty sector in Ref. [37].In Fig. 10, the charm-quark fragmentation-fraction ratio f s / ( f u + f d ) is compared with previous measure-ments of strangeness suppression factor γ s from the ALICE [5], H1 [90], ZEUS [91], and ATLAS [18]Collaborations. They were divided by a factor two to account for the difference between γ s and the ratioof fragmentation fractions f s / ( f u + f d ) . The theoretical uncertainties in case of the H1 result includethe branching ratio uncertainty and the model dependencies of the acceptance determination, while forthe ATLAS result the extrapolation uncertainties to the full phase space are included. All the values arecompatible within uncertainties and with the average of measurements at LEP [83]. The experimentalpoints are also compared to the value obtained from PYTHIA 8 simulations with Monash-13 tune [72]and found to be compatible with it within the uncertainties, even if a tension of about 2.7 standard devi-ations (including both statistical and systematic uncertainties) is observed for the result presented in thispaper.A similar procedure was followed to obtain the fragmentation fraction of beauty quarks to beauty-strange mesons divided by the one to non-strange beauty mesons, starting from the measured non-promptD + s / ( D + D + ) ratio. In the case of non-prompt D mesons, an additional correction factor was necessaryto account for the fraction of non-prompt D + s mesons not originating from B decays and that of non-18on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration ) d f + u f /( s f charm = 5.02 TeV s ALICE, pp = 7 TeV s ALICE, pp = 7 TeV s , pp s/d γ× ATLAS 0.5 s γ× p 0.5 γ ZEUS s γ× H1 ep 0.5 Z m = s , − e + LEP e
PYTHIA8 > 0 T p c (D) > 2.5 GeV/ T p (D) > 0 T p c (D) > 3.8 GeV/ T p (D) > 0 T p constant fit T p , c (D) > 1 GeV/ T p average theory sys Figure 10:
Charm-quark fragmentation-fraction ratio f s / ( f u + f d ) compared with previous measurements per-formed by the ALICE [5], H1 [90], ZEUS [91], and ATLAS [18] Collaborations and to the average of LEPmeasurements [83]. The total experimental uncertainties (bars) and the theoretical uncertainties (shaded boxes)are shown. The experimental measurements are compared to the value obtained from PYTHIA 8 simulations withMonash-13 tune [72]. prompt D and D + mesons not originating from non-strange B-meson decays. This correction factorwas computed from FONLL+PYTHIA 8 and a systematic uncertainty was assigned by varying the setof beauty fragmentation fractions and the beauty-hadron branching ratios, as described in Section 5.1.In the case of D + s mesons, B and non-strange B mesons are expected to contribute almost equally tothe non-prompt D + s cross section as shown in the right panel of Fig. 9, while most of the non-promptD and D + mesons come from non-strange B-meson decays. The p T -differential ratio of beauty-quarkfragmentation fractions was then computed as (cid:18) f s f u + f d (cid:19) beauty = (cid:20) N ( D + s ← B ) N ( D + s ← H b ) × N ( D , D + ← H b ) N ( D , D + ← B , + ) (cid:21) FONLL + PYTHIA 8 × (cid:18) D + s D + D + (cid:19) non − prompt , (9)and fitted with a constant function, as done for the prompt D mesons. The result is (cid:18) f s f u + f d (cid:19) beauty = . ± . ( stat ) ± . ( syst ) ± . ( BR ) ± . ( th ) , (10)where the theoretical uncertainty arises from the correction factor in Eq. 9 for the fractions of D + s (D and D + ) mesons originating from B (B , + )-meson decays.The beauty-quark fragmentation-fraction ratio f s / ( f u + f d ) is compared with previous measurementsfrom CDF [92], LHCb [37, 44], and ATLAS [20] Collaborations in Fig. 11. The ATLAS measurementwas divided by a factor two assuming isospin symmetry for the u and d quarks, which implies f u = f d . Allthe f s / ( f u + f d ) values measured in pp and pp collisions are found to be compatible with the LEP average,computed by the HFLAV Collaboration [93] and the value obtained from PYTHIA 8 simulations withMonash-13 tune [72]. It is also interesting to note that the fragmentation-fraction ratios f s / ( f u + f d ) aresimilar for the charm and beauty sectors and are consistent with the ratio of light strange to non-strangeparticle production in pp and e + e − collisions [94]. 19on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration ) d f + u f /( s f beauty = 5.02 TeV s ALICE, pp = 13 TeV s LHCb, pp = 7 TeV s LHCb, pp = 7 TeV s , pp d f / s f × ATLAS 0.5 = 1.96 TeV s pCDF, p Z m = s , d f / s f × − e + LEP e c (B) > 7 GeV/ T p c (B) > 8 GeV/ T p constant fit T p (B) > 0, T p c (B) > 4 GeV/ T p constant fit T p , c (D) > 2 GeV/ T p HFLAV average
PYTHIA8 > 0 T p theory sys Figure 11:
Beauty-quark fragmentation-fraction ratio f s / ( f u + f d ) from non-prompt D-meson measurements com-pared with previous measurements performed by the CDF [92], LHCb [37, 44], and ATLAS [20] Collaborationsand to the average of LEP measurements [93]. The total experimental uncertainties (bars) and the theoretical un-certainties (shaded boxes) are shown. The experimental measurements are compared to the value obtained fromPYTHIA 8 simulations with Monash-13 tune [72]. bbbbbb production cross section The bb production cross section per unit of rapidity at midrapidity ( | y | < .
