Measurement of the helicity asymmetry E for the γ→ p→ → pπ reaction in the resonance region : The CLAS Collaboration

Abstract

The double-spin-polarization observable E for γ→ p→ → pπ has been measured with the CEBAF Large Acceptance Spectrometer (CLAS) at photon beam energies Eγ from 0.367 to 2.173GeV (corresponding to center-of-mass energies from 1.240 to 2.200GeV) for pion center-of-mass angles, cosθπ0c.m. , 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.

Metadata

Funding Information: This work was supported in part by the U. S. Department of Energy, Office of Science, Office of Nuclear Physics under Awards No. DE–SC0016583 and DE–SC0016582; by the U. K. Science and Technology Facilities Council grants, ST/P004385/2, ST/T002077/1, ST/V001035/1, ST/V002570/1, and ST/L00478X/2; by the EU Horizon 2020 research by innovation program, STRONG–2020 project (under grant agreement No. 824093), as well as by the Russian Science Foundation RSF22–22–00722 grant. We also acknowledge the outstanding efforts of the staff of the Accelerator and Physics Divisions at Jefferson Lab that made this experiment possible. The Southeastern Universities Research Association (SURA) operated the Thomas Jefferson National Accelerator Facility for the United States Department of Energy under contract DE–AC05–06OR23177. Further support was provided by the National Science Foundation, the Italian Istituto Nazionale di Fisica Nucleare, the Chilean Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), the Chilean Agency of Research and Development (ANID), the French Centre National de la Recherche Scientifique, the French Commissariat à l’Energie Atomique, and the National Research Foundation of Korea. Publisher Copyright: © 2023, The Author(s).

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