PoS - Proceedings of Science
Volume 297 - XXV International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS2017) - WG6 Spin and 3D Structure
3D structure of hadrons by generalized distribution amplitudes and gravitational form factors
S. Kumano*, Q.T. Song and O. Teryaev
Full text: pdf
Pre-published on: December 31, 2017
Published on: January 16, 2018
Generalized distribution amplitudes (GDAs) are one type of three-dimensional structure functions, and they are related to the generalized distribution functions (GPDs) by the $s$-$t$ crossing of the Mandelstam variables. The GDA studies provide information on three-dimensional tomography of hadrons. The GDAs can be investigated by the two-photon process $\gamma^* \gamma \to h\bar h$, and the GPDs are studied by the deeply virtual Compton scattering $\gamma^* h \to \gamma h$. The GDA studies had been pure theoretical topics, although the GPDs have been experimentally investigated, because there was no available experimental measurement. Recently, the Belle collaboration reported their measurements on the $\gamma^* \gamma \to \pi^0 \pi^0$ differential cross section, so that it became possible to find the GDAs from their measurements. Here, we report our analysis of the Belle data for determining the pion GDAs. From the GDAs, the timelike gravitational form factors $\Theta_1 (s)$ and $\Theta_2 (s)$ can be calculated, which are mechanical (pressure, shear force) and mass (energy) form factors, respectively. They are converted to the spacelike form factors by using the dispersion relation, and then gravitational radii are evaluated for the pion. The mass and mechanical radii are obtained from $\Theta_2$ and $\Theta_1$ as $\sqrt {\langle r^2 \rangle _{\text{mass}}} =0.56 \sim 0.69$ fm and $\sqrt {\langle r^2 \rangle _{\text{mech}}} =1.45 \sim 1.56$ fm, whereas the experimental charge radius is $\sqrt {\langle r^2 \rangle _{\text{charge}}} =0.672 \pm 0.008$ fm for the charged pion. Future developments are expected in this new field to explore gravitational physics in the quark and gluon level.
DOI: https://doi.org/10.22323/1.297.0244
How to cite

Metadata are provided both in "article" format (very similar to INSPIRE) as this helps creating very compact bibliographies which can be beneficial to authors and readers, and in "proceeding" format which is more detailed and complete.

Open Access
Creative Commons LicenseCopyright owned by the author(s) under the term of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.