Abstract
The double-polarization observable and helicity-dependent cross sections , have been measured for the photoproduction of pairs off quasifree protons and neutrons at the Mainz MAMI accelerator with the Crystal Ball/TAPS setup. A circularly polarized photon beam was produced by bremsstrahlung from longitudinally polarized electrons and impinged on a longitudinally polarized deuterated butanol target. The reaction products were detected with an almost covering calorimeter. The results reveal for the first time the helicity- and isospin-dependent structure of the reaction. They are compared to predictions from reaction models in view of nucleon resonance contributions and also to a refit of one model that predicted results for the proton and for the neutron target. The comparison of the prediction and the refit demonstrates the large impact of the new data.
- Received 10 January 2020
- Revised 17 May 2020
- Accepted 15 July 2020
DOI:https://doi.org/10.1103/PhysRevLett.125.062001
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society