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arXiv · 2208.12532

Kinematical higher-twist corrections in $\gamma^* \gamma \to \pi \pi $

Cédric Lorcé·Bernard Pire·Qin-Tao Song
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Abstract

We apply the Braun-Manashov technique to improve the description of $\gamma^*(q_1) \gamma(q_2) \to M(p_1) M(p_2)$ amplitudes at large $Q^2=-q_1^2$ and small $s=(q_1+q_2)^2$. We derive the kinematical higher-twist contributions of order $s/Q^2$ and $m^2/Q^2$ to the helicity amplitudes and estimate their sizes in the kinematics accessible at Belle and Belle II.Since pion GPDs cannot be directly measured by experiment, $\pi \pi$ GDAs are the best way to investigate the energy-momentum tensor form factors for pions.

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Cédric Lorcé, Bernard Pire, Qin-Tao Song. 2022-08-26. Kinematical higher-twist corrections in $\gamma^* \gamma \to \pi \pi $. https://arxiv.org/abs/2208.12532

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