arXiv subjects

Raghunath Sahoo

Publications and source records attributed to Raghunath Sahoo.

At least 91 records · Page 5Linked to original sources

arXiv2023

Conductivity, diffusivity, and violation of Wiedemann-Franz Law in a hadron resonance gas with van der Waals interactions

In this work, a hadron resonance gas under van der Waals (VDW) interactions has been studied. Both attractive and repulsive interactions between the meson-meson and (anti)baryon-(anti)baryon have been taken into consideration. Various transport properties such as electrical conductivity ($σ_{\rm el}$) and thermal conductivity ($κ_{\rm th}$) have been estimated by solving the Boltzmann transport equation under the relaxation time approximation. The effect of baryochemical potential ($μ_{\rm B}$) and temperature is also explicitly explored for the mentioned observables. Comparisons have been made with the results obtained from other existing theoretical models. We observe the violation of Wiedemann-Franz law in a hadron resonance gas at a high-temperature regime. The corresponding diffusivities have also been estimated, which can help us to understand the system in a better way.

hep-ph↗

arXiv2023

Understanding the QCD medium by the diffusion of charm quarks using a Color String Percolation Model

We study the drag and diffusion coefficients of the charm quark in the deconfined matter produced in the ultra-relativistic collisions by taking the Color String Percolation Model (CSPM) approach. CSPM, being a QCD-inspired model, can give us essential information about the hot and dense system produced in ultra-relativistic collisions. With the information on initial percolation temperature and percolation density, we estimate the relaxation time ($τ_{c}$), drag coefficient ($γ$), transverse momentum diffusion coefficient ($B_{0}$), and spatial diffusion coefficient ($D_{s}$) of charm quark inside a deconfined medium. Finally, we compare the obtained results with lattice QCD and with various other theoretical models. A good agreement can be observed between the results obtained from CSPM and lattice QCD.

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arXiv2022

Predictions on global properties in O+O collisions at the Large Hadron Collider using a multi-phase transport model

Oxygen ($^{16}$O) ions are planned to be injected at the Large Hadron Collider (LHC) in its next runs, and a day of physics run is anticipated for O+O collisions at $\sqrt{s_{\rm{NN}}}$ = 7 TeV. As the system size of O+O collisions has the final state multiplicity overlap with those produced in pp, p+Pb and Pb+Pb collisions, the study of global properties in O+O collisions may provide a deeper insight into the heavy-ion-like behavior observed in small collision systems and its similarities/differences with a larger system like Pb+Pb collisions. In the present work, we report the predictions for global properties in O+O collisions at $\sqrt{s_{\rm{NN}}}$ = 7 TeV using a multi-phase transport model (AMPT). We report the mid-rapidity charged-particle multiplicity, transverse mass, Bjorken energy density, pseudo-rapidity distributions, squared speed of sound, transverse momentum ($p_{\rm T}$) spectra, the kinetic freeze-out parameters, and $p_{\rm T}$-differential particle ratio as a function of collision centrality. Further, we have studied the transverse momentum-dependent elliptic flow of charged particles. The results are shown for Woods-Saxon and harmonic oscillator nuclear density profiles. In addition, we have compared the results with an $α$-clustered structure incorporated inside the oxygen nucleus. Average charged-particle multiplicity and the Bjorken energy density show a significant increase in most central collisions for the harmonic oscillator density profile, while other global properties show less dependence on the density profiles considered in this work. The results from the $α$-clustered structure incorporated inside the oxygen nucleus show similar initial energy density and final charged-particle multiplicity as observed for the harmonic oscillator density profile.

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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.

nucl-th↗

arXiv2022

Analysis of identified particle transverse momentum spectra produced in pp, p--Pb and Pb--Pb collisions at the LHC using Tsallis--Pareto-type function

In the framework of a multi-source thermal model at the partonic-level, we have analyzed transverse momentum spectra of hadrons measured by the ALICE Collaboration in proton-proton ($pp$ or $p$-$p$) collisions at the center-of-mass energy of $\sqrt{s}=7$ and 13 TeV, proton-lead ($p$-Pb) collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV, and lead-lead (Pb-Pb) collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV. For meson(baryon), the contributions of two(three) constituent quarks are considered, in which each quark contributes to hadron transverse momentum to obey the revised phenomenological Tsallis transverse momentum distribution for the Maxwell-Boltzmann particles (the TP-like function in short) with isotropic random azimuthal angle. Three main parameters, namely, the revised index $a_0$, effective temperature $T$, and entropy-related index $n$ are obtained, which show the same tendency for small and large systems with respect to the centrality (or multiplicity) of events, rest mass of hadrons, and constituent mass of quarks.

