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Title: First measurement of the polarization observable E and helicity-dependent cross sections in single π 0 photoproduction from quasi-free nucleons

The double-polarization observable Eand the helicity-dependent cross sections σ 1/2 and σ 3/2have been measured for the first time for single π0photoproduction from protons and neutrons bound in the deuteron at the electron accelerator facility MAMI in Mainz, Germany. The experiment used a circularly polarized photon beam and a longitudinally polarized deuterated butanol target. The reaction products, recoil nucleons and decay photons from the π0meson were detected with the Crystal Ball and TAPS electromagnetic calorimeters. Effects from nuclear Fermi motion were removed by a kinematic reconstruction of the π 0N final state. A comparison to data measured with a free proton target showed that the absolute scale of the cross sections is significantly modified by nuclear final-state interaction (FSI) effects. However, there is no significant effect on the asymmetry E since the σ 1/2 and σ 3/2components appear to be influenced in a similar way. Thus, the best approximation of the two helicity-dependent cross sections for the free neutron is obtained by combining the asymmetry E measured with quasi-free neutrons and the unpolarized cross section corrected for FSI effects under the assumption that the FSI effects are similar for neutrons and protons.
Authors:
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  1. Univ. of Basel (Switzerland)
  2. Univ. of Mainz (Germany)
  3. Univ. of Bonn (Germany)
  4. Univ. of Regina, SK (Canada)
  5. Kent State Univ., Kent, OH (United States)
  6. Univ. of Glasgow, Scotland (United Kingdom)
  7. Univ. of Edinburgh, Scotland (United Kingdom)
  8. Joint Inst. of Nuclear Research, Dubna (Russia)
  9. Istituto Nazionale di Fisica Nucleare (INFN), Pavia (Italy)
  10. George Washington Univ., Washington, DC (United States)
  11. Saint Marys Univ., Halifax (Canada)
  12. Univ. of Mainz (Germany); George Washington Univ., Washington, DC (United States)
  13. Univ. of Glasgow, Scotland (United Kingdom); Univ. of Edinburgh, Scotland (United Kingdom)
  14. Joint Inst. for Nuclear Research (JINR), Dubna (Russian Federation)
  15. Mount Allison Univ., Sackville, NB (Canada)
  16. Rudjer Boskovic Inst., Zagreb (Croatia)
  17. Mount Allison Univ., Sackville, NB (Canada); Univ. of Mainz (Germany)
  18. Univ. of Giessen (Germany)
  19. Ruhr Univ., Bochum (Germany)
  20. Univ. of Massachusetts, Amherst, MA (United States)
  21. Joint Inst. for Nuclear Research (JINR), Dubna (Russian Federation); Univ. of Massachusetts, Amherst, MA (United States). Dept. of Chemistry
  22. Univ. of Mainz (Germany); Univ. of California, Los Angeles, CA (United States)
  23. Hebrew Univ. of Jerusalem (Israel)
  24. Univ. of Basel (Switzerland); Univ. of Glasgow, Scotland (United Kingdom)
Publication Date:
Grant/Contract Number:
FG02-88ER40415; FG02-99ER41110; FG02-01ER41194; SC0016583
Type:
Published Article
Journal Name:
Physics Letters. Section B
Additional Journal Information:
Journal Volume: 770; Journal Issue: C; Journal ID: ISSN 0370-2693
Publisher:
Elsevier
Research Org:
Univ. of Massachusetts, Amherst, MA (United States); George Washington Univ., Washington, DC (United States)
Sponsoring Org:
USDOE Office of Science (SC), Office of Nuclear Physics Research Division; USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; meson photoproduction
OSTI Identifier:
1356438
Alternate Identifier(s):
OSTI ID: 1424752; OSTI ID: 1439813