International Conference on Exotic Atoms and Related Topics - EXA2017

Tomography and gravitational radii for hadrons by three-dimensional structure functions S. Kumano, Qin-Tao Song, and O. V. Teryaev Hadron tomography can be investigated by three-dimensional structure functions such as generalized parton distributions (GPDs), transverse-momentum-dependent parton distribution (TMDs), and generalized distribution amplitudes (GDAs). The GPDs and GDAs contain information on spacelike and timelike transverse form factors of the energy-momentum tensor, so that they probe gravitational-interaction radii of hadrons [1]. Although charge radii of the nucleons are determined, mass radii have not been measured for any hadrons. Here, we extract the GDAs, which are s-t crossed quantities of the GPDs, from cross-section measurements of hadron-pair production process gamma+gamma^* to h+hbar [1]. The GDAs are expressed by a number of parameters and they are determined from pion-pair production data of KEKB. We discuss the dependence on parton-momentum fraction z in the GDAs and also time-like form factor of the energy-momentum tensor [1]. Our studies should be valuable for probing three-dimensional structure of hadrons, especially for applications to exotic hadron candidates which cannot be used as fixed targets for GPD and TMD measurements [2]. In addition, the results indicate the gravitational-interaction radius for the pion [1]. The GDA studies are also possible by the two-photon process into a hadron pair by ultra-peripheral collisions at LHC and RHIC. In future, there is a possibility to investigate the GPDs at J-PARC for nucleon tomography [3]. [1] S. Kumano, Qin-Tao Song, and O. V. Teryaev, KEK-TH-1959, J-PARC-TH-0086, to be submitted for publication. [2] S. Kumano and H. Kawamura, Phys.Rev. D89 (2014) 054007. [3] S. Kumano, M. Strikman, and K. Sudoh, Phys. Rev. D80 (2009) 074003; T. Sawada, Wen-Chen Chang, S. Kumano, Jen-Chieh Peng, S. Sawada, and K. Tanaka, Phys. Rev. D 93 (2016) 114034.