Ambiguities in the partial-wave analysis of pseudoscalar-meson photoproduction

Ambiguities in pseudoscalar-meson photoproduction, arising from incomplete experimental data, have analogs in pion-nucleon scattering. Amplitude ambiguities have important implications for the problems of amplitude extraction and resonance identification in partial-wave analysis. The effect of these ambiguities on observables is described. We compare our results with those found in earlier studies.Comment: 12 pages of text. No figure

The size of the proton - closing in on the radius puzzle

We analyze the recent electron-proton scattering data from Mainz using a dispersive framework that respects the constraints from analyticity and unitarity on the nucleon structure. We also perform a continued fraction analysis of these data. We find a small electric proton charge radius, r_E^p = 0.84_{-0.01}^{+0.01} fm, consistent with the recent determination from muonic hydrogen measurements and earlier dispersive analyses. We also extract the proton magnetic radius, r_M^p = 0.86_{-0.03}^{+0.02} fm, consistent with earlier determinations based on dispersion relations.Comment: 4 pages, 2 figures, fit improved, small modifications, section on continued fractions modified, conclusions on the proton charge radius unchanged, version accepted for publication in European Physical Journal

Influence of spin-rotation measurements on partial-wave analyses of elastic pion-nucleon scattering

Recent measurements of spin-rotation parameters in elastic $\pi^+ p$ scattering are in marked disagreement with predictions of the Carnegie-Mellon$-$Berkeley and Karlsruhe-Helsinki analyses. Using the method of Barrelet, we show how this discrepancy can be removed. We then show how this Barrelet transformation alters the partial-wave amplitudes. The effect of unitarity and analyticity constraints is also considered.Comment: 9 pages, 4 figures. Postscript figures also available from ftp://clsaid.phys.vt.edu/pub/said/pin/barrele