Browsing by Author "Mishra, Madhukar"

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Bottomonium suppression at √sNN=2.76 TeV using a model based on color screening and gluonic dissociation with collisional damping
(APS, 2013-10) Mishra, Madhukar
We present a model to explain the bottomonium suppression in Pb+Pb collisions at midrapidity obtained from Large Hadron Collider (LHC) energy, √sNN=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 quasiparticle model (QPM) is used as equation of state (EOS) for the quark-gluon plasma (QGP) medium. The feed-down from higher Υ states, such as Υ(1P), Υ(2S), and Υ(2P), dilated formation times for bottomonium states, and viscous effect of the 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 pT integrated survival probability) for bottomonium states at midrapidity is obtained as a function of centrality, and the result is then compared both quantitatively and qualitatively with the recent LHC experimental data in the midrapidity region recently published by the CMS Collaboration. We find that the current model, based on Debye color screening plus gluonic dissociation along with collisional damping, better describes the centrality dependence of bottomonium suppression at LHC energy as compared to the color screening model alone.
Bottomonium suppression in PbPb collisions at energies available at the CERN Large Hadron Collider
(APS, 2021-09) Mishra, Madhukar
High energy collisions are the laboratories within our reach to study strongly interacting matter under extreme temperatures. In the present study, we use a quarkonia suppression scheme to explain the bottomonium production at the two energies available at the CERN Large Hadron Collider. We employ echo-qgp to model the (3+1)-dimensional relativistic viscous hydrodynamic evolution of the medium. Bottomonia produced in the early stage dissociates due to color screening, gluonic dissociation, and collisional damping in addition to shadowing as an initial state effect. In the color screening mechanism, the temperature from hydrodynamics is used to find the screening radii at each centrality and rapidity. The shadowing effect utilizes the parton distribution functions obtained from the CT14 global analysis and shadowing factors from EPPS16. A lattice QCD based equation of state from the Wuppertal-Budapest Collaboration has been used. The experimental values of pion (π+) spectra were used to constrain the initial conditions of the dynamics. The bottomonium suppression is determined as a function of centrality, transverse momentum, and rapidity for Υ(1S) and Υ(2S) states at the LHC energies of 2.76 and 5.02TeV. We find a fairly good agreement between our theoretically calculated survival probability and the measured nuclear modification factor (RAA) at the two energies.
Centrality and transverse momentum dependent suppression of and in p–Pb and Pb–Pb collisions at the CERN Large Hadron Collider
(Springer, 2019-02) Mishra, Madhukar
Deconfined QCD matter in heavy-ion collisions has been a topic of paramount interest for many years. Quarkonia suppression in heavy-ion collisions at the relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) experiments indicate the quark-gluon plasma (QGP) formation in such collisions. Recent experiments at LHC have given indications of hot matter effect in asymmetric p–Pb nuclear collisions. Here, we employ a theoretical model to investigate the bottomonium suppression in Pb–Pb at , 5.02 TeV, and in p–Pb at TeV center-of-mass energies under a QGP formation scenario. Our present formulation is based on an unified model consisting of suppression due to color screening, gluonic dissociation along with the collisional damping. Regeneration due to correlated pairs has also been taken into account in the current work. We obtain here the net bottomonium suppression in terms of survival probability under the combined effect of suppression plus regeneration in the deconfined QGP medium. We mainly concentrate here on the centrality, and transverse momentum, dependence of and states suppression in Pb–Pb and p–Pb collisions at mid-rapidity. We compare our model predictions for and suppression with the corresponding experimental data obtained at the LHC energies. We find that the experimental observations on and dependent suppression agree reasonably well with our model predictions
Color screening scenario for quarkonia suppression in a quasiparticle model compared with data obtained from experiments at the CERN SPS, BNL RHIC, and CERN LHC
(APS, 2013-03) Mishra, Madhukar
We present a modified color screening model for J/ψ suppression in the quark-gluon plasma (QGP) using the quasiparticle model (QPM) as the equation of state (EOS). Other theoretical ingredients incorporated in the model are feed-down from higher resonances, namely, χc, and ψ′, dilated formation time for quarkonia, and viscous effects of the QGP medium. By assuming further that the QGP is expanding with Bjorken's hydrodynamical expansion, the present model is used to analyze the centrality dependence of the J/ψ suppression in the mid-rapidity region and compare it with the data obtained from Super Proton Synchrotron, Relativistic Heavy Ion Collider, and Large Hadron Collider experiments. We find that the centrality dependence of the data for the survival probability at all energies is well reproduced by our model. We further compare our model predictions with the results obtained from the bag model EOS for QGP which has usually been used earlier in all such calculations
Comment on the paper "Energy Loss of Charm Quarks in the Quark-Gluon Plasma : Collisional vs Radiative"
(ARXIV, 2007-08) Mishra, Madhukar
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≠0 case are also made).
