Kinematical higher-twist corrections in γ* → M1M2γ: Neutral meson production

We carry out the calculation of kinematical higher-twist corrections to the cross section of & gamma;& DBLBOND; & RARR; M1M2 & gamma; up to twist 4, where Mi is a scalar or pseudoscalar neutral meson. The three independent helicity amplitudes are presented in terms of the twist-2 generalized distribution amplitudes (GDAs), which are important nonperturbative quantities for understanding the 3D structure of hadrons. Since this process can be measured by BESIII in e thorn e- collisions, we perform the numerical estimate of the kinematical higher-twist corrections by using the kinematics of BESIII. We adopt the & pi;& pi; GDA extracted from Belle measurements and the asymptotic & pi;& pi; GDA to study the size of the kinematical corrections in the case of pion meson pair, and a model & eta;& eta;GDA is used to see the impact of target mass corrections Oom2=s thorn for & gamma;& DBLBOND; & RARR; & eta;& eta;& gamma;. Our results show that the kinematical higher-twist corrections account for & SIM;20% of the cross sections at BESIII on the average, and it is necessary to include them if one tries to extract GDAs from experimental measurements precisely. We also comment the case of & pi;0 & eta; production which is important for the search of hybrid mesons.