Cross section and single transverse target spin asymmetry for backward   pion electroproduction
  Nucleon to meson transition distribution amplitudes (TDAs), non-diagonal matrix elements of nonlocal three quark operators between a nucleon and a meson states, arise within the collinear factorized description of hard exclusive electroproduction of mesons off nucleons in the backward direction. Below we address the problem of modelling pion to nucleon TDAs. We suggest a factorized Ansatz for quadruple distributions with input from the soft pion theorem for pi N TDAs. In order to satisfy the polynomiality property in its full form the spectral representation is complemented with a D-term like contribution from the nucleon exchange in the u-channel of the reaction. We present our estimates for the backward pion electroproduction unpolarized cross section and its transverse target single spin asymmetry within our composite model for pi N TDAs. 
B. Pire, K. Semenov-Tian-Shansky and L. Szymanowski
hep-ph hep-ex nucl-ex nucl-th