5) was computed following asimilar procedure as the one adopted to derive the p T -integrated production cross sections of non-promptD mesons. In this case, the extrapolation factor α bbextr was computed as α bbextr = d σ bb / d y | FONLL | y | < . σ FONLL + PYTHIA 8b → D ( p minT < p T < p maxT , | y | < . ) , (11)where d σ bb / d y | FONLL | y | < . is the bb production cross section obtained with FONLL calculations with acorrection for the different shapes of the rapidity distributions of beauty hadrons and bb pairs, and σ FONLL + PYTHIA 8b → D ( p minT < p T < p maxT , | y | < . ) is the non-prompt D meson cross section in the measuredphase space from the FONLL+PYTHIA 8 model. The correction for the bb rapidity distribution iscomposed of two factors. The first factor accounts for the different rapidity distributions of beautymesons and single beauty quarks and it was evaluated to be unity in the relevant rapidity range basedon FONLL calculations. A 1% uncertainty on this factor was evaluated from the difference betweenvalues from FONLL and PYTHIA 8. The second correction factor is the ratio ( d σ bb / d y ) / ( d σ b / d y ) ,which was estimated from NLO pQCD calculations (POWHEG [95]) as d σ | y | < . / d σ | y | < . = .
06. A1% uncertainty on this factor was estimated from the difference among the values obtained varying thefactorisation and renormalisation scales in the POWHEG calculation and using different sets of PDFs(CT10NLO [96] and CT14NLO [82]). The other sources of systematic uncertainty on the extrapolationfactor, i.e. FONLL, BR(H b → D + X), and f ( b → H b ) , are the same as those described in Section 5.1 forthe extrapolation of the p T -integrated production cross sections of non-prompt D meson.The d σ bb / d y was computed separately for each D-meson species and the three values were then averagedusing the inverse of the quadratic sum of the absolute statistical and uncorrelated systematic uncertainties20on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration b) µ ( =0 y | y /d bb σ d |<0.5 y D average | → b |<0.5 y | +s D → b |<0.5 y | + D → b |<0.5 y | D → b |<0.8 POWHEG e η Dielectron | |<0.8 PYTHA6 e η Dielectron |
ALICE = 5.02 TeVspp, FONLLNNLOdata sysextrap sys
Figure 12:
Estimates of d σ bb / d y at midrapidity from dielectron [97] and non-prompt D , D + , and D + s mesonmeasured in pp collisions at √ s = .
02 TeV compared to FONLL [56, 57, 79] and NNLO [65] predictions. Theaverage d σ bb / d y of the estimates from the single D-meson species is also reported. as weights. The systematic uncertainties related to the tracking uncertainty and the extrapolationuncertainties related to FONLL and the beauty fragmentation fractions were treated as fully correlatedamong the three D-meson species, while all the other sources as uncorrelated. The resulting bb crosssection at midrapidity isd σ bb d y (cid:12)(cid:12)(cid:12)(cid:12) | y | < . = . ± . ( stat ) ± . ( syst ) ± . ( lumi ) ± . ( BR ) + . − . ( extr ) ± . ( rap . shape ) µ b . (12)Figure 12 shows the extrapolated d σ bb / d y from each D-meson species and their average, compared tothose obtained from dielectron [97] along with a comparison to FONLL and NNLO calculations. Thevalues extracted from the three D-meson species are compatible within uncertainties among each otherand with those obtained from the other two ALICE measurements, as well as with the FONLL andNNLO predictions. As compared to FONLL calculations, the inclusion of NNLO corrections leads toa slightly larger central value, more in agreement with the experimental result based on non-prompt Dmesons, and to reduced theoretical uncertainties. The measurements in pp collisions at √ s = .
02 TeVare also shown in Fig. 13 along with the other existing measurements in pp collisions by the ALICE[10–13] and PHENIX [48] Collaborations at different centre-of-mass energies, and in pp collisions bythe CDF [53] and UA1 [51] Collaborations. The experimental results are found to be compatible withFONLL and NNLO calculations.
The p T -differential cross sections of prompt and non-prompt D , D + , and D + s mesons were measuredat midrapidity ( | y | < .
5) in pp collisions at √ s = .
02 TeV using a machine-learning technique basedon Boosted Decision Trees. A data-driven method was employed for the evaluation of the fractionof non-prompt D mesons, f non-prompt , and for the validation of the FONLL-based method adopted inthe measurement of prompt D mesons. In comparison to previously published results based on the21on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaboration − − × (TeV) s −
10 110 b ) µ ( = y | y / d bb σ d |<1.5 y PHENIX pp, ||<1.5 y , |pUA1 p |<0.6 y , |pCDF p ALICE pp |<0.5 y D | → b |<0.8 e η dielectron ||<0.9 y | ψ J/ → b |<0.8 y e | → b fit with PYTHIA6fit with POWHEG FONLLNNLO
Figure 13:
Beauty production cross section per rapidity unit at midrapidity as a function of √ s as measured inpp collisions by the ALICE [10–13] and PHENIX [48] Collaborations and in pp collisions by the CDF [53] andUA1 [51] Collaborations. The ALICE data points are shifted in the √ s -axis for better visibility. The solid anddashed lines with the shaded band represents the FONLL [56, 57, 79] and NNLO [65] calculations with theiruncertainties, respectively. same data sample [3], the cross sections of prompt D + and D + s mesons have total uncertainties reducedby a factor ranging from 1.05 to 1.60 and cover an extended transverse-momentum range, down to p T = p T = / c for D + and D + s mesons, respectively. The measurements of non-promptmesons were performed in the interval 1 < p T <
24 GeV / c for D mesons, 2 < p T <
16 GeV / c forD + mesons, and 2 < p T <
12 GeV / c for D + s mesons. The measured p T -differential cross sections arecompatible with FONLL calculations in the full p T range of the measurements. For prompt D mesons,the measured values lie on the upper edge of the FONLL uncertainty band, while the measured non-prompt D-meson cross sections are in better agreement with the central value of the predictions obtainedusing the beauty-hadron cross section from FONLL calculations and the H b → D + X decay kinematicsfrom the PYTHIA 8 decayer. The GM-VFNS calculations also describe the measured prompt D-mesoncross sections, while they underestimate by a factor ranging between 2 and 10 depending on p T thenon-prompt D-meson cross sections. This deviation could be caused by the modelling of the b → D + Xtransition with a single step rather than as a two-step process in which the b → H b fragmentation andthe H b → D + X decay kinematics are factorised. As discussed in Ref [63], the latter approach provideslarger cross sections. Therefore, this does not invalidate the GM-VFNS calculation of the cross sectionof the partonic process, nor the validity of the collinear factorisation, but it confirms the importance ofproperly modelling the fragmentation process and the decay kinematics.The ratios of production cross sections as well as the fragmentation fraction to strange mesons dividedby the one to non-strange mesons for charm quarks, (cid:18) f s f u + f d (cid:19) charm = . ± . ( stat ) ± . ( tot . syst ) , √ s = .
