Empirical Emission Functions for LPM Suppression of Photon Emission from Quark-Gluon Plasma

The LPM suppression of photon emission rates from the quark gluon plasma have been studied at different physical conditions of the plasma given by temperature and chemical potentials.The integral equation for the transverse vector function (f(p_t)) consisting of multiple scattering effects is solved for the parameter set {p,k,kappa,T}, for bremsstrahlung and AWS processes. The peak positions of these distributions depend only on the dynamical variable x=(T/kappa)|1/p-1/(p+k)|. Integration over these distributions multiplied by x^2 factor also depends on this variable x,leading to a unique global emission function g(x) for all parameters. Empirical fits to this dimensionless emission function, g(x), are obtained. The photon emission rate calculations with LPM suppression effects reduce to one dimensional integrals involving folding over the empirical g(x) function with appropriate distribution functions and the kinematic factors. Using this approach, the suppression factors for both bremsstrahlung and AWS have been estimated for various chemical potentials and compared with the variational method

Photon Production in Heavy Ion Collisions

The production of photons in heavy ion collisions is dicussed.Comment: Latex, 9 pages, 1 figur

Photon and lepton pair production in a quark-gluon plasma

We discuss the production of real or virtual photons in a quark-gluon plasma.Comment: 10 pages, 7 postscript figures, based on talks given in July 2000 at QCD 00, Montpellier, France, and at ICHEP2000, Osaka, Japa

On the photoproduction of jets at HERA

We discuss the inclusive jet production at HERA in the next-to-leading logarithm approximation. Theoretical uncertainties are considered in some details. We show the importance of the jet rapidity distribution to constrain the parton densities in the photon. A comparison is made with the recent H1 data.Comment: 10 + 7 figures included uuencoded tar-compressed ([email protected]) , ENSLAPP-A-484/94, LPTHE Orsay 94-8

DTUJET--93 Sampling inelastic proton--proton and antiproton--proton collisions according to the two--component Dual Parton Model

A new version of a Monte Carlo Program for hadronic multi-particle production is presented. It is based on the two-component Dual Parton Model which includes the dual topological unitarization of soft and hard cross sections. The model treats both soft (low $p_{\perp}$) and hard (minijet, large $p_{\perp}$) processes in a unified and consistent way. The unified description is important at TeV-energies of hadron colliders, where the hard perturbative cross sections of QCD become large and comparable to the total cross sections.Comment: 20 pages , PHYSZZX, SI-93-

Enhanced thermal production of hard dileptons by 3→23\to 2 processes

In the framework of the Hard Thermal Loop effective theory, we calculate the two-loop contributions to hard lepton pair production in a quark-gluon plasma. We show that the result is free of any infrared and collinear singularity. We also recover the known fact that perturbation theory leads to integrable singularities at the location of the threshold for $q\bar{q}\to\gamma^*$. It appears that the process calculated here significantly enhances the rate of low mass hard dileptons.Comment: 32 latex pages, 14 postscript figure

Anomalous prompt photon production in hadronic collisions at low-xTx_T

We investigate the discrepancy that exists at low-$x_T=2p_T/\sqrt{s}$ between the next--to--leading order QCD calculations of prompt photon production and the measured cross section. The central values of the measured cross section are of order 100\% larger than QCD predictions in this region. It has been suggested that the bremsstrahlung contribution may account for this discrepancy. The quark fragmentation function $D_{\gamma/q}(z)$ has not been measured and an exactly known asymptotic form is normally used in calculations. We examine the effect of much larger fragmentation functions on the QCD predictions. After illustrating the effect of the large fragmentation functions in some detail for recent CDF data at $\sqrt{s}$=1.8~TeV, we perform a $\chi^2$ fit to 8 prompt photon data sets ranging in CMS energy from 24~GeV to 1.8~TeV. While a large fragmentation function normalization may prove to play an important role in resolving the discrepancy, the present theoretical and experimental uncertainties prevent any definite normalization value from being determined.Comment: 14 pages, LBL-33122 and UCB-PTH-92/38. 13 figures available by email, specify postscript or topdrawe