arXiv subjects

Surasree Mazumder

Publications and source records attributed to Surasree Mazumder.

14 recordsLinked to original sources

arXiv2024

Transport coefficients of the heavy quark in the domain of the non-perturbative and non-eikonal gluon radiation

Drag and diffusion coefficients of the Heavy Quarks (HQs), such as charm and bottom, are one of the prime tools for discerning the properties of the deconfined QCD medium created in the Heavy Ion Collisions experiments. The innate non-perturbative nature of the QCD medium renders it imperative to estimate the transport coefficients in that domain. The present work evaluates the drag and diffusion coefficients of the moving HQ interacting with the medium particles via two-body collisional and three-body radiative processes to the first order in opacity by employing Gribov mechanism for the non-perturbative regime. We proffer the latest results of the HQ transport coefficients computed for the non-perturbative and non-eikonal gluon radiation off the HQ. The calculations show significant increment of the transport coefficients with the increasing non-eikonality by juxtaposing the results with those of the pertubative and eikonal regions. We hope to shed fresh light towards explaining the experimental data on the nuclear modification facor, $R_{AA}$, the elliptic flow, $v_2$ of the HQ by advocating the importance of the non-eikonality of the gluon radiation off the HQ.

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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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arXiv2020

Momentum broadening of heavy quark in a magnetized thermal QCD medium

Anisotropic momentum diffusion coefficients of heavy quarks have been computed in a strongly magnetized quark-gluon plasma beyond the static limit within the framework of Langevin dynamics. Depending on the orientation of the motion of the heavy quark with respect to the direction of the magnetic field, five momentum diffusion coefficients of heavy quark have been estimated in the magnetized thermal medium. Specifically, we have focussed our attention to temperature range and strength of magnetic field satisfying the condition, $\it{i.e.}$ $M\gg\sqrt{eB}\gg T$, $M$ being the mass of heavy quark. The light quarks/antiquarks follow $1+1-$dimensional lowest Landau level (LLL) kinematics, and heavy quark dynamics are not directly affected by the magnetic field in the medium. The thermal gluon contribution to the diffusion coefficient is proportions to $T^3$, whereas, the contribution of light quarks in the lowest Landau state to the same is seen to be proportional to $T|eB|$. Furthermore, it is observed that for the case of heavy quark motion parallel to the magnetic field, the component of diffusion coefficient transverse both to the field and the heavy quark velocity $(κ^{\parallel}_{TT})$ turns out to be dominant as compared to the component longitudinal to both the field and motion $(κ^{\parallel}_{LL})$, $i.e.$, $κ^{\parallel}_{TT}\gg κ^{\parallel}_{LL}$. Further, for the case of heavy quark moving perpendicular to the magnetic field, it is seen that the diffusion coefficients transverse to the magnetic field are dominant, i.e., $κ^{\perp}_{LT}, κ^{\perp}_{TT}\gg κ^{\perp}_{TL}$.

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arXiv2020

HQ Collisional energy loss in a magnetized medium

We study the effect of the magnetic field on the collisional energy loss of heavy quark (HQ) moving in a magnetized thermal partonic medium. This is investigated in the strong field approximation where the lowest Landau level (LLL) becomes relevant. We work in the limit $g\sqrt{eB}\ll T\ll \sqrt{eB}$ which is relevant for heavy ion collisions. Effects of the magnetic field are incorporated through the resummed gluon propagator in which the dominant contribution arises from the quark loop. We also take the approximation $\sqrt{eB}\ll M$, M being the HQ mass, so that the HQ is not Landau quantized. It turns out that there are only two types of scatterings that contribute to the energy loss of HQ; the Coulomb scattering of HQ with light quarks/anti-quarks and the t-channel Compton scattering. It is observed that for a given magnetic field, the dominant contribution to the collisional energy loss arises from Compton scattering process i.e., $Qg\rightarrow Qg$. On the other hand, of the two processes, the Coulomb scattering i.e., $Qq\rightarrow Qq$ is more sensitive to the magnetic field. The net collisional energy loss is seen to increase with increase in the magnetic field. For a reasonable strength of the magnetic field, the field dependent contribution to the collisional energy loss is of the same order as to the case without magnetic field which can be important for the jet quenching phenomena in the heavy ion collision experiments.

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arXiv2017

Majorana flipping of quarkonium spin states in transient magnetic field

We demonstrate that spin flipping transitions occur between various quarkonium spin states due to transient magnetic field produced in non central heavy ion collisions (HICs). The inhomogeneous nature of the magnetic field results in \textit{non adiabatic evolution} of (spin)states of quarkonia moving inside the transient magnetic environment. Our calculations explicitly show that the consideration of azimuthal inhomogeneity gives rise to dynamical mixing between different spin states owing to Majorana spin flipping. Notably, this effect of non-adiabaticity is novel and distinct from previously predicted mixing of the singlet and one of the triplet states of quarkonia in the presence of a static and homogeneous magnetic field.

