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Understanding quark and gluon confinement in Quantum Chromodynamics is one of the main issue in hadronic physics. Electromagnetic probes, real and virtual photons, are a powerful tool to investigate how the QCD-partons manifest themselves in strong interaction at the energy scale of the nucleon mass (GeV). The CLAS Collaboration in Hall B at Jefferson Lab (USA) has a broad scientific program ranging from the static and dynamic properties of constituent quarks to the investigation of possible exotic baryon configurations. After a brief description of the CLAS detector, some selected results will be outlined showing the richness of this non-perturbative physics. [ABSTRACT FROM AUTHOR]

One of the foremost challenges in hadron physics is to obtain an understanding of the effective degrees of freedom which lead to the formation of mesons and baryons and govern their inner structure. The ELSA facility of the university of Bonn provides essential tools to investigate the baryon mass spectrum up to high excitations through the systematic study of single and multiple meson production. This comprises a 3.5 GeV electron accelerator, highly polarized nucleon targets and a 4π spectrometer for charged and neutral particle detection. In this contribution an overview on the instrumentation and the program is given. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present a precision measurement of the mass of the Λc+ and studies of the production and decay of the Ωc0 and [cap_xi]c0 charm baryons using data collected by the BABAR experiment. To keep the systematic uncertainty as low as possible, the Λc+ mass measurement is performed using the low Q-value decays, Λc+ → Λ0KS0K+ and Λc+ → Σ0KS0K+. Several hadronic final states involving an Ω- and a [cap_xi]- hyperon are analyzed to reconstruct the [cap_xi]c0 and the Ωc0. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We study S-wave interactions of the baryon decuplet with the octet of pseudoscalar mesons using the lowest order chiral Lagrangian. We find two bound states in the SU(3) limit corresponding to the octet and decuplet representations. These are found to split into eight different trajectories in the complex plane when the SU(3) symmetry is broken gradually. Finally, we are able to provide a reasonable description for a good number of 4-star 3/2- resonances listed by the Particle Data Group. In particular, the [cap_xi](1820), the Λ(1520) and the Σ(1670) states are well reproduced. We predict a few other resonances and also evaluate the couplings of the observed resonances to the various channels from the residues at the poles of the scattering matrix from where partial decay widths into different channels can be evaluated. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A combined analysis of new π0 and η photoproduction data from CB-ELSA collaboration was performed including the earlier data from SAID data base, new data on beam asymmetry from the GRAAL collaboration and data on γp → KΛ and KΣ. Three baryon resonances have a substantial coupling to ηN, the well known N(1535)S11, N(1720)P13 and the newly observed N(2070)D15 resonance. A new P11 state with mass 1840 MeV and width 140 MeV was observed contributing to most of the fitted reactions. The data also demand the presence of two D13 states at 1870 and 2170 MeV. The properties of observed states and their contributions to different observables are discussed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We study the Λ(1520) resonance in a coupled channel approach involving the πΣ(1385), K[cap_xi](1530), KN and πΣ channels. Implementing unitarity in coupled channels, we make an analysis of the relative importance of the different mechanisms which contribute to the dynamical structure of this resonance. From experimental information on some partial wave amplitudes and constraints imposed by unitarity, we get a comprehensive description of the amplitudes and hence the couplings to the different channels. We test these amplitudes in different reactions like K-p → Λππ, γp → K+K-p, γp → K+π0π0Λ and π-p → K0K-p and find a fair agreement with the experimental data. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The K-p → π0π0Σ0 reaction is studied within a chiral unitary model. The distribution of π0Σ0 states forming the Λ(1405) shows, in agreement with a recent experiment, a peak at 1420 MeV and a relatively narrow width of Γ = 38 MeV. We use these data in combination with those of the π-p → K0πΣ reaction and elements of chiral unitary theory to prove that there are two Λ(1405) states instead of one as so far assumed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A program to measure the two-pion production in nucleon-nucleon collisions exclusively and in all channels from threshold up to Tp = 1360 MeV has been started at CELSIUS-WASA. First preliminary results for ppπ+π¯ and ppπ0π0 channels are presented. In the near-threshold region they are consistent with a dominance of the Roper excitation and its successive decay into Nσ and Δπ channels. At energies Tp > 1 GeV we observe a very different behavior, which is at variance with theoretical predictions. At COSY-TOF exclusive measurements of the pp → ppπ+π¯ reaction have been carried out with polarized beam. Preliminary results show non-zero analyzing powers which point to a sizeable admixture of l ≠ 0 partial waves indicating possibly an influence of the ρ-channel. [ABSTRACT FROM AUTHOR]

Progress in computing the spectrum of excited baryons and mesons in lattice QCD is described. Large sets of spatially-extended hadron operators are used. The need for multi-hadron operators in addition to single-hadron operators is emphasized, necessitating the use of a new stochastic treatment of the low-lying modes of quark propagation which exploits Laplacian Heaviside quark-field smearing. A new glueball operator is tested and computing the mixing of this glueball operator with a quark-antiquark operator and multiple two-pion operators is shown to be feasible. [ABSTRACT FROM AUTHOR]

Meson resonances are linear combinations of qq and meson-meson (MM) baryon resonances are combinations of qqq and meson-baryon. Mixing between these combinations arises via decays of confined states to meson-meson or meson-baryon. There is a useful analogy with the covalent bond in molecular physics. One eigenstate is lowered by the mixing. Cusps arise at thresholds. At sharp thresholds due to S-wave 2-particle decays, these cusps play a conspicuous role in many sets of data. [ABSTRACT FROM AUTHOR]

Using a chiral unitary approach for meson-baryon scattering in the strangeness zero sector, where the N*(1535) and Δ*(1700) resonances are dynamically generated, we study the reactions γp → π0ηp and γp → π0K0Σ+ at photon energies at which the final states are produced close to threshold. Among several reaction mechanisms, we find the most important is the excitation of the Δ*(1700) state which subsequently decays into a pseudoscalar meson and the N*(1535). Hence, the reaction provides useful information with which to test current theories of the dynamical generation of the low-lying 1/2- and 3/2- states. Predictions are made for cross sections and invariant mass distributions which can be compared with forthcoming experiments at ELSA. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We study two distinct phases of nuclear matter, a baryon-meson phase and a quark-gluon phase (QGP). For the baryon-meson phase we develop an equation of state (EoS) using a quark-meson formulation based on a new version of the fuzzy bag model with scalar-isoscalar, vector-isoscalar and vector-isovector meson-quark couplings and leptonic degrees of freedom as well as the constraints of chemical equilibrium, baryon number and electric charge conservation. For the QGP phase we model an EoS for asymptotically free massless quarks and gluons using the MIT approach and a temperature and baryon chemical potential dependent bag constant, B(T,μ), which allows an isentropic equilibrium phase transition from a QGP to a hadron gas. Our main results indicate the EoS and static global properties of neutron stars and protoneutron stars at low and moderate values of temperature are slightly modified in comparison to the predictions based on the MIT bag model with a constant B. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]