Timelike Compton scattering on a spin-0 target with kinematic twist-4 precision

We calculate the kinematic twist-3 and twist-4 corrections to the leading-order amplitude of timelike Compton scattering (TCS) on a (pseudo)scalar target, in the recently developed framework based on the conformal operator-product expansion. This allows us to compute the complete set of helicity amplitudes of the process, in particular those that vanish at leading twist. We compare the effects of higher-twist contributions to TCS with those in deeply virtual Compton scattering. Our estimates, based on a <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>π</a:mi></a:math>-meson GPD model, indicate that these contributions are sizeable and will play a crucial role in the interpretation of data from current and forthcoming experiments.