  The proposed measurement is a dedicated study of the exclusive
electroproduction process,1H(e,e'p)pi0, in the backward-angle regime (u-channel
process) above the resonance region. The produced pi0 is emitted 180 degrees
opposite to the virtual-photon momentum. This study also aims to apply the
well-known Rosenbluth separation technique that provides the model-independent
differential cross-sections at the never explored u-channel kinematics region.
Currently, the "soft-hard transition" in u-channel meson production remains an
interesting and unexplored subject. The available theoretical frameworks offer
competing interpretations for the observed backward-angle cross section peaks.
In a "soft" hadronic Regge exchange description, the backward meson production
comes from the interference between nucleon exchange and the meson produced via
re-scattering within the nucleon. Whereas in the "hard" GPD-like backward
collinear factorization regime, the scattering amplitude factorizes into a hard
subprocess amplitude and baryon to meson transition distribution amplitudes
(TDAs), otherwise known as super skewed parton distributions (SuperSPDs). Both
TDAs and SPDs are universal non-perturbative objects of nucleon structure
accessible only through backward-angle kinematics. The separated cross
sections:sigma_T,sigma_L and T/L ratio at Q2=2-6 GeV2, provide a direct test of
two predictions from the TDA model. The magnitude and u-dependence of the
separated cross sections also provide a direct connection to the re-scattering
Regge picture. The extracted interaction radius (from u-dependence) at
different Q2 can be used to study the soft-hard transition in the u-channel
kinematics. The acquisition of these data will be an important step forward in
validating the existence of a backward factorization scheme of the nucleon
structure function and establishing its applicable kinematic range.
