Linearly polarised photon beams at ELSA and measurement of the beam asymmetry in $ \pi^{0}_{}$ photoproduction off the proton

Abstract

At the electron accelerator ELSA a linearly polarised tagged photon beam is produced by coherent bremsstrahlung off a diamond crystal. Orientation and energy range of the linear polarisation can be deliberately chosen by accurate positioning of the crystal with a goniometer. The degree of polarisation is determined by the form of the scattered electron spectrum. Good agreement between experiment and expectations on basis of the experimental conditions is obtained. Polarisation degrees of Pγ = 40% are typically achieved at half of the primary electron energy. The determination of Pγ is confirmed by measuring the beam asymmetry, Σ, in π 0 photoproduction and a comparison of the results to independent measurements using laser backscattering.PACS. 13.60.-r Photon and charged-lepton interactions with hadrons -13.60.Le Meson production -13.88.+e Polarization in interactions and scattering a present address: FZ

Beam Asymmetries in π[sup 0] Photoproduction on the Proton

“…α = 0 corresponds to photons polarized in a plane parallel to the floor of the experimental hall (xz plane), whereas for α = The photon beam asymmetries extracted from the data set with a coherent peak position at 1305 MeV. The filled (red) circles (•) denote this preliminary analysis, the (green) stars ( * ) our previous CBELSA/TAPS analysis [4], and the open (blue) circles (•) the GRAAL results [5]. The black solid line shows the recent solution of the Bonn-Gatchina partial wave analysis [6] and the grey solid line shows the SAID SP09 prediction [2,7].…”

“…Some sample φ distributions are shown in Figure 4. [4], and the open (blue) circles (•) the GRAAL results [5]. The black solid line shows the recent solution of the Bonn-Gatchina partial wave analysis [6] and the grey solid line shows the SAID SP09 prediction [2,7].…”

“…π 0 with 33 MeV wide E γ bins. This photon energy bin width was chosen to facilitate a comparison with the GRAAL [5] and previous CBELSA/TAPS [4] results. Small energy shifts between the different data sets are still present for some of the bins.…”

Resonance Dynamics in Coupled Channels

“…38,39,40). The dashed curves are obtained by switching off the contact current other than the Kroll-Ruderman term, 17 i.e.…”

Measurement of Polarization Observables in Neutral Double Pion Photoproduction Off the Proton With the Cbelsa/Taps Experiment

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