02 TeV ALICE Collaborationand beauty quarks, (cid:18) f s f u + f d (cid:19) beauty = . ± . ( stat ) ± . ( tot . syst ) , are compatible with previous measurements by other experiments for different centre-of-mass energiesand colliding systems.The bb production cross section at midrapidity per unit of rapidity in pp collisions at √ s = .
02 TeV wasestimated from the measured production cross sections of non-prompt D , D + , and D + s mesons usingthe predictions based on FONLL calculations for the beauty-hadron cross section and the PYTHIA 8decayer for the description of the H b → D + X decay kinematics. The extrapolated d σ bb / d y from eachD-meson species are compatible among each other and with previous ALICE measurements based ondielectrons [97], and with FONLL and NNLO calculations. The d σ bb / d y determined from the averageof the three D-meson species isd σ bb d y (cid:12)(cid:12)(cid:12)(cid:12) | y | < . = . ± . ( stat ) + . − . ( tot . syst ) µ b . The measurements presented in this paper provide an important test for pQCD calculations in the charmand beauty sectors and a precise reference for studies in heavy-ion collisions.
Acknowledgements
The ALICE Collaboration would like to thank all its engineers and technicians for their invaluable con-tributions to the construction of the experiment and the CERN accelerator teams for the outstandingperformance of the LHC complex. The ALICE Collaboration gratefully acknowledges the resources andsupport provided by all Grid centres and the Worldwide LHC Computing Grid (WLCG) collaboration.The ALICE Collaboration acknowledges the following funding agencies for their support in buildingand running the ALICE detector: A. I. Alikhanyan National Science Laboratory (Yerevan Physics In-stitute) Foundation (ANSL), State Committee of Science and World Federation of Scientists (WFS),Armenia; Austrian Academy of Sciences, Austrian Science Fund (FWF): [M 2467-N36] and National-stiftung für Forschung, Technologie und Entwicklung, Austria; Ministry of Communications and HighTechnologies, National Nuclear Research Center, Azerbaijan; Conselho Nacional de DesenvolvimentoCientífico e Tecnológico (CNPq), Financiadora de Estudos e Projetos (Finep), Fundação de Amparo àPesquisa do Estado de São Paulo (FAPESP) and Universidade Federal do Rio Grande do Sul (UFRGS),Brazil; Ministry of Education of China (MOEC) , Ministry of Science & Technology of China (MSTC)and National Natural Science Foundation of China (NSFC), China; Ministry of Science and Educationand Croatian Science Foundation, Croatia; Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear(CEADEN), Cubaenergía, Cuba; Ministry of Education, Youth and Sports of the Czech Republic, CzechRepublic; The Danish Council for Independent Research | Natural Sciences, the VILLUM FONDEN andDanish National Research Foundation (DNRF), Denmark; Helsinki Institute of Physics (HIP), Finland;Commissariat à l’Energie Atomique (CEA) and Institut National de Physique Nucléaire et de Physiquedes Particules (IN2P3) and Centre National de la Recherche Scientifique (CNRS), France; Bundesmin-isterium für Bildung und Forschung (BMBF) and GSI Helmholtzzentrum für SchwerionenforschungGmbH, Germany; General Secretariat for Research and Technology, Ministry of Education, Researchand Religions, Greece; National Research, Development and Innovation Office, Hungary; Departmentof Atomic Energy Government of India (DAE), Department of Science and Technology, Governmentof India (DST), University Grants Commission, Government of India (UGC) and Council of Scientificand Industrial Research (CSIR), India; Indonesian Institute of Science, Indonesia; Istituto Nazionaledi Fisica Nucleare (INFN), Italy; Institute for Innovative Science and Technology , Nagasaki Institute23on-prompt and prompt D-meson production in pp collisions at √ s = .
02 TeV ALICE Collaborationof Applied Science (IIST), Japanese Ministry of Education, Culture, Sports, Science and Technology(MEXT) and Japan Society for the Promotion of Science (JSPS) KAKENHI, Japan; Consejo Nacionalde Ciencia (CONACYT) y Tecnología, through Fondo de Cooperación Internacional en Ciencia y Tec-nología (FONCICYT) and Dirección General de Asuntos del Personal Academico (DGAPA), Mexico;Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), Netherlands; The Research Coun-cil of Norway, Norway; Commission on Science and Technology for Sustainable Development in theSouth (COMSATS), Pakistan; Pontificia Universidad Católica del Perú, Peru; Ministry of Education andScience, National Science Centre and WUT ID-UB, Poland; Korea Institute of Science and Technol-ogy Information and National Research Foundation of Korea (NRF), Republic of Korea; Ministry ofEducation and Scientific Research, Institute of Atomic Physics and Ministry of Research and Innova-tion and Institute of Atomic Physics, Romania; Joint Institute for Nuclear Research (JINR), Ministry ofEducation and Science of the Russian Federation, National Research Centre Kurchatov Institute, Rus-sian Science Foundation and Russian Foundation for Basic Research, Russia; Ministry of Education,Science, Research and Sport of the Slovak Republic, Slovakia; National Research Foundation of SouthAfrica, South Africa; Swedish Research Council (VR) and Knut & Alice Wallenberg Foundation (KAW),Sweden; European Organization for Nuclear Research, Switzerland; Suranaree University of Technology(SUT), National Science and Technology Development Agency (NSDTA) and Office of the Higher Edu-cation Commission under NRU project of Thailand, Thailand; Turkish Atomic Energy Agency (TAEK),Turkey; National Academy of Sciences of Ukraine, Ukraine; Science and Technology Facilities Coun-cil (STFC), United Kingdom; National Science Foundation of the United States of America (NSF) andUnited States Department of Energy, Office of Nuclear Physics (DOE NP), United States of America.
