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M. G. Mustafa

Publications and source records attributed to M. G. Mustafa.

15 recordsLinked to original sources
arXiv2019

The role of the stochastic color field fluctuations on $J/ψ$ suppression in ultra-relativistic heavy-ion collisions

We consider the effect of the stochastic color field fluctuations in addition to the collisional as well as the radiative energy losses in the propagation of charm quarks in the hot and dense deconfined medium of quarks and gluons created in ultra-relativistic heavy-ion collisions. These fluctuations lead to energy gain of the propagating charm quarks. We construct and solve Langevin transport equations for charm quarks under the evolving background matter described by the ($3+1$)-D relativistic viscous hydrodynamics. Considering the energy gain of charm quarks, the nuclear modification factor $R_{AA}$ of $J/ψ$ is calculated. Interestingly, the experimental measurements for $J/ψ$ suppression in $Au-Au$ collisions at $\sqrt{s_{NN}} = 200$ GeV by PHENIX Collaboration and $Pb-Pb$ collisions at $\sqrt{s_{NN}} = 2.76$ TeV by ALICE and CMS Collaborations, can be nicely described with the effect of these field fluctuations without invoking the regeneration phenomena.

hep-ph↗
arXiv2008

Radiative and Collisional Jet Energy Loss in a Quark-Gluon Plasma

We calculate radiative and collisional energy loss of hard partons traversing the quark-gluon plasma created at RHIC and compare the respective size of these contributions. We employ the AMY formalism for radiative energy loss and include additionally energy loss by elastic collisions. Our treatment of both processes is complete at leading order in the coupling, and accounts for the probabilistic nature of jet energy loss. We find that a solution of the Fokker-Planck equation for the probability density distributions of partons is necessary for a complete calculation of the nuclear modification factor $R_{AA}$ for pion production in heavy ion collisions. It is found that the magnitude of $R_{AA}$ is sensitive to the inclusion of both collisional and radiative energy loss, while the average energy is less affected by the addition of collisional contributions. We present a calculation of $R_{AA}$ for $π^0$ at RHIC, combining our energy loss formalism with a relativistic (3+1)-dimensional hydrodynamic description of the thermalized medium.

hep-ph↗
arXiv2000

Finite Temperature Meson Correlation Functions in HTL Approximation

We calculate temporal correlators and their spectral functions with meson quantum numbers in the deconfined phase of QCD using the hard thermal loop (HTL) approximation for the quark propagator. Although this approach does not result in a complete next-to-leading order perturbative calculation it takes into account important medium effects such as thermal quark masses and Landau damping in the quark-gluon plasma. We show that both effects lead to competing modifications of the free mesonic correlation functions. We find that correlators in scalar channels are only moderately influenced by the HTL medium effects, while the HTL-vertex corrections lead to divergent vector correlators.

hep-ph↗
arXiv2000

Hadron Correlators in the Deconfined Phase

Temporal meson correlators and their spectral functions are calculated in the deconfined phase using the hard thermal loop resummation technique. The spectral functions exhibit strong medium effects coming from the hard thermal loop approximation for the quark propagator. The correlators, on the other hand, do not differ significantly from free correlators, for which bare quark propagators are used. This is in contrast to lattice calculations showing a clear deviation from the free correlations functions.

hep-ph↗
arXiv1999

Gluon Condensate and Non-Perturbative Quark-Photon Vertex

We evaluate the quark-photon vertex non-perturbatively taking into account the gluon condensate at finite temperature. This vertex is related to the previously derived effective quark propagator by a QED like Ward-Takahashi identity. The importance of the effective vertex for the dilepton production rate from a quark-gluon plasma is stressed.

hep-ph↗
arXiv1999

Surface Tension at Finite Tempearture in the MIT Bag Model

At $ T = 0 $ the surface tension $ σ^{1/3} $ in the MIT bag model for a single hadron is known to be negligible as compared to the bag pressure $ B^{1/4}$. We show that at finite temperature it has a substantial value of 50 - 70 MeV which also differ from hadron to hadron. We also find that the dynamics of the Quark-Gluon Plasma is such that the creation of hybrids $(s\bar{s}g)$ with massive quarks will predominate over the creation of $ (s\bar{s}) $ mesons.

hep-ph↗
arXiv1997

Effect of colour singletness of quark-gluon plasma in quark-hadron phase transition

Consequences of the constraint of SU(3) colour singletness of quark-gluon plasma are studied. This restriction increases the free energy barrier for the formation of hadronic bubble in supercooled phase and influences significantly the dynamics of the initial stage of quark-hadron phase transition. It also introduces terms dependent on the volume occupied by the plasma in the energy density and the pressure. These modifactions vanish in the limit of an infinite volume. The last stage of the hadronization of the QGP likely to be formed in relativistic heavy ion collisions is necessarily characterized by a decreasing volume containing the quark matter, and thus these corrections become important. The nucleation of plasma droplets at AGS energies is also seen to be strongly affected by the requirement of colour singletness, and the choice of prefactor.

