arXiv subjects

Dhananjaya Thakur

Publications and source records attributed to Dhananjaya Thakur.

12 recordsLinked to original sources

arXiv2022

Dynamics of Hot QCD Matter -- Current Status and Developments

The discovery and characterization of hot and dense QCD matter, known as Quark Gluon Plasma (QGP), remains the most international collaborative effort and synergy between theorists and experimentalists in modern nuclear physics to date. The experimentalists around the world not only collect an unprecedented amount of data in heavy-ion collisions, at Relativistic Heavy Ion Collider (RHIC), at Brookhaven National Laboratory (BNL) in New York, USA, and the Large Hadron Collider (LHC), at CERN in Geneva, Switzerland but also analyze these data to unravel the mystery of this new phase of matter that filled a few microseconds old universe, just after the Big Bang. In the meantime, advancements in theoretical works and computing capability extend our wisdom about the hot-dense QCD matter and its dynamics through mathematical equations. The exchange of ideas between experimentalists and theoreticians is crucial for the progress of our knowledge. The motivation of this first conference named "HOT QCD Matter 2022" is to bring the community together to have a discourse on this topic. In this article, there are 36 sections discussing various topics in the field of relativistic heavy-ion collisions and related phenomena that cover a snapshot of the current experimental observations and theoretical progress. This article begins with the theoretical overview of relativistic spin-hydrodynamics in the presence of the external magnetic field, followed by the Lattice QCD results on heavy quarks in QGP, and finally, it ends with an overview of experiment results.

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arXiv2021

Extension of Glauber-like model for Proton-Proton collisions using anisotropic and inhomogeneous density profile

Results from proton-proton ($pp$) collisions have routinely been used as a baseline to analyze and understand the production of QCD matter expected to be produced in nuclear collisions. But recent studies of small systems formed in $pp$ collisions at the LHC energies hint at the possibility of producing medium with collective behavior. Therefore, results from $pp$ collisions required more careful investigation to understand whether QCD matter is produced in high multiplicity $pp$ collisions. With this motivation, the Glauber model traditionally used to study the heavy-ion collision dynamics at high energy is applied here to understand the dynamics of $pp$ collisions. We have used anisotropic and inhomogeneous quark/gluon-based proton density profile, a realistic picture obtained from deep inelastic scattering results and this model explains the charged particle multiplicity distribution of $pp$ collisions at LHC energies very well. Collision geometric properties like impact parameter and mean number of binary collisions ($\langle N_{coll} \rangle$), mean number of participants ($\langle N_{part} \rangle$) at different multiplicities are determined for $pp$ collisions. We further used these collision geometric properties to estimate average charged-particle pseudorapidity density ($\langle dN_{ch}/dη\rangle$) and found it to be comparable with the experimental results. Knowing $\langle N_{coll} \rangle$, we have obtained nuclear modification-like factor ($R_{pp}$) in $pp$ collisions which has not been done before to the best of our knowledge.

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arXiv2021

Investigating Heavy-flavor vs Light-flavor Puzzle with Event Topology and Multiplicity in Proton+Proton Collisions at $\sqrt{s}$ = 13 TeV using PYTHIA8

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/$ψ$, $\rm D^{0}$ and $Λ_{c}^{+}$ 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 $Λ_{c}^{+}$/$\rm D^{0}$ and $Λ^{0}$/$K^{-}$ 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.

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arXiv2020

Multiplicity Dependence of J/$ψ$ Production and QCD Dynamics in $p+p$ Collisions at $\sqrt{s}$ = 13 TeV

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/$ψ$. At the LHC, an approximately linear increase of the relative J/$ψ$ 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/$ψ$ production using pQCD inspired event generator, PYTHIA8 tune 4C, in $p+p$ collisions at $\sqrt{s} =$13 TeV by investigating relative J/$ψ$ yield and relative $\langle p_{\rm T} \rangle$ of J/$ψ$ 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/$ψ$ 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.

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arXiv2020

$J/ψ$ Production Dynamics: Event shape, Multiplicity and Rapidity dependence in Proton+Proton Collisions at LHC energies using PYTHIA8

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/$ψ$ 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/$ψ$ 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/$ψ$ 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/$ψ$ production. Furthermore, we have studied the production dynamics through the dependence of thermodynamic parameters on event multiplicity and transverse spherocity.

