skip to main content

DOE PAGESDOE PAGES

Title: Helicity-dependent cross sections and double-polarization observable E in η photoproduction from quasifree protons and neutrons

Precise helicity-dependent cross sections and the double-polarization observable E were measured for η photoproduction from quasifree protons and neutrons bound in the deuteron. The η → 2γ and η → 3π 0 → 6γ decay modes were used to optimize the statistical quality of the data and to estimate systematic uncertainties. The measurement used the A2 detector setup at the tagged photon beam of the electron accelerator MAMI in Mainz. A longitudinally polarized deuterated butanol target was used in combination with a circularly polarized photon beam from bremsstrahlung of a longitudinally polarized electron beam. The reaction products were detected with the electromagnetic calorimeters Crystal Ball and TAPS, which covered 98% of the full solid angle. The results show that the narrow structure observed earlier in the unpolarized excitation function of η photoproduction off the neutron appears only in reactions with antiparallel photon and nucleon spin (σ 1/2). It is absent for reactions with parallel spin orientation (σ 3/2) and thus very probably related to partial waves with total spin 1/2. The behavior of the angular distributions of the helicity-dependent cross sections was analyzed by fitting them with Legendre polynomials. The results are in good agreement with a model from themore » Bonn-Gatchina group, which uses an interference of P 11 and S 11 partial waves to explain the narrow structure.« less
Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; « less
Publication Date:
Grant/Contract Number:
FG02-88ER40415; FG02-99ER41110; FG02-01ER41194; 227431; PHY-1039130; FG02-99-ER41110; SC0016583
Type:
Published Article
Journal Name:
Physical Review C
Additional Journal Information:
Journal Volume: 95; Journal Issue: 5; Journal ID: ISSN 2469-9985
Publisher:
American Physical Society (APS)
Research Org:
Univ. of Massachusetts, Amherst, MA (United States); George Washington Univ., Washington, DC (United States)
Sponsoring Org:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26); German Research Foundation (DFG); Science and Technology Facilities Council (STFC) (United Kingdom); Natural Sciences and Engineering Research Council of Canada (NSERC); National Science Foundation (NSF)
Contributing Orgs:
A2 Collaboration at MAMI
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 74 ATOMIC AND MOLECULAR PHYSICS; Particles & Fields; Nuclear Physics; protons; Helicities
OSTI Identifier:
1354757
Alternate Identifier(s):
OSTI ID: 1425343; OSTI ID: 1439805