Abstract
An overview of the GW SAID and ITEP groups effort to analyze pion photoproduction on the neutron-target will be given. The disentanglement the isoscalar and isovector EM couplings of N∗ and Δ∗ resonances does require compatible data on both proton and neutron targets. The final-state interaction plays a critical role in the state-of-the-art analysis in extraction of the γ n → π N data from the deuteron target experiments. It is important component of the current JLab, MAMI-C, SPring-8, ELSA, and ELPH programs.
Highlights
The N∗ family of nucleon resonances has many well established members [1], several of which exhibit overlapping resonances with very similar masses and widths but with different JP spin- parity values
The existing γn → π−p database contains mainly differential cross sections and 15% of which are from polarized measurements
We found a sizeable Finalstate interaction (FSI)-effect from S-wave part of pp-FSI at small angles
Summary
The N∗ family of nucleon resonances has many well established members [1], several of which exhibit overlapping resonances with very similar masses and widths but with different JP spin- parity values. Apart from the N(1535)1/2− state, the known proton and neutron photodecay amplitudes have been determined from analyses of single-pion photoproduction. The present work reviews the region from the threshold to the upper limit of the SAID analyses, which is CM energy W = 2.5 GeV. Up to W ∼ 1800 MeV, this region encompasses a sequence of six overlapping states: N(1650)1/2−, N(1675)5/2−, N(1680)5/2+, N(1700)3/2−, N(1710)1/2+, and N(1720)3/2+. Incoherent pion photoproduction on the deuteron is interesting in various aspects of nuclear physics, and provides information on the elementary reaction on the neutron, i.e., γn → πN. The FSI was first considered in Refs. [6,7] as responsible for the near-threshold enhancement (Migdal-Watson effect) in the NN mass spectrum of the meson production reaction NN → NNx. In Ref. In Ref. [8], the FSI amplitude was studied in detail
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