Observation of a unitary cusp in the threshold {gamma}p{r_arrow}{pi}{sup 0}p reaction
- Department Physics and Laboratory for Nuclear Science, MIT, Cambridge Massachussetts 02139 (United States)
- Institut fuer Kernphysik, Johannes-Gutenberg-Universitaet Mainz, D-55099 Mainz (Germany)
- II. Physikalisches Institut, Universitaet Gieen, D-35392 Gieen (Germany)
A rigorous multipole analysis of the recent {gamma}p{r_arrow}{pi}{sup 0}p cross-section measurement is presented. The data were taken using the photon spectrometer TAPS at the tagged photon beam of the Mainz microtron. The s and p wave multipoles were extracted using minimal model assumptions. The predicted unitary cusp for the s-wave multipole E{sub 0+} due to the two step {gamma}p{r_arrow}{pi}{sup +}n{r_arrow}{pi}{sup 0}p reaction was observed. The results are consistent with one-loop chiral perturbation theory calculations for which three low-energy constants have been determined by a fit to the data. The uncertainties in the analysis and the need for polarization observables are discussed. {copyright} {ital 1997} {ital The American Physical Society}
- OSTI ID:
- 515655
- Journal Information:
- Physical Review, C, Journal Name: Physical Review, C Journal Issue: 3 Vol. 55; ISSN 0556-2813; ISSN PRVCAN
- Country of Publication:
- United States
- Language:
- English
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