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A The ALICE Collaboration
S. Acharya , D. Adamová , A. Adler , J. Adolfsson , G. Aglieri Rinella , M. Agnello , N. Agrawal ,Z. Ahammed , S. Ahmad , S.U. Ahn , Z. Akbar , A. Akindinov , M. Al-Turany , D. Aleksandrov ,B. Alessandro , H.M. Alfanda , R. Alfaro Molina , B. Ali , Y. Ali , A. Alici , N. Alizadehvandchali ,A. Alkin , J. Alme , T. Alt , L. Altenkamper , I. Altsybeev , M.N. Anaam , C. Andrei , D. Andreou ,A. Andronic , V. Anguelov , F. Antinori , P. Antonioli , C. Anuj , N. Apadula , L. Aphecetche ,H. Appelshäuser , S. Arcelli , R. Arnaldi , I.C. Arsene , M. Arslandok , , A. Augustinus ,R. Averbeck , S. Aziz , M.D. Azmi , A. Badalà , Y.W. Baek , X. Bai , R. Bailhache , Y. Bailung ,R. Bala , A. Balbino , A. Baldisseri , M. Ball , D. Banerjee , R. Barbera , L. Barioglio , , M. Barlou ,G.G. Barnaföldi , L.S. Barnby , V. Barret , C. Bartels , K. Barth , E. Bartsch , F. Baruffaldi ,N. Bastid , S. Basu , , G. Batigne , B. Batyunya , D. Bauri , J.L. Bazo Alba , I.G. Bearden ,C. Beattie , I. Belikov , A.D.C. 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Casula , F. Catalano ,C. Ceballos Sanchez , P. Chakraborty , S. Chandra , W. Chang , S. Chapeland , M. Chartier ,S. Chattopadhyay , S. Chattopadhyay , A. Chauvin , T.G. Chavez , C. Cheshkov , B. Cheynis ,V. Chibante Barroso , D.D. Chinellato , S. Cho , P. Chochula , P. Christakoglou , C.H. Christensen ,P. Christiansen , T. Chujo , C. Cicalo , L. Cifarelli , F. Cindolo , M.R. Ciupek , G. Clai II , ,J. Cleymans , F. Colamaria , J.S. Colburn , D. Colella , , A. Collu , M. Colocci , , M. Concas III , ,G. Conesa Balbastre , Z. Conesa del Valle , G. Contin , J.G. Contreras , T.M. Cormier , P. Cortese ,M.R. Cosentino , F. Costa , S. Costanza , P. Crochet , E. Cuautle , P. Cui , L. Cunqueiro , A. Dainese ,F.P.A. Damas , , M.C. Danisch , A. Danu , I. Das , P. Das , P. Das , S. Das , S. Dash , S. De , A. DeCaro , G. de Cataldo , L. De Cilladi , J. de Cuveland , A. De Falco , D. De Gruttola , N. De Marco ,C. De Martin , S. De Pasquale , S. Deb , H.F. Degenhardt , K.R. Deja , L. Dello Stritto , S. Delsanto ,W. Deng , P. Dhankher , D. Di Bari , A. Di Mauro , R.A. Diaz , T. Dietel , Y. Ding , R. Divià ,D.U. Dixit , Ø. Djuvsland , U. Dmitrieva , J. Do , A. Dobrin , B. Dönigus , O. Dordic , A.K. Dubey ,A. Dubla , , S. Dudi , M. Dukhishyam , P. Dupieux , T.M. Eder , R.J. Ehlers , V.N. Eikeland ,D. Elia , B. Erazmus , F. Ercolessi , A. Erokhin , M.R. Ersdal , B. Espagnon , G. Eulisse , D. Evans ,S. Evdokimov , L. Fabbietti , M. Faggin , J. Faivre , F. Fan , A. Fantoni , M. Fasel , P. Fecchio ,A. Feliciello , G. Feofilov , A. Fernández Téllez , A. Ferrero , A. Ferretti , V.J.G. Feuillard ,J. Figiel , S. Filchagin , D. Finogeev , F.M. Fionda , G. Fiorenza , F. Flor , A.N. Flores ,S. Foertsch , P. Foka , S. Fokin , E. Fragiacomo , U. Fuchs , N. Funicello , C. Furget , A. Furs ,J.J. Gaardhøje , M. Gagliardi , A.M. Gago , A. Gal , C.D. Galvan , P. Ganoti , C. Garabatos ,J.R.A. Garcia , E. Garcia-Solis , K. Garg , C. Gargiulo , A. Garibli , K. Garner , P. Gasik ,E.F. 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Hong , D. Horak , S. Hornung ,R. Hosokawa , P. Hristov , C. Huang , C. Hughes , P. Huhn , T.J. Humanic , H. Hushnud ,L.A. Husova , N. Hussain , D. Hutter , J.P. Iddon , , R. Ilkaev , H. Ilyas , M. Inaba ,G.M. Innocenti , M. Ippolitov , A. Isakov , , M.S. Islam , M. Ivanov , V. Ivanov , V. Izucheev , √ s = .
