Measurement of the gravitational form factors at Belle

Three dimensional tomography for hadrons has developed recently by using generalized parton distributions and generalized distribution amplitudes. This development makes us possible to study gravitational form factors for hadrons experimentally. We have measured differential cross section of pi0 pair production in single-tag two-photon collisions, gamma*gamma→pi0pi0, based on a data sample of 759 fb^-1 collected with the Belle detector at the KEKB asymmetric-energy e⁺e⁻ collider. Two types of gravitational form factors which indicate mechanical distributions and gravitational mass distributions are extracted from the Belle data and converted to the corresponding gravitational radii for a pion. I would like to talk about the analysis and future prospects of gravitational pion radii.