Deeply inelastic pions in the exclusive reaction $p(e,e'\pi^+)n$ above the resonance region

Understand

A model for the $p(e,e'\pi^+)n$ reaction which combines an improved treatment of gauge invariant meson--exchange currents and hard deep--inelastic scattering (DIS) of virtual photons off nucleons is proposed.

• It is shown that DIS dominates and explains the transverse response at moderate and high photon virtualities $Q^2$ whereas the longitudinal response is dominated by hadronic degrees of freedom and the pion electromagnetic form factor.
• This leads to a combined description of the longitudinal and transverse components of the cross section in a wide range of photon virtuality $Q^2$ and momentum transfer to the target $t$ and solves the longstanding problem of the observed large transverse cross sections.
• The latter are shown to be sensitive to the intrinsic transverse momentum distribution of partons.