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Title: 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 $$\gamma p \rightarrow p\pi^0(e^+e^-(\gamma))$$ 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.
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Publication Date:
Report Number(s):
JLAB-PHY-18-2673; DOE/OR/23177-4403; arXiv:1712.10314
Journal ID: ISSN 2469-9985
Grant/Contract Number:
AC05-06OR23177; SC0016583
Type:
Published Article
Journal Name:
Physical Review C
Additional Journal Information:
Journal Volume: 98; Journal Issue: 1; Journal ID: ISSN 2469-9985
Publisher:
American Physical Society (APS)
Research Org:
Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); George Washington Univ., Washington, DC (United States)
Sponsoring Org:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
Contributing Orgs:
CLAS Collaboration
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; nuclear structure & decays; particle interactions
OSTI Identifier:
1461599
Alternate Identifier(s):
OSTI ID: 1461455; OSTI ID: 1462020; OSTI ID: 1464055