Exclusive high- Q2 electroproduction: light-cone wave functions and electromagnetic form factors of mesons

Abstract

In the light-cone technique, one can describe exclusive electroproduction treating mesons and baryons as (non-pointlike) partons of the nucleon. In this technique, the non-perturbative light-cone wave function of the meson-baryon Fock state of the physical nucleon defines the universal, projectile independent, density (flux) of on-mass-shell mesons in the proton. We apply the light-cone technique to electroproduction reaction ep → eπ + n long considered as a means of measuring the electromagnetic form factor of the pion. We show that the interpretation of the long-standing puzzle of large transverse cross section ( σ T ) in terms of the γ ∗ ϱ → π transition on the ϱ mesons in the light-cone proton is possible, but requires quite a slow decrease of the F ϱπ ( Q 2) form factor. This interpretation can be tested in the related ep → eπ 0 p reaction. Corrections which are due to the final-state meson-baryon interactions (FSI) are evaluated and are shown to amount to a 25% effect at moderately large Q 2. Vanishing FSI with increasing Q 2 — the color transparency phenomenon — is shown to be very strong.