Neutral-Pion Photoproduction on the Deuteron

Abstract

Large-angle cross sections for yd-^ Tr^Jare systematically measured in the photon energy range between 500 and 1000 MeV. A good fit is obtained by use of a Glauber-model calculation which includes the dibaryon resonances ^F3(2.26) and ^G4(2.51), but the fit has an unusual nature in the role of resonance and nonresonance contributions.

Perturbative QCD and factorization of coherent pion photoproduction on the deuteron

“…The on-shell condition requires the center-of-mass angle of pion photoproduction on the nucleon N 1 to be commensurate with the center-of-mass angle of pion photoproduction on the deuteron. The reduced amplitude prediction is consistent with the constituent counting rule p [14] and the available γp → π 0 p data [16][17][18][19][20] shows good qualitative agreement between the perturbative QCD prediction and experiment over a large range of momentum transfers and center-of-mass angles. It would be useful to confirm or deny this agreement with further measurements on both proton and deuteron targets.…”

“…The underlying principle of the analysis is [14], and the crosses and open circles are our predictions from the γp → π 0 p data presented in Refs. [16][