arXiv subjects

Santosh K Das

Publications and source records attributed to Santosh K Das.

16 recordsLinked to original sources

arXiv2023

Non-perturbative diffusion of Heavy Quark moving in a hot and magnetised Quark Gluon Plasma

Heavy Quarks (HQs) serve as excellent probes to understand various characteristics of deconfined hot QCD medium, comprising light quarks and gluons, created in the Heavy Ion Collisions (HICs). Strong magnetic fields in non-central HICs may significantly affect HQ dynamics in this medium. Exploring the impact of the magnetic field on the perturbative and non-perturbative transport coefficients of HQ is an intriguing endeavor. This necessitates the development of a comprehensive theoretical framework accommodating the non-perturbative Quantum Chromo Dynamics(npQCD) description alongside perturbative QCD(pQCD). The present work provides such a formulation in which Quarkonium potential in the hot and magnetic QCD medium is implemented as the effective gluon propagator to calculate the rate of elastic scattering between HQ and the light partons inside a medium of hot Quark Gluon Plasma(QGP) in the presence of a strong but uniform magnetic field. Diffusion coefficients of a charm quark have been computed for a short-range Yukawa potential ( pQCD) as well as a long-range confining/non-perturbative potential (npQCD) for two cases in which the velocity of the charm quark is parallel and perpendicular to the magnetic field respectively. Non-perturbative contribution is seen to dominate over the perturbative one in the regime of low temperatures and low to intermediate momenta of charm quark. As the momentum of charm quark as well as the temperature of the medium increase pQCD starts to gain on the npQCD contribution, ultimately prevailing at higher temperatures and charm momenta.

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arXiv2019

Heavy quark diffusion in a Polyakov loop plasma

We calculate the transport coefficients, drag and momentum diffusion, of a heavy quark in a thermalized plasma of light quarks in the background of Polyakov loop. Quark thermal mass and the gluon Debye mass are calculated in a non-trivial Polyakov loop background. The constituent quark masses and the Polyakov loop is estimated within a Polyakov loop quark meson (PQM) model. The relevant scattering amplitudes for heavy quark and light partons in the background of Polyakov loop has been estimated within the matrix model. We have also compared the results with the Polyakov loop parameter estimated from lattice QCD simulations. We have studied the temperature and momentum dependence of heavy quark drag and diffusion coefficients. It is observed that the temperature dependence of the drag coefficient is quite weak which may play a key role to understand heavy quark observables at RHIC and LHC energies.

hep-ph↗

arXiv2015

Toward an understanding of the $R_{AA}$ and $v_2$ puzzle for heavy quarks

One of the primary aims of the ongoing nuclear collisions at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies is to create a Quark Gluon Plasma (QGP). The heavy quarks constitutes a unique probe of the QGP properties. Both at RHIC and LHC energies a puzzling relation between the nuclear modification factor $R_{AA}(p_T)$ and the elliptic flow $v_2(p_T)$ related to heavy quark has been observed which challenged all the existing models.\\ We discuss how the temperature dependence of the heavy quark drag coefficient can address for a large part of such a puzzle. We have considered four different models to evaluate the temperature dependence of drag and diffusion coefficients propagating through a quark gluon plasma (QGP). All the four different models are set to reproduce the same $R_{AA}(p_T)$ experimentally observed at RHIC energy. We have found that for the same $R_{AA}(p_T)$ one can generate $2-3$ times more $v_{2}$ depending on the temperature dependence of the heavy quark drag coefficient.

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arXiv2012

Drag and diffusion coefficients of $B$ mesons in hot hadronic matter

The drag and diffusion coefficients of a hot hadronic medium consisting of pions, kaons and eta using open beauty mesons as a probe have been evaluated. The interaction of the probe with the hadronic matter has been treated in the framework of chiral perturbation theory. It is observed that the magnitude of both the transport coefficients are significant, indicating substantial amount of interaction of the heavy mesons with the thermal bath. The results may have significant impact on the experimental observables like the suppression of single electron spectra originating from the decays of heavy mesons produced in nuclear collisions at RHIC and LHC energies

hep-ph↗

arXiv2012

Examination of the Gunion-Bertsch formula for soft gluon radiation

The spectrum of emitted gluons from the process g+g -> g+g+g has been evaluated by relaxing some of the approximations used in earlier works. The difference in the results from earlier calculations have been pointed out. The formula obtained in the present work has been applied to estimate physical quantities like equilibration rate of gluons and the energy loss of fast gluon in the gluonic plasma.

