Abstract
In inelastic \(p+p\) collisions, the interacting objects are quarks and gluons (partons). It is believed that there are multiple interactions between the partons in a single \(p+p\) event. Recent studies of multiplicity dependence of particle production in \(p+p\) collisions have gathered considerable interest in the scientific community. According to several theoretical calculations, multiple gluon participation in hadronic collisions is the cause of high-multiplicity events. If the interaction is hard enough (large \(p_{\mathrm{T}}\) transfer), the semi-hard processes of multiple interactions of partons might also lead to the production of heavy particles like J/\(\psi \). At the LHC, an approximately linear increase of the relative J/\(\psi \) yield with charged particle multiplicity is observed in \(p+p\) collisions. In the present work, we have studied the contribution of quarks and gluons to the multiplicity dependence of J/\(\psi \) production using pQCD inspired event generator, PYTHIA8 tune 4C, in \(p+p\) collisions at \(\sqrt{s} =\)13 TeV by investigating relative J/\(\psi \) yield and relative \(\langle p_{\mathrm{T}} \rangle \) of J/\(\psi \) as a function of charged particle multiplicity for different hard-QCD processes. We have estimated a newly defined ratio, \(r_{pp} = {\langle p_{\mathrm{T}}^{2} \rangle }_{i}/{\langle p_{\mathrm{T}}^{2} \rangle }_{\mathrm{MB}}\), to gain understanding of J/\(\psi \) production in high-multiplicity \(p+p\) collisions. For the first time we attempt to study the nuclear modification factor-like observables (\(R_{\mathrm{pp}}\) and \(R_{\mathrm{cp}}\)) to describe the QCD medium formed in high-multiplicity \(p+p\) collisions.
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Data Availability Statement
This manuscript has no associated data or the data will not be deposited. [Authors’ comment: Raw simulated data were generated at the LHC grid computing facility at Variable Energy Cyclotron Center, Kolkata. Some of the derived data supporting the findings of this study are available within the article and other can be obtained from the corresponding author on request.]
Notes
J/\(\psi \)from all Hard-QCD processes: It includes all the NRQCD processes (LO processes) such as gluon fusion, quark annihilation, flavor excitation and the semi-hard MPIs, which themselves are governed by NRQCD. For color-octet states, one additional gluon is emitted in the transition to the physical color-singlet state. Production of any \(^3S_1\), \(^3P_J\) and \(^3D_J\) states via color-singlet and color-octet mechanisms are included through the Onia process in PYTHIA8. In order to have quarkonia (here charmonia is of our interest) production, the Charmonium:all flag in PYTHA8 is included, which allows for quarkonia production through the NRQCD framework [27,28,29]. The production of all the states of charmonia is included in PYTHIA8 and their decay products make a significant contribution to J/\(\psi \). The heavier charmonium states can decay into a J/\(\psi \) meson by emitting photons or pions which contribute to the inclusive J/\(\psi \) production.
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Acknowledgements
DT acknowledges UGC, New Delhi, Government of India for financial supports. SD and RNS acknowledge the financial supports from ALICE Project No. SR/MF/PS-01/2014-IITI(G) of Department of Science & Technology, Government of India. The authors gratefully acknowledge Professor Leif Lönnblad for valuable discussions. This research used resources of the LHC grid computing facility at Variable Energy Cyclotron Center, Kolkata. We would like to thank Prof. B.K. Nandi for carefully reading the final version of the manuscript and providing useful comments.
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Appendix
Appendix
For completeness, we have listed the numerical values of relative yield (Table 1) and relative \(\langle p_{\mathrm{T}} \rangle \) (Table 2) of J/\(\psi \) for HardQCD, gg\(\rightarrow C\) and q\({\bar{q}}\rightarrow C\) processes as a function of multiplicity (\(N_{\mathrm{ch}}\)-bin) along with their uncertainties.
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Deb, S., Thakur, D., De, S. et al. Multiplicity dependence of J/\(\psi \) production and QCD dynamics in \(p+p\) collisions at \(\sqrt{s}\) = 13 TeV. Eur. Phys. J. A 56, 134 (2020). https://doi.org/10.1140/epja/s10050-020-00138-4
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DOI: https://doi.org/10.1140/epja/s10050-020-00138-4