A polarization relation and the measurement of the longitudinal response in pseudoscalar meson electroproduction off the nucleon
AbstractFor pseudoscalar meson electroproduction off the nucleon in parallel kinematics a relation between three polarization observables is derived. It is shown that, without Rosenbluth separation, a measurement of the longitudinal strength can be achieved through three different ways. They are discussed with preliminary MAMI data for the 
$$p(\vec e, e' \vec p)\pi ^0 $$
 reaction in the energy range of the Δ(1232) resonance.