https://doi.org/10.1140/epja/s10050-020-00334-2
Regular Article – Experimental Physics
Measurement of the helicity asymmetry E for the reaction 
The CBELSA/TAPS Collaboration
1
Helmholtz–Institut für Strahlen– und Kernphysik, Universität Bonn, Bonn, Germany
2
Physikalisches Institut, Universität Bonn, Bonn, Germany
3
Petersburg Nuclear Physics Institute, Gatchina, Russia
4
Physikalisches Institut, Universität Gießen, Gießen, Germany
5
Physikalisches Institut, Universität Basel, Basel, Switzerland
6
Institut für Experimentalphysik I, Ruhr–Universität Bochum, Bochum, Germany
7
Department of Physics, Florida State University, 32306, Tallahassee, FL, USA
Received:
20
May
2019
Accepted:
28
November
2020
Published online:
28
January
2021
A measurement of the double-polarization observable E for the reaction 
is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C
H
OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from 
to 2310 MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.
© The Author(s) 2021
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