Heavy Flavor Enhancement as a Signal of Color Deconfinement

We argue that the color deconfinement in heavy ion collisions may lead to enhanced production of hadrons with open heavy flavor (charm or bottom). We estimate the upper bound of this enhancement.Comment: 7 pages, LaTeX, 3 PS-figure

Development Strategies for Pythia version 7

This document describes the strategies for the development of the Pythia7 program. Both the internal and external structure of the program is discussed. Some comments on relationship to other software is given as well as some comments on coding conventions and other technical details.Comment: 27 pages, 3 eps figure

Bloom-Gilman duality of the nucleon structure function and the elastic peak contribution

The occurrence of the Bloom-Gilman duality in the nucleon structure function is investigated by analyzing the Q**2-behavior of low-order moments, both including and excluding the contribution arising from the nucleon elastic peak. The Natchmann definition of the moments has been adopted in order to cancel out target-mass effects. It is shown that the onset of the Bloom-Gilman duality occurs around Q**2 ~ 2 (GeV/c)**2 if only the inelastic part of the nucleon structure function is considered, whereas the inclusion of the nucleon elastic peak contribution leads to remarkable violations of the Bloom-Gilman duality.Comment: in Proc. of the XVI European Conference on Few-body Problems in Physics, Autrans (France), July 199

The xx-Region of Shadowing Corrections in Nucleon Structure Functions

We discuss the experimental indications on the behaviour of F_2(x,Q^2) at small x both in proton and nuclear targets. By comparing the parametrizations of the data we conclude that shadowing correction effects in a proton target can appear at a noticeable level for x=(2 - 4)\times10^{-4} and Q^2\sim 10^1 GeV^2, namely inside the HERA regime.Comment: 5 pages, Latex, no figure

ExHuME: A Monte Carlo Event Generator for Exclusive Diffraction

We have written the Exclusive Hadronic Monte Carlo Event (ExHuME) generator. ExHuME implements the perturbative QCD calculation of Khoze, Martin and Ryskin of the process pp-> p+X+p, where X is a centrally produced colour singlet system.Comment: 11 pages, 3 figure

Projet: Jet Cross Sections in Deeply Inelastic Electron Proton Scattering (VERSION 4.1)

PROJET is a parton level Monte Carlo program for the calculation of jet cross sections in deeply inelastic electron proton scattering. In its present version it contains the Born level diagrams for the production of (1+1), (2+1) and (3+1) jets and the next-to-leading order corrections for the production cross sections of (1+1) and (2+1) jets for all polarisations of the exchanged virtual photon. In particular, the full angular correlations between the lepton and jet momenta are implemented. The program permits the application of acceptance cuts on all external momenta. For this purpose, the program creates an event record accessible to the user program with all momenta in the laboratory frame and in the center of momentum frame of the proton and the virtual photon. This option is indispensable for phenomenological studies because of the strong dependence of cross sections on phase space restrictions and the large uncertainty of fragmentation corrections in the proton direction. Since PROJET uses the Monte Carlo integration method for the evaluation of phase space integrals, the weights of the generated events can be used to produce distributions of observables related to jet momenta.Comment: 28 pages (LaTeX), CERN-TH.7420/9

Obtaining the nuclear gluon distribution from heavy quark decays to lepton pairs in pAA collisions

We have studied how lepton pairs from decays of heavy-flavoured mesons produced in p$A$ collisions can be used to determine the modifications of the gluon distribution in the nucleus. Since heavy quark production is dominated by the $gg$ channel, the ratio of correlated lepton pair cross sections from $D\bar D$ and $B\bar B$ decays in p$A$ and pp collisions directly reflects the ratio $R_g^A \equiv f_g^A/f_g^p$. We have numerically calculated the lepton pair cross sections from these decays in pp and p$A$ collisions at SPS, RHIC and LHC energies. We find that ratio of the p$A$ to pp cross sections agrees quite well with the input $R_g^A.$ Thus, sufficiently accurate measurements could be used to determine the nuclear modification of the gluon distribution over a greater range of $x$ and $Q^2$ than presently available, putting strong constraints on models.Comment: 19 pages, 6 figure

Podróz : uma viagem ao passado pelo bairro de Alto Paraguaçu

Orientadora: Prof. Dra. Valquíria JohnTrabalho de conclusão de curso (graduação) - Universidade Federal do Paraná, Setor de Artes, Comunicação e Design, Curso de Graduação em JornalismoInclui referênciasNão inclui resum

Nonlinear corrections to the DGLAP equations in view of the HERA data

The effects of the first nonlinear corrections to the DGLAP evolution equations are studied by using the recent HERA data for the structure function $F_2(x,Q^2)$ of the free proton and the parton distributions from CTEQ5L and CTEQ6L as a baseline. By requiring a good fit to the H1 data, we determine initial parton distributions at $Q_0^2=1.4$ GeV$^2$ for the nonlinear scale evolution. We show that the nonlinear corrections improve the agreement with the $F_2(x,Q^2)$ data in the region of $x\sim 3\cdot 10^{-5}$ and $Q^2\sim 1.5$ GeV$^2$ without paying the price of obtaining a worse agreement at larger values of $x$ and $Q^2$. For the gluon distribution the nonlinear effects are found to play an increasingly important role at x\lsim 10^{-3} and Q^2\lsim10 GeV$^2$, but rapidly vanish at larger values of $x$ and $Q^2$. Consequently, contrary to CTEQ6L, the obtained gluon distribution at $Q^2=1.4$ GeV$^2$ shows a power-like growth at small $x$. Relative to the CTEQ6L gluons, an enhancement up to a factor $\sim6$ at $x=10^{-5}$, $Q_0^2=1.4$ GeV$^2$ reduces to a negligible difference at Q^2\gsim 10 GeV$^2$.Comment: 13 pages, 5 eps-figures; revision: references added, Fig. 3 revise