Aspects of a 0 0-f 0 mixing in the reaction pn \to dX

Possibilities to study the a ⁰ ₀-f ₀ mixing amplitude in meson production reactions in nucleon-nucleon collisions are discussed. It is argued that, even without knowing the production operator, it is possible to gain valuable insights from these reactions.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.60.Le Meson production - 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy GeV) - 14.40.Cs Other mesons with S = C = 0, mass < 2.5 GeV     

Cross-sections and spin observables in proton-proton elastic scattering: Results from EDDA at COSY

At the Cooler-Synchrotron COSY/Jülich polarized and unpolarized elastic proton-proton scattering has been investigated with the EDDA-Experiment in the energy range ( -2.5 GeV). By taking scattering data during the acceleration of the beam with a large-acceptance ( - ) detector, precise excitation functions for differential cross-section and analyzing power have been measured in small energy steps with consistent normalization with respect to luminosity and polarization. These data have helped to improve the determination of phase-shifts at higher energies and impose tight quantitative upper bounds on possible resonant contributions to pp elastic scattering, as they might arise from exotic 6-quark configurations. Recently, with polarized beam and target, the spin-correlation parameters , , and have been determined at 10 energies between 0.8 and 2.5 GeV. The observable has been measured the first time above 800 MeV and our results are in sharp contrast to phase-shift predictions at higher energies.Received: 30 September 2002, Published online: 22 October 2003PACS: 24.70. + s Polarization phenomena in reactions - 25.40.Cm Elastic proton scattering - 11.80.Et Partial-wave analysis - 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.)     

Progress in hypernuclear physics

The recent progress in hypernuclear physics is discussed in this paper. The topics include recent results on hypernuclear gamma-ray spectroscopy, non-mesonic weak decay, and double- hypernuclei. Future prospects at the 50 GeV PS are also discussed.Received: 30 September 2002, Published online: 22 October 2003PACS: 21.80. + a Hypernuclei - 25.80.-e Meson- and hyperon-induced reactions     

Experimental review of charmonium spectroscopy

Charmonium spectroscopy is one of the best means of making precision study of QCD, the strong-interaction component of the Standard Model of particle physics. Recent progress in the study of charmonium, the need for additional precision data, and the opportunities that the new facilities offer, are discussed.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.38.Qk Quantum chromodynamics: Experimental tests - 12.39.Pn Potential models - 13.25.Gv Decays of , , and other quarkonia - 14.40.Gx Mesons with S = C = B = 0, GeV (including quarkonia)     

Investigation of the a 0 + (980)-resonance with ANKE

Two experiments on the production of the a ₀ ⁺ (980)-resonance in the reaction were performed with the ANKE spectrometer at COSY-Jülich. The decay channels and were measured simultaneously at energies T = 2.65 GeV and T = 2.83 GeV. For the reaction a total production cross-section of nb has been deduced for T = 2.65 GeV. Further goals of the data analysis are to determine differential cross-sections like angular distributions and the branching ratio .Received: 30 September 2002, Published online: 22 October 2003PACS: 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) - 25.40.Ve Other reactions above meson production thresholds (energies > 400 MeV)P. Fedorets: For the ANKE Collaboration: Complete collaboration list available via: http: //www.fz-juelich.de/ikp/ankeV. Kleber: For the ANKE Collaboration: Complete collaboration list available via: http: //www.fz-juelich.de/ikp/anke     

Nucleon deformation

The conjectured deformation of hadrons and its experimental verification offer a particularly fertile ground for understanding the intricate dynamics of their constituents and QCD at the confiment scale. The detailed study of the transition is viewed as the preferred method of experimental investigation of this central issue in hadronic physics. A brief overview of the field is presented, followed by a presentation of the most recent results from Bates program. The new Bates/OOPS data at Q ² = 0.127 GeV/c ²) yield and and they exclude a spherical nucleon and/or . The magnitude and the origin of the deformation is the focus of the ongoing and planned investigations.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.60.Le Meson production - 13.88. + e Polarization in interactions and scattering - 13.40.Gp Electromagnetic form factors - 14.20.Gk Baryon resonances with S = 0C.N. Papanicolas: Invited plenary talk     