Conversion of Emitted Axionic Dark Matter to Photons for Non-Rotating Magnetized Neutron Stars
(ARXIV, 2024-02) Sarkar, Tapomoy Guha; Mishra, Madhukar
We attempt to find the impact of a modified Tolman Oppenheimer Volkoff (TOV) system of equations on the luminosities of direct photons, neutrinos and axions for a particular axion mass in the presence of a magnetic field. We employ two different equation of states (EoSs) namely APR and FPS to generate the profiles of mass and pressure for spherically symmetric and non-rotating Neutron stars (NSs). We then compute the axions and neutrino emission rates by employing the Cooper-pair-breaking and formation process (PBF) in the core using the NSCool code. We also examine the possibility of axion to photon conversion in the magnetosphere of NSs. Furthermore, we investigate the impact of the magnetic field on the actual observables, such as the energy spectrum of axions and axion-converted photon flux for three different NSs. Our comparative study indicates that axions energy spectrum and axion-converted photon flux changes significantly due to an intense magnetic field.
Cooling of neutron stars through emission of neutrinos and photons: effects of modified gravity and magnetic field using tov equations
(2024-12) Mishra, Madhukar
The existence of dark matter has long been extensively studied in the past few decades. In this study, we investigate the emission of neutrinos and photons from neutron stars (NSs) by employing the modified theory of gravity and the corresponding Tolman-Oppenheimer-Volkoff (TOV) system of equations. The extreme matter density and magnetic field inside the NSs provide a unique laboratory for studying fundamental physics, including the interplay between gravity and quantum field effects. The impact of a strong magnetic field has also been incorporated into the corresponding TOV equations. We here attempt to see how neutrinos and photons emissions from these compact objects are impacted by the modified TOV equations due to modified theory of gravity; f(R,T) gravity or scalar-tensor theory and strong magnetic fields. Our analysis focuses on how these modifications influence the structure, cooling, and photon/neutrino luminosities of NS. We computed the surface temperature of NSs for normal Einstein gravity and modified gravity theories with and without magnetic field for three EoSs; namely APR, FPS and SLY. On comparison of our predicted values of surface temperature with the observed surface temperature for three NSs, we find that modified gravity along with inside magnetic field-based predictions shows reasonable agreement with the corresponding observed values.
Debye screening versus Gauss law in electrostatics: Finite size effects
(Elsevier, 2007-10) Mishra, Madhukar
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, total charge of the system, role of the electrostatic Gauss law, short-distance behaviour of the potential and incorrectly normalized pair correlation functions. We give a new formulation (incorporating finite size effects) such that ionic numbers are maintained, the total charge of the system has physically correct value, the Gauss law boundary conditions are rigorously obeyed, short-distance behaviour of the potential is guaranteed automatically, and correlation functions are correctly normalized. Numerical differences between the two approaches show up if the screening length μ−1 becomes comparable to the size R of the system.
Effect of geometrical size of the particles in a hot and dense hadron gas
(APS, 2007-08) Mishra, Madhukar
Incorporation of the finite size of baryons into the equation of state (EOS) of a hot and dense hadron gas (HG) in a thermodynamically consistent manner has been a much studied problem. We first review its current status. Various models have been proposed in order to account for the repulsive force generated by the hard-core geometrical size of the baryons resulting in an excluded volume effect in the EOS. We examine the criterion of the thermodynamical consistency of these models and summarize their shortcomings. In order to remove the shortcomings, we propose a new model which incorporates the excluded volume effect in a thermodynamically consistent manner. We find that the new model works even for the cases of extremely large temperatures and densities where most of other approaches fail. Furthermore, the new expressions for thermodynamical variables resemble in form with those obtained from thermodynamically inconsistent models and thus a useful correction factor has been suggested here which converts inconsistent expressions into thermodynamically consistent ones. Finally we compare the predictions of new model with those obtained from various old models.