02 TeV ALICE Collaboration
B. Jacak , N. Jacazio , P.M. Jacobs , S. Jadlovska , J. Jadlovsky , S. Jaelani , C. Jahnke , ,M.J. Jakubowska , M.A. Janik , T. Janson , M. Jercic , O. Jevons , F. Jonas , , P.G. Jones ,J. Jowett , , J. Jung , M. Jung , A. Junique , A. Jusko , P. Kalinak , A. Kalweit , V. Kaplin , S. Kar ,A. Karasu Uysal , D. Karatovic , O. Karavichev , T. Karavicheva , P. Karczmarczyk , E. Karpechev ,A. Kazantsev , U. Kebschull , R. Keidel , M. Keil , B. Ketzer , Z. Khabanova , A.M. Khan , S. Khan ,A. Khanzadeev , Y. Kharlov , A. Khatun , A. Khuntia , B. Kileng , B. Kim , , D. Kim , D.J. Kim ,E.J. Kim , J. Kim , J.S. Kim , J. Kim , J. Kim , J. Kim , M. Kim , S. Kim , T. Kim , S. Kirsch ,I. Kisel , S. Kiselev , A. Kisiel , J.L. Klay , J. Klein , S. Klein , C. Klein-Bösing , M. Kleiner ,T. Klemenz , A. Kluge , A.G. Knospe , C. Kobdaj , M.K. Köhler , T. Kollegger , A. Kondratyev ,N. Kondratyeva , E. Kondratyuk , J. Konig , S.A. Konigstorfer , P.J. Konopka , , G. Kornakov ,S.D. Koryciak , L. Koska , O. Kovalenko , V. Kovalenko , M. Kowalski , I. Králik , A. Kravˇcáková ,L. Kreis , M. Krivda , , F. Krizek , K. Krizkova Gajdosova , M. Kroesen , M. Krüger , E. Kryshen ,M. Krzewicki , V. Kuˇcera , C. Kuhn , P.G. Kuijer , T. Kumaoka , L. Kumar , S. Kundu ,P. Kurashvili , A. Kurepin , A.B. Kurepin , A. Kuryakin , S. Kushpil , J. Kvapil , M.J. Kweon ,J.Y. Kwon , Y. Kwon , S.L. La Pointe , P. La Rocca , Y.S. Lai , A. Lakrathok , M. Lamanna ,R. Langoy , K. Lapidus , P. Larionov , E. Laudi , L. Lautner , , R. Lavicka , T. Lazareva ,R. Lea , , J. Lee , J. Lehrbach , R.C. Lemmon , I. León Monzón , E.D. Lesser , M. Lettrich , ,P. Lévai , X. Li , X.L. Li , J. Lien , R. Lietava , B. Lim , S.H. Lim , V. Lindenstruth , A. Lindner ,C. Lippmann , A. Liu , J. Liu , I.M. Lofnes , V. Loginov , C. Loizides , P. Loncar , J.A. Lopez ,X. Lopez , E. López Torres , J.R. Luhder , M. Lunardon , G. Luparello , Y.G. Ma , A. Maevskaya ,M. Mager , T. Mahmoud , A. Maire , R.D. Majka I , , M. Malaev , Q.W. Malik , L. Malinina IV , ,D. Mal’Kevich , N. Mallick , P. Malzacher , G. Mandaglio , , V. Manko , F. Manso , V. Manzari ,Y. Mao , J. Mareš , G.V. Margagliotti , A. Margotti , A. Marín , C. Markert , M. Marquard ,N.A. Martin , P. Martinengo , J.L. Martinez , M.I. Martínez , G. Martínez García , S. Masciocchi ,M. Masera , A. Masoni , L. Massacrier , A. Mastroserio , , A.M. Mathis , O. Matonoha ,P.F.T. Matuoka , A. Matyja , C. Mayer , A.L. Mazuecos , F. Mazzaschi , M. Mazzilli , ,M.A. Mazzoni , A.F. Mechler , F. Meddi , Y. Melikyan , A. Menchaca-Rocha , E. Meninno , ,A.S. Menon , M. Meres , S. Mhlanga , , Y. Miake , L. Micheletti , L.C. Migliorin , D.L. Mihaylov ,K. Mikhaylov , , A.N. Mishra , , D. Mi´skowiec , A. Modak , A.P. Mohanty , B. Mohanty , M. MohisinKhan , Z. Moravcova , C. Mordasini , D.A. Moreira De Godoy , L.A.P. Moreno , I. Morozov ,A. Morsch , T. Mrnjavac , V. Muccifora , E. Mudnic , D. Mühlheim , S. Muhuri , J.D. Mulligan ,A. Mulliri , M.G. Munhoz , R.H. Munzer , H. Murakami , S. Murray , L. Musa , J. Musinsky ,C.J. Myers , J.W. Myrcha , R. Nair , B.K. Nandi , R. Nania , E. Nappi , M.U. Naru , A.F. Nassirpour ,C. Nattrass , A. Neagu , L. Nellen , S.V. Nesbo , G. Neskovic , D. Nesterov , B.S. Nielsen ,S. Nikolaev , S. Nikulin , V. Nikulin , F. Noferini , S. Noh , P. Nomokonov , J. Norman ,N. Novitzky , P. Nowakowski , A. Nyanin , J. Nystrand , M. Ogino , A. Ohlson , J. Oleniacz ,A.C. Oliveira Da Silva , M.H. Oliver , A. Onnerstad , C. Oppedisano , A. Ortiz Velasquez , T. Osako ,A. Oskarsson , J. Otwinowski , K. Oyama , Y. Pachmayer , S. Padhan , D. Pagano , G. Pai´c ,A. Palasciano , J. Pan , S. Panebianco , P. Pareek , J. Park , J.E. Parkkila , S.P. Pathak , B. Paul ,J. Pazzini , H. Pei , T. Peitzmann , X. Peng , L.G. Pereira , H. Pereira Da Costa , D. Peresunko ,G.M. Perez , S. Perrin , Y. Pestov , V. Petráˇcek , M. Petrovici , R.P. Pezzi , S. Piano , M. Pikna ,P. Pillot , O. Pinazza , , L. Pinsky , C. Pinto , S. Pisano , M. Płosko´n , M. Planinic , F. Pliquett ,M.G. Poghosyan , B. Polichtchouk , S. Politano , N. Poljak , A. Pop , S. Porteboeuf-Houssais ,J. Porter , V. Pozdniakov , S.K. Prasad , R. Preghenella , F. Prino , C.A. Pruneau , I. Pshenichnov ,M. Puccio , S. Qiu , L. Quaglia , R.E. Quishpe , S. Ragoni , A. Rakotozafindrabe , L. Ramello ,F. Rami , S.A.R. Ramirez , A.G.T. Ramos , R. Raniwala , S. Raniwala , S.S. Räsänen , R. Rath ,I. Ravasenga , K.F. Read , , A.R. Redelbach , K. Redlich V , , A. Rehman , P. Reichelt , F. Reidt ,R. Renfordt , Z. Rescakova , K. Reygers , A. Riabov , V. Riabov , T. Richert , , M. Richter ,W. Riegler , F. Riggi , C. Ristea , S.P. Rode , M. Rodríguez Cahuantzi , K. Røed , R. Rogalev ,E. Rogochaya , T.S. Rogoschinski , D. Rohr , D. Röhrich , P.F. Rojas , P.S. Rokita , F. Ronchetti ,A. Rosano , , E.D. Rosas , A. Rossi , A. Rotondi , A. Roy , P. Roy , N. Rubini , O.V. Rueda ,R. Rui , B. Rumyantsev , A. Rustamov , E. Ryabinkin , Y. Ryabov , A. Rybicki , H. Rytkonen ,W. Rzesa , O.A.M. Saarimaki , R. Sadek , S. Sadovsky , J. Saetre , K. Šafaˇrík , S.K. Saha , S. Saha ,B. Sahoo , P. Sahoo , R. Sahoo , S. Sahoo , D. Sahu , P.K. Sahu , J. Saini , S. Sakai , S. Sambyal ,V. Samsonov I , , , D. Sarkar , N. Sarkar , P. Sarma , V.M. Sarti , M.H.P. Sas , J. Schambach , ,H.S. Scheid , C. Schiaua , R. Schicker , A. Schmah , C. Schmidt , H.R. Schmidt , M.O. Schmidt , √ s = .
02 TeV ALICE Collaboration
M. Schmidt , N.V. Schmidt , , A.R. Schmier , R. Schotter , J. Schukraft , Y. Schutz , K. Schwarz ,K. Schweda , G. Scioli , E. Scomparin , J.E. Seger , Y. Sekiguchi , D. Sekihata , I. Selyuzhenkov , ,S. Senyukov , J.J. Seo , D. Serebryakov , L. Šerkšnyt˙e , A. Sevcenco , T.J. Shaba , A. Shabanov ,A. Shabetai , R. Shahoyan , W. Shaikh , A. Shangaraev , A. Sharma , H. Sharma , M. Sharma ,N. Sharma , S. Sharma , O. Sheibani , K. Shigaki , M. Shimomura , S. Shirinkin , Q. Shou ,Y. Sibiriak , S. Siddhanta , T. Siemiarczuk , T.F. Silva , D. Silvermyr , G. Simonetti , B. Singh ,R. Singh , R. Singh , R. Singh , V.K. Singh , V. Singhal , T. Sinha , B. Sitar , M. Sitta ,T.B. Skaali , G. Skorodumovs , M. Slupecki , N. Smirnov , R.J.M. Snellings , C. Soncco , J. Song ,A. Songmoolnak , F. Soramel , S. Sorensen , I. Sputowska , J. Stachel , I. Stan , P.J. Steffanic ,S.F. Stiefelmaier , D. Stocco , M.M. Storetvedt , C.P. Stylianidis , A.A.P. Suaide , T. Sugitate ,C. Suire , M. Suljic , R. Sultanov , M. Šumbera , V. Sumberia , S. Sumowidagdo , S. Swain ,A. Szabo , I. Szarka , U. Tabassam , S.F. Taghavi , G. Taillepied , J. Takahashi , G.J. Tambave ,S. Tang , , Z. Tang , M. Tarhini , M.G. Tarzila , A. Tauro , G. Tejeda Muñoz , A. Telesca ,L. Terlizzi , C. Terrevoli , G. Tersimonov , S. Thakur , D. Thomas , R. Tieulent , A. Tikhonov ,A.R. Timmins , M. Tkacik , A. Toia , N. Topilskaya , M. Toppi , F. Torales-Acosta , S.R. Torres ,A. Trifiró , , S. Tripathy , , T. Tripathy , S. Trogolo , , G. Trombetta , V. Trubnikov , W.H. Trzaska ,T.P. Trzcinski , B.A. Trzeciak , A. Tumkin , R. Turrisi , T.S. Tveter , K. Ullaland , A. Uras ,M. Urioni , G.L. Usai , M. Vala , N. Valle , S. Vallero , N. van der Kolk , L.V.R. van Doremalen ,M. van Leeuwen , P. Vande Vyvre , D. Varga , Z. Varga , M. Varga-Kofarago , A. Vargas ,M. Vasileiou , A. Vasiliev , O. Vázquez Doce , V. Vechernin , E. Vercellin , S. Vergara Limón ,L. Vermunt , R. Vértesi , M. Verweij , L. Vickovic , Z. Vilakazi , O. Villalobos Baillie , G. Vino ,A. Vinogradov , T. Virgili , V. Vislavicius , A. Vodopyanov , B. Volkel , M.A. Völkl , K. Voloshin ,S.A. Voloshin , G. Volpe , B. von Haller , I. Vorobyev , D. Voscek , J. Vrláková , B. Wagner ,M. Weber , A. Wegrzynek , S.C. Wenzel , J.P. Wessels , J. Wiechula , J. Wikne , G. Wilk ,J. Wilkinson , G.A. Willems , E. Willsher , B. Windelband , M. Winn , W.E. Witt , J.R. Wright ,Y. Wu , R. Xu , S. Yalcin , Y. Yamaguchi , K. Yamakawa , S. Yang , S. Yano , , Z. Yin ,H. Yokoyama , I.-K. Yoo , J.H. Yoon , S. Yuan , A. Yuncu , V. Zaccolo , A. Zaman , C. Zampolli ,H.J.C. Zanoli , N. Zardoshti , A. Zarochentsev , P. Závada , N. Zaviyalov , H. Zbroszczyk ,M. Zhalov , S. Zhang , X. Zhang , Y. Zhang , V. Zherebchevskii , Y. Zhi , D. Zhou , Y. Zhou ,J. Zhu , , Y. Zhu , A. Zichichi , G. Zinovjev , N. Zurlo Affiliation notes I Deceased II Also at: Italian National Agency for New Technologies, Energy and Sustainable Economic Development(ENEA), Bologna, Italy
III
Also at: Dipartimento DET del Politecnico di Torino, Turin, Italy IV Also at: M.V. Lomonosov Moscow State University, D.V. Skobeltsyn Institute of Nuclear, Physics, Moscow,Russia V Also at: Institute of Theoretical Physics, University of Wroclaw, Poland
