EXTRACTION OF RESONANCE PARAMETERS AND ROLE OF THE FINAL STATE INTERACTIONS

I I Strakovsky ,A E Kudryavtsev ,W J Briscoe ,V E Tarasov

doi:10.1142/s2010194514600829

Abstract

We present an overview of the SAID group effort to analyze new γn → π-p cross sections vs. the world database to get new multipoles and determine neutron electromagnetic couplings. The differential cross section for the processes γn → π-p was extracted from new measurements at CLAS and MAMI-B accounting for Fermi motion effects in the impulse approximation (IA) as well as NN- and πN-FSI effects beyond the IA. We evaluated results of several pion photoproduction analyses and compared πN PWA results as a constraint for analyses of pion photoproduction data (Watson's theorem).

Highlights

We evaluated results of several pion photoproduction analyses and compared πN PWA results as a constraint for analyses of pion photoproduction data (Watson’s theorem)
An accurate evaluation of the electromagnetic (EM) couplings N ∗(∆∗) → γN from meson photoproduction data remains a paramount task in hadron physics
Extraction of the two-body cross sections requires the use of a model-dependent nuclear correction, which mainly comes from final-state interactions (FSI).[3]

Summary

Introduction

An accurate evaluation of the electromagnetic (EM) couplings N ∗(∆∗) → γN from meson photoproduction data remains a paramount task in hadron physics. Of new data for meson photoproduction is becoming available from nuclear facilities worldwide. These measurements are beginning to have a significant impact on both the resonance spectrum and its decay properties. We focus on the single-pion production data and note that a complete solution requires couplings from both charged and neutral resonances,[1,2] the latter requiring π−p and π0n photoproduction off a neutron target, typically a neutron bound in a deuteron target. Our knowledge of the neutral resonance couplings is less precise than that of the charged values for well-known low-laying baryons

Neutron-target Data for Pion Photoproduction

Findings

Watson’s Theorem