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arXiv2020

Glauber model for small system using anisotropic and inhomogeneous density profile of proton

Recent studies reveal that at high energies, collisions of small system like $p+p$ gives signatures similar to that widely observed in heavy ion collisions hinting towards a possibility of forming a medium with collective behaviour. With this motivation, we have used the Glauber model, which is traditionally applied to heavy ion collisions, in small system using anisotropic and inhomogeneous density profile of proton and found that the proposed model reproduces the charged particle multiplicity distribution of $p+p$ collisions at LHC energies very well. Collision geometric properties like mean impact parameter, mean number of binary collisions ($\langle N_{coll} \rangle$) and mean number of participants ($\langle N_{part} \rangle$) at different multiplicities are determined. Having estimated $\langle N_{coll} \rangle$, we have calculated nuclear modification-like factor ($R_{HL}$) in $p+p$ collisions. We also estimated eccentricity and elliptic flow as a function of charged particle multiplicity using the linear response to initial geometry.

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arXiv2019

Quarkonium production as a function of charged-particle multiplicity in pp and p--Pb collisions measured by ALICE at the LHC

Quarkonium production as a function of the charged-particle multiplicity could provide an insight into particle production processes at the partonic level in hadronic collisions. It is believed that multiple partonic interactions play an important role in particle production and affect both soft and hard processes. The study of correlations between quarkonia and charged-particle multiplicity may provide information about this. In this contribution, ALICE measurements of J$/ψ$ and $Υ$ production as a function of charged-particle multiplicity are presented for pp collisions at center-of-mass energies $\sqrt{s}$ = 5.02 and 13 TeV. A similar measurement performed in p\textendash Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 8.16 TeV at both forward and backward rapidity is also discussed.

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arXiv2018

$J/ψ$ production as a function of charged-particle multiplicity with ALICE at the LHC

At LHC energies, the charged-particle multiplicity dependence of particle production is a topic of considerable interest in $pp$ collisions. It has been argued that multiple partonic interactions play an important role in particle production mechanisms, not only affecting the soft processes but also the hard processes. Recently, ALICE has measured $J/ψ$ production as a function of charged-particle multiplicity to study the correlation between soft and hard processes. In this contribution, we present the $J/ψ$ production versus multiplicity for $pp$ and $p-Pb$ collisions measured by ALICE. We compare the results with different theoretical models.

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arXiv2018

Insight into Multiple Partonic Interactions and Production of Charmonia in p+p Collisions at the LHC energies

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 $\rm J/ψ$ 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.

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arXiv2018

Role of Multi-Parton Interactions on $J/ψ$ production in $p+p$ collisions at LHC Energies

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 $J/ψ$ yield ($\frac{dN_{J/ψ}/dy}{ }$) with relative charged particle multiplicity density ($\frac{dN_{ch}/dy}{ }$). 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 $J/ψ$ production. The ratio of $ψ(2S)$ to $J/ψ$ is also studied as a function of charged particle multiplicity at LHC energies.

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arXiv2017

Estimation of Stopped Protons at Energies Relevant for a Beam Energy Scan at the BNL Relativistic Heavy-Ion Collider

The recent net-proton fluctuation results of the STAR (Solenoidal Tracker At RHIC) experiment from beam energy scan (BES) program at the BNL Relativistic Heavy Ion Collider (RHIC) have drawn much attention to exploring the QCD critical point and the nature of deconfinement phase transition. There has been much speculation that the non-monotonic behavior of $κσ^{2}$ of the produced protons around $\sqrt{s_{\rm NN}}$ = 19.6 GeV in the STAR results may be due to the existence of QCD critical point. However, the experimentally measured proton distributions contain protons from heavy resonance decays, from baryon stopping and from direct production processes. These proton distributions are used to estimate the net-proton number fluctuation. Because it is difficult to disentangle the protons from the above-mentioned sources, it is better to devise a method which will account for the directly produced baryons (protons) to study the dynamical fluctuation at different center-of-mass energies. This is because, it is assumed that any associated criticality in the system could affect the particle production mechanism and hence the dynamical fluctuation in various conserved numbers. In the present work, we demonstrate a method to estimate the number of stopped protons at RHIC BES energies for central $0-5\%$ \auau collisions within STAR acceptance and discuss its implications on the net-proton fluctuation results.

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arXiv2016

Indication of a Differential Freeze-out in Proton-Proton and Heavy-Ion Collisions at RHIC and LHC energies

The experimental data from the RHIC and LHC experiments of invariant pT spectra in A+A and p + p collisions are analysed with Tsallis distributions in different approaches. The information about the freeze-out surface in terms of freeze-out volume, temperature, chemical potential and radial flow velocity for different particle species are obtained. Further, these parameters are studied as a function of the mass of the secondary particles. A mass-dependent differential freeze-out is observed which does not seem to distinguish between particles and their antiparticles. Further a mass-hierarchy in the radial flow is observed, meaning heavier particles suffer lower radial flow. Tsallis distribution function at finite chemical potential is used to study the mass dependence of chemical potential. The peripheral heavy-ion and proton-proton collisions at the same energies seem to be equivalent in terms of the extracted thermodynamic parameters.

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