nucl-th↗
arXiv1997

Radiative Energy-Loss of Heavy Quarks in a Quark-Gluon Plasma

We estimate the radiative energy-loss of heavy quarks, produced from the initial fusion of partons, while propagating in a quark-gluon plasma which may be formed in the wake of relativistic heavy ion collisions. We find that the radiative energy-loss for heavy quarks is larger than the collisional energy-loss for all energies. We point out the consequences on possible signals of the quark-gluon plasma.

nucl-th↗
arXiv1996

Expanding Quark-Gluon Plasmas: Transverse Flow, Chemical Equilibration and Electromagnetic Radiation

We investigate the chemical equilibration of the parton distributions in collisions of two heavy nuclei. We use initial conditions obtained from a self-screened parton cascade calculation and, for comparison, from the HIJING model. We consider a one-dimensional, as well as a three-dimensional expansion of the parton plasma and find that the onset of the transverse expansion impedes the chemical equilibration. At energies of 100 GeV/nucleon, the results for one-dimensional and three-dimensional expansion are quite similar except at large values of the transverse radius. At energies of several TeV/nucleon, the plasma initially approaches chemical equilibrium, but then is driven away from it, when the transverse velocity gradients develop. We find that the total parton multiplicity density remains essentially unaffected by the flow, but the individual concentrations of quarks, antiquarks, and gluons are sensitive to the transverse flow. The consequences of the flow are also discernible in the transverse momenta of the partons and in the lepton pair spectra, where the flow causes a violation of the so-called $M_T$ scaling.

nucl-th↗
arXiv1995

A Heavy Glueball in a Bag Model at Finite Temperature

We obtain a heavy glueball (much heavier than the ones studied by others which usually are in the range of 1-2 GeV) in a bag model calculation with exact discrete single particle states of gluons at finite temperature. This heavy glueball, within the cosmological context, is what Abbas has recently predicted (hep-ph/9504430).

hep-ph↗
arXiv1995

A Heavy Glueball with Color-Singletness Restriction at Finite Temperature

We show that a heavy glueball (much heavier than that studied by others which is in the range of 1-2 GeV) is generated in a pure gluon plasma when color-singletness condition is imposed on the partition function at finite temperature. This confirms Abbas's recent prediction (hep-ph/9504430) of the existence of a heavy glueball within the framework of the early universe scenario.

hep-ph↗
arXiv1995

Colour-singlet strangelets at finite temperature

Considering massless $u$ and $d$ quarks, and massive (150 MeV) $s$ quarks in a bag with the bag pressure constant $B^{1/4} = 145$ MeV, a colour-singlet grand canonical partition function is constructed for temperatures $T = 1-30$ MeV. Then the stability of finite size strangelets is studied minimizing the free energy as a function of the radius of the bag. The colour-singlet restriction has several profound effects when compared to colour unprojected case: (1) Now bulk energy per baryon is increased by about $250$ MeV making the strange quark matter unbound. (2) The shell structures are more pronounced (deeper). (3) Positions of the shell closure are shifted to lower $A$-values, the first deepest one occuring at $A=2$, famous $H$-particle ! (4) The shell structure at $A=2$ vanishes only at $T\sim 30$ MeV, though for higher $A$-values it happens so at $T\sim 20$ MeV.

nucl-th↗
arXiv1995

Temperature dependent Nucleon Mass and entropy bound inequality

Mass of a baryon as a function of temperature is calculated using colour-singlet partition function for massless quarks (with two flavours) and abelian gluons confined in a bag with a temperature dependent bag pressure constant $B(T)$. The non-perturbative aspect of QCD interaction is included through colour-singlet restriction on quark-gluon partition function in a phenomenological way. The entropy bound inequality $ S/E \ \leq \ 2πR/\hbar c $, where $S, \ E $ and $R$ are entropy, energy and radius, respectively of the enclosed system with $\hbar c \ = \ 197.331 $ MeVfm, is found to be consistent with the equilibrium solutions of the baryon mass upto a temperature $T_E$. There is a region of temperature $T_E < T < T_C$ ($T_C$ is critical temperature for quark-gluon plasma formation) in which no admissible equilibrium states exist for the bag. We say that the system expriences a phase jump from hadron to quark-gluon plasma through thermodynamic non-equlibrium processes.

nucl-th↗
arXiv1995

Strangelets at finite temperature

Within the MIT bag model picture of QCD, we have studied the stability of finite size strangelets at finite temperature with baryon number $A \leq 100$. The light quarks $u$ and $d$ are considered massless while mass of the $s$ quark is taken as $150$ MeV. Using discrete eigen energies of the non-interacting quarks in the bag, grand canonical partition function is constructed and then the free energy is minimized with respect to the bag radius. In the $T\rightarrow 0$ limit clear shell structures are found which persist upto about $T=10$ MeV. Infact for $A=6$ the shell structure disappears only at $T > 20$ MeV.

nucl-th↗