Single $$\pi ^0$$ production off neutrons bound in deuteron with linearly polarized photons

The quasifree $$\overrightarrow{\gamma } d\rightarrow \pi ^0n(p)$$ γ → d → π 0 n ( p ) photon beam asymmetry, $$\varSigma $$ Σ , has been measured at photon energies, $$E_\gamma $$ E γ , from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first time. The data were collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49$$^\circ $$ ∘ to 148$$^\circ $$ ∘ . In this kinematic region, polarization observables are sensitive to contributions from the $$\varDelta (1232)$$ Δ ( 1232 ) and N(1440) resonances. The extracted values of $$\varSigma $$ Σ have been compared to predictions based on partial-wave analyses (PWAs) of the existing pion photoproduction database. Our comparison includes the SAID, MAID and Bonn–Gatchina analyses; while a revised SAID fit, including the new $$\varSigma $$ Σ measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict $$\pi ^0n$$ π 0 n photoproduction observables, based on fits to published data in the channels $$\pi ^0p$$ π 0 p , $$\pi ^+n$$ π + n and $$\pi ^-p$$ π - p .

Measurements of the tensor analyzing power T20 of the reaction γd → dπ0

The paper presents the results of measurements of the tensor analyzing power component [Formula: see text] for the coherent neutral pion photoproduction on the deuteron. The measurements were performed in the Budker Institute of Nuclear Physics using the internal tensor polarized deuterium target at VEPP-3 storage ring. The measurements covered the region of the photon energy 240 — 420[Formula: see text]MeV and the region of the center-of-mass pion polar angle 100–140[Formula: see text]. The results of measurements were compared with the calculations performed within frameworks of several theoretical models.

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