The general spin structure of the matrix element, taking into account the
two--photon exchange contribution, for the elastic electron (positron)
--deuteron scattering has been derived using general symmetry properties of
the hadron electromagnetic interaction, such as P--, C-- and T--invariances
as well as lepton helicity conservation in QED at high energy. Taking into account also crossing symmetry, the amplitudes of $e^{\\mp}d-$scattering can be
parametrized in terms of fifteen real functions. The expressions for the differential cross
section and for all polarization observables are given in terms of these
functions. We consider the case of an arbitrary polarized
deuteron target and polarized electron beam (both longitudinal
and transverse). The transverse polarization of the electron beam
induces a single--spin asymmetry which is non--zero in presence of
two--photon exchange. It is shown that elastic deuteron electromagnetic form factors can still be extracted in presence of two photon exchange, from the
measurements of the differential cross section and of one polarization
observable (for example, the tensor asymmetry) for electron and
positron deuteron elastic scattering, in the same kinematical conditions. |