The effect of temperature gradient on heavy quark anti-quark potential using gravity dual model
(OUP, 2020-12) Mishra, Madhukar
Thermal systems have traditionally been modeled via Euclideanized space by analytical continuation of time to an imaginary time. We extend the concept to static thermal gradients by recasting the temperature variation as a variation in the Euclidean metric. We apply this prescription to determine the quark–antiquark potential in a system with a thermal gradient. A naturally occurring QCD medium with thermal gradients is a quark–gluon plasma (QGP). However, the QGP evolves in time. Hence, we use a quasi-stationary approximation, which is applicable only if the rate of time evolution is slow. The application of our proposal to a quark–antiquark potential in QGP can be seen as a step towards a more exact theory that would incorporate time-varying thermal gradients. The effect of a static temperature gradient on the quark–antiquark potential is analyzed using a gravity dual model. A non-uniform black string metric is developed by perturbing the Schwarzschild metric, which allows us to incorporate the temperature gradient in the dual anti-de Sitter space. Finally, an expression for the quark–antiquark potential in the presence of a static temperature gradient is derived.
Emission properties of non-rotating neutron stars with magnetic field using modified TOV equations
(Springer, 2024-07) Mishra, Madhukar; Sarkar, Tapomoy Guha
Emission properties of the Astrophysical objects such as Neutron Stars are found using mass, pressure profile and thermal cooling rate. In this current work, we determine the cooling rate of spherically symmetric neutron star as a function of time and distance from the star’s centre using NSCool code. Here we first find the mass, pressure and baryon number density profile of the non-rotating neutron stars using modified Tolman-Oppenheimer-Volkoff (TOV) system of equations in the presence of intense magnetic field. We used here a constant value of magnetic field and a distance dependent magnetic field in TOV equations to obtain the profile. We employ three different equation of states to solve the TOV equations by assuming that the core of Neutron Stars is composed of a hadronic matter. By employing above profile, we obtain the cooling rate with and without magnetic field to examine the effect of magnetic field for three different equations of states. Observed temperature of a few Neutron Stars have also been plotted along with calculated values for comparison. Finally, emissivity of axions as a dark matter candidates has been calculated as a result of the nucleon Bremsstrahlung mechanism with and without magnetic field.
Freeze-out volume of hot dense fireball
(Elsevier, 2007-07) Mishra, Madhukar
A thermodynamically consistent excluded volume model is proposed to account for the particle multiplicities obtained from lowest SIS energies to the highest RHIC energies. The chemical freeze-out volumes lying in a slice of one unit of rapidity for pions and kaons are separately inferred from this analysis and the results are compared with the corresponding thermal freeze-out volumes obtained from the Hanbury–Brown Twiss (HBT) pion interferometry. Furthermore, we extract the variations of freeze-out number densities for pions and nucleons with the center-of-mass energy in our model and compare them with the HBT data.
Gauss law constraints on Debye-Hückel screening
(Springer, 2007-10) Mishra, Madhukar
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 introduction of a test charge q b . 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 rigorously. In contrast, the standard Debye-Hückel potential ϕ D(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.
J/ψ suppression in Au+ Au collisions at RHIC: Colour screening scenario in the bag model at variable participant numbers
(Elsevier, 2007-11) Mishra, Madhukar
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 of , and is also considered in this scenario. We have applied above formulation to the recent PHENIX experimental data of suppression in collisions at RHIC. We find that the model gives a good description of data at mid-rapidity in terms of survival probability versus number of participants without any necessity of implementing ()-dimensional expansion of the deconfined medium
J/ψ suppression vs centrality at forward and mid-rapidity in Au+Au collisions at RHIC in colour screening mechanism
(Springer, 2011-07) Mishra, Madhukar
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.
