Exclusive photoproduction of ${\pi }^0$ up to large values of Mandelstam variables $s,t$ and $u$ with CLAS

Abstract

Exclusive photoproduction cross sections have been measured for the process $\gamma p\to p{\pi }^0(e^{+}{e}^{-}(\gamma ))$ with the Dalitz decay final state using tagged photon energies in the range of $E_{\gamma }=1.275-5.425$ GeV. The complete angular distribution of the final state ${\pi }^0$, for the entire photon energy range up to large values of $t$ and $u$, has been measured for the first time. The data obtained show that the cross section $d\sigma /dt$, at mid to large angles, decreases with energy as $s^{-6.89\pm 0.26}$. This is in agreement with the perturbative QCD quark counting rule prediction of $s^{-7}$. Paradoxically, the size of angular distribution of measured cross sections is greatly underestimated by the QCD based Generalized Parton Distribution mechanism at highest available invariant energy $s=11$ GeV${}^2$. At the same time, the Regge exchange based models for ${\pi }^0$ photoproduction are more consistent with experimental data.

7 pages, 6 figures

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• Twist-3 contributions to wide-angle photoproduction of pions
• Global analysis of charge exchange meson production at high energies
• Moravcsik's theorem on complete sets of polarization observables reexamined
• Unitarity constraints on meson electroproduction at backward angles
• Photoproduction of the $f_2(1270)$ meson using the CLAS detector
• Wide-angle photo- and electroproduction of pions to twist-3 accuracy
• Photoproduction of $\eta$ mesons off the proton for $1.2<E_{\gamma }<4.7$ GeV using CLAS at Jefferson Laboratory
• Twist-3 contribution to deeply virtual electroproduction of pions
• High Energy Behaviour of Light Meson Photoproduction
• Pseudoscalar and Scalar Meson Photoproduction Interpreted by Regge Phenomenology
• New graphical criterion for the selection of complete sets of polarization observables and its application to single-meson photoproduction as well as electroproduction