Uncovering the scaling laws of hard exclusive hadronic processes in a comprehensive endpoint model

Abstract

We show that an endpoint-overlap model can explain the scaling laws observed in exclusive hadronic reactions at large momentum transfer. The model assumes one of the valence quarks carries most of the hadron momentum. Hadron form factors and fixed-angle scattering are related directly to the quark wave function, which can be directly extracted from experimental data. A universal linear endpoint behavior explains the proton electromagnetic form factor, proton–proton fixed-angle scattering, and the 𝑡 -dependence of proton–proton scattering at large 𝑠>>𝑡. Endpoint constituent counting rules relate the number of quarks in a hadron to the power-law behavior. All proton reactions surveyed are consistent with three quarks participating. The model is applicable at laboratory energies and does not need assumptions of asymptotically high energy regime. A rich phenomenology of lepton–hadron scattering and hadron–hadron scattering processes is found in remarkably simple relationships between diverse processes.