Multiplicity dependence of J/$\psi$ production and QCD dynamics in $p+p$ collisions at $\sqrt{s}$ = 13 TeV

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.

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.

Table 1 Relative yield of J/$\psi$$(N_{\mathrm{J/\psi }}^{i}/N_{\mathrm{J/\psi }}^{\mathrm{MB}})$ for hard QCD, gg$\rightarrow C$, q${\bar{q}}\rightarrow C$ processes as a function of charged particle multiplicity in $p+p$ collision at $\sqrt{s}$ = 13 TeV using PYTHIA

Table 2 Relative $\langle p_{\mathrm{T}} \rangle$ of J/$\psi$$(\langle p_{\mathrm{T}} \rangle _{\mathrm{J/\psi }}^{i}/\langle p_{\mathrm{T}} \rangle _{\mathrm{J/\psi }}^{\mathrm{MB}})$ as a function of charged particle multiplicity for hard QCD, gg$\rightarrow C$, q${\bar{q}}\rightarrow C$ processes in $p+p$ collision at $\sqrt{s}$  = 13 TeV using PYTHIA