Measurement of polarization observables in neutral double pion photoproduction off the proton with the CBELSA/TAPS experiment

Data on the reaction γp → pπ0π0 were taken with the CBELSA/TAPS experiment at ELSA where linearly polarized photons impinged on a transversely polarized butanol target. Target asymmetries and double polarization observables were extracted and entered the BnGa-PWA. Systematic differences in the branching ratios of N* and Δ* resonances hint at the internal structure of these states

Study of d∗(2380) resonance in a chiral constituent quark model

Studies on newly observed dibaryon resonance [Formula: see text] ([Formula: see text]) with a compact structure in recent years are reviewed. In terms of a dynamical calculation with a chiral constituent quark model by using Resonating Group Method, the general characteristics of this resonance, like its mass, binding energy, root-mean-square radius, as well as, its strong double pion decays of [Formula: see text] and [Formula: see text], its strong single pion decays of [Formula: see text], and its electromagnetic form factors, are given and compared with the experimental data. It is shown that the compact hexaquark dominant structure might be a reasonable interpretation for this dibaryon resonance and the charge distribution might be a new observable to judge different theoretical assumptions for its structure. Moreover, possible experimental tests are also discussed briefly.

EXCLUSIVE MEASUREMENTS OF OMEGA ELECTROPRODUCTION OFF THE PROTON IN THE RESONANCE REGION

A complete theory of strong interactions must describe the excited baryon spectrum as well as the structure of prominent states, which reflects the dynamics of nonperturbative QCD. Beyond the discriminating power of exclusive single- and double-pion electroproduction, the ω channel provides an additional probe of high-mass excited states. The current analysis provides preliminary differential and integrated cross sections of ω electroproduction off the proton from W = 1.7 to 3.2 GeV and Q2 = 1.5 to 5.5 GeV2. The data was collected by JLab's CLAS detector during two run periods and comprises the largest sample of exclusive resonance-region ω electroproduction ever analyzed. Preliminary Legendre decomposition of the cross sections supports previous indications of s-channel contributions to cross sections in the resonance region.

MEASUREMENT OF POLARIZATION OBSERVABLES IN NEUTRAL DOUBLE PION PHOTOPRODUCTION OFF THE PROTON WITH THE CBELSA/TAPS EXPERIMENT

The Crystal Barrel/TAPS experiment is ideally suited to measure neutral mesons decaying into photons due to its high detection efficiency for photons, good energy resolution, and the nearly complete solid angle coverage. In combination with a longitudinally or transversely polarized target and an energy tagged, linearly or circularly polarized photon beam the experiment allows the measurement of a large set of polarization observables. The presented preliminary results for polarization observables of neutral double pion production obtained with a transversely polarized target show significant deviations from current predictions of partial wave analyses. This clearly indicates that 2π0-photoproduction is not yet understood.