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arXiv2012

Probing Quark Gluon Plasma by Heavy Flavors

The drag and diffusion coefficients of charm and bottom quarks propagating through quark gluon plasma (QGP) have been evaluated within the framework of perturbative Quantum Chromodynamics (pQCD). Both radiative and collisional processes of dissipation are included in evaluating these transport coefficients. The dead cone as well as the LPM effects on radiative energy loss of heavy quarks have also been considered. The Fokker Planck equation has been solved to study the dissipation of heavy quarks momentum in QGP. The nuclear suppression factor, $R_{\mathrm AA}$ and the elliptic flow $v_2^{HF}$ of the non-photonic electrons resulting from the semi-leptonic decays of hadrons containing charm and bottom quarks have been evaluated for RHIC and LHC nuclear collision conditions. We find that the observed $R_{\mathrm AA}$ and $v_2$ at RHIC can be reproduced simultaneously within the pQCD framework.

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arXiv2011

Momentum dependence of drag coefficients and heavy flavour suppression in quark gluon plasma

The momentum dependence of the drag coefficient of heavy quarks propagating through quark gluon plasma (QGP) has been evaluated. The results have been used to estimate the nuclear suppression factor of charm and bottom quarks in QGP. We observe that the momentum dependence of the transport coefficients plays crucial role in the suppression of the heavy quarks and consequently in discerning the properties of QGP using heavy flavours as a probe. We show that the large suppression of the heavy quarks observed at RHIC and LHC is predominantly due to the radiative losses. The suppression of $D^0$ in Pb+Pb collisions at LHC energy - recently measured by the ALICE collaboration has also been studied.

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arXiv2011

Dragging $D$ mesons by hot hadrons

We evaluate the drag and diffusion coefficients of a hot hadronic medium consisting of pions, nucleons, kaons and eta using open charm mesons as a probe. The interaction of the probe with the hadronic matter has been treated in the framework of effective field theory. It is observed that the magnitude of both the transport coefficients are significant, indicating substantial amount of interaction of the heavy mesons with the thermal hadronic system. The results may have noticeable impact on the experimental observable like the suppression of single electron spectra originating form the decays of heavy mesons in nuclear collisions at relativistic energies.

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arXiv2011

Transport coefficients of gluonic fluid

The shear ($η$) and bulk ($ζ$) viscous coefficients have been evaluated for a gluonic fluid. The elastic, $gg \rightarrow gg$ and the inelastic, number non-conserving, $gg\rightarrow ggg$ processes have been considered as the dominant perturbative processes in evaluating the viscous co-efficients to entropy density ($s$) ratios. Recently the processes: $gg \rightarrow ggg$ has been revisited and a correction to the widely used Gunion-Bertsch (GB) formula has been obtained. The $η$ and $ζ$ have been evaluated for gluonic fluid with the formula derived recently. The sensitivity of the quantity, $η/s$ on the running coupling constant is also discussed. At $α_s=0.3$ we get $η/s=0.24$ which is close to the value obtained from the analysis of the elliptic flow at RHIC experiments.

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arXiv2011

Heavy flavour suppression and flow

The drag and diffusion coefficients of charm and bottom quarks propagating through quark gluon plasma have been evaluated for conditions relevant to nuclear collisions at Large Hadron Collider and Relativistic Heavy Ion Collider. Both the radiative and collisional processes of energy loss are included in evaluating the {\it effective} drag and diffusion coefficients. The Landau-Pomeronchuk-Migdal (LPM) and the dead cone effects on the radiative energy loss of heavy quarks have been included. With the effective transport coefficients the Fokker Plank (FP) equation has been solved for the evolution of heavy quarks in QGP. The solution of the FP equation has been used to evaluate the nuclear suppression factor, $R_{\mathrm AA}$ and the elliptic flow, $v_2^{HF}$ for the non-photonic single electron spectra resulting from the semi-leptonic decays of hadrons containing charm and bottom quarks. It is observed that the experimental data from RHIC on $R_{\mathrm AA}$ and $v_2^{HF} $ can be reproduced simultaneously within the pQCD framework for the same set of inputs.

