[en] The antiproton-proton annihilation into K⁺K^-π⁰ was studied at 900 and 1642 MeV/c with the Crystal Barrel detector at LEAR. The Dalitz plots are analyzed using a partial wave formalism that integrates over production angle. In the f/θ region around 1.7 GeV/c² the K⁺K^- system shows structure containing at least two resonances, in addition to the vector resonance ρ/φ(1700): one tensor at 1620 MeV/c² (Γ=280 MeV), which is possibly the first radial excitation of the well-known a₂(1320), and one state at 1770 MeV/c² (Γ=110 MeV) with spin 0 (slightly preferred) or 2. The rate of the latter is similar to that observed for the f₀(1500). A scalar with these properties would complete the mixing scheme of the low-lying 0⁺⁺ states. (orig.)

[en] The fixed target COMPASS experiment at CERN offers the opportunity to search for exotic mesons and glueball candidates in the light quark sector with unprecedented statistics. Preliminary results from the 2008 data taken with an incoming negative hadron beam (190 GeV/c, mainly pions) on a liquid hydrogen target are presented. New detectors dedicated to hadron beam measurements have been added. These give access to rare neutral and kaonic channels. An amplitude analysis which will allow to fit simultaneously, diffractively and/or centrally produced resonances will be described and compared with those used in the CERN WA102 and BNL E852 experiments. (authors)

[en] The COMPASS experiment at CERN studies diffractively produced states in the light quark sector with unprecedented statistics. The observation of f₀(1500)/f₂'(1525) decaying to ηη in 2008 data with incoming negative pion beam at 190 GeV/c poses the question whether it is produced centrally or formed by the decay of a heavier diffractively produced π₁(1800)/π₂(1880). To decide, a dedicated amplitude analysis which includes different production mechanisms is formulated and compared with one which was used to fit centrally produced resonances including f₀(1500) by the WA102 experiment. Unbinned mass-dependent log-likelihood fitting methods may serve to solve the ambiguities which are present in binned, mass-independent partial wave analyses.

[en] Data from the Fermilab E835 experiment have been used to study the reaction pp→ηηπ⁰ at 5.2 GeV/c. A sample of 22 million six photon events has been analyzed to construct the Dalitz plot containing ∼80k ηηπ⁰ events. A partial wave analysis of the data has been done. Six f_J-states decaying into ηη and five a_J-states decaying into ηπ⁰ are identified in the mass region ∼1.3 and 2.4 GeV, and their masses, widths, and spins are determined by maximum likelihood analysis of the data. Two f₀ states are identified with the popular candidates for the lightest scalar glueball, f₀(1500) and f₀(1710)

[en] Crystal Barrel data are presented for p-bar p→ωπ⁺π^-π⁰ at rest, with ω→π⁺π^-π⁰. A small but definite signal confirms a₀(1450) decaying to ωρ. Its branching ratio to ωρ is a factor 10.7±2.3 larger than to ηπ, where it was first identified. When fitted with a Breit-Wigner amplitude which includes the s-dependence of the ωρ channel, the pole position is M=1440⁺⁴⁰_-15-i(55±7) MeV. The exotic π₁(1600) is observed decaying to b₁π with orbital angular momenta L=0 and 2. There is also a strong J^PC=1⁺⁺ signal consistent with a₁(1640) decaying to ωρ and a much weaker signal for decays to [b₁(1235)π]_L=1. The strongest contribution to the data is a J^PC=0^-+ signal in ωρ suggesting a pole at M=1470±15-i(57±7) MeV

[en] We report on the decay to two photons of the χ_c0(1 ³P₀) charmonium resonance formed in p-bar p interactions at Fermilab experiment E835. We have measured the product of branching ratios BR(χ_c0→p-bar p)xBR(χ_c0→γγ)=(6.52±1.18(stat)^+0.48_-0.72(sys))x10^-8. Using values from the 2002 PDG, this measurement leads to the partial width Γ(χ_c0→γγ)=2.9±0.9 keV.

[en] Data are presented on antiproton neutron annihilation at rest into ωπ^-π⁰ taken with the Crystal Barrel detector at LEAR (CERN) using a liquid deuterium target. The partial wave analysis shows evidence for at least two ωπ vector resonances above the ρ(770) ground-state. Possible evidence for a third ρ' state with a mass around 1180 MeV is discussed. The results are compared to model dependent predictions concerning the nature of the ρ' states

[en] Fermilab experiment E835 has measured the cross section for the reaction p-bar p→e⁺e^- at s=11.63, 12.43, 14.40 and 18.22 GeV². From the analysis of the 66 observed events new high-precision measurements of the proton magnetic form factor are obtained

[en] Annihilation of antiprotons and protons at rest into neutral particles has been studied with the Crystal Barrel detector at LEAR. Annihilation frequencies are determined for final states containing π⁰, η, η' and ω mesons using a liquid and a room temperature, 12 bar, gaseous hydrogen target. Including annihilation frequencies for production of neutral kaons from other experiments, the identified reactions for annihilation in liquid hydrogen add up to a branching fraction of (3.56±0.28)% per annihilation compared to the frequency of (3.50±0.30)% with which we observe the all-neutral decay modes inclusively. Since the exclusive final states are normalized to the Crystal Barrel measurement of the π⁰π⁰ branching ratio, the latter result is strongly supported by this present study

[en] The resonance parameters of the charmonium ground state, η_c(1¹S₀), have been measured by means of the reaction p-bar p→η_c→γγ. The mass and total width are determined to be 2984.1±2.1±1.0 MeV/c² and 20.4^+7.7_-6.7±2.0 MeV, respectively. The product of branching ratios B(p-bar p→η_c)B(η_c→γγ) is determined to be 22.4^+3.8_-3.7±2.0x10^-8, from which B(η_c→γγ)=1.87^+0.32+0.95_-0.31-0.50x10^-4, and Γ(η_c→γγ)=3.8^+1.1+1.9_-1.0-1.0 keV are derived using B(η_c→p-bar p)=(12±4)x10^-4 from the literature.