Narrow Results

Considering the strong coupling to a field of two particles bound by a quark–quark-like potential, we calculate the energy and width of a hybrid state in a simplified model.

A major component of the approved upgrade of the GSI facility in Darmstadt, Germany is the High Energy Storage Ring (HESR) for high intensity, phase space cooled antiprotons with momenta up to 15 GeV/c. At this facility a wide physics program is planned to investigate both the structure of hadrons in the charmonium mass range and the spectroscopy of double hypernuclei. To serve the many experiments planned at this new facility, a general purpose detector called PANDA (Proton ANtiproton Detector Array) is planned. An overview of the PANDA detector concept, as well as selected results from simulation of the detector's performance will be presented.

Recently GSI presented the plans for a major new international research facility, called FAIR. A key feature of this new facility will be the delivery of intense, high-quality secondary beams which embody the production of antiprotons. For the antiproton beams a High Energy Storage Ring (HESR) is comprised. The design luminosity is 2·10³²cm^-2s^-1. Experiments will take place at an internal target. The rich spectroscopy program on exotic hadrons with antiproton beams is presented.

Glueballs and hybrids are predicted to exist but searches for them have failed to provide conclusive evidence. One–gluon exchange is not an important part of strong interactions in this energy regime. Instead, quarks seem to interact indirectly, via changes of the QCD vacuum. Strong interactions seem to be governed by instanton–induced interactions; the chiral soliton model gives a more suitable interpretation of the Θ⁺(1540) than models based on the dynamics of four quarks and one antiquark.

This paper gives an introduction to the hadron physics program and the planned PANDA experiment at the future FAIR facility located at GSI in Germany.

Investigations of the mass and decays of the J^PC=1^-+ hybrid are reviewed, including calculation of the π₁(1^-+)→ηπ, η′π decay widths within the QCD sum rules technique. In this calculation, the recently-proposed η, η′ quark mixing scheme is employed. The results indicate that the decay width Γ_π1→ηπ≈250 MeV is large compared with the decay width Γ_{π1→η′π}≈20 MeV. Inspired by these results, some phenomenological approaches are suggested to gain an understanding of the underlying mechanism of ηπ and η′π hybrid decays.

A new resonance X(1835) in the J/psi radiative decays, a couple of significant enhancements near threshold, and clear evidences for a broad 1^-- resonant structure of K⁺K^-, the σ and κ mesons in the J/psi hadronic decays from BES are reported. Favored interpretations of these observations are discussed.

We examine resonances for two systems consisting of a particle coupled to a massless boson's field. The field is the free field in the whole space. In the first system, the particle is confined inside a ball. We show that besides the usual energy levels of the particle, which have become complex through the coupling to the field, other resonances are to be taken into account if the ball's radius is comparable to the particle's Compton wavelength. In the second system, the particle is in a finite-depth square-well potential. We study the way the resonances' energy and width depend on the extent of the uncoupled particle's wave functions. In both cases, we limit ourselves to considering two levels of the particle only.

We calculate resonances which are formed by a particle in a potential which is either Coulombian or quadratic when the particle is strongly coupled to a massless boson, taking only two energy levels into consideration. From these calculations we derive how the moving away of the particle from its attraction center goes together with the energy lowering of hybrid states that this particle forms with the field. We study the width of these states and we show that stable states may also appear in the coupling.

We present results from a Partial-Wave Analysis (PWA) of diffractive dissociation of 190 GeV/c π^- into π^-π⁺π^- final states on nuclear targets. A PWA of the data sample taken during a COMPASS pilot run in 2004 on a Pb target showed a significant spin-exotic J^PC = 1^-+ resonance consistent with the controversial π₁(1600), which is considered to be a candidate for a non- mesonic state. In 2008 COMPASS collected a large diffractive π^-π⁺π^- data sample using a hydrogen target. A first comparison with the 2004 data shows a strong target dependence of the production strength of states with spin projections M = 0 and 1.

The COMPASS experiment at CERN is well designed for light-hadron spectroscopy with emphasis on the detection of new states, in particular the search for J^PC-exotic states and glueballs. We have collected data with 190 GeV/c charged hadron beams on a liquid hydrogen and nuclear targets in 2008/09. The spectrometer features good coverage by electromagnetic calorimetry and a RICH detector further provides π K separation, allowing for studying final states involving neutral particles like π⁰ or η as well as hidden strangeness, respectively. We discuss the status of ongoing analyses with specific focus on diffractively produced (π⁰π⁰π)^- as well as final states.