Department of Physics

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    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.
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    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
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    Temperature-dependent formation-time approach for Υ suppression at energies available at the CERN Large Hadron Collider
    (APS, 2015-03) Mishra, Madhukar
    We present here a comprehensive model to describe the bottomonium suppression data obtained from the CERN Large Hadron Collider (LHC) at a center-of-mass energy of √sNN=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¯b pair. We propose a method for determining the temperature-dependent formation time of bottomonia using the solution of the time-independent Schrödinger equation and compare it with another approach based on time-dependent Schrödinger wave equation simulation. We find that these two independent methods based on different axioms give similar results for the formation time. Cold nuclear matter effects and feed-down from higher resonance states of Υ have also been included in the present work. The suppression of the bottomonium states at midrapidity is determined as a function of centrality. The results compare closely with the recent centrality-dependent suppression data at the energies available at the CERN LHC in the midrapidity region.
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    Unified description of charmonium suppression in a quark-gluon plasma medium at RHIC and LHC energies
    (APS, 2015-09) Mishra, Madhukar
    Recent experimental and theoretical studies suggest that the quarkonium suppression in a thermal QCD medium created in 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 include shadowing as the dominant cold-nuclear-matter effect. Further, gluonic dissociation and collision damping are included, which provide width to the spectral function of charmonia in a thermal medium and cause the dissociation of charmonium along with the usual color screening. We include color screening by using our recently proposed modified Chu–Matsui model. Furthermore, we incorporate the recombination of uncorrelated charm and anticharm quarks for the regeneration of charmonium over the entire temporal evolution of the QGP medium. Finally, we do a feed-down correction from the excited states to calculate the survival probability of charmonium. We find that our unified model suitably and simultaneously describes the experimental nuclear modification data of J/ψ at RHIC and LHC.
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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.