arXiv subjects

Tapan K. Nayak

Publications and source records attributed to Tapan K. Nayak.

At least 37 records · Page 2Linked to original sources

arXiv2013

Baseline study for higher moments of net-charge distribution at RHIC energies

Lattice QCD models predict the presence of a critical point in the QCD phase diagram where the first order phase transition between the hadron gas and Quark-Gluon Plasma ceases to exist. Higher moments of conserved quantities, such as net-charge, net-baryon number and net-strangeness, are proposed to be sensitive probes for locating the critical point. The moments of net-charge distributions have been studied as a function of centrality for {Au+Au} collisions at $\sqrt{s_{\rm NN}}$ = 7.7 to 200 GeV using three event generators, {\it viz.}, UrQMD, HIJING, and THERMINATOR-2. The effect of centrality selection, resonance production, as well as contributions from particle species to the net-charge moments and their products have been studied. It is observed that mean of the net-charge distributions are dominated by net-protons, whereas standard deviation, skewness and kurtosis closely follow net-pion distributions. These results, along with the predictions from Hadron Resonance Gas (HRG) model, are presented.

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arXiv2012

Heavy Ions: Results from the Large Hadron Collider

On November 8, 2010 the Large Hadron Collider (LHC) at CERN collided first stable beams of heavy ions (Pb on Pb) at center-of-mass energy of 2.76 TeV/nucleon. The LHC worked exceedingly well during its one month of operation with heavy ions, delivering about 10 microbarn-inverse of data, with peak luminosity reaching to $L_{0} = 2 \times 10^{25}{\rm cm}^{-2}{\rm s}^{-1}$ towards the end of the run. Three experiments, ALICE, ATLAS and CMS, recorded their first heavy ion data, which were analyzed in a record time. The results of the multiplicity, flow, fluctuations, and Bose-Einstein correlations indicate that the fireball formed in nuclear collisions at the LHC is hotter, lives longer, and expands to a larger size at freeze-out as compared to lower energies. We give an overview of these as well as new results on quarkonia and heavy flavour suppression, and jet energy loss.

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arXiv2011

Probing the QGP Phase Boundary with Thermal Properties of $ϕ$ Mesons

A novel attempt has been made to probe the QCD phase boundary by using the experimental data for transverse momenta of ϕ mesons produced in nuclear collisions at AGS, SPS and RHIC energies. The data are confronted with simple thermodynamic expectations and lattice QCD results. The experimental data indicate a first-order phase transition, with a mixed phase stretching the energy density between \sim1 and 3.2 GeV/fm3 corresponding to SPS energies.

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arXiv2010

Small-x Physics with the ALICE experiment at the CERN-LHC

High energy p-p, p-Pb and Pb-Pb collisions at the CERN-LHC offer unprecedented opportunities for studying wide variety of physics at small Bjorken-x. Here we discuss capabilities of the ALICE experiment at the CERN-LHC for probing small-x QCD physics. A new forward electromagnetic calorimeter is being proposed as an ALICE upgrade to explore the small-x region in more detail.

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arXiv2009

Study of the Fluctuations of Net-charge and Net-protons Using Higher Order Moments

We present the STAR preliminary results on mid-rapidity and low transverse momentum mean, standard deviation, skewness, and kurtosis of net-charge and net-proton distributions in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV for various collision centralities. All the measured high moments of these distributions can be scaled by the number of participating nucleons, consistent with the soft process emissions. The ratios of fourth to second order cumulants of both the net-charge and net-proton distributions are consistent with models without QCD critical point.

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arXiv2009

$ϕ$ Meson As a Probe of QCD Equation of State

In this work, we extract the QCD Equation of State (EoS) using experimental results of the $ϕ$ meson produced in nuclear collisions at AGS, SPS and RHIC energies. The data are confronted to simple thermodynamic expectations and lattice results. The experimental data indicate a first order phase transition, with a mixed phase stretching energy density between $\sim$ 1 and 3.2 GeV/$fm^3$.

hep-ph↗

arXiv2009

The QCD Equation of State with Thermal Properties of $ϕ$ mesons

In this work a first attempt is made to extract the Equation of State (EoS) using experimental results of the $ϕ$ meson produced in nuclear collisions at AGS, SPS and RHIC energies. The data are confronted to simple thermodynamic expectations and lattice results. The experimental data indicate a first order phase transition, with a mixed phase stretching energy density between $\sim$ 1 and 3.2 GeV/$fm^3$.

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arXiv2008

Quark-Gluon Plasma: Present and Future

We review a sample of the experimental results from AGS to SPS and RHIC and their interpretations towards understanding of the Quark-Gluon Plasma. We discuss extrapolations of these results to the upcoming LHC experiments. Finally, we present the plans to probe the QCD critical point with an energy scan at RHIC and FAIR facilities.

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arXiv2007

Overview of event-by-event analysis of high energy nuclear collisions

The event-by-event analysis of high energy nuclear collisions aims at revealing the richness of the underlying event structures and provide unique measures of dynamical fluctuations associated with QGP phase transition. The major challenge in these studies is to separate the dynamical fluctuations from the many other sources which contribute to the measured values. We present the fluctuations in terms of event multiplicity, mean transverse momentum, elliptic flow, source sizes, particle ratios and net charge distributions. In addition, we discuss the effect of long range correlations, disoriented chiral condensates and presence of jets. A brief review of various probes used for fluctuation studies and available experimental results are presented.