Exclusive \eta production in pp reactions

Angular distributions for the exclusive reaction observed via the decay channel have been measured at GeV, 2.50 GeV and 2.85 GeV (excess energies Q = 324 MeV, 412 MeV and 554 MeV). The polar angle of the shows an anisotropy with respect to the beam direction for the lowest energy, which vanishes for the higher energies. The anisotropy of the pp polar angle increases slightly with the beam energy.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) - 14.40.Aq , K, and mesons - 25.40.Ve Other reactions above meson production thresholds (energies > 400 MeV)Y. Bedfer: Present address: DAPNIA/SPhN, CEA Saclay, France.A. Brenschede: Present address: Syngenio AG, StuttgartF. Brochard: Present address: LPHNHE, Ecole Polytechnique 91128 Palaiseau, France.Seonho Choi: Present address: Temple University, Philadelphia, PA, USA.R. Dressler: Present address: Paul Scherrer Institut, Villigen, CH-5232.J. Foryciarz: Present address: Motorola Polska Software Center, Kraków, Poland.H.-W. Pfaff: Present address: d-fine GmbH, Eschborn.     

Electromagnetic form factors of the $\Delta(1232)$ excitation

In the resonance region we have precisely determined the electromagnetic properties of the -resonance, in particular the E2/M1 ratio . For pion electroproduction recent experimental data from Mainz, Bates, Bonn and JLab for Q² up to 4.0 (GeV/c)² have been analyzed with the isobar model MAID. The extracted E2/M1 ratio shows, starting from a small and negative value at the real photon point, a clear tendency to cross zero, and becomes positive with increasing Q². This is a possible indication of a very slow approach toward the pQCD region. The C2/M1 ratio near the photon point is found as . At high Q², the absolute value of the ratio is strongly increasing, a further indication that pQCD is not yet reached. The electromagnetic-transition form factors of the excitation are parameterized and fitted to the electroproduction data. This also shows a zero-crossing of the electric form factor G_E^* at (GeV/c)².Received: 1 November 2002, Published online: 15 July 2003PACS:   13.40.Gp Electromagnetic form factors - 13.60.Le Meson production - 14.20.Gk Baryon resonances with S=0 - 25.20.Lj Photoproduction reactions     

The DISTO program on meson and hyperon production

A summary of the present status of the analysis of the DISTO data on pseudoscalar and vector meson production at 3.67 GeV/c is presented. The new data on spin observales for the exclusive reaction \(\vec pp \to pK^ + \vec \Lambda \) at the three beam momenta: 3.67, 3.31 and 2.94 GeV/c are also discussed.     

Forward-backward angle asymmetry and polarization observables in high-energy deuteron photodisintegration

Deuteron two-body photodisintegration is analysed within the framework of the Quark-Gluon Strings Model. It is found that the forward-backward angle asymmetry predicted by the model is confirmed by the recent data at different photon energies from JLab. New calculations for polarization observables, the cross-section asymmetry and the polarization transfer , for photon energies GeV are presented and compared with the data available up to 2 GeV.Received: 7 July 2003, Published online: 26 November 2003PACS: 13.40.-f Electromagnetic processes and properties - 25.20.-x Photonuclear reactions     

Electron-positron pairs as a probe for hadrons in dense matter

In this paper the latest results from the analysis of e ⁺ e ^--pairs emitted in Pb + Au collisions at 40 AGeV/c and a combined analysis of all data available at 158 AGeV/c are presented. The enhancement of low-mass e ⁺ e ^--pairs (m _ee > 0.2 GeV/c ²) with respect to the expected yield from hadron decays first reported at 158 AGeV/c is also found at 40 AGeV/c and is even larger there. Comparing to various theoretical models based on annihilation, the data can only be reproduced, if the properties of the intermediate in the hot and dense medium are modified. Hadron data taken at the same beam energies sheds light on the dynamical evolution of the fireball and addresses the question whether the medium modification is linked to baryon density rather than temperature. In the future e ⁺ e ^--pairs emitted in heavy-ion collisions will be measured at the LHC with the ALICE Transition Radiation Detector (TRD). Here, special emphasis will be put on the production of heavy vector mesons ( , ).Received: 30 September 2002, Published online: 22 October 2003PACS: 25.75.-q Relativistic heavy-ion collisions - 12.38.Mh Quark-gluon plasma - 13.85.Qk Inclusive production with identified leptons, photons, or other nonhadronic particles     

