Exclusive photoproduction of π 0 up to large values of Mandelstam variables s, t, and u with CLAS.
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.
Physical Review C
Kunkel, M. C.; Amaryan, J.; Strakovsky, I. I.; Ritman, J.; Goldstein, G. R.; Adhikari, K. P.; Adhikari, S.; Biselli, Angela; and CLAS Collaboration, "Exclusive photoproduction of π 0 up to large values of Mandelstam variables s, t, and u with CLAS." (2018). Physics Faculty Publications. 143.
Kunkel, M. C., M. J. Amaryan, I. I. Strakovsky, J. Ritman, G. R. Goldstein, K. P. Adhikari, S. Adhikari, Biselli, A. et al [CLAS Collaboration]. "Exclusive photoproduction of π 0 up to large values of Mandelstam variables s, t, and u with CLAS." Physical Review C 98, no. 1 (2018): 015207. DOI:https://doi.org/10.1103/PhysRevC.98.015207