ZPC 1.0.1: a parton cascade for ultrarelativistic heavy ion collisions

A Monte Carlo program solving Boltzmann equation for partons via cascade method is presented. At presented, only gluon-gluon elastic scattering is included. The scattering cross section is regulated by a medium generated screening mass. Three different geometric modes (3 dimension expansion, 1-d expansion, and scattering inside a box) are provided for theoretical study of the parton transport and the applicability of the cascade method. Space cell division is available to save the number of computer operations. This improves the speed of the calculation by a large factor and makes the code best optimized for simulation of parton cascade in ultrarelativistic heavy ion collisions.Comment: LaTex, 25 pages, 3 figure

Looking for Gluon Substructure at the Tevatron

The impact of nonrenormalizable gluon operators upon inclusive jet cross sections is studied. Such operators could arise in an effective strong interaction Lagrangian from gluon substructure and would induce observable cross section deviations from pure QCD at high transverse jet energies. Comparison of the theoretical predictions with recent CDF data yields a lower limit on the gluon compositeness scale $\Lambda$. We find \Lambda > 2.03 \TeV at $95\%$~CL.Comment: 12 pages with 2 figures not included but available upon request, CALT-68-1872, HUTP-93/A01

Prompt photon processes in photoproduction at HERA

We present results for the photoproduction of inclusive prompt photons and for prompt photons accompanied by jets, measured with the ZEUS detector at HERA. Cross sections as a function of pseudorapidity and transverse energy are presented for 5 5 GeV in the centre of mass energy range 120-270 GeV. Comparisons are made with predictions from leading logarithm parton shower Monte Carlos and next-to-leading order QCD calculations using currently available models of the photon structure. NLO QCD calculations describe the shape and magnitude of the measurements reasonably well.Comment: Talk given at Photon99 Conference, Freiburg, German

New Interactions in Top Quark Production and Decay at the Tevatron Upgrade

New interactions in top-quark production and decay are studied under the conditions of the Tevatron upgrade. Studying the process q qbar --> t tbar --> b mu nu tbar, it is shown how the lepton rapidity and transverse energy distribution are modified by nonstandard modifications of the g-t-tbar and the t-b-W vertex.Comment: Latex File and 3 eps Figure

Dijet Production at Large Rapidity Intervals

We examine dijet production at large rapidity intervals at Tevatron energies, by using the theory of Lipatov and collaborators which resums the leading powers of the rapidity interval. We analyze the growth of the Mueller-Navelet $K$-factor in this context and find it to be negligible. However, we do find a considerable enhancement of jet production at large transverse momenta. In addition, we show that the correlation in transverse momentum and azimuthal angle of the tagging jets fades away as the rapidity interval is increased.Comment: 12 pages, preprint DESY 93-139, SCIPP 93/3

Parton-Parton Elastic Scattering and Rapidity Gaps at Very High Energies

The theory of the perturbative pomeron, due to Lipatov and collaborators, is used to compute the probability of observing parton-parton elastic scattering and rapidity gaps between jets in hadron collisions at very high energies.Comment: 15 page

Popping out the Higgs boson off vacuum at Tevatron and LHC

In the prospect of diffractive Higgs production at the LHC collider, we give an extensive study of Higgs boson, dijet, diphoton and dilepton production at hadronic colliders via diffraction at both hadron vertices. Our model, based on non factorizable Pomeron exchange, describes well the observed dijet rate observed at Tevatron Run I. Taking the absolute normalization from data, our predictions are given for diffractive processes at Tevatron and LHC. Stringent tests of our model and of its parameters using data being taken now at Tevatron Run II are suggested. These measurements will also allow to discriminate between various models and finally to give precise predictions on diffractive Higgs boson production cross-section at the LHC.Comment: 27 pages, 16 figures. Published version, incorporating corrections listed in the Erratum to appea

New Strong Interactons at the Tevatron ?

Recent results from CDF indicate that the inclusive cross section for jets with $E_T > 200$ GeV is significantly higher than that predicted by QCD. We describe here a simple flavor-universal variant of the ``coloron" model of Hill and Parke that can accommodate such a jet excess, and which is not in contradiction with other experimental data. As such, the model serves as a useful baseline with which to compare both the data and other models proposed to describe the jet excess. An interesting theoretical feature of the model is that if the global chiral symmetries of the quarks remain unbroken in the confining phase of the coloron interaction, it realizes the possibility that the ordinary quarks are composite particles.Comment: added $1/Lambda^4$ contributions to scattering cross-sections; 10 pages, LaTeX, includes 1 figure. Full postscript version at http://smyrd.bu.edu/htfigs/htfigs.htm

Radiative Energy-Loss of Heavy Quarks in a Quark-Gluon Plasma

We estimate the radiative energy-loss of heavy quarks, produced from the initial fusion of partons, while propagating in a quark-gluon plasma which may be formed in the wake of relativistic heavy ion collisions. We find that the radiative energy-loss for heavy quarks is larger than the collisional energy-loss for all energies. We point out the consequences on possible signals of the quark-gluon plasma.Comment: 5 papes, REVTE