Repositório RCAAP

We first give a brief survey of theoretical evaluations of light vector mesons in hadronic matter, focusing on results from hadronic many-body theory. We emphasize the importance of imposing model constraints in obtaining reliable results for the in-medium spectral densities. The latter are subsequently applied to the calculation of dilepton spectra in high-energy heavy-ion collisions, with comparisons to recent NA60 data at the CERN-SPS. We discuss aspects of space-time evolution models and the decomposition of the excess spectra into different emission sources.

We investigate stopping and particle production in heavy-ion collisions in a Relativistic Diffusion Model (RDM). Using three sources for particle production, the energy- and centrality dependence of rapidity distributions of net protons, and pseudorapidity distributions of charged hadrons in heavy systems at RHIC energies are precisely reproduced in the analytical model. The transport coefficients are then extrapolated from Au + Au at RHIC energies (<FONT FACE=Symbol>Ö</FONT>sNN=19.6 - 200 GeV) to Pb + Pb at LHC energies of <FONT FACE=Symbol>Ö</FONT>sNN= 5.52 TeV. Rapidity distributions for net protons, and pseudorapidity spectra for produced charged particles are obtained and discussed in a three-sources model at LHC energies.

Multiparticle production in lepton and hadron processes is studied by means of the Gluon Dominance Model (GDM) which is based on the Quantum Chromodynamics (QCD) and phenomenological scheme of hadronization. The model describes the multiplicity distributions and their moments very well. It has revealed an active role of gluons in multiparticle production and confirmed the fragmentation mechanism of hadronization in e+e- annihilation and its change to a recombination mechanism in hadron and nucleus interactions. The GDM explains the shoulder structure of multiplicity distributions. The hadron-pion ratio obtained by GDM has turned out to be in agreement with the experimental RHIC data of Au+Au peripheral collisions. Besides, development of GDM allows one to study the multiplicity behavior of p$p\bar{p}$ annihilation at tens of GeV. The mechanism of soft-photon production and estimates of their emission region have been offered in the framework of this model. The experimental data (project "Thermalization", U-70, IHEP) indicated the cluster nature of multiparticle production revealed by using GDM.

The recent data on the enhancement of the low mass dilepton yield in heavy ion collisions are interpreted as an effect of the "prolonged life" of resonances in the hadron gas phase. The value of the enhancement factor gives an upper limit for the duration time of this phase.

This paper presents recent measurements of the inclusive DIS cross section performed by the H1 and ZEUS collaborations at the HERA collider. We discuss relations of the HERA results with the upcoming experiments at the LHC. Importance of the planed measurement of the longitudinal proton structure function F L is commented.

In this contribution we present recent investigation on the extraction of the skewing factor, defined as the ratio of the imaginary parts of the amplitudes Im ${\cal A}$(gamma* p <FONT FACE=Symbol>® g</FONT>* p)/ Im ${\cal A}$(gamma* p <FONT FACE=Symbol>® g</FONT> p). This factor is extracted from the data using the recent DVCS and the inclusive inelastic cross section measurements at DESY-HERA. We compare the results to the theoretical predictions for NLO QCD and the color dipole approach.

In this paper we investigate the saturation physics in diffractive deep inelastic electron-ion scattering. We estimate the energy and nuclear dependence of the ratio sigmadiff/sigmatot. We show that saturation physics predicts that up to 37 % of the events observed at eRHIC should be diffractive. We have also studied how our results depend on the prescription to extend the saturation scale to the nuclear case.

We report new diffraction results obtained by the CDF collaboration in proton-antiproton collisions at the Fermilab Tevatron collider at <FONT FACE=Symbol>Ö</FONT>s = 1.96 TeV. The first experimental evidence of exclusive dijet and diphoton production is presented. The exclusive results are discussed in context of the exclusive Higgs production at LHC. We also present the measurement of the Q² and t dependence of the diffractive structure function.

In this contribution we present an exploratory QCD analysis of the neutrino structure functions in charged current DIS using the color dipole formalism. The corresponding dipole cross sections are taken from recent phenomenological and theoretical studies in deep inelastic inclusive production, including nuclear shadowing corrections. The theoretical predictions are compared to the available experimental results in the small-x region.

Measurements from the H1 and ZEUS collaborations of the diffractive deep-inelastic scattering process, ep -&gt; eXY, where Y is a proton or a low mass proton excitation, are presented for photon virtualities in the range 2.2 < Q² < 1600 GeV² and squared four-momentum transfer at the proton vertex satisfying | t | < 1 GeV². Diffractive parton distribution functions and their uncertainties are determined from a next-to-leading order DGLAP QCD analysis. Combining measurements of the inclusive diffractive deep-inelastic scattering process with an analysis of diffractive dijet production allows a very sensitive determination of both quark and gluon distributions.

