Repositório RCAAP

In this contribution we estimate the influence of the shadowing effect and initial state parton energy loss in the quarkonium production at HERA-B. We analyze the xF behavior of the effective exponent alpha(xF) and present a comparison with the preliminary HERA-B data for J/psi production. Moreover, we present our predictions for <FONT FACE=Symbol>¡</FONT> production at HERA-B. The magnitude of these effects in the J/psi production at RHIC is also analyzed.

In this work we try to understand the phenomena of neutrino oscillations, and use this to obtain a more precise description of the atmospheric neutrino data. The two neutrino oscillation mechanism solves the problem of the up-down muon neutrino asymmetry successfully. Our main motivation is to describe the excess of events of electron-neutrino type found in the SuperKamiokande results at low energies when compared with the predictions of the two-generation neutrino oscillation. To do this we generalize the oscillation model from two to three neutrino flavors, opening the possibility of oscillation between electron neutrino type and the others. Then we obtain a semi-analytic solution of the three flavors problem using the neutrino phenomenological limits on oscillation parameters, squared masses differences and mixing angles. For this we must take into account matter effects on the electronic neutrino when it cross the Earth and has its oscillation pattern changed.

There is a recent proposal of identifying the Higgs particle of the Standard Model as a pseudo Nambu-Goldstone boson. This new broken symmetry introduces new particles and new interactions. Among these new interactions a central role to get an experimental signal of a new physics is played by the new neutral gauge bosons, A H and Z H. We study the associated production of general new neutral gauge boson Z¢ and a hard photon in the process e+ + e- <FONT FACE=Symbol>® m</FONT> + + µ- + gamma. For M AH < <FONT FACE=Symbol>Ö</FONT>S we show that the hard photon energy distribution in e+ + e- <FONT FACE=Symbol>® g</FONT> + f + f can present a model dependence and establish the theoretical origin of a new possible heavy neutral gauge boson.

We obtain results for the average number of muons at sea level in a proton-initiated vertical atmospheric cascade using a simple model of hadronic interactions based on the Hillas splitting algorithm. We study the muon yield at sea level as a function of the proton primary energy, varying the parameters of the interaction model in order to see the behavior of our results. We find that our results are in agreement with experimental data and with those of more sophisticated simulation models for some particular values of the model parameters.

Using experimental results at the Z-pole, and considering the ansatz of Matsuda as an specific texture for the quark mass matrices, we perform a chi2 fit at 95% CL to obtain family-dependent bounds to Z' mass and Z-Z' mixing angle in the framework of the main versions of 331 models. The allowed regions depend on the assignment of the physical quark families into different representations that cancel anomalies. Allowed regions on other possible 331 models are also obtained.

We analyze the possible origin of high-energy neutrinos coming from galactic sources. A model is proposed for neutrino hadroproduction in binary systems. Our results show that neutrino observatories like IceCube can establish whether TeV neutrinos and gamma rays emitted by microquasars are the decay products of pions. Such pions can be produced where the jet collides with the stellar wind of the companion star giving rise to hadronic interactions. We improve previous predictions by considering energy dependent pion multiplicities, particularly significant at high energies, and the most recent values for the parameters of the system. We also discuss the gamma-ray flux associated with neutrino emission.

It has been shown that the transition to the saturation regime of high energy QCD is similar to the formation of the front of a traveling wave. In particular, it can be verified that Balitsky-Kovchegov (BK) evolution equation reduces, after some approximations, to the nonlinear Fisher and Kolmogorov-Petrovsky-Piscounov (FKPP) equation, well-known from statistical physics. In these proceedings, based on the current knowledge of the asymptotic solutions of the BK equation, we propose a parametrization for the forward scattering amplitude which interpolates between the traveling wave solution and the saturation region.

Inspired by analytic results obtained for a systematic expansion of the memory kernel in dissipative quantum mechanics, we propose a phenomenological procedure to incorporate non-markovian corrections to the Langevin dynamics of an order parameter in field theory systematically. In this note, we restrict our analysis to the onset of the evolution. As an example, we consider the process of phase conversion in the chiral transition.

The discovery of the jet quenching in central Au + Au collisions at the Relativistic Heavy-ion Collider (RHIC) has provided clear evidence for the formation of strongly interacting dense matter. It has been predicted to occur due to the energy loss of high energy partons that propagate through the quark gluon plasma. Since the medium is not static and it cools while expands, the strong coupling is not fixed, running with the evolution of the system. In this work, we present an investigation of the dependence on the value of the strong coupling in the parton energy loss due to elastic scatterings in a parton plasma. We analyze different prescriptions for the QCD coupling and calculate the energy and length dependence of the fractional energy loss. Moreover, the quenching factor for light and heavy quarks is estimated. We found that the predicted enhancement of heavy to light hadrons (D/pi) ratio is strongly dependent on the running of the QCD coupling constant.

