Ron L. Workman

Updated analysis of pi N elastic scattering data to 2.1-GeV: The Baryon spectrum

We present the results of energy-dependent and single-energy partial-wave analyses of {pi}{ital N} elastic scattering data with laboratory kinetic energies below 2.1 GeV. Resonance structures have been extracted using Breit-Wigner fits, speed plots, and a complex plane mapping of the associated poles and zeros. This is the first set of resonance parameters from a VPI analysis constrained by fixed-{ital t} dispersion relations. We have searched our solutions for structures which may have been missed in our previous analyses, finding candidates in the {ital S}{sub 11} and {ital F}{sub 15} partial-wave amplitudes. Our results are compared with those found by the Karlsruhe, Carnegie-Mellon--Berkeley, and Kent State groups.

Updated resonance photodecay amplitudes to 2 GeV.

We present the results of an energy-dependent and set of single-energy partial-wave analyses of single-pion photoproduction data. These analyses extend from threshold to 2 GeV in the laboratory photon energy, and update our previous analyses to 1.8 GeV. Photo-decay amplitudes are extracted for the baryon resonances within this energy range. We consider two photoproduction sum rules and the contributions of two additional resonance

Nucleon-nucleon elastic scattering to 3 GeV

A partial-wave analysis (PWA) of NN elastic scattering data has been completed. This analysis covers an expanded energy range, from threshold to a laboratory kinetic energy of 3 GeV, in order to include recent elastic pp polarized scattering measurements performed at SATURNE II. Results of the energy-dependent fit are compared with single-energy solutions and Saclay amplitudes obtained via the direct-reconstruction approach. We also comment on the status of {epsilon}{sub 1} in the low-energy region. (c) 2000 The American Physical Society.

Updated analysis of NN elastic scattering data to 1.6 GeV.

An energy-dependent and set of single-energy partial-wave analyses of [ital NN] elastic scattering data have been completed. The fit to 1.6 GeV has been supplemented with a low-energy analysis to 400 MeV. Using the low-energy fit, we study the sensitivity of our analysis to the choice of [pi][ital NN] coupling constant. We also comment on the possibility of fitting [ital np] data alone. These results are compared with those found in the recent Nijmegen analyses.

Nucleon-nucleon elastic scattering analysis to 2.5 GeV

A partial-wave analysis of NN elastic scattering data has been completed. This analysis covers an expanded energy range, from threshold to a laboratory kinetic energy of 2.5 GeV, in order to include recent elastic pp scattering data from the EDDA Collaboration. The results of both single-energy and energy-dependent analyses are described. {copyright} {ital 1997} {ital The American Physical Society}

Unified Chew-Mandelstam SAID analysis of pion photoproduction data

A wealth of N ! �N data, for single- and doublepolarization observables, is anticipated from electromagnetic facilities worldwide over the coming months and years. These data will be pivotal in determining the underlying amplitudes in complete experiments, and in discerning between various microscopic models of multichannel reaction theory. The focus of precision electromagnetic measurements, over the nucleon resonance region, is to more fully map the non-perturbative regime of quantum chromodynamics, the fundamental theory of the strong interaction, to shed light on its confining and chiral symmetry breaking properties. These electromagnetic data take the field to the next and necessary level of precision. This is required in order to obtain a theoretical description of the nucleon that both explains and subsumes the simple constituent quark model, which has provided a qualitative picture of nucleon structure and reactions. The expected data heralds an era of precision hadron spectroscopy, particularly for baryons, and has ushered in a renaissance in hadronic reaction theory. Significant refinements in the quality and quantity of available data offer the opportunity to develop more sophisticated models of hadronic reactions, constrained by fundamental principles of field theory, such as unitarity and gauge invariance, which have model dependencies under better control, if not eliminated. Such a complete and successful phenomenology would appear to be a prerequisite for a deeper understanding in terms of quarks and gluons [1]. The present manuscript details multipole analyses of the single-pion photoproduction data using a parametrization form related to, but an improvement upon, previous SAID parametrizations [2–4]. The energy-dependent (ED) analysis is performed over the center-of-mass energy (W) range from the near-threshold region to about 2.5 GeV, including resonances through

Analysis of the reaction pi +d-->pp to 500 MeV.

An energy-dependent and set of single-energy partial-wave analyse have been completed for the reaction [pi][sup +][ital d][r arrow][ital pp]. Amplitudes are presented for pion laboratory kinetic energies from threshold to 500 MeV. These results are compared with those found in other recent analyses. We comment on the present database and make suggestions for future experiments.

Analysis of the reaction [pi][sup +][ital d][r arrow][ital pp] to 500 MeV

An energy-dependent and set of single-energy partial-wave analyse have been completed for the reaction [pi][sup +][ital d][r arrow][ital pp]. Amplitudes are presented for pion laboratory kinetic energies from threshold to 500 MeV. These results are compared with those found in other recent analyses. We comment on the present database and make suggestions for future experiments.

Form-factors and photoproduction amplitudes

We examine the use of phenomenological form factors in tree level amplitudes for meson photoproduction. Two common recipes are shown to be fundamentally incorrect. An alternate form consistent with gauge invariance and crossing symmetry is proposed.

Baryon photo-decay amplitudes at the pole

We derive relations for baryon photo-decay amplitudes both for the Breit-Wigner and the pole positions. With an updated SAID partial wave analysis, technically similar to the earliest Virginia Tech analysis of photoproduction data, we compare photo-decay amplitudes at both resonance positions for a few selected nucleon resonances. Comparisons are made and a qualitative similarity, seen between the pole and Breit-Wigner values extracted by the Bonn-Gatchina group, is confirmed in the present study.