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Sourendu Gupta

Publications and source records attributed to Sourendu Gupta.

At least 109 records · Page 6Linked to original sources
arXiv2001

Quenched QCD at finite temperature with chiral Fermions

We study physics at temperatures just above the QCD phase transition (Tc) using chiral (overlap) Fermions in the quenched approximation of lattice QCD. Exact zero modes of the overlap Dirac operator are localized and their frequency of occurrence drops with temperature. This is closely related to axial U(1) symmetry, which remains broken up to 2Tc. After subtracting the effects of these zero modes, chiral symmetry is restored, as indicated by the behavior of the chiral condensate. The pseudoscalar and vector screening masses are close to ideal gas values.

hep-lat↗
arXiv2001

A precise determination of T_c in QCD from scaling

Existing lattice data on the QCD phase transition are analyzed in renormalized perturbation theory. In quenched QCD it is found that T_c scales for lattices with only 3 time slices, and that T_c/Lambda_msbar=1.15 \pm 0.05. A preliminary estimate in QCD with two flavours of dynamical quarks shows that this ratio depends on the quark mass. For realistic quark masses we estimate T_c/Lambda_msbar=0.49 \pm 0.02. We also investigate the equation of state in quenched QCD at 1-loop order in renormalised perturbation theory.

hep-lat↗
arXiv2001

Quark number susceptibilities, strangeness and dynamical confinement

We report first results on the strange quark number susceptibility, chi_s, over a large range of temperatures, mainly in the plasma phase of QCD. Chi_s jumps across the phase transition temperature, T_c, and grows rapidly with temperature above but close to T_c. For all quark masses and susceptibilities in the entire temperature range studied, we found significant departures from ideal-gas values. We also observed a strong correlation between these quantities and the susceptibility in the scalar/pseudo-scalar channel, supporting ideas of ``dynamical confinement'' in the high temperature phase of the QCD plasma.

hep-lat↗
arXiv2001

A QCD Analysis of Polarised Parton Densities

We present the results of a QCD fit to global data on deep-inelastic polarised lepton-hadron scattering. We find that it is possible to fit the data with strongly broken SU(2) flavour for the polarised sea densities. This can easily be tested in $W$ production at polarised RHIC. The data fails to pin down polarised singlet sea quark and gluon densities. We explore the uncertainties in detail and show that improvement in statistics, achievable at polarised HERA for measurement of A_1 at moderately low values of x, have large payoffs in terms of the improvement in measurement of gluon and sea quark densities.

hep-ph↗
arXiv2000

Obstructions to dimensional reduction in hot QCD

I describe results on screening masses in hot gauge theories. Wilsonian effective long distance theories called dimensionally reduced (DR) theories describe very well the longest screening length in pure gauge theories. In the presence of fermions, meson-like screening lengths dominate the long-distance physics for 3T_c/2 < T < 3 T_c, and thus obstruct perturbative DR. Extrapolation of our results indicates that a form of this obstruction may remain till temperatures of 10 T_c or higher, and therefore affect the entire range of temperature expected to be reached even at the Large Hadron Collider.

hep-lat↗
arXiv2000

Fermions obstruct dimensional reduction in hot QCD

We have studied, for the first time, screening masses obtained from glueball-like correlators in Quantum Chromodynamics with four light dynamical flavours of quarks in the temperature range 1.5T_c < T < 3T_c, where T_c is the temperature at which the chiral transition occurs. We have also studied pion-like and sigma-like screening masses, and found that they are degenerate in the entire range of T. These obstruct perturbative dimensional reduction since the lowest glueball screening mass is heavier than them. Extrapolation of our results suggests that this obstruction may affect the entire range of temperature expected to be reached even at the Large Hadron Collider.

hep-lat↗
arXiv2000

QCD Working Group Report

This is the report of the QCD working group at WHEPP 6. Discussions and work on heavy ion collisions, polarised scattering, and collider phenomenology are reported.

hep-ph↗
arXiv1999

Probing the quark-gluon plasma with a new Fermionic correlator

We present the first measurement of a new correlation function of Fermion bilinears in finite temperature QCD with and without dynamical quarks in a quantum number channel in which non-trivial correlations are known to be present for purely gluonic operators. We find that the Fermion correlator vanishes for $T \ge 3T_c/2$, in agreement with the expectation for weakly interacting quarks in a quark-gluon plasma.

