Speaker
Description
Generalized distribution amplitudes (GDAs) are the s-t crossing quantities of generalized parton distributions (GPDs), which can be measured in the process of $\gamma^* + \gamma \rightarrow M_1+ M_2$. In 2016, the Belle Collaboration released the measurements of differential cross section for $\gamma^* + \gamma \rightarrow \pi+ \pi$, from which the pion GDAs were extracted by using the leading-twist amplitude. Given the kinematics of Belle measurements, higher-twist contributions of order $s/Q^2$ and $m^2/Q^2$ should also be important in the cross section. Recently, a separation of kinematic and dynamical contributions in the operator product of two electromagnetic currents was proven, and the kinematic corrections of order $t/Q^2$ and $m^2/Q^2$ were estimated for Deeply Virtual Compton Scattering (DVCS) up to twist 4. In this work, we apply similar techniques to the process of $\gamma^* + \gamma \rightarrow M_1+ M_2$. We calculate the kinematic contributions where only the leading-twist GDA is involved, and show the size of the kinematic contributions in comparison with the leading-twist amplitude numerically. Since Belle II collaboration just started taking data at the Super KEKB with a much higher luminosity, precise measurements of $\gamma^* + \gamma \rightarrow M_1+ M_2$ are expected in the near future. In this case, the accurate description of the amplitudes for the GDA study requires the inclusion of kinematic contributions up to twist 4. Moreover, our work will also impact the studies on the energy-momentum tensor (EMT) in QCD, as the GDAs can provide us a good alternative way for constraining the EMT form factors of hadrons.
| Submitted on behalf of a Collaboration? | No |
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