arXiv subjects

J. Alam

Publications and source records attributed to J. Alam.

5 recordsLinked to original sources

arXiv2007

Thermal Dileptons at LHC

We predict dilepton invariant-mass spectra for central 5.5 ATeV Pb-Pb collisions at LHC. Hadronic emission in the low-mass region is calculated using in-medium spectral functions of light vector mesons within hadronic many-body theory. In the intermediate-mass region thermal radiation from the Quark-Gluon Plasma, evaluated perturbatively with hard-thermal loop corrections, takes over. An important source over the entire mass range are decays of correlated open-charm hadrons, rendering the nuclear modification of charm and bottom spectra a critical ingredient.

hep-ph↗

arXiv2005

Initiative in Nuclear Theory at the Variable Energy Cyclotron Centre

We recall the path breaking contributions of the nuclear theory group of the Variable Energy Cyclotron Centre, Kolkata. From a beginning of just one person in 1970s, the group has steadily developed into a leading group in the country today, with seminal contributions to almost the entire range of nuclear physics, viz., low energy nuclear reactions, nuclear structure, deep inelastic collisions, fission, liquid to gas phase transitions, nuclear matter, equation of state, mass formulae, neutron stars, relativistic heavy ion collisions, medium modification of hadron properties, quark gluon plasma, and cosmology of early universe.

nucl-th↗

arXiv2000

Diffractive $ϕ$ Production in a Perturbative QCD Model

The elastic leptoproduction of $ϕ$ measured by the H1 collaboration at HERA is described by a perturbative QCD model, based on open $s\bar{s}$ production and parton hadron duality, proposed by Martin et al. We observe that both the total cross section and the ratio of the longitudinal and transverse cross sections are well reproduced with an effective strange-quark mass $m_s \sim 320- 380 $ MeV for various gluon distribution functions. Possible connection of the effective mass and the momentum dependent dynamical mass associated with dynamical breaking of chiral symmetry is also discussed.

hep-ph↗

arXiv2000

Validity of the Color Dipole Approximation for Diffractive Production of Heavy Quarkonium

We study the diffractive photo- and leptoproductions of $J / ψ$ and $ψ'$ on the proton, and examine the validity of the small-size color dipole approximation to the production of radially excited heavy quarkonium. The dipole model predicts a small ratio of $ψ'$ to $J / ψ$ photoproduction cross sections, which does not agree with experimental data. We show that this discrepancy originates from a large transverse size of $ψ'$ which makes the convergence of the transverse size expansion questionable, and the calculation without the dipole approximation turns out to be consistent with the data. Productions of $Υ'(2S,3S)$ are also discussed, and the dipole approximation is found to be reasonable for the $Υ$-family.

hep-ph↗

arXiv1995

Flavour Equilibration in Quark-Gluon Plasma

Within the framework of a dynamical and physically transparent model developed earlier, we study the time evolution of various quark flavours in the baryon-free region in ultrarelativistic heavy ion collisions. We show that even under optimistic conditions, the quark-gluon system fails to achieve chemical equilibrium.

hep-ph↗