hep-ph↗

arXiv2022

Charmonium suppression in ultra-relativistic proton-proton collisions at LHC energies: A hint for QGP in small systems

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 of the system produced in $pp$ collisions at relativistic energies.In this work we investigate the charmonium suppression in $pp$ collisions at $\sqrt{s} = 5.02, 7$ and $13$ TeV energies. Further, 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 regeneration due to correlated $c\bar c$ pairs. Here we obtain a net suppression of charmonia at high-multiplicity events indicating the possibility of the formation of quark-gluon plasma in $pp$ collisions.

hep-ph↗

arXiv2022

Estimating Elliptic Flow Coefficient in Heavy Ion Collisions using Deep Learning

Machine Learning (ML) techniques have been employed for the high energy physics (HEP) community since the early 80s to deal with a broad spectrum of problems. This work explores the prospects of using Deep Learning techniques to estimate elliptic flow ($v_2$) in heavy-ion collisions at the RHIC and LHC energies. A novel method is developed to process the input observables from particle kinematic information. The proposed DNN model is trained with Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV minimum bias events simulated with AMPT model. The predictions from the ML technique are compared to both simulation and experiment. The Deep Learning model seems to preserve the centrality and energy dependence of $v_2$ for the LHC and RHIC energies. The DNN model is also quite successful in predicting the $p_{\rm T}$ dependence of $v_2$. When subjected to event simulation with additional noise, the proposed DNN model still keeps the robustness and prediction accuracy intact up to a reasonable extent.

hep-ph↗

arXiv2022

Event topology and constituent-quark scaling of elliptic flow in heavy-ion collisions at the Large Hadron Collider using a multiphase transport model

Transverse spherocity is an event shape observable, which separates the events based on their geometrical shapes. In this work, we use transverse spherocity to study the identified light flavor production in heavy-ion collisions using A Multi-Phase Transport (AMPT) model. We obtain the elliptic flow coefficients for pions, kaons and protons in Pb+Pb collisions at $\sqrt{s_{\rm{NN}}} = 5.02$ TeV as a function of transverse spherocity and collision centrality. Also, we study the number of constituent-quark (NCQ) scaling of elliptic flow which interprets the dominance of the quark degrees of freedom at the early stages of the collision. We observe a clear dependence of the elliptic flow for identified particles on transverse spherocity. It is found that the NCQ-scaling is strongly violated in events with low transverse spherocity compared to transverse spherocity-integrated events, confirming the fragmentation-based hadronization mechanism for high-momentum partons involved in the dynamics of jetty-like events.

hep-ph↗

arXiv2022

Exploring the effect of hadron cascade-time on particle production in Xe+Xe collisions at $\sqrt{s_{\rm{NN}}}$ = 5.44 TeV through a multi-phase transport model

Heavy-ion collisions at ultra-relativistic energies provide extreme conditions of energy density and temperature to produce a deconfined state of quarks and gluons. Xenon (Xe) being a deformed nucleus further gives access to the effect of initial geometry on final state particle production. This study focuses on the effect of nuclear deformation and hadron cascade-time on the particle production and elliptic flow using A Multi-Phase Transport (AMPT) model in Xe+Xe collisions at $\sqrt{s_{\rm NN}}$ = 5.44 TeV. We explore the effect of hadronic cascade-time on identified particle production through the study of $p_{\rm T}$-differential particle ratios. The effect of hadronic cascade-time on the generation of elliptic flow is studied by varying the cascade-time between 5 and 25 fm/$c$. This study shows the final state interactions among particles generate additional anisotropic flow with increasing hadron cascade-time, especially at very low and high-$p_{\rm T}$.

hep-ph↗

arXiv2022

Possible Formation of a Perfect Fluid in $pp$, $p$-Pb, Xe-Xe and Pb-Pb Collisions at the Large Hadron Collider Energies: A Color String Percolation Approach

