Proton-proton ($pp$) collision has been considered as a baseline to study the system produced in relativistic heavy-ion (AA) collisions with the basic assumption that no thermal medium is formed in $pp$ collisions. This warrants a cautious analysis o
f the system produced in $pp$ collisions at relativistic energies.In this work we investigate the charmonium suppression in $pp$ collisions at $sqrt{s} = 7$ and $13$ TeV to inspect the system formed in these collisions. In this work, charmonium suppression has been studied for various event multiplicities and transverse momenta by including the mechanisms of color screening, gluonic dissociation, collisional damping along with the regeneration due to correlated $cbar c$ pairs. Here we obtain a net suppression of charmonia at high-multiplicity events indicating the possibility towards the formation of quark-gluon plasma in $pp$ collisions.
The primordial matter of quarks and gluons, which filled our universe just after few micro-seconds of its creation through Big Bang, is expected to be created in the laboratory by colliding nuclei at relativistic energies. The ongoing nuclear collisi
on programs at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) are two experimental facilities, where matter in the state of Quark-Gluon Plasma (QGP) can be created and characterized. Heavy quarks, mainly charm and bottom quarks, are considered as novel probes to characterize QGP, and hence the QCD matter. Heavy quark diffusion coefficients play a significant role to understand the properties of QCD matter. Experimental measurements of nuclear suppression factor and elliptic flow are able to constrain the heavy quark diffusion coefficients, which is a key ingredient for the phenomenological study and disentangle different energy loss models. We give a general perspective of heavy quark diffusion coefficient in QGP and discuss its potential as a probe to disentangle different hadronization mechanisms, as well as to probe the initial electromagnetic field produced in non-central collisions. Experimental perspective on future measurements are discussed with special emphasis on heavy-flavors as next generation probes.
The possibility of formation of Bose-Einstein Condensation (BEC) is studied in $pp$ collisions at $sqrt s$ = 7 TeV at the Large Hadron Collider. A thermodynamically consistent non-extensive formulation of the identified hadron transverse momentum dis
tributions is used to estimate the critical temperature required to form BEC of charged pions, which are the most abundant species in a multi-particle production process in hadronic and nuclear collisions. The obtained results have been contrasted with the systems produced in Pb-Pb collisions to have a better understanding. We observe an explicit dependency of BEC critical temperature and number of particles in the pion condensates on the non-extensive parameter $q$, which is a measure of degree of non-equilibrium -- as $q$ decreases, the critical temperature increases and approaches to the critical temperature obtained from Bose-Einstein statistics without non-extensivity. Studies are performed on the final state multiplicity dependence of number of particles in the pion condensates in a wide range of multiplicity covering hadronic and heavy-ion collisions, using the inputs from experimental transverse momentum spectra.
Heavy-flavored hadrons are unique probes to study the properties of hot and dense QCD medium produced in ultra-relativistic heavy-ion collisions at RHIC and the LHC. Transverse spherocity is one of the event-topology variables used to separate jetty
and isotropic events from the pool of event samples. This study aims to understand the production dynamics of heavy-flavors through the transverse momentum spectra, double differential yield and mean transverse momentum of J/$psi$, $rm D^{0}$ and $Lambda_{c}^{+}$ as a function of charged-particle multiplicity and transverse spherocity. Further to investigate the possibility of hardonization of the charm quarks, transverse spherocity dependence ratios like $Lambda_{c}^{+}$/$rm D^{0}$ and $Lambda^{0}$/$K^{-}$ are studied. For the current analysis, the events are generated by using 4C tuned PYTHIA8 for pp at $sqrt{s}$ = 13 TeV, which is quite successful in explaining the heavy-flavor particle production at the LHC energies.
Transverse spherocity is an event shape observable having a very unique capability to separate the events based on their geometrical shapes. Recent results from experiments at the LHC suggest that transverse spherocity is an important event classifie
r in small collision systems. In this work, we use transverse spherocity for the first time in heavy-ion collisions and perform an extensive study on azimuthal anisotropy of charged particles produced in Pb-Pb collisions at $sqrt{s_{rm{NN}}} = 5.02$ TeV using A Multi-Phase Transport Model (AMPT). The azimuthal anisotropy is estimated using the 2-particle correlation method, which suppresses the non-flow effects significantly with an appropriate pseudorapidity gap of particle pairs. The results from AMPT are compared with estimations from PYTHIA8 (Angantyr) model and it is found that with the chosen pseudorapidity gap the residual non-flow effects become negligible. We found that the high spherocity events have nearly zero elliptic flow while low spherocity events contribute significantly to elliptic flow of spherocity-integrated events. Our studies indicate that using transverse spherocity in heavy-ion collisions, one can enhance and/or suppress the collective effects.
In the present work, we study the recent collision energy and multiplicity dependence of the charged particle transverse momentum spectra as measured by the ALICE collaboration in $pp$ collisions at $sqrt{s}$ = 5.02 and 13 TeV using the non-extensive
Tsallis distribution and the Boltzmann-Gibbs Blast Wave (BGBW) model. A thermodynamically consistent form of the Tsallis distribution is used to extract the kinetic freeze-out parameters from the transverse momentum spectra of charged particles at mid-rapidity. In addition, a comprehensive study of fitting range dependence of transverse momentum spectra on the freeze-out parameters is done using Tsallis statistics. The applicability of BGBW model is verified by fitting the transverse momentum spectra of the bulk part ($sim 2.5~ {rm GeV}/c$)for both 5.02 and 13 TeV energies and also in different multiplicity classes. The radial flow, $<beta>$ is almost independent of collision energy and multiplicity whereas the behavior of kinetic freeze-out temperature significantly depends on multiplicity classes. It is found that the Tsallis distribution generally leads to a better description for the complete transverse momentum spectra whereas the BGBW model explains the bulk part of the system.
Transport coefficients serve as important probes in characterizing the QCD matter created in high-energy heavy-ion collisions. Thermal and electrical conductivities as transport coefficients have got special significance in studying the time evolutio
n of the created matter. We have adopted color string percolation approach for the estimation of thermal conductivity ($kappa$), electrical conductivity ($sigma_{el}$) and their ratio, which is popularly known as Wiedemann-Franz law in condensed matter physics. The ratio $kappa/sigma_{el}T$, which is also known as Lorenz number ($mathbb{L}$) is studied as a function of temperature and is compared with various theoretical calculations. We observe that the thermal conductivity for hot QCD medium is almost temperature independent in the present formalism and matches with the results obtained in ideal equation of state (EOS) for quark-gluon plasma with fixed coupling constant ($alpha_s$). The obtained Lorenz number is compared with the Stefan-Boltzmann limit for an ideal gas. We observe that a hot QCD medium with color degrees of freedom behaves like a free electron gas.
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 t
hat 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.
Recently, transport coefficients viz. shear viscosity, electrical conductivity etc. of strongly interacting matter produced in heavy-ion collisions have drawn considerable interest. We study the normalised electrical conductivity ($sigma_{rm el}$/T)
of hot QCD matter as a function of temperature (T) using the Color String Percolation Model (CSPM). We also study the temperature dependence of shear viscosity and its ratio with electrical conductivity for the QCD matter. We compare CSPM estimations with various existing results and lattice Quantum Chromodynamics (lQCD) predictions with (2+1) dynamical flavours. We find that $sigma_{rm el}$/T in CSPM has a very weak dependence on the temperature. We compare CSPM results with those obtained in Boltzmann Approach to Multi-Parton Scatterings (BAMPS) model. A good agreement is found between CSPM results and predictions of BAMPS with fixed strong coupling constant.
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.
