19 May, 14:00

via Zoom

Speaker: Qin-Tao Song

Title: Kinematical higher-twist corrections in γ* γ → M1 M2 and γ* → M1 M2 γ

Abstract: We carry out the calculation of kinematical higher-twist corrections to the cross sections ofγ* γ → M1 M2 and γ* → M1 M2 γ 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 non-perturbative quantities for understanding the 3D structure of hadrons. Since those processes can be measured in e+e- collisions, we also perform the numerical estimate of the kinematical corrections for γ* γ → M1 M2 and γ* → M1 M2 γ by using the kinematics of Belle and BESIII, respectively. We adopt the π π GDA extracted from Belle measurements and the asymptotic π π GDA to study the size of the kinematical corrections in the case of pion meson pair, and a model η η GDA is used to see the impact of target mass corrections O(m2/s) for γ* γ → η η and γ* → η η γ. Our results show that the kinematical higher-twist corrections account for ~ 20% of the cross sections on the average, and it is necessary to include them if one tries to extract GDAs from experimental measurements precisely.