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arXiv2016

Soft Gluon Radiation off Heavy Quarks beyond Eikonal Approximation

We calculate the soft gluon radiation spectrum off heavy quarks (HQs) interacting with light quarks (LQs) beyond small angle scattering (eikon- ality) approximation and thus generalize the dead-cone formula of heavy quarks extensively used in the literatures of Quark-Gluon Plasma (QGP) phenomenology to the large scattering angle regime which may be im- portant in the energy loss of energetic heavy quarks in the deconfined Quark-Gluon Plasma medium. In the proper limits, we reproduce all the relevant existing formulae for the gluon radiation distribution off energetic quarks, heavy or light used in the QGP phenomenology.

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arXiv2015

Heavy quark diffusion in pre-equilibrium stage of heavy ion collisions

The drag and diffusion coefficients of heavy quarks (HQs) have been evaluated in the pre-equilibrium phase of the evolving fireball produced in heavy ion collisions at RHIC and LHC energies. The KLN and classical Yang-Mills spectra have been used for describing the momentum distributions of the gluons produced just after the collisions but before they thermalize. The interaction of the HQs with these gluons has been treated within the framework of perturbative QCD. We have observed that the HQs are dragged almost equally by the kinetically equilibrated and out-of-equilibrium gluonic systems. We have also noticed that the HQs diffusion in the pre-equilibrium gluonic phase is as fast as in the kinetically equilibrated gluons. Moreover, the diffusion is faster in the pre-equilibrium phase than in the chemically equilibrated quark-gluon plasma. These findings may have significant impact on the analysis of experimental results on the elliptic flow and the high momentum suppression of the open charm and beauty hadrons.

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arXiv2013

A random walk with heavy flavours

We focus on evaluating transport coefficients like drag and diffusion of heavy quarks (HQ) passing through Quark Gluon Plasma using perturbative QCD (pQCD). Experimental observable like nuclear suppression factor (RAA) of HQ is evaluated for both zero and non-zero baryonic chemical potential (μ_B) scenarios using Fokker- Planck equation. Theoretical estimates of RAA are contrasted with experiments.

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arXiv2013

Gluon bremsstrahlung by heavy quarks - its effects on transport coefficients and equilibrium distribution

The effects of gluon radiation by charm quarks on the transport coefficients {\it e.g.} drag, longitudinal and transverse diffusion and shear viscosity have been studied within the ambit of perturbative quantum chromodynamics (pQCD) and kinetic theory. We found that while the soft gluon radiation has substantial effects on the transport coefficients of the charm quarks in the quark gluon plasma its effects on the equilibrium distribution function is insignificant.

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arXiv2013

Radiative Processes in Quark-Gluon Plasma

The spectrum of emitted gluons from the process $\mathrm{gg\rightarrow ggg}$ has been evaluated by relaxing some of the approximations used in earlier works. The formula obtained in the present work has been applied to several physical quantities. A general expression for the dead cone of gluons radiated by virtual partons has been derived. It is observed that the suppression caused by the high virtuality is overwhelmingly large as compared to that on account of conventional dead-cone of heavy quarks.

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arXiv2013

Drag and diffusion co-efficients of heavy quarks in hard thermal loop approximations

The drag and diffusion coefficients of heavy quarks propagating through quark gluon plasma (QGP) have been evaluated using Hard Thermal Loop (HTL) approximations. The HTL corrections to the relevant propagators and vertices have been considered. It is observed that the magnitudes of both the transport coefficients are changed significantly from values obtained by earlier approaches where either (i) the $t$ channel divergence in T=0 pQCD matrix element is shielded simply by Debye mass. or (ii) only HTL resummed propagator is used ignoring the HTL corrections at the interaction vertices. The implications of these changes in the transport coefficients on the heavy ion phenomenology have been discussed.

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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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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

Effects of equation of state on nuclear suppression and the initial entropy density of quark gluon plasma

We study the effects of the equation of state on the nuclear suppression of heavy flavours in quark gluon plasma and estimate the initial entropy density of the system produced at the highest RHIC energy. For this purpose we have used the experimental data on the charged particle multiplicity and the nuclear suppression of single electron spectra originating from the semi-leptonic decays of open charm and beauty mesons. We have used inputs from lattice QCD to minimize the model dependence of the results. We obtain the value of the initial entropy density which varies from 20 to 59 /fm$^3$ depending on the value of the velocity of sound that one uses for the analysis. Our investigation leads to a conservative value of the initial entropy density $\sim 20/$fm$^3$ with corresponding initial temperature $\sim 210$ MeV well above the value of the transition temperature predicted by lattice QCD.

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