Collaboration Institutes A.I. Alikhanyan National Science Laboratory (Yerevan Physics Institute) Foundation, Yerevan, Armenia AGH University of Science and Technology, Cracow, Poland Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine, Kiev, Ukraine Bose Institute, Department of Physics and Centre for Astroparticle Physics and Space Science (CAPSS),Kolkata, India Budker Institute for Nuclear Physics, Novosibirsk, Russia California Polytechnic State University, San Luis Obispo, California, United States Central China Normal University, Wuhan, China Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Havana, Cuba Centro de Investigación y de Estudios Avanzados (CINVESTAV), Mexico City and Mérida, Mexico Chicago State University, Chicago, Illinois, United States China Institute of Atomic Energy, Beijing, China Chungbuk National University, Cheongju, Republic of Korea √ s = .
02 TeV ALICE Collaboration Comenius University Bratislava, Faculty of Mathematics, Physics and Informatics, Bratislava, Slovakia COMSATS University Islamabad, Islamabad, Pakistan Creighton University, Omaha, Nebraska, United States Department of Physics, Aligarh Muslim University, Aligarh, India Department of Physics, Pusan National University, Pusan, Republic of Korea Department of Physics, Sejong University, Seoul, Republic of Korea Department of Physics, University of California, Berkeley, California, United States Department of Physics, University of Oslo, Oslo, Norway Department of Physics and Technology, University of Bergen, Bergen, Norway Dipartimento di Fisica dell’Università ’La Sapienza’ and Sezione INFN, Rome, Italy Dipartimento di Fisica dell’Università and Sezione INFN, Cagliari, Italy Dipartimento di Fisica dell’Università and Sezione INFN, Trieste, Italy Dipartimento di Fisica dell’Università and Sezione INFN, Turin, Italy Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN, Bologna, Italy Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN, Catania, Italy Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN, Padova, Italy Dipartimento di Fisica e Nucleare e Teorica, Università di Pavia and Sezione INFN, Pavia, Italy Dipartimento di Fisica ‘E.R. Caianiello’ dell’Università and Gruppo Collegato INFN, Salerno, Italy Dipartimento DISAT del Politecnico and Sezione INFN, Turin, Italy Dipartimento di Scienze e Innovazione Tecnologica dell’Università del Piemonte Orientale and INFN Sezionedi Torino, Alessandria, Italy Dipartimento di Scienze MIFT, Università di Messina, Messina, Italy Dipartimento Interateneo di Fisica ‘M. Merlin’ and Sezione INFN, Bari, Italy European Organization for Nuclear Research (CERN), Geneva, Switzerland Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, University of Split, Split,Croatia Faculty of Engineering and Science, Western Norway University of Applied Sciences, Bergen, Norway Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague, CzechRepublic Faculty of Science, P.J. Šafárik University, Košice, Slovakia Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt, Germany Fudan University, Shanghai, China Gangneung-Wonju National University, Gangneung, Republic of Korea Gauhati University, Department of Physics, Guwahati, India Helmholtz-Institut für Strahlen- und Kernphysik, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn,Germany Helsinki Institute of Physics (HIP), Helsinki, Finland High Energy Physics Group, Universidad Autónoma de Puebla, Puebla, Mexico Hiroshima University, Hiroshima, Japan Hochschule Worms, Zentrum für Technologietransfer und Telekommunikation (ZTT), Worms, Germany Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania Indian Institute of Technology Bombay (IIT), Mumbai, India Indian Institute of Technology Indore, Indore, India Indonesian Institute of Sciences, Jakarta, Indonesia INFN, Laboratori Nazionali di Frascati, Frascati, Italy INFN, Sezione di Bari, Bari, Italy INFN, Sezione di Bologna, Bologna, Italy INFN, Sezione di Cagliari, Cagliari, Italy INFN, Sezione di Catania, Catania, Italy INFN, Sezione di Padova, Padova, Italy INFN, Sezione di Roma, Rome, Italy INFN, Sezione di Torino, Turin, Italy INFN, Sezione di Trieste, Trieste, Italy Inha University, Incheon, Republic of Korea Institute for Gravitational and Subatomic Physics (GRASP), Utrecht University/Nikhef, Utrecht, Netherlands Institute for Nuclear Research, Academy of Sciences, Moscow, Russia √ s = .
