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Register a new userRole of Multi-Parton Interactions on $J/psi$ production in $p+p$ collisions at LHC Energies
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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.
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At the LHC energies, the underlying observables are of major topic of interest in high multiplicity $p+p$ collisions. Multiple Parton Interactions (MPI) is one of them, in which several interactions occur in a single $p+p$ collision. It is believed that MPI is the main reason behind the high multiplicity in $p+p$ collisions at the LHC. It was believed that MPI has only effect to the soft particle production, but recent ALICE result reveals that it can also affect the hard-particle production. In such case, the self normalized yield of heavy particle like $rm J/psi$ shows an increasing trend with event multiplicity. In the present contribution, we discuss the energy and multiplicity dependence of charmonium production to understand the effects of MPI on charmonium production.
High-multiplicity pp collisions at the Large Hadron Collider (LHC) energies have created special importance in view of the Underlying Event (UE) observables. The recent results of LHC, such as long range angular correlation, flow-like patterns, strangeness enhancement etc. in high multiplicity events are not yet completely understood. In the same direction, the understanding of multiplicity dependence of J/$psi$ production is highly necessary. Transverse spherocity, which is an event shape variable, helps to investigate the particle production by isolating the hard and the soft components. In the present study, we have investigated the multiplicity dependence of J/$psi$ production at mid-rapidity and forward rapidity through the transverse spherocity analysis and tried to understand the role of jets by separating the isotropic and jetty events from the minimum bias collisions. We have analyzed the J/$psi$ production at the mid-rapidity and forward rapidities via dielectron and dimuon channels, respectively using 4C tuned PYTHIA8 event generator. The analysis has been performed in two different center-of-mass energies: $sqrt{s}$ = 5.02 and 13 TeV, to see the energy dependence of jet contribution to the multiplicity dependence study of J/$psi$ production. Furthermore, we have studied the production dynamics through the dependence of thermodynamic parameters on event multiplicity and transverse spherocity.
$J/psi$ production in p-p ultra-peripheral collisions through the elastic and inelastic photoproduction processes, where the virtual photons emitted from the projectile interact with the target, are studied. The comparisions between the exact treatment results and the ones of equivalent photon approximation are expressed as $Q^{2}$ (virtuality of photon), $z$ and $p_{T}$ distributions, and the total cross sections are also estimated. The method developed by Martin and Ryskin is employed to avoid double counting when the different production mechanism are considered simultaneously. The numerical results indicate that, the equivalent photon approximation can be only applied to the coherent or elastic electromagnetic process, the improper choice of $Q^{2}_{mathrm{max}}$ and $y_{mathrm{max}}$ will cause obvious errors. And the exact treatment is needed to deal accurately with the $J/psi$ photoproduction.
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 $p_{rm T}$ transfer), the semi-hard processes of multiple interactions of partons might also lead to 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 $langle p_{rm T} rangle$ of J/$psi$ as a function of charged particle multiplicity for different hard-QCD processes. We have estimated a newly defined ratio, $r_{pp} = {langle p_{rm T}^{2} rangle}_{i}/{langle p_{rm T}^{2} rangle}_{rm MB}$, to understand J/$psi$ production in high-multiplicity $p+p$ collisions. For the first time we attempt to study the nuclear modification factor like observables ($R_{rm pp}$ and $R_{rm cp}$) to understand the QCD medium formed in high-multiplicity $p+p$ collisions.
We present theoretical model comparison with published ALICE results for D-mesons (D$^0$, D$^+$ and D$^{*+}$) in $p$+$p$ collisions at $sqrt{s}$ = 7 TeV and $p$+Pb collisions at $sqrt{s_{NN}}$ = 5.02 TeV. Event generator HIJING, transport calculation of AMPT and calculations from NLO(MNR) and FONLL have been used for this study. We found that HIJING and AMPT model predictions are matching with published D-meson cross-sections in $p$+$p$ collisions, while both under-predict the same in $p$+Pb collisions. Attempts were made to explain the $R_{pPb}$ data using NLO-pQCD(MNR), FONLL and other above mentioned models.
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