On the extraction of cross sections for π0 and η photoproduction off neutrons from deuteron data

Abstract

We discuss the procedure of extracting the photoproduction cross section for neutral pseudoscalar mesons off neutrons from deuteron data. The main statement is that the final-state interaction (FSI) corrections for the proton and neutron target are in general not equal, but for π 0 production there are special cases were they have to be identical and there are large regions in the parameter space of incident photon energy and pion polar angle, θ * , where they happen to be quite similar. The corrections for both target nucleons are practically identical for π 0 production in the energy range of the ∆(1232)3/2 + resonance due to the specific isospin structure of this excitation. Also above the ∆-isobar range large differences between proton and neutron correction factors are only predicted for extreme forward angles (θ * < 20 • ), but the results are similar for larger angles. The case of η photoproduction is also shortly considered. Numerical results for the γp → π 0 p and γn → π 0 n correction factors are discussed. Also the model description for the available data on the differential γd → π 0 pn cross sections are given.

Extraction of γn→πN observables from deuteron-target data

“…Equations (2)-(4) agree with the formula presented in Ref. [12,13,[26][27][28]. I also note that the relation between the γd and γn cross sections in Eqs.…”

“…(5) below] neglects a possible effect from the nucleon Fermi motion, which needs a validation. The authors also analyzed d(γ, π 0 )pn [13] without including the π-exchange mechanism which was assumed to be negligible. Their predicted FSI corrections for γN → π 0 N cross sections turned out to be even qualitatively different from what has been found in the MAMI analysis [7,11], which clearly calls for a further study.…”

“…recent JLab analyses [1,3,4]. The previous theoretical works [12,13] presented a formula similar to Eq. (2), but did not use it either.…”

“…On the other hand, in Ref. [13] where FSI corrections for extracting γn → π 0 n cross sections were theoretically estimated, the authors did not consider the π-exchange mechanism, assuming its effect negligible. As a result, the estimated FSI effects are only from the N -exchange mechanism and are visible only in the forward pion kinematics (cos θ > ∼ 0.85 for E γ = 787 MeV, for example).…”

Radiative Decay Width of Neutral non-Strange Baryons from PWA

“…The γn → π 0 n case is much more complicate vs. γn → π − p because π 0 n final state can come from both γn and γp initial interactions [20]. The leading diagrams for γd → π 0 pn are similar as given on Fig, 2.…”