https://doi.org/10.1140/epja/i2017-12395-1
Regular Article - Experimental Physics
Beam helicity asymmetries in 
electroproduction off the proton at low Q2
1
Institut für Kernphysik, Johannes Gutenberg-Universität, D-55099, Mainz, Germany
2
GSI Helmholtz Centre for Heavy Ion Research, D-64291, Darmstadt, Germany
3
Department of Physics, Faculty of Science, University of Zagreb, HR-10000, Zagreb, Croatia
4
Nuclear Physics Institute, 25068, Řež, Czech Republic
5
University of Ljubljana and Institut “Jožef Stefan”, SI-1000, Ljubljana, Slovenia
6
Department of Physics, Tohoku University, 980-8578, Sendai, Japan
7
Yerevan Physics Institute, 375036, Yerevan, Armenia
8
Department of Physics, Florida International University, 33174, Miami, FL, USA
9
Helmholtz Institute Mainz, D-55099, Mainz, Germany
10
Department of Physics, Hampton University, 23668, Hampton, VA, USA
* e-mail: achenbach@uni-mainz.de
Received:
9
March
2017
Accepted:
21
September
2017
Published online:
17
October
2017
Beam helicity asymmetries in the 
reaction have been measured at unprecedentedly low four-momentum transfers 
(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 
, 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 
. 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 without significant changes of the interference pattern in the electroproduction process.
© SIF, Springer-Verlag GmbH Germany, 2017