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arXiv2007

Proton-proton physics in ALICE

The ALICE experiment has several unique features which makes it an important contributor to proton-proton physics at the LHC, in addition to its specific design goal of studying the physics of strongly interacting matter in heavy-ion collisions. The unique capabilities include its low transverse momentum (\pT) acceptance, excellent vertexing, particle identification over a broad \pT range and jet reconstruction. In this report, a brief review of ALICE capabilities is given for studying bulk properties of produced particles which characterize the underlying events, and the physics of heavy-flavour, quarkonia, photons, di-leptons and jets.

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arXiv2006

Event-by-event fluctuations and the QGP phase transition

Fluctuations of thermodynamic quantities are fundamental to the study of QGP phase transition. Event-by-event fluctuations of many quantities have been studied by dedicated heavy-ion experiments. A brief review of recent experimental results is presented. The prospect for future study of fluctuations is discussed.

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arXiv2005

Opto-Electronics in Large Array Gas Detector Systems

Large array gas detector systems are used in particle and nuclear physics experiments involving high-energy nucleon-nucleon and heavy-ion collisions. We have observed that in large array gas detector systems the momentary discharges inside the detector cells result in slowdown of High Voltage conditioning and possible hindrances in signal processing. We have explored the opto-electronic devices like the opto-coupler, optical fibre and signal processing circuit, which provide successful monitoring procedures and preventive measures to overcome the challenges produced in such complex detector systems.

physics.ins-det↗

arXiv2003

Indication of a Co-Existing Phase of Quarks and Hadrons in Nucleus - Nucleus Collisions

The variation of average transverse mass of identified hadrons with charge multiplicity have been studied for AGS, SPS and RHIC energies. The observation of a plateau in the average transverse mass for multiplicities corresponding to SPS energies is attributed to the formation of a co-existence phase of quark gluon plasma and hadrons. A subsequent rise for RHIC energies may indicate a deconfined phase in the initial state. Several possibilities which can affect the average transverse mass are discussed. Constraints on the initial temperature and thermalization time have been put from the various experimental data available at SPS energies.

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arXiv2002

Evolution of Fluctuation in relativistic heavy-ion collisions

We have studied the time evolution of the fluctuations in the net baryon number for different initial conditions and space time evolution scenarios. We observe that the fluctuations at the freeze-out depend crucially on the equation of state (EOS) of the system and for realistic EOS the initial fluctuation is substantially dissipated at the freeze-out stage. At SPS energies the fluctuations in net baryon number at the freeze-out stage for quark gluon plasma and hadronic initial state is close to the Poissonian noise for ideal as well as for EOS obtained by including heavier hadronic degrees of freedom. For EOS obtained from the parametrization of lattice QCD results the fluctuation is larger than Poissonian noise. It is also observed that at RHIC energies the fluctuations at the freeze-out point deviates from the Poissonian noise for ideal as well as realistic equation of state, indicating presence of dynamical fluctuations.

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arXiv2001

Multiplicity Distributions and Charged-Neutral Fluctuations

We discuss the importance of event-by-event fluctuations in relativistic heavy-ion collisions. We present results of multiplicity fluctuations of photons and charged particles produced in 158$\cdot A$ GeV Pb+Pb collisions at CERN-SPS. Multiplicity fluctuations agree with participant model calculations indicating the absence of critical fluctuation. Localized fluctuations in charged particles to photons have been analyzed and compared to various mixed events. The results show localized fluctuations in both charged particles and photons. However, no correlated DCC-like fluctuation is observed.

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arXiv2001

Photons from Nucleus-Nucleus Collisions at Ultra-Relativistic Energies

We compare the photon emission rates from hot hadronic matter with in-medium mass shift and Quark Gluon Plasma (QGP). It is observed that the WA98 data can be well reproduced by hadronic initial state with initial temperature $\sim 200$ MeV if the universal scaling of temperature dependent hadronic masses are assumed and the evolution of temperature with time is taken from transport model or (3+1) dimensional hydrodynamics. The data can also be reproduced by QGP initial state with similar initial temperature and non-zero initial radial velocity.

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arXiv2001

Multiplicity Distributions and Charged-neutral Fluctuations

Results from the multiplicity distributions of inclusive photons and charged particles, scaling of particle multiplicities, event-by-event multiplicity fluctuations, and charged-neutral fluctuations in 158$\cdot A$ GeV Pb+Pb collisions are presented and discussed. A scaling of charged particle multiplicity as $N_{part}^{1.07\pm 0.05}$ and photons as $N_{part}^{1.12\pm 0.03}$ have been observed, indicating violation of naive wounded nucleon model. The analysis of localized charged-neutral fluctuation indicates a model-independent demonstration of non-statistical fluctuations in both charged particles and photons in limited azimuthal regions. However, no correlated charged-neutral fluctuations are observed.

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arXiv2001

Photons from Pb-Pb Collisions at CERN SPS

High energy photon emission rate from matter created in Pb + Pb collisions at CERN SPS energies is evaluated. The evolution of matter from the initial state up to freeze-out has been treated within the framework of (3+1) dimensional hydrodynamic expansion. We observe that the photon spectra measured by the WA98 experiment are well reproduced with hard QCD photons and photons from a thermal source with initial temperature ~ 200 MeV. The effects of the spectral changes of hadrons with temperature on the photon emission rate and on the equation of state are studied. Photon yield for Au + Au collisions at RHIC energies is also estimated.

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