https://doi.org/10.1140/epja/s10050-023-01123-3
Regular Article - Experimental Physics
Measurement of the helicity asymmetry 
for the 
reaction in the resonance region
The CLAS Collaboration
1
Argonne National Laboratory, 60439, Argonne, IL, USA
2
Arizona State University, 85287, Tempe, AZ, USA
3
California State University, Dominguez Hills, 90747, Carson, CA, USA
4
Canisius College, 14208, Buffalo, NY, USA
5
Carnegie Mellon University, 15213, Pittsburgh, PA, USA
6
The Catholic University of America, 20064, Washington, DC, USA
7
IRFU, CEA, Universitè Paris-Saclay, 91191, Gif-sur-Yvette, France
8
Christopher Newport University, 23606, Newport News, VA, USA
9
University of Connecticut, 06269, Storrs, CT, USA
10
Duquesne University, 15282, Pittsburgh, PA, USA
11
Fairfield University, 06824, Fairfield, CT, USA
12
Università di Ferrara, 44121, Ferrara, Italy
13
Florida International University, 33199, Miami, FL, USA
14
Florida State University, 32306, Tallahassee, FL, USA
15
The George Washington University, 20052, Washington, DC, USA
16
GSI Helmholtzzentrum fur Schwerionenforschung GmbH, 64291, Darmstadt, Germany
17
INFN, Sezione di Ferrara, 44100, Ferrara, Italy
18
INFN, Sezione di Genova, 16146, Genova, Italy
19
INFN, Sezione di Roma Tor Vergata, 00133, Rome, Italy
20
INFN, Sezione di Torino, 10125, Torino, Italy
21
INFN, Sezione di Pavia, 27100, Pavia, Italy
22
Institut für Kernphysik, Johannes Gutenberg University of Mainz, 55099, Mainz, Germany
23
Kyungpook National University, 41566, Daegu, South Korea
24
Lamar University, 77710, Beaumont, TX, USA
25
Massachusetts Institute of Technology, 02139, Cambridge, MA, USA
26
Mississippi State University, 39762, Mississippi State, MS, USA
27
National Research Centre Kurchatov Institute, Institute for Theoretical and Experimental Physics, 117259, Moscow, Russia
28
New Mexico State University, 88003, Las Cruces, NM, USA
29
Norfolk State University, 23504, Norfolk, VA, USA
30
National Research Centre Kurchatov Institute, Petersburg Nuclear Physics Institute, 188300, Gatchina, Russia
31
Ohio University, 45701, Athens, OH, USA
32
Old Dominion University, 23529, Norfolk, VA, USA
33
II Physikalisches Institut, Justus Liebig University Giessen, 35392, Giessen, Germany
34
Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 119234, Moscow, Russia
35
Temple University, 19122, Philadelphia, PA, USA
36
Thomas Jefferson National Accelerator Facility, 23606, Newport News, VA, USA
37
Universitè Paris-Saclay, CNRS/IN2P3, IJCLab, 91405, Orsay, France
38
University of New Hampshire, 03824, Durham, NH, USA
39
University of Richmond, 23173, Richmond, VA, USA
40
Università di Roma Tor Vergata, 00133, Rome, Italy
41
University of South Carolina, 29208, Columbia, SC, USA
42
Universidad Tècnica Federico Santa María, Casilla 110-V, Valparaìso, Chile
43
Università degli Studi di Brescia, 25123, Brescia, Italy
44
University of California Riverside, 92521, Riverside, CA, USA
45
University of Glasgow, G12 8QQ, Glasgow, UK
46
University of York, YO10 5DD, York, UK
47
Virginia Polytechnic Institute and State University, 24061, Blacksburg, VA, USA
48
University of Virginia, 22901, Charlottesville, VA, USA
49
College of William and Mary, 23187, Williamsburg, VA, USA
50
Yerevan Physics Institute, 375036, Yerevan, Armenia
51
Montgomery College, 20876, Germantown, MD, USA
52
University of Nebraska, 68198, Omaha, NE, USA
Received:
11
May
2023
Accepted:
31
August
2023
Published online:
26
September
2023
The double-spin-polarization observable for 
has been measured with the CEBAF Large Acceptance Spectrometer (CLAS) at photon beam energies 
from 0.367 to 
(corresponding to center-of-mass energies from 1.240 to 
) for pion center-of-mass angles, 
, between 
0.86 and 0.82. These new CLAS measurements cover a broader energy range and have smaller uncertainties compared to previous CBELSA data and provide an important independent check on systematics. These measurements are compared to predictions as well as new global fits from The George Washington University, Mainz, and Bonn-Gatchina groups. Their inclusion in multipole analyses will allow us to refine our understanding of the single-pion production contribution to the Gerasimov-Drell-Hearn sum rule and improve the determination of resonance properties, which will be presented in a future publication.
© The Author(s) 2023
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