Recent results from the H1 and ZEUS experiments on exclusive processes in diffractive ep collisions at HERA are reviewed. The measurements discussed here include dijets and charm in photoproduction as well as in deep inelastic scattering. Such processes are sensitive to the partonic structure of the diffractive exchange, particularly to the gluon content, and represent complementary tests for the validity of QCD factorization in diffraction. The measurements are compared to theoretical models, including NLO predictions, using the most recent diffractive parton densities as extracted from inclusive measurements. Recent results on exclusive vector meson production and deeply virtual compton scattering are also presented.

We present a formalism which modifies the Mueller Dipole Model such that it incorporates energy-momentum conservation as well as important colour suppressed effects in the cascade evolution. The formalism is implemented in a Monte Carlo simulation program, and the results are compared to inclusive data from HERA and the Tevatron. We here find a generally very good agreement between our model and the experimental data.

The leading- and higher-twist distribution amplitudes of the pion, the rho-meson and real and virtual photons are analyzed in the instanton liquid model.

Experimental evidence from RHIC indicates that matter having an energy density far in excess of the value required for the creation of a deconfined phase is produced in ultrarelativistic Au+Au collisions at <FONT FACE=Symbol>Ö</FONT>sNN=200 GeV. This matter thermalizes rapidly, is strongly interacting, and displays hydrodynamic properties akin to a fluid with very low viscosity. Studies of the interaction of hard scattered partons with this matter provide an important probe of its properties. In fact, studies of the suppression of high-pT hadrons have been one of the key arguments used by the RHIC experiments that the matter created is something fundamentally new and exciting. I review the current experimental picture that has emerged from the data collected at RHIC, with an emphasis on the effort to extract quantitative measurements from the suppression of high-pT hadrons.

Presented are the latest results of jet fragmentation studies at the Tevatron using the CDF Run II detector. Studies include the distribution of transverse momenta (Kt) of particles jets, two-particle momentum correlations, and indirectly global event shapes in p$\bar{p}$ collisions. Results are discussed within the context of recent Next-to-Leading Log calculations as well as earlier experimental results from the Tevatron and e+e- colliders.

New generalization of the z-scaling in inclusive particle production is proposed. The scaling variable z is expressed in terms of the momentum fractions x1 and x2 of the incoming protons. Explicit dependence of z on the momentum fractions y a and y b of the scattered and recoil constituents carried by the inclusive particle and recoil object is included. The scaling function psi (z) for charged and identified hadrons produced in proton-proton collisions is constructed. The scheme allows unique description of data on inclusive cross sections of charged hadrons, pions, kaons, antiprotons and lambdas produced at RHIC energies. The obtained results suggest that the z-scaling may be used as a tool for searching for new physics phenomena of particle production in high transverse momentum and high multiplicity region at proton-proton colliders RHIC and LHC.

Relying on the existing estimates for the production cross sections of mini black holes in models with large extra dimensions, we review strategies for identifying those objects at collider experiments. We further consider a possible stable final state of such black holes and discuss their characteristic signatures.

A measurement of W -> enu + n-jet cross sections in p$\bar{p}$ collisions at <FONT FACE=Symbol>Ö</FONT>s = 1.96 TeV using the Collider Detector at Fermilab in Run II is presented. The measurement is based on an integrated luminosity of 320 pb-1, and includes events with jet multiplicity from > 1 to > 4. In each jet multiplicity sample the differential and cumulative cross sections with respect to the transverse energy of the n th-leading jet are measured. For W+ > 2 jets the differential cross section with respect to the 2-leading jets invariant mass m j1j2 and angular separation deltaRj1j2 is also reported. The data are compared to predictions from Monte Carlo simulations.

We present results on inclusive jet production in proton-antiproton collisions at <FONT FACE=Symbol>Ö</FONT>s = 1.96 TeV. The measurements are based on 1.0 fb-1 of CDF Run II data and were carried out for jets in five different jet rapidity regions up to |Y| = 2.1. Both the midpoint cone based algorithm and kT algorithm were investigated to reconstruct the jets. The results are compared to next-to-leading order perturbative QCD predictions.

The most recent results of jet cross section measurements at HERA collider in photoproduction and deep inelastic scattering are presented. The forward jet and multiple jet productions are discussed from point of view of QCD dynamics. Results of precise extractions of the strong coupling alphas are presented.