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arXiv2010

Elliptic flow of heavy flavors

The propagation of charm and bottom quarks through an ellipsoidal domain of quark gluon plasma has been studied within the ambit of non-equilibrium statistical mechanics. Energy dissipation of heavy quarks by both radiative and collisional processes are taken in to account. The experimental data on the elliptic flow of the non-photonic electrons resulting from the semi-leptonic decays of hadrons containing heavy flavours has been reproduced with the same formalism that has been used earlier to reproduce the nuclear suppression factors. The elliptic flow of the non-photonic electron from heavy meson decays produced in nuclear collisions at LHC and low energy RHIC run have also been predicted.

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arXiv2010

Radial Flow from Electromagnetic Probes and Signal of Quark Gluon Plasma

A first attempt has been made to extract the evolution of radial flow from the analysis of the experimental data on electromagnetic probes experimentally measured at SPS and RHIC energies. The $p_T$ spectra of photons and dileptons measured by WA98 and NA60 collaborations respectively at CERN-SPS and the photon spectra obtained by PHENIX collaboration at BNL-RHIC have been used to constrain the theoretical models, rendering the outcome of the analysis largely model independent. We argue that the variation of the radial velocity with invariant mass is indicative of a phase transition from initially produced partons to hadrons at SPS and RHIC energies.

nucl-th↗

arXiv2010

Dragging Heavy Quarks in Quark Gluon Plasma at the Large Hadron Collider

The drag and diffusion coefficients of charm and bottom quarks propagating through quark gluon plasma (QGP) have been evaluated for conditions relevant to nuclear collisions at Large Hadron Collider (LHC). The dead cone and Landau-Pomeronchuk-Migdal (LPM) effects on radiative energy loss of heavy quarks have been considered. Both radiative and collisional processes of energy loss are included in the {\it effective} drag and diffusion coefficients. With these effective transport coefficients we solve the Fokker Plank (FP) equation for the heavy quarks executing Brownian motion in the QGP. The solution of the FP equation has been used to evaluate the nuclear suppression factor, $R_{\mathrm AA}$ for the non-photonic single electron spectra resulting from the semi-leptonic decays of hadrons containing charm and bottom quarks. The effects of mass on $R_{\mathrm AA}$ has also been highlighted.

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arXiv2010

Nuclear suppression at low energy heavy ion collisions

The effects of non-zero baryonic chemical potential on the drag and diffusion coefficients of heavy quarks propagating through a baryon rich quark gluon plasma have been studied. The nuclear suppression factor, $R_{\mathrm AA}$ for non-photonic single electron spectra resulting from the semileptonic decays of hadrons containing heavy flavours have been evaluated for low energy collisions. The role of non-zero baryonic chemical potential on $R_{\mathrm AA}$ has been highlighted.

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arXiv2009

Equilibration in Quark Gluon Plasma

The hydrodynamic expansion rate of quark gluon plasma (QGP) is evaluated and compared with the scattering rate of quarks and gluons within the system. Partonic scattering rates evaluated within the ambit of perturbative Quantum Choromodynamics (pQCD) are found to be smaller than the expansion rate evaluated with ideal equation of state (EoS) for the QGP. This indicate that during the space-time evolution the system remains out of equilibrium. Enhancement of pQCD cross sections and a more realistic EoS keep the partons closer to the equilibrium.

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arXiv2009

Probing quark gluon plasma properties by heavy flavours

The Fokker Planck (FP) equation has been solved to study the interaction of non-equilibrated heavy quarks with the Quark Gluon Plasma (QGP) expected to be formed in heavy ion collisions at RHIC energies. The solutions of the FP equation have been convoluted with the relevant fragmentation functions to obtain the $D$ and $B$ meson spectra. The results are compared with experimental data measured by STAR collaboration. It is found that the present experimental data can not distinguish between the $p_T$ spectra obtained from the equilibrium and non-equilibrium charm distributions. Data at lower $p_T$ may play a crucial role in making the distinction between the two. The nuclear suppression factor, $R_{\mathrm AA}$ for non-photonic single electron spectra resulting from the semileptonic decays of hadrons containing heavy flavours have been evaluated using the present formalism. It is observed that the experimental data on nuclear suppression factor of the non-photonic electrons can be reproduced within this formalism by enhancing the pQCD cross sections by a factor of 2 provided the expansion of the bulk matter is governed by the velocity of sound, $c_s\sim 1/\sqrt{4}$. Ideal gas equation of state fails to reproduce the data even with the enhancement of the pQCD cross sections by a factor of 2.

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