hep-lat↗
arXiv1999

Screening Masses in SU(2) Pure Gauge Theory

We perform a systematic scaling study of screening masses in pure gauge SU(2) theory at temperatures above the phase transition temperature. The major finite volume effect is seen to be spatial deconfinement. We extract the screening masses in the infinite volume and zero lattice spacing limit. We find that these physical results can be deduced from runs on rather coarse lattices. Dimensional reduction is clearly seen in the spectrum.

hep-lat↗
arXiv1999

Double Asymptotic Scaling in Drell-Yan Processes

Double scaling may be observed in the Drell-Yan process at the Tevatron and in the ALICE detector at the Large Hadron Collider in a window of masses. In the double scaling limit of the cross section, the higher order QCD corrections are quite large, and are driven by the rise in gluon densities in the double scaling regime. The naive parton model cannot be valid even at asymptotic energies in the region of phase space where double scaling holds.

hep-ph↗
arXiv1999

Representations of Fermionic Correlators at Finite Temperatures

The symmetry group of the staggered Fermion transfer matrix in a spatial direction is constructed at finite temperature. Hadron-like operators carrying irreducible representations of this group are written down from the breaking of the zero temperature group. Analysis of the correlators in a free fermion theory suggests new measurements which can test current interpretations.

hep-lat↗
arXiv1998

Dimensional Reduction in High Temperature Gauge Theories

Screening masses in the equilibrium thermodynamics of gauge theories were measured. The spectroscopy of these screening masses gives strong evidence for dimensional reduction at $T\ge2T_c$. A perturbative explanation of these masses is ruled out. The mass ratios in the high temperature phase are consistent with those in the pure gauge theory in three dimensions.

hep-ph↗
arXiv1998

Dimensional Reduction and Screening Masses in Pure Gauge Theories at Finite Temperature

We studied screening masses in the equilibrium thermodynamics of SU(2) and SU(3) pure gauge theories on the lattice. At a temperature of 2 Tc we found strong evidence for dimensional reduction in the non-perturbative spectrum of screening masses. Mass ratios in the high temperature SU(3) theory are consistent with those in the pure gauge theory in three dimensions. At the first order SU(3) phase transition we report the first measurement of the true scalar screening mass.

hep-lat↗
arXiv1998

Quarkonium Polarization in Non-relativistic QCD and the Quark-Gluon Plasma

We examine angular distributions of leptons arising from the decay of J/psi in inclusive hadroproduction. Taking into account feed-down contributions from chi_{1,2}, a flat distribution emerges without fine tuning parameters. Changes in the ratio of direct to total J/psi cross sections would change this distribution significantly. Such angular distributions are, therefore, confirmatory tests of the J/psi suppression signal for the production of a quark-gluon plasma. Related effects are predicted for the Upsilon.

hep-ph↗
arXiv1997

Single Polarisation Asymmetries for Quarkonia in Non-relativistic QCD

We find that single spin asymmetries in NRQCD are non-vanishing in general. They are proportional to the imaginary parts of some non-perturbative matrix elements. With statistics of about 10^6 identified J/psi's, or 10^5 identified chi_2, it is possible to measure these imaginary parts even if they are an order of magnitude smaller than the real parts. Such statistics are quite reasonable at polarised HERA N and other future experiments.

hep-ph↗
arXiv1997

Chi_1 and Polarisation Asymmetries for Quarkonia at High Orders in Non-relativistic QCD

We study doubly polarised asymmetries of c-cbar and b-bbar mesons in hadro- and photo-production at low transverse momentum in non-relativistic QCD to high orders in the relative velocity of the pair, v. We give the complete set of expressions required for the asymmetries up to order v^9. The asymmetries in the production of eta_{c,b} states are a stable measure of the polarised gluon densities. The asymmetries for chi_{c,b}, J/psi, psi', and the various Upsilon states are stringent tests of the NRQCD scaling relations.

hep-ph↗
arXiv1997

Is there Anomalous J/psi Suppression in Present-day Heavy-ion Collisions?

We re-analyse the data on J/psi cross sections for proton-nucleus and nucleus-nucleus collisions obtained by the CERN experiments NA38, NA51 and NA50. Our systematic analysis of error propagation shows that the no anomalous suppression of J/psi in Pb-Pb collisions can be substantiated at 95% confidence limit. The significance of the NA50 result would be enhanced by more precise p-A data on J/psi cross sections.

hep-ph↗