engleski

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

Beam helicity asymmetries in the ep → eK+Λ reaction have been measured at unprecedentedly low four-momentum transfersQ2 =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 dσLT/dΩc.m. K , 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 Q2. The data is also in disagreement with a Regge-plusresonance model that predicts the incorrect sign of the structure function. The combination of the MAMI results with data taken at higher four-momentum transfers measured at Jefferson Lab indicates a smooth transition in Q2 without significant changes of the interference pattern in the electroproduction process.

Beam helicity asymmetries

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