Modification of heavy quark hadronization in high-multiplicity collisions at LHCb

. The ratio of heavy flavor hadrons is very sensitive to the hadronization mechanism. This proceeding will present recent LHCb results on the cross-section ratios of D + s / D + , Ξ + c / Λ + c and Λ 0 b / B 0 in di ff erent collision systems. The significantly enhanced production ratios D + s / D + and Λ 0 b / B 0 with the increase of multiplicity may imply that hadronization mechanisms are modified in high-multiplicity events.


Introduction
At hadron colliders, the heavy quarks are mainly produced by hard parton-parton interactions in the initial stages of the collisions, and are well described by perturbative QCD calculations.These calculations are based on the factorisation theorem, according to which the heavy-flavour hadrons cross-sections are dependence on the parton distribution functions of the incoming nucleons, the hard parton-parton scattering cross-section, and the fragmentation functions.The baryon-to-meson and meson-to-meson production ratios of heavy quarks are very sensitive to the fragmentation functions since the contributions from parton distribution function and parton-parton scattering terms cancel in the ratio.The fragmentation functions are typically parameterised from measurements performed in  or   collisions, assuming that the hadronization of heavy quarks is a universal process independent of the colliding systems [1].However, some recent measurements from the LHCb experiment have shown that heavy quark hadronization differs between low-multiplicity and high-multiplicity collisions.These results suggest the existence of other hadronization mechanisms than fragmentation.

The cross-sections ratio 𝐵 0
/ 0 versus multiplicity in   collisions at This LHCb measurement [2] shows cross-sections ratio  0  / 0 as a function of charged particle multiplicity and  T in   collisions at  The Figure 1 shows cross-sections ratio  0  / 0 as a function of these two multiplicity matrices.The charged particle multiplicity is normalized to the mean value found in NoBias events which

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Modification of heavy quark hadronization in high-multiplicity collisions at LHCb Chenxi Gu are only selected based on the LHC beam clock.The left panel shows an increasing trend with the normalized N VELO tracks .The right panel shows no significant dependence on the normalized N back tracks and the values consistent with the values measured in  collisions [3].This implies that the ratio increase is related to the local particle density.The Figure 2 shows cross-sections ratio  0  / 0 as a function of normalized N VELO tracks in different  T intervals.In the 0 <  T < 6 GeV/ interval, the ratio increases with normalized N VELO tracks and has a closer trend to the PYTHIA8 predictions including color reconnection (CR) [4] compare to without color reconnection.The slope of a line fit to these data deviates from zero by 3.4.In the 6 <  T < 12 GeV/ and 12 <  T < 20 GeV/ interval, these ratios show no significant dependence on the normalized N VELO tracks and are consistent with the measurement from  collisions [3].This is qualitatively consistent with the expectation of coalescence mechanism.

The cross-sections ratio 𝐷 +
/ + in Pb collisions at

TeV
This LHCb measurement (preliminary) shows cross-sections ratio  +  / + in Pb collisions at √  NN = 5.02 TeV.There are two different collision configurations due to the asymmetry of the colliding beam energies.The forward collisions where the proton beam points towards the LHCb arm cover the range of 1.5 <  * < 4.0, and the backward collisions where the lead beam points towards the LHCb arm cover the range of −5.0 <  * < −2.5.The  * is the rapidity in the nucleonnucleon center-of-mass system.The average charged particle multiplicity in the backward collisions is higher than that in the forward collisions.
The Figure 3 shows cross-sections ratio  +  / + as a function of  T and  * in different data sample.The cross-sections ratio  +  / + from backward Pb collisions is slightly higher than that in forward Pb collisions and   collisions [5].The cross-sections ratios  +  / + results from LHCb collaboration are consistent with the results from ALICE collaboration in Pb [6] collisions and in   [7] collisions within error.

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Modification of heavy quark hadronization in high-multiplicity collisions at LHCb The data sample used to calculate Λ +  / 0 is selected by 1000 <   < 10000 which   is the number of clusters in VELO detector.The Glauber Monte Carlo (GMC) [9] is used to estimate the centrality (corresponds to 65-90%) and the mean number of nucleons participating in the collision (< N part >) from recorded data [10].The Figure 4 shows the cross-sections ratio Λ +  / 0 has no dependence on < N part > and is lower than the results from STAR collaboration in AuAu collisions [11] in different < N part > intervals.The Figure 5 shows cross-sections ratio Λ +  / 0 as a function of  T and  * in different data sample.In the left panel, Λ +  / 0 decreases with  T , a trend similar to the results from ALICE collaboration in PbPb collisions [12], but is systematically lower than their within error.In the right panel, Λ +  / 0 shows no significant dependence on rapidity and is systematically lower than the results from ALICE collaboration in   and Pb collisions [13,14].The Λ +  / 0 from LHCb is systematically lower than that from STAR and ALICE, which may come from the fact that these

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Modification of heavy quark hadronization in high-multiplicity collisions at LHCb Chenxi Gu detectors cover different rapidity regions, resulting in different particle densities and thus different recombination mechanism contributions.

Summary and outlook
The latest baryon-to-meson and meson-to-meson production ratios of heavy quarks from LHCb in high-multiplicity collisions have been discussed, including  0  / 0 in   collisions at TeV.Both  0  and  0 are reconstructed by same final state (/ +  − ).The charged particle multiplicity is represented by N VELO tracks and N back tracks .N VELO tracks is the total number of charged tracks reconstructed in the VELO detector.N back tracks is the subset of N VELO tracks which points away from LHCb detector.

Figure 1 :
Figure 1: The cross-sections ratio  0  / 0 as a function of normalized N VELO tracks and N back tracks

Figure 2 :
Figure 2: The cross-sections ratio  0  / 0 as a function of normalized N VELO tracks in different  T intervals

Figure 3 : 4 .
Figure 3: The cross-sections ratio  +  / + as a function of  T (left panel) and  * (right panel)

Figure 4 :
Figure 4: The cross-sections ratio Λ +  / 0 as a function of < N part >

Figure 5 :
Figure 5: The cross-sections ratio Λ +  / 0 as a function of  T (left panel) and  * (right panel) TeV,  +  / + in Pb collisions at √  NN = 5.02 TeV and Λ +  / 0 in peripheral PbPb collisions at √  NN = 5.02 TeV.All results imply potential modification of the hadronization mechanism in highmultiplicity collisions and this potential mechanism is related to the local particle density.Many other measurements are ongoing or planned to further shed light on hadronization mechanisms.In past Run 2, looking forward to the LHCb collaboration releasing open charm results in Pb collisions at √  NN = 8.16 TeV.For the upcoming Run 3, the upgraded LHCb detector will reduce hardware limitations and allow to access higher centrality PbPb collisions.PoS(HardProbes2023)103Modification of heavy quark hadronization in high-multiplicity collisions at LHCb Chenxi Gu [6] ALICE collaboration, Measurement of prompt D 0 , D + , D * + , and D + S production in p-Pb collisions at √ s NN = 5.02 TeV, JHEP 12 (2019) 092 [1906.03425].[7] ALICE collaboration, Measurement of D 0 , D + , D * + and D + s production in pp collisions at √ s = 5.02 TeV with ALICE, Eur.Phys.J. C 79 (2019) 388 [1901.07979].[8] LHCb collaboration, Measurement of the Λ +  to D 0 production ratio in periphera PbPb collisions at √  NN = 5.02 TeV, JHEP 06 (2023) 132 [2210.06939].