Hadrons' Physics

Abstract

Hadron Physics studies systems dominated by strong interactions. This area has appeared in the seventies and incorporates concepts, methods and procedures from Nuclear and Elementary Particle Physics. The main theoretical tool of Hadron Physics is Quantum Chromodynamics (QCD), which allows the description of a large number of problems. At high energies, the quark structure of hadrons shows up and perturbative techniques are allowed. At low energies, interactions are dominated by non-Abelian processes, the QCD vacuum manifests itself as a quark-antiquark condensate and one needs nonperturbative methods. As a consequence the area is characterized by models designed to describe the structure and interactions of systems involving quarks and gluons. Nowadays, one is doing a strong and consistent experimental effort with the goal of determing the responses of hadronic systems to both electroweak and strong probes. In many experimental facilities, some of which are rather large, experiments are being carried on or planned. This will produce a new generation of data and allow a better understanding of the various energy regions. In Brazil there are about 100 researchers and students working in Hadron Physics and the main groups are located in São Paulo, Rio Grande do Sul, Rio de Janeiro e Santa Catarina. Researchers from the state of São Paulo have a central role and are responsible for about 30% of the papers published in the area and half of the post graduate training. The purpose of the present project is to support and mantain the activities of a reference group, which has an important presence in Brazil. Our research programmes deal with various aspects of the description of hadronic systems and their interactions, such as: .QCD sum rules, that relate hadronic properties with parameters that characterize the vacuum, such as quark and gluon condensates. Meson cloud model, that describes the nucleon properties due to the quark sea by assuming the nucleon to be a composite baryon-meson system. Hadronic processes in astrophysics, where one studies the effects of nucler interactions in acrescion disks around black holes and neutron stars. Non linear chiral effective Lagrangians, which allow the precise description of two and three body forces in Nuclear Physics. Chiral models for the interacion of pions with hyperons and mesons with charm, that contribute to the description of the hadronic phase in high energy collisions. Electromagnetic exchange currents, that manifest themselves in the interactions of photons with nuclei. (AU)