Abstract
The production mechanism of quarkonia states in hadronic collisions is still to be understood by the scientific community. In high-multiplicity $p+p$ collisions, Underlying Event (UE) observables are of major interest. The Multi-Parton Interactions (MPI) is a UE observable, where several interactions occur at the partonic level in a single $p+p$ event. This leads to dependence of particle production on event multiplicity. If the MPI occurs in a harder scale, there will be a correlation between the yield of quarkonia and total charged particle multiplicity. The ALICE experiment at the Large Hadron Collider (LHC) in $p+p$ collisions at $\sqrt{s}$ = 7 and 13 TeV has observed an approximate linear increase of relative $J/\psi$ yield ($\frac{dN_{J/\psi}/dy}{<dN_{J/\psi}/dy>}$) with relative charged particle multiplicity density ($\frac{dN_{ch}/dy}{<dN_{ch}/dy>}$). In our present work we have performed a comprehensive study of the production of charmonia as a function of charged particle multiplicity in $p+p$ collisions at LHC energies using pQCD-inspired multiparton interaction model, PYTHIA8 tune 4C, with and without Color Reconnection (CR) scheme. A detail multiplicity and energy dependent study is performed to understand the effects of MPI on $J/\psi$ production. The ratio of $\psi(2S)$ to $J/\psi$ is also studied as a function of charged particle multiplicity at LHC energies.
Highlights
Understanding the production mechanisms of quarkonia states in proton-proton collisions is a great challenge for existing theoretical models
It is found that PYTHIA8 describes the hpTi as a function of charged-particle multiplicity by including the multiparton interactions (MPIs) with color reconnection (CR) [18] as well as explains the flowlike pattern in pp collisions [19]
We found a maximum of 60% deviation of Monte Carlo (MC) pT spectra from data for 13 TeV in certain pT bins except for two low-pT bins, where deviation is larger
Summary
Understanding the production mechanisms of quarkonia states in proton-proton collisions is a great challenge for existing theoretical models. In MPIs, several interactions at the partonic level occur in a single p þ p collision This leads to a strong dependence of particle production on total event multiplicity. An early study of the NA27 experiment reported that the charged-particle multiplicity distributions are affected by the UEs with open charm production [13]. The multiplicity dependence study in p þ p collisions is very interesting to understand the MPI effects on quarkonia production. It is found that PYTHIA8 describes the hpTi as a function of charged-particle multiplicity by including the MPI with CR [18] as well as explains the flowlike pattern in pp collisions [19]. J=ψ production as a function of charged-particle multiplicity using a 4C-tuned [20] PYTHIA8 event generator at different LHC energies.
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