Scalar mesons and the search for the O + + glueball

The possibility that gluonic excitations of hadronic matter or of the QCD vacuum may exist is perhaps one of the most fascinating topics in hadron spectroscopy. Glueballs are predicted by many models; in particular, present-day lattice gauge calculations require their existence. All these models agree that the lightest glueball should have scalar quantum numbers and a mass around 1.6GeV, which corresponds to the mass region where the scalar -mesons are expected. Therefore, mixing effects can complicate the search for the glueball. Experiments indeed show an overpopulation of states, for which many different interpretations exist. This reflects the complexity of the situation. New data from various experiments on scalar states give hints toward an interpretation of the scalar states. But still many questions remain.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.39.Mk Glueball and nonstandard multi-quark/gluon states - 12.38.-t Quantum chromodynamics - 14.70.Dj Gluons     

Exploring superdense matter at RHIC

I report first results on Au + Au collisions at GeV per nucleon pair from all four experiments at the Relativistic Heavy Ion Collider.Received: 30 September 2002, Published online: 22 October 2003PACS: 25.75.Dw Particle and resonance production     

Experiments on the search for the NN-decoupled NN\pi-resonance d’

The status on the search for NN-decoupled -resonances is reviewed with regard to recent experimental searches in the pionic double-charge exchange in nuclei, the two-pion production in nucleon-nucleon collisions, the photo pion-production on the deuteron and the electro pion-production in nuclei.Received: 30 September 2002, Published online: 22 October 2003PACS: 14.20.Gk Baryon resonances with S = 0 - 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy GeV) - 25.40.Ve Other reactions above meson production thresholds (energies 400 MeV)     

A new analysis of $\pi K$ scattering from Roy and Steiner type equations

With the aim of generating new constraints on the OZI suppressed couplings of chiral perturbation theory a set of six equations of the Roy and Steiner type for the S- and P-waves of the scattering amplitudes is derived. The range of validity and the multiplicity of the solutions are discussed. Precise numerical solutions are obtained in the range GeV which make use as input, for the first time, of the most accurate experimental data available at GeV for both and amplitudes. Our main result is the determination of a narrow allowed region for the two S-wave scattering lengths. Present experimental data below 1 GeV are found to be in generally poor agreement with our results. A set of threshold expansion parameters, as well as sub-threshold parameters are computed. For the latter, a matching with the SU(3) chiral expansion at NLO is performed.Received: 28 October 2003, Revised: 12 December 2003, Published online: 13 February 2004Work supported in part by the EU RTN contract HPRN-CT-2002-00311 (EURIDICE) and by IFCPAR contract 2504-1.     

Strangeness production and other recent results from Hall B at Jefferson Lab

Recent results using the CLAS detector at Jefferson Lab are discussed. We emphasize strangeness photo- and electro-production in the baryon resonance region between W = 1.6 and 2.3 GeV, where indications of s-channel structure are suggestive of high-mass baryon resonances coupling to kaons and hyperons in the final state. Other CLAS results, for the E _{1 +} /M _{1 +} transition form factor at the first -resonance, two-pion electroproduction, and photoproduction are also briefly mentioned.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.30.-a Decays of baryons - 13.30.Eg Hadronic decays - 13.40.-f Electromagnetic processes and properties - 13.60.-r Photon and charged-lepton interactions with hadronsR.A. Schumacher: For the CLAS Collaboration     

Tests of the standard model and constraints on new physics from measurements of fermion-pair production at 189-209 GeV at LEP

Cross-sections and angular distributions for hadronic and lepton-pair final states in e ⁺ e^- collisions at centre-of-mass energies between 189 GeV and 209 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. The measurements are used to determine the electromagnetic coupling constant at LEP 2 energies. In addition, the results are used together with OPAL measurements at 91-183 GeV within the S-matrix formalism to determine the -Z interference term and to make an almost model-independent measurement of the Z mass. Limits on extensions to the Standard Model described by effective four-fermion contact interactions or the addition of a heavy Z boson are also presented.Received: 28 August 2003, Published online: 18 February 2004