Abstract
High statistics measurements of the photon asymmetry $\mathrm{\Sigma}$ for the $\overrightarrow{\gamma}$p$\rightarrow\pi^{0}$p reaction have been made in the center of mass energy range W=1214-1450 MeV. The data were measured with the MAMI A2 real photon beam and Crystal Ball/TAPS detector systems in Mainz, Germany. The results significantly improve the existing world data and are shown to be in good agreement with previous measurements, and with the MAID, SAID, and Bonn-Gatchina predictions. We have also combined the photon asymmetry results with recent cross-section measurements from Mainz to calculate the profile functions, $\check{\mathrm{\Sigma}}$ (= $\sigma_{0}\mathrm{\Sigma}$), and perform a moment analysis. Comparison with calculations from the Bonn-Gatchina model shows that the precision of the data is good enough to further constrain the higher partial waves, and there is an indication of interference between the very small $F$-waves and the $N(1520) 3/2^{-}$ and $N(1535) 1/2^{-}$ resonances.
Highlights
Quantum Chromodynamics (QCD) successfully describes many of the phenomena associated with elementary particles at high energies
The results are in good agreement with previous measurements from Mainz, GRAAL, and Yerevan in regions where there is overlap, and provide new highstatistics measurements in kinematic regions not covered by these previous experiments
The high statistics provide the opportunity to carry out a moment analysis, where angular distributions of the profile function of the beam asymmetry, Σ (= σ0Σ), are fitted with associated Legendre polynomials
Summary
Quantum Chromodynamics (QCD) successfully describes many of the phenomena associated with elementary particles at high energies. Beyond elastic pion-nucleon scattering, single-pion photoproduction remains the most studied source of resonance information [2] and many recent efforts have been directed towards obtaining complete, or nearly complete, measurements in meson-nucleon photoproduction reactions using double-polarization observables [3,4]. Highstatistics measurements of single-polarization observables, over a wide photon energy and angular range remain vitally important in determining the photoproduction amplitudes from which the underlying resonance information may be extracted. This work exploits the linearly polarized, tagged photon beam at the MAMI 1.6 GeV electron microtron in Mainz to provide beam asymmetry measurements for beam energies, Eγ = 0.32–0.65 GeV, corresponding to a center-of-mass energy range of W = 1.214–1.450 GeV. In addition the new results have much finer binning in W (typically 3 MeV).
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