Isothermal compressibility ($κ_{\rm T}$) is an important thermodynamic observable which gives information about the deviation of a system from perfect fluid behavior. In this work, for the first time we have estimated the isothermal compressibility of QCD matter formed in high energy hadronic and nuclear collisions using color string percolation model (CSPM), where we investigate the change in $κ_{\rm T}$ as a function of final state charged particle multiplicity and initial percolation temperature across various collision species. The estimated initial percolation temperature for different collision systems at different collision energies helps us to have a better understanding of the system at the initial phase of evolution. The comparison of the CSPM results for isothermal compressibility with that for the well known fluids, indicates that the matter formed in heavy-ion collisions might be the {\it closest perfect fluid} found in nature. This estimation complements the well-known observation of minimum shear viscosity to entropy density ratio for a possible QGP medium created in heavy-ion collision experiments. A threshold of pseudorapidity density of charged particles, $\langle dN_{\rm ch}/dη\rangle \geq 20 $ in the final state event multiplicity is observed, after which one may look for a possible QGP formation at the LHC energies.

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arXiv2022

Jet Transport Coefficient at the Large Hadron Collider Energies in a Color String Percolation Approach

Within the color string percolation model (CSPM), jet transport coefficient, $\hat{q}$, is calculated for various multiplicity classes in proton-proton and centrality classes in nucleus-nucleus collisions at the Large Hadron Collider energies for a better understanding of the matter formed in ultra-relativistic collisions. $\hat{q}$ is studied as a function of final state charged particle multiplicity (pseudorapiditydensity at midrapidity), initial state percolation temperature and energy density. The CSPM results are then compared with different theoretical calculations from the JET Collaboration those incorporate particle energy loss in the medium.

hep-ph↗

arXiv2022

Event topology and global observables in heavy-ion collisions at the Large Hadron Collider

Particle production and event topology are very strongly correlated in high-energy hadronic and nuclear collisions. Event topology is decided by the underlying particle production dynamics and medium effects. Transverse spherocity is an event shape observable, which has been used in pp and heavy-ion collisions to separate the events based on their geometrical shapes. It has the unique capability to distinguish between jetty and isotropic events. In this work, we have implemented transverse spherocity in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV using A Multi-Phase Transport Model (AMPT). While awaiting for experimental explorations, we perform a feasibility study of dependence of transverse spherocity on some of the global observables in heavy-ion collisions at the Large Hadron Collider energies. These global observables include the Bjorken energy density ($ε_{\rm B_j}$), speed of sound ($c_{\rm s}^2$) in the medium and the kinetic freeze-out properties for different collision centralities. The present study reveals about the usefulness of event topology dependent measurements in heavy-ion collisions in contrast to proton-proton collisions.

hep-ph↗

arXiv2022

Possible early universe signals in proton collisions at the Large Hadron Collider

Our universe was born about 13.8 billion years ago from an extremely hot and dense singular point, in a process known as the Big Bang. The hot and dense matter which dominated the system within a few microseconds of its birth was in the form of a soup of elementary quarks and gluons, known as the quark-gluon plasma (QGP). Signatures compatible with the formation of the QGP matter have experimentally been observed in heavy-ion (such as Au or Pb) collisions at ultra-relativistic energies. Recently, experimental data of proton-proton (pp) collisions at the CERN Large Hadron Collider (LHC) have also shown signals resembling those of the QGP formation, which made these studies quite stimulating as to how the collision of small systems features in producing the early universe signals. In this article, we report on some of the compelling experimental results and give an account of the present understanding. We review the pp physics program at the LHC and discuss future prospects in the context of exploring the nature of the primordial matter in the early universe.

hep-ph↗

arXiv2021

Charming Charm, Beautiful Bottom, and Quark-Gluon Plasma in the Large Hadron Collider Era

