Beam helicity asymmetries in K+Λ electroproduction off the proton at low Q2

. Beam helicity asymmetries in the e → p → e K + Λ reaction have been measured at unprecedentedly low four-momentum transfers 〈 Q 2 〉 = 0 . 05 ( GeV / c ) 2 . At the Mainz Microtron (MAMI), the experiment was performed with a longitudinally polarized beam and an out-of-plane detection of the scattered electron. This experiment probed the associated helicity-dependent structure function d σ L T / d Ω K c . m . , which is sensitive to the details of resonances of the proton. The results were compared to models for kaon electroproduction using effective Lagrangians. The MAMI data is not supporting the Kaon-Maid isobar model, which uses strong longitudinal couplings of the virtual photon to nucleon resonances and predicts a strong peaking of the structure function at forward angles and low Q 2 . The data is also in disagreement with a Regge-plus-resonance model that predicts the incorrect sign of the structure function. The combination of the MAMI results wih data taken at higher four-momentum transfers measured at Jefferson Lab indicates a smooth transition in Q 2 without significant changes of the interference pattern in the electroproduction process.