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., et al. (2018). Exclusive photoproduction of π0 up to large values of Mandelstam variables s, t, and u with CLAS. PHYSICAL REVIEW C, 98(1) [10.1103/PhysRevC.98.015207].
Exclusive photoproduction of π0 up to large values of Mandelstam variables s, t, and u with CLAS
D'Angelo, A.Membro del Collaboration Group
;Lanza, L.;Rizzo, A.Membro del Collaboration Group
;
2018-07-25
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=11GeV2. At the same time, the Regge-exchange-based models for π0 photoproduction are more consistent with experimental data.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
