Measuring C-odd correlations at lepton–proton and photon–proton collisions

Abstract

We consider the charge-odd correlations (COC) in cross sections of charged particle production. The cases of a muonic pair and pion systems π+π−, π+π−π0 production are considered in detail for electron–proton or photon–proton collisions in the proton fragmentation region kinematics. COC arise from the interference of amplitudes which describe the different mechanisms of charged leptons (pions) production. One of them corresponds to the production of particles in the charge-odd state (one virtual photon or vector meson annihilation to this system of particles) and the other corresponds to the charge-even state of produced particles (creation by two photons). COC for a muon–antimuon pair creation have a pure QED nature and can be considered as a normalization process. The processes with pion production are sensitive to some characteristics of proton wavefunctions and, besides, can be used for checking the anomalous and normal parts of the effective pionic Lagrangian. The matrix element of three electromagnetic current operators can be measured in photon–proton interactions with lepton pair production. For this aim a charge-odd combination of cross sections can be constructed as a conversion of leptonic 3-rank tensor with hadronic ones. These experiments can be considered as an alternative to deep virtual Compton scattering.