We demonstrate that integral dispersion relations for hadron-hadron scattering amplitudes can be replaced by differential relations, without the usual high-energy approximation. We obtain analytical expressions for the corrections associated with the low energy region and exemplify the applicability of the novel relations in the context of an analytical parametrization for proton-proton and antiproton-proton total cross sections.

Little Higgs models were recently proposed as an alternative for models of electroweak symmetry breaking. They can be regarded as one of the important candidates of the new physics beyond the Standard Model. We consider here the phenomenology of the minimal model of this type, the "Littlest Higgs Model" (LHM). It predicts the existence of the new gauge bosons Z H and A H. We calculate the contributions of these new particles to the forward-backward and left-right asymmetries in the processes e+ + e- -> f + $ e^+ + e^- \longrightarrow f + \bar f $. We study the possibility of detecting the lightest new gauge boson, A H, in the future e+e- colliders with c.m. energies of 500 GeV and 1 TeV and compare the LHM predictions with other models.

We investigate the two-meson decay modes for f0(1370). In this calculation we consider this resonance as a glueball. The Fock-Tani formalism is introduced to calculate the decay width.

The structure of the dissipative relativistic hydrodynamics is discussed. The second order thermodynamics developed by Israel, Stewart and Müller is briefly reviewed to be incorporated in the scheme of SPH formalism.

By means of an almost model-independent parametrization for the elastic hadron-hadron amplitude, as a function of the energy and the momentum transfer, we obtain good descriptions of the physical quantities that characterize elastic proton-proton and antiproton-proton scattering (total cross section, r parameter and differential cross section). The parametrization is inferred on empirical grounds and selected according to high energy theorems and limits from axiomatic quantum field theory. Based on the predictive character of the approach we present predictions for the above physical quantities at the Brookhaven RHIC, Fermilab Tevatron and CERN LHC energies.

In this contribution we study the photoproduction of heavy quarks in coherent proton-nucleus (pA) and nucleus-nucleus (AA) interactions for RHIC and LHC energies and analyze if this process can be used to determine the QCD dynamics at high energies. The integrated cross section and rapidity distribution are estimated. Our results indicate that the nonlinear dynamics can be proven in those reactions, which are well suited for studing saturation effects.

We perform phenomenological applications of modified gluon propagators and running coupling constants in scattering processes in Quantum Chromodynamics (QCD). The modified forms of propagators and running coupling constant are obtained by non-perturbative methods. The processes investigated includes the diffractive ones - proton-proton elastic scattering, light vector meson photo-production and double vector meson production in gamma-gamma scattering - as well as the pion and kaon meson form factors. The results are compared with experimental data (if available), showing a good agreement with a gluon with dynamical mass but do not indicate the correct gluon propagator functional form.

Bose-Einstein correlations of pairs of identical charged pions produced in hadronic Z decays are analyzed in terms of various parametrizations. A good description is achieved using a Lévy stable distribution in conjunction with a hadronization model having highly correlated configuration and momentum space, the tau-model. Using these results, the source function is reconstructed.

In this talk I first present a short review of fluctuations in e+e--annihilations. I then describe some new results on FD correlations. Experimental analyses of pp and <FONT FACE=Symbol>L L</FONT> correlations indicate a very small production radius. This result relies very strongly on comparisons with MC simulations. A study of the approximations and uncertainties in these simulations implies that it is premature to draw such a conclusion from the data.

Electron-proton (ep) collisions at HERA can be regarded as an interaction between a virtual photon and the proton. The interaction gives a unique opportunity for studying particle production in the hadronic final state of the ep collisions. This contribution reviews the momentum distribution of fragmented hadrons and strange meson and baryon production. Also the Bose-Einstein correlation length and azimuthal asymmetry were measured.

The NA49 experiment at CERN SPS has acquired a huge data set of Pb+Pb events over a broad range of energy and centrality during the last several years. This high statistics data set, coupled with a state-of-the-art analysis technique, allows for the first model-independent extraction and energy scan of 3D emission sources for pion pairs at SPS energies. These 3D pion emission sources provide new insights into the nature of a long-range source previously reported by PHENIX at RHIC. Preliminary results indicate that the pion source function is essentially Gaussian from 20 AGeV to 80 AGeV but it displays significant non-Gaussian tails at 158 AGeV.