Exclusive photoproduction of π0 up to large values of Mandelstam variables s, t, and u with CLAS
© 2018 authors. Published by the American Physical Society. 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=11GeV2. At the same time, the Regge-exchange-based models for π0 photoproduction are more consistent with experimental data.
Kunkel, M. C.; Amaryan, M. J.; Strakovsky, I. I.; Ritman, J.; Goldstein, G. R.; Adhikari, K. P.; Adhikari, S.; Avakian, H.; Ball, J.; Balossino, I.; Barion, L.; Battaglieri, M.; Batourine, V.; Bedlinskiy, I.; Biselli, A. S.; Boiarinov, S.; Briscoe, W. J.; Brooks, W. K.; Bültmann, S.; Burkert, V. D.; Cao, F.; Carman, D. S.; Celentano, A.; Charles, G.; Chetry, T.; Ciullo, G.; Clark, L.; Cole, P. L.; Contalbrigo, M.; Cortes, O.; Fedotov, G.; and Hicks, K., "Exclusive photoproduction of π0 up to large values of Mandelstam variables s, t, and u with CLAS" (2018). Physics & Astronomy Open Access Publications. 91.