Threshold pion photoproduction revisited
The authors show that the low energy expressions for the CGLN pion photoproduction invariant amplitudes when evaluated at threshold yield a 26% enhancement of the de Baenst {gamma}p {r_arrow}{pi}{sup 0}p threshold electric dipole amplitude. One can recover the de Baenst result, to lowest two orders in m{sub {pi}}/M{sub N}, by assuming that the Goldberger-Treiman (GT) relation f{sub {pi}}g = m{sub N}g{sub A} is exact. However, accounting for the observed 5% GT discrepancy, and the recent modifications of the Saclay and Mainz threshold data, and comparing the data to the enhanced de Baenst amplitude leads to a large explicit breaking of chiral symmetry. The magnitude of the explicit chiral symmetry breaking is not cleanly extracted from the threshold data because of the GT-like cancellations in the exact {gamma}p{r_arrow}{pi}{sup 0}p threshold electric dipole amplitude.
- OSTI ID:
- 243530
- Report Number(s):
- CONF-9304297--
- Journal Information:
- Bulletin of the American Physical Society, Journal Name: Bulletin of the American Physical Society Journal Issue: 2 Vol. 38; ISSN BAPSA6; ISSN 0003-0503
- Country of Publication:
- United States
- Language:
- English
Similar Records
New estimate of quark mass parameters
Chiral anomalies and quark masses