Madhukar Mishra

Abstract. We demand that the Gauss law at the edge must be obeyed by the electric potential φ(r) generated within a neutral plasma/electrolyte of strictly finite size by the in-troduction of a test charge qb. Our proposal has the nice features that total ionic numbers are conserved, the point-Coulomb behaviour of φ(r) is guaranteed at short-distance, and accumulation of induced charges near the centre and the surface can be demonstrated rig-orously. In contrast, the standard Debye–Hückel potential φD(r) applicable to unbounded plasma has the strange features that the Gauss law cannot be obeyed at the plasma’s edge, total ionic numbers themselves are altered, the short-distance Coulomb behaviour has to be imposed by hand, and induced charge appearance at the surface cannot be built-in.

In the article by M. G. Mustafa published in Phys. Rev. C {\bf 72}, 014905 (2005) the author has estimated the total energy loss of a charm quark and quenching of hadron spectra due to the collisional energy loss of energetic partons in an expanding quark-gluon plasma employing Fokker-Planck equation. We wish to point out through this Comment that some of conceptual and numerical results of the said paper are unreliable. For the sake of clarity our discussion will focus on the massless case (although a few remarks on the $m\neq 0$ case are also made).

We determine the temperature dependent cross section for $c\bar{c}$ recombination to produce $J/\psi$. This calculation is carried out in the framework of perturbative QCD (pQCD) and a $J/\psi$ wavefunction is obtained by employing a temperature dependent phenomenological potential between $c\bar c$. A set of coupled rate equations are established which incorporates color screening, gluo-dissociation, collisional damping and recombination in the presence of Quark-Gluon Plasma (QGP) medium expanding under Bjorken scaling law. The final $J/\psi$ suppression thus calculated at mid rapidity for various centrality regions are compared with the experimental data obtained from the Large Hadron Collider (LHC) at $\sqrt{s_{NN}} = 2.76$ TeV. Keywords : Color screening, Recombination, Gluonic dissociation, Collisional damping, Survival probability, pQCD PACS numbers : 12.38.Mh, 12.38.Gc, 25.75.Nq, 24.10.Pa

The present work is a further development over our recent paper [Phys. Rev. C 88, 044908 (2013)] in which we described the bottomonium suppression in Pb+Pb collisions at Large Hadron Collider (LHC), at $\sqrt{s_{NN}}=2.76$ TeV by using the quasi-particle model (QPM) equation of state (EOS) for the Quark-Gluon Plasma (QGP) expanding under Bjorken's hydrodynamical expansion. The current model includes the modification of the formation time based on the temperature of QGP and cold nuclear matter (CNM) effects in addition to color screening during bottomonium production, gluon induced dissociation and collisional damping modeled previously. The final suppression of the bottomonium states is calculated as a function of centrality. The results compare closely with the CMS data at LHC in the mid rapidity region for various centrality bins.

Recent experimental and theoretical studies suggest that the quarkonia suppression in a thermal QCD medium created at heavy ion collisions is a complex interplay of various physical processes. In this article we put together most of these processes in a unified way to calculate the charmonium survival probability (nuclear modification factor) at energies available at relativistic heavy ion collider (RHIC) and large hadron collider (LHC) experiments. We have included shadowing as the dominant cold nuclear matter (CNM) effect. Further, gluo-dissociation and collision damping has been included which provide width to the spectral function of charmonia in a thermal medium and causes the dissociation of charmonium along with usual colour screening. We include the colour screening using our recently proposed modified Chu and Matsui model. Furthermore we incorporate the recombination of uncorrelated charm and anti-charm quark for the regeneration of charmonium over the entire temporal evolu...

We present here a comprehensive model to describe the bottomonium suppression data obtained from the CERN Large Hadron Collider (LHC) at center-of-mass energy of $\sqrt{s_{NN}}=2.76$ TeV. We employ a quasiparticle model (QPM) equation of state for the quark-gluon plasma (QGP) expanding under Bjorken's scaling law. The current model includes the modification of the formation time based on the temperature of the QGP, color screening during bottomonium production, gluon induced dissociation and collisional damping due to the imaginary part of the potential between the $b\bar b$ pair. We propose a method for determining the temperature-dependent formation time of bottomonia using the solution of the time-independent Schr\"{o}dinger equation and compare it with another approach based on time-dependent Schr\"{o}dinger wave equation simulation. We find that these two independent methods based on different axioms give similar results for the formation time. Cold nuclear matter...

We have modified the colour screening theory of Chu and Matsui by properly incorporating bag model equation of state for quark–gluon plasma (QGP). We have also chosen the pressure parametrization rather than parameterizing energy density in the transverse plane. We assume that the QGP dense medium is expanding in the longitudinal direction obeying Bjorken boost invariant scaling law. Sequential melting

We revisit the well-known topics of self-and induced-screening in an otherwise isotropic neutral plasma/colloid. It is pointed out that the standard Debye–Hückel (DH) theory (ignoring finite size effects) suffers from many ambiguities related to net ionic numbers, ...

We extend our previous formalism [Phys. Lett. B 656 45 (2007)] on J/ψ suppression at midrapidity using the colour screening framework. Our formalism is more general as the complete rapidity, transverse momentum and centrality dependence including J/ψ suppression at forward as well as mid-rapidity can be computed directly from it. We have assumed that QGP fluid is expanding obeying Bjorken’s boost invariant scaling law and bag model EOS is used. Sequential melting of χ c (1P) as well as ψ′ (2S) higher resonances is incorporated. We find that our model shows a reasonable agreement with the mid and forward rapidity data. Furthermore, we observe a larger suppression at forward rapidity in our model which is again well supported by the PHENIX data.

Interesting relationships have been found between the electron density parameter, average bond length, homopolar energy gap, heteropolar energy gap, ionicity, bulk modulus and microhardness for binary tetrahedral semiconductors. The estimated values of these parameters are in good agreement with the available experimental values and theoretical findings. The electron density parameter data are the only input data to estimate all the above properties.

We consider a relativistic elastic collision between a projectile of momentum p with a target atom of momentum k in a general inertial frame. We employ one space plus one time Minkowski geometry and calculate the momentum transfer vector qmu suffered by the projectile calculated via a Lorentz transformation to the barycentric frame and then eliminate k. The resulting expression

We present a model to explain the bottomonium suppression in Pb+Pb collisions at mid rapidity obtained from Large Hadron Collider (LHC) energy, $\sqrt{s_{NN}}=2.76$ TeV. The model consists of two decoupled mechanisms namely, color screening during bottomonium production followed by gluon induced dissociation along with collisional damping. The quasi-particle model (QPM) is used as equation of state (EOS) for the Quark-Gluon Plasma (QGP) medium. The feed-down from higher $\Upsilon$ states, such as $\Upsilon(1P)$, $\Upsilon(2S)$ and $\Upsilon(2P)$, dilated formation times for bottomonium states and viscous effect of QGP medium are other ingredients included in the current formulation. We further assume that the QGP is expanding according to (1+1)-dimensional Bjorken's boost invariant scaling law. The net suppression (in terms of $p_T$ integrated survival probability) for bottomonium states at mid rapidity is obtained as a function of centrality and the result is then compared both...