After a few microseconds of the creation of our Universe through the Big Bang, the primordial matter was believed to be a soup of the fundamental constituents of matter -- quarks and gluons. This is expected to be created in the laboratory by colliding heavy nuclei at ultra-relativistic speeds. A plasma of quarks and gluons, called Quark-Gluon Plasma (QGP) can be created at the energy and luminosity frontiers in the Relativistic Heavy Ion Collider (RHIC), at Brookhaven National Laboratory, New York, USA, and the Large Hadron Collider (LHC) at CERN, Geneva, Switzerland. Heavy quarks, namely the charm and bottom quarks, are considered as novel probes to characterize QGP, and hence the produced Quantum Chromodynamics (QCD) matter. Heavy quark transport coefficients play a significant role in understanding the properties of QGP. Experimental measurements of nuclear suppression factor and elliptic flow can constrain the heavy quark transport coefficients, which are key ingredients for phenomenological studies, and they help to disentangle different energy loss mechanisms. We give a general perspective of the heavy quark drag and diffusion coefficients in QGP and discuss their potentials as probes to disentangle different hadronization mechanisms, as well as to probe the initial electromagnetic fields produced in non-central heavy-ion collisions. Experimental perspectives on future measurements are discussed with special emphasis on heavy-flavors as next-generation probes in view of new technological developments.

hep-ph↗

arXiv2021

Thermodynamic and Transport Properties of Matter Formed in $pp$, $p$-Pb, Xe-Xe and Pb-Pb Collisions at the Large Hadron Collider using Color String Percolation Model

To have a better understanding of the matter formed in ultra-relativistic collisions, using the Color String Percolation Model (CSPM), we have estimated initial energy density, mean free path, squared speed of sound, shear viscosity to entropy density ratio ($η/s$), bulk viscosity to entropy density ratio and bulk modulus for $pp$, $p$-Pb, Xe-Xe and Pb-Pb collisions at the Large Hadron Collider (LHC). These observables are studied as a function of final state charged particle multiplicity density and initial state percolation temperature. The results from this work are compared with the results from well known QCD models and with the transport properties of matter found in day-to-day life. These observables allow us to conclude an array of important findings about the matter formed in high energy collisions at the LHC. This work gives a threshold of charged particle multiplicity $\langle dN_{ch}/dη\rangle \simeq$ 20, after which there are indications of change in the dynamics of the systems. The critical initial energy density and temperature as estimated by lattice QCD, are observed to be achieved for events with final state multiplicity $\langle dN_{ch}/dη\rangle \geq$ 20. In addition, for these high-multiplicity events, the estimated $η/s$ are comparable with that is observed for heavy-ion collisions, which is an indication of a strongly coupled Quark Gluon Plasma. This makes LHC high-multiplicity $pp$ collision events as probable candidates for the search of QGP droplets.

hep-ph↗

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.

hep-ph↗

arXiv2021

Study of the jet transport coefficient at the Large Hadron Collider energies using Color String Percolation Model

In order to have a better understanding of the matter formed in ultra-relativistic collisions, we estimate the jet transport coefficient, $\hat q$, within the Color Sting Percolation Model (CSPM) for various multiplicity classes in proton-proton collisions and centrality classes in nucleus-nucleus collisions at the Large Hadron Collider energies. We study $\hat q$ as a function of final state charged-particle multiplicity and initial percolation temperature. Finally, we compare our obtained results with those calculated from the JET collaboration.

hep-ph↗

arXiv2021

Implementation of machine learning techniques to predict impact parameter and transverse spherocity in heavy-ion collisions at the LHC

Machine learning techniques have been quite popular recently in the high-energy physics community and have led to numerous developments in this field. In heavy-ion collisions, one of the crucial observables, the impact parameter, plays an important role in the final-state particle production. This being extremely small (i.e. of the order of a few fermi), it is almost impossible to measure impact parameter in experiments. In this work, we implement the ML-based regression technique via Gradient Boosting Decision Trees (GBDT) to obtain a prediction of impact parameter in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV using A Multi-Phase Transport (AMPT) model. After its successful implementation in small collision systems, transverse spherocity, an event shape observable, holds an opportunity to reveal more about the particle production in heavy-ion collisions as well. In the absence of any experimental exploration in this direction at the LHC yet, we suggest an ML-based regression method to estimate centrality-wise transverse spherocity distributions in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV by training the model with minimum bias collision data. Throughout this work, we have used a few final state observables as the input to the ML-model, which could be easily made available from collision data. Our method seems to work quite well as we see a good agreement between the simulated true values and the predicted values from the ML-model.

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