Threshold pion photoproduction and chiral symmetry

Journal Article · Tue Dec 01 04:00:00 EST 1992 · Bulletin of the American Physical Society

OSTI ID:127807

Bernstein, A M; Guillian, E

Experiments on the {gamma}p{yields}{pi}{sup o}p threshold reaction (performed at Saclay and Mainz) have attracted considerable attention because they test low energy, QCD related, predictions. The latest analyses of these data have indicated that the threshold value for the (s wave) electric dipole amplitude (E{sub o+}) is in agreement with {open_quotes}low energy theorems{close_quotes} based on current algebra (PCAC). However there was a strong energy dependence for this amplitude which makes it problematical to compare theory and experiment at only one point, the x{sup o} threshold. All of the previous analyses made model dependent assumptions about the p wave multipoles. The authors have performed, for the first time, a model independent analysis of the total and differential cross section data. In agreement with their previous analysis, and with the PCAC prediction, they obtain a threshold value of E{sub o+}= (2.0 {plus_minus} 0.2) x 10{sup {minus}3}/m{sub {pi}}. However the slope of this amplitude does not vary rapidly with energy which makes the question of what energy to compare the threshold values with theory less of a problem. A comparison with theory and previous analyses will be presented.

• OSTI ID: 127807
• Report Number(s): CONF-920376--
• Journal Information: Bulletin of the American Physical Society, Journal Name: Bulletin of the American Physical Society Journal Issue: 9 Vol. 37; ISSN BAPSA6; ISSN 0003-0503
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
CHIRAL SYMMETRY
PHOTON-PROTON INTERACTIONS
PHOTOPRODUCTION
PIONS NEUTRAL
PROTONS
THRESHOLD ENERGY