Differential cross section and photon-beam asymmetry for the gamma p -> pi- Delta++(1232) reaction at forward pi- angles for Egamma=1.5-2.95 GeV

Abstract

Differential cross sections and photon-beam asymmetries for the gamma p -> pi- Delta++(1232) reaction have been measured for 0.7<cos(theta)<1 and Egamma=1.5-2.95 GeV at SPring-8/LEPS. The first-ever high statistics cross section data are obtained in this kinematical region, and the asymmetry data for 1.5<Egamma(GeV)<2.8 are obtained for the first time. This reaction has a unique feature for studying the production mechanisms of a pure $u\bar{u}$ quark pair in the final state from the proton. Although there is no distinct peak structure in the cross sections, a non-negligible excess over the theoretical predictions is observed at Egamma=1.5-1.8 GeV. The asymmetries are found to be negative in most of the present kinematical regions, suggesting the dominance of pi-exchange in the t-channel. The negative asymmetries at forward meson production angles are different from the asymmetries previously measured for the photoproduction reactions which produce a $d\bar{d}$ or an $s\bar{s}$ quark pair in the final state. Advanced theoretical models introducing nucleon resonances and additional unnatural parity exchanges are needed to reproduce the present data.

arXiv commentAccepted by Phys. Rev. Lett., 5 pages, 4 figures

References in corpus (17)

• The Spin Structure of the Nucleon
• Quasi-Two-Body Decays of Nonstrange Baryons
• Differential Cross Sections for gamma + p --> K+ + Y for Lambda and Sigma0 Hyperons
• The gamma + p to K+ + Lambda and gamma + p to K+ + Sigma0 reactions at forward angles with photon energies from 1.5 to 2.4 GeV
• Differential cross section and recoil polarization measurements for the gamma p to K+ Lambda reaction using CLAS at Jefferson Lab
• ${\pi }^{+}$ photoproduction on the proton for photon energies from 0.725 to 2.875 GeV
• Measurement of the beam asymmetry in eta-photoproduction off the proton
• Differential cross sections and recoil polarizations for the reaction gamma p -> K+ Sigma0
• Differential cross section and photon beam asymmetry for the gamma n -> K+ Sigma- reaction at Egamma=1.5-2.4 GeV
• Photoproduction of $\Lambda$ and ${\Sigma }^0$ hyperons using linearly polarized photons
• Beam asymmetry for pi+ and pi0 photoproduction on the proton for photon energies from 1.102 to 1.862 GeV
• Development of High Intensity Laser-Electron Photon Beams up to 2.9 GeV at the SPring-8 LEPS Beamline
• Photon beam asymmetry $\Sigma$ for $\eta$ and ${\eta }^{\prime }$ photoproduction from the proton
• Measurement of the Beam Asymmetry $\Sigma$ in the Forward Direction for pi0 Photoproduction
• Photoproduction of $\Lambda$ and ${\Sigma }^0$ hyperons off protons with linearly polarized photons at $E_{\gamma }=1.5-3.0$ GeV
• Differential cross section and photon beam asymmetry for the gamma p -> pi+ n reaction at forward pi+ angles at Egamma=1.5-2.95 GeV
• Charged pion photoproduction with the Delta(1232) baryon beyond the resonance region

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