Variable Energy Cyclotron Center

Kolkata, India

Variable Energy Cyclotron Center

Kolkata, India
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Schenke B.,Brookhaven National Laboratory | Tribedy P.,Variable Energy Cyclotron Center | Venugopalan R.,Brookhaven National Laboratory
Physical Review Letters | Year: 2012

We compute initial conditions in heavy ion collisions within the color glass condensate framework by combining the impact parameter dependent saturation model with the classical Yang-Mills description of initial Glasma fields. In addition to fluctuations of nucleon positions, this impact parameter dependent Glasma description includes quantum fluctuations of color charges on the length scale determined by the inverse nuclear saturation scale Q s. The model naturally produces initial energy fluctuations that are described by a negative binomial distribution. The ratio of triangularity to eccentricity ε 3/ε 2 is close to that in a model tuned to reproduce experimental flow data. We compare transverse momentum spectra and v 2,3,4(p T) of pions from different models of initial conditions using relativistic viscous hydrodynamic evolution. © 2012 American Physical Society.


Tribedy P.,Variable Energy Cyclotron Center | Venugopalan R.,Brookhaven National Laboratory
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

In a previous paper (arXiv:1011.1895), we showed that saturation models, constrained by e+p HERA data on inclusive and diffractive cross-sections, are in good agreement with p+p data at LHC in the soft sector. Particularly impressive was the agreement of saturation models with the multiplicity distribution as a function of n ch.. In this Letter, we extend these studies further and consider the agreement of these models with data on bulk distributions in A+A collisions. We compare our results to data on central and forward particle production in d+Au collisions at RHIC and make predictions for inclusive distributions in p+Pb collisions at the LHC. © 2012 Elsevier B.V.


Sarkar S.,Variable Energy Cyclotron Center
Advances in High Energy Physics | Year: 2013

The steps essentially involved in the evaluation of transport coefficients in linear response theory using Kubo formulas are to relate the defining retarded correlation function to the corresponding time-ordered one and to evaluate the latter in the conventional perturbation expansion. Here we evaluate the viscosities of a pion gas carrying out both the steps in the real-time formulation. We also obtain the viscous coefficients by solving the relativistic transport equation in the Chapman-Enskog approximation to leading order. An in-medium π π cross-section is used in which spectral modifications are introduced in the propagator of the exchanged ρ. © 2013 Sourav Sarkar.


Mohanty B.,Variable Energy Cyclotron Center
Journal of Physics G: Nuclear and Particle Physics | Year: 2011

We present the first results using the STAR detector from the beam energy scan program at the Relativistic Heavy-Ion Collider (RHIC). In this program, Au ion collisions at the center of mass energies (√sNN) of 7.7, 11.5 and 39 GeV allowed the RHIC to extend its study of the QCD phase diagram from baryonic chemical potential values of 20 to about 400 MeV. For the high net-baryon density matter at midrapidity, formed in these collisions, we report several interesting measurements. These include the observation of the difference between anti-particle and particle elliptic flow, disappearance of the difference in dynamical azimuthal correlations with respect to the event plane between same and opposite signed charged particles, change in the slope o√f the eccentricity at freeze-out and directed flow of protons as a function of sNN and the deviation of higher order fluctuations from hadron resonance gas and Poissonian expectations. Possible interpretations of these observations are also discussed. © 2011 IOP Publishing Ltd.


Bhattacharyya T.,Variable Energy Cyclotron Center
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

The spectrum of emitted gluons from the process g+g→g+g+g has been evaluated by relaxing some of the approximations used in earlier works. The differences in the results from earlier calculations have been pointed out. The formula obtained in the present work has been applied to estimate physical quantities like equilibration rate of gluons and the energy loss of fast gluon in the gluonic plasma. © 2012 American Physical Society.


Ghosh P.,Variable Energy Cyclotron Center
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

Experiments at the Large Hadron Collider (LHC) have measured multiplicity distributions in proton-proton collisions at a new domain of center-of-mass energy (√s) in limited pseudorapidity intervals. We analyze multiplicity distribution data of proton-proton collisions at LHC energies as measured by the Compact Muon Solenoid (CMS) experiment in terms of characteristic parameters of the negative binomial distribution (NBD) function that has played a significant role in describing multiplicity distribution data of particle production in high-energy physics experiments, in the pre-LHC energy range, in various kinds of collisions for a wide range of collision energy and for different kinematic ranges. Beside a single NBD, we apply the formalism of weighted superposition of two NBDs to examine if the multiplicity distribution data of CMS could be better explained. The weighted superposition of two NBDs indeed explains the distribution data better at the highest available LHC energy and in large intervals of phase space. The two-NBD formalism further reveals that the energy invariance of the multiplicity distribution of the soft component of particle production in hadronic collisions is valid at LHC also, as it is at RHIC and Tevatron. We analyze the data further in terms of clan parameters in the framework of the two-NBD model. © 2012 American Physical Society.


Chaudhuri A.K.,Variable Energy Cyclotron Center
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2010

We explore the possibility of observing elliptic flow in low multiplicity events in central pp collisions at LHC energy, s=14 TeV. It is assumed that the initial interactions produce a number of hot spots. Hydrodynamical evolution of two or more hot spots can generate sufficiently large elliptic flow to be accessible experimentally in 4th order cumulant analysis. © 2010 Elsevier B.V.


Chaudhuri A.K.,Variable Energy Cyclotron Center
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

In a hydrodynamic model, with fluctuating initial conditions, the correlation between triangular flow and initial spatial triangularity is studied. The triangular flow, even in ideal fluid, is not strongly correlated with the initial triangularity. The correlation is largely reduced in viscous fluid. Elliptic flow on the other hand appears to be strongly correlated with initial eccentricity. Weak correlation between triangular flow and initial triangularity indicates that a part of triangular flow is unrelated to initial triangularity. Triangularity acquired during the fluid evolution also contributes to the triangular flow. © 2012.


Chaudhuri A.K.,Variable Energy Cyclotron Center
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

In heavy ion collisions, event-by-event fluctuations in participating nucleon positions can lead to triangular flow. With fluctuating initial conditions, flow coefficients will also fluctuate. In a hydrodynamic model, we study the fluctuations in elliptic and triangular flow, due to fluctuating initial conditions. Both elliptic and triangular flow fluctuates strongly, triangular flow more strongly than the elliptic flow. Strong fluctuations greatly reduce the sensitivity of elliptic and triangular flow to viscosity. © 2012 Elsevier B.V.


Mohanty B.,Variable Energy Cyclotron Center
New Journal of Physics | Year: 2011

A quantum chromodynamics (QCD) phase diagram is usually plotted as the temperature (T) versus the chemical potential associated with the conserved baryon number (μB). Two fundamental properties of QCD, related to confinement and chiral symmetry, allow for two corresponding phase transitions when T and μB are varied. Theoretically, the phase diagram is explored through non-perturbative QCD calculations on a lattice. The energy scale for the phase diagram (Aqcd ~ 200 MeV) is such that it can be explored experimentally by colliding nuclei at varying beam energies in the laboratory. In this paper, we review some aspects of the QCD phase structure as explored through experimental studies using high-energy nuclear collisions. Specifically, we discuss three observations related to the formation of a strongly coupled plasma of quarks and gluons in the collisions, the experimental search for the QCD critical point on the phase diagram and the freeze-out properties of the hadronic phase. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

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