02 TeV ALICE Collaboration Institute of Experimental Physics, Slovak Academy of Sciences, Košice, Slovakia Institute of Physics, Homi Bhabha National Institute, Bhubaneswar, India Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic Institute of Space Science (ISS), Bucharest, Romania Institut für Kernphysik, Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt, Germany Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico City, Mexico Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Brazil Instituto de Física, Universidad Nacional Autónoma de México, Mexico City, Mexico iThemba LABS, National Research Foundation, Somerset West, South Africa Jeonbuk National University, Jeonju, Republic of Korea Johann-Wolfgang-Goethe Universität Frankfurt Institut für Informatik, Fachbereich Informatik undMathematik, Frankfurt, Germany Joint Institute for Nuclear Research (JINR), Dubna, Russia Korea Institute of Science and Technology Information, Daejeon, Republic of Korea KTO Karatay University, Konya, Turkey Laboratoire de Physique des 2 Infinis, Irène Joliot-Curie, Orsay, France Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble-Alpes, CNRS-IN2P3, Grenoble,France Lawrence Berkeley National Laboratory, Berkeley, California, United States Lund University Department of Physics, Division of Particle Physics, Lund, Sweden Moscow Institute for Physics and Technology, Moscow, Russia Nagasaki Institute of Applied Science, Nagasaki, Japan Nara Women’s University (NWU), Nara, Japan National and Kapodistrian University of Athens, School of Science, Department of Physics , Athens, Greece National Centre for Nuclear Research, Warsaw, Poland National Institute of Science Education and Research, Homi Bhabha National Institute, Jatni, India National Nuclear Research Center, Baku, Azerbaijan National Research Centre Kurchatov Institute, Moscow, Russia Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark Nikhef, National institute for subatomic physics, Amsterdam, Netherlands NRC Kurchatov Institute IHEP, Protvino, Russia NRC «Kurchatov»Institute - ITEP, Moscow, Russia NRNU Moscow Engineering Physics Institute, Moscow, Russia Nuclear Physics Group, STFC Daresbury Laboratory, Daresbury, United Kingdom Nuclear Physics Institute of the Czech Academy of Sciences, ˇRež u Prahy, Czech Republic Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States Ohio State University, Columbus, Ohio, United States
Petersburg Nuclear Physics Institute, Gatchina, Russia
Physics department, Faculty of science, University of Zagreb, Zagreb, Croatia
Physics Department, Panjab University, Chandigarh, India
Physics Department, University of Jammu, Jammu, India
Physics Department, University of Rajasthan, Jaipur, India
Physikalisches Institut, Eberhard-Karls-Universität Tübingen, Tübingen, Germany
Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
Physik Department, Technische Universität München, Munich, Germany
Politecnico di Bari and Sezione INFN, Bari, Italy
Research Division and ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum für SchwerionenforschungGmbH, Darmstadt, Germany
Russian Federal Nuclear Center (VNIIEF), Sarov, Russia
Saha Institute of Nuclear Physics, Homi Bhabha National Institute, Kolkata, India
School of Physics and Astronomy, University of Birmingham, Birmingham, United Kingdom
Sección Física, Departamento de Ciencias, Pontificia Universidad Católica del Perú, Lima, Peru
St. Petersburg State University, St. Petersburg, Russia
Stefan Meyer Institut für Subatomare Physik (SMI), Vienna, Austria
SUBATECH, IMT Atlantique, Université de Nantes, CNRS-IN2P3, Nantes, France
Suranaree University of Technology, Nakhon Ratchasima, Thailand √ s = .
02 TeV ALICE Collaboration
Technical University of Košice, Košice, Slovakia
The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Cracow, Poland
The University of Texas at Austin, Austin, Texas, United States
Universidad Autónoma de Sinaloa, Culiacán, Mexico
Universidade de São Paulo (USP), São Paulo, Brazil
Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil
Universidade Federal do ABC, Santo Andre, Brazil
University of Cape Town, Cape Town, South Africa
University of Houston, Houston, Texas, United States
University of Jyväskylä, Jyväskylä, Finland
University of Kansas, Lawrence, Kansas, United States
University of Liverpool, Liverpool, United Kingdom
University of Science and Technology of China, Hefei, China
University of South-Eastern Norway, Tonsberg, Norway
University of Tennessee, Knoxville, Tennessee, United States
University of the Witwatersrand, Johannesburg, South Africa
University of Tokyo, Tokyo, Japan
University of Tsukuba, Tsukuba, Japan
Université Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France
Université de Lyon, CNRS/IN2P3, Institut de Physique des 2 Infinis de Lyon , Lyon, France
Université de Strasbourg, CNRS, IPHC UMR 7178, F-67000 Strasbourg, France, Strasbourg, France
Université Paris-Saclay Centre d’Etudes de Saclay (CEA), IRFU, Départment de Physique Nucléaire (DPhN),Saclay, France
Università degli Studi di Foggia, Foggia, Italy
Università di Brescia and Sezione INFN, Brescia, Italy
Variable Energy Cyclotron Centre, Homi Bhabha National Institute, Kolkata, India
Warsaw University of Technology, Warsaw, Poland
Wayne State University, Detroit, Michigan, United States
Westfälische Wilhelms-Universität Münster, Institut für Kernphysik, Münster, Germany
Wigner Research Centre for Physics, Budapest, Hungary
Yale University, New Haven, Connecticut, United States