J/ψsuppression at forward rapidity as a potential probe for QGP formation in colour screening scenario
(ARXIV, 2008) Mishra, Madhukar
In order to study the properties of J/ψ (1S) in the deconfining medium, we extend our previous formalism [Phys. Lett. B {\bf 656}, 45 (2007)] on J/ψ suppression at mid-rapidity 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. Careful attention is paid to the role of the medium's proper time in determining the locus of the screening region where J/ψ gets suppressed. Other important ingredients in the calculation are bag model equation of state for QGP, the longitudinal expansion of the QGP fluid obeying Bjorken's boost invariant scaling law and non-sequential/sequential melting of χc (1P) as well as ψ′ (2S) higher resonances. Upon comparison with the recent data of PHENIX collaboration on J/ψ suppression at forward and mid-rapidity regions, we find that our model shows a reasonable agreement with the data without incorporating any sequential decay mechanism of higher charmonia states. Furthermore, we observe a larger suppression at forward rapidity in our model which is again well supported by the PHENIX data and also gives a hint that a scenario based on directly produced J/ψ's is preferable.
Momentum-energy change in elastic relativistic binary collisions
(AIP, 2009-05) Mishra, Madhukar
We consider a relativistic elastic collision between a projectile of momentum with a target atom of momentum in a general inertial frame. We employ one space plus one time Minkowski geometry and calculate the momentum transfer vector suffered by the projectile calculated via a Lorentz transformation to the barycentric frame and then eliminate ⁠. The resulting expression for reproduces several known cases, its algebraic behavior can be interpreted physically, and it leads to a simple understanding of the relativistic equipartition law.
pQCD approach to charmonium regeneration in QGP at the LHC
(Elsevier, 2016-03) Mishra, Madhukar
We analyze the applicability of perturbative QCD (pQCD) approach to the issue of recombination at the Large Hadron Collider (LHC), and calculate the recombination cross section for recombination to form as a function of temperature. The charmonium wavefunction is obtained by employing a temperature dependent phenomenological potential between the pair. The temperature dependent formation time of charmonium is also employed in the current work. A set of coupled rate equations is established which incorporates color screening, gluonic dissociation, collisional damping and recombination of uncorrelated pair in the quark–gluon plasma (QGP) medium. The final suppression, thus determined as a function of centrality is compared with the ALICE experimental data at both mid and forward rapidity and CMS experimental data at mid rapidity obtained from the Large Hadron Collider (LHC) at center of mass energy .
Profile and cooling rate of non-rotating magnetars using strange quark matter equation of states
(Springer, 2024-07) Mishra, Madhukar
Various astrophysical objects like Neutron Stars, Magnetars, Blackholes, etc. have been extensively studied in the last few decades in order to predict and analyze observations pertaining to such compact objects. Despite of multiple attempts, the exact nature of the matter located inside the core of the above compact objects is still an open problem in Astrophysics. In this work, we attempt to find the profile of spherically symmetric non-rotating Neutron Stars by assuming that the core of the Neutron Star is made up of strange quark matter. The calculation has also been carried out with a core consisting of non-strange quark matter for comparison. We also include the impact of the magnetic field on the profile of the Neutron Stars employing a modified Tolmann-Oppenheimer-Volkoff system of equations. Using the profile thus obtained, the Neutron Star cooling rate with time and as a function of the radius has also been calculated with and without magnetic field effects using NSCool code. Two approaches namely; a fixed value of the magnetic field and a more realistic distance-dependent magnetic field obtained by using a fitted eight-order polynomial have been used in the current calculation. Finally, we plot the Neutron cooling rate with and without magnetic fields by using the different equations of states (EOS) along with corresponding observed data for a few neutron Stars.
psi(2S) enhancement in p–Pb collision as an indication of quark–gluon plasma formation at the Large
(IOP, 2018-02) Mishra, Madhukar
Proton–nucleus collisions serve as an important baseline for the understanding and interpretation of the nucleus–nucleus collisions. These collisions have been employed to characterize the cold nuclear matter effects at SPS and Relativistic Heavy-Ion Collider energies for the past several years, as it was thought that quark–gluon plasma (QGP) is not formed in such collisions. However, at the Large Hadron Collider (LHC), there seems a possibility that QGP is formed during proton–lead (p–Pb) collisions. In this work, we have derived an expression for gluon induced excitation of to , using pNRQCD, and show that the relative enhancement of vis-à-vis , especially at high pT, gives further indication that the QGP is indeed formed in p–Pb collisions at the most central collisions at LHC energy. and suppression effects seen at ALICE are also qualitatively explained.