Exclusive Photoproduction of Pi Degrees up to Large Values of Mandelstam Variables s, t, and u with CLAS

Authors

M. C. Kunkel
M. J. Amaryan
I. I. Strakovsky
J. Ritman
G. R. Goldstein
K. P. Adhikari
S. Adhikari
Gerard P. Gilfoyle, University of RichmondFollow
et. al.

DOI

10.1103/PhysRevC.98.015207

Abstract

Exclusive photoproduction cross sections have been measured for the process γp -> pπ⁰ [e⁺ e^- (γ)] with the Dalitz decay final state using tagged photon energies in the range of Eγ = 1.275 – 5.425 GeV. The complete angular distribution of the final state π⁰, 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 dσ / dt, at mid to large angles, decreases with energy as s^{-6.89 +/- 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 GeV². At the same time, the Regge-exchange-based models for π⁰ photoproduction are more consistent with experimental data.

Document Type

Article

Publication Date

7-25-2018

Publisher Statement

Copyright © 2018 American Physical Society. This article first appeared in Physical Review C 98, no. 1 (July 25, 2018): 015207: 1-8. doi: 10.1103/PhysRevC.98.015207.

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Recommended Citation

Kunkel, M. C., M. J. Amaryan, I. I. Strakovsky, J. Ritman, G. R. Goldstein, K. P. Adhikari, S. Adhikari, G. Gilfoyle, et al. “Exclusive Photoproduction of Pi Degrees up to Large Values of Mandelstam Variables s, t, and u with CLAS.” Physical Review C 98, no. 1 (July 25, 2018): 015207. https://doi.org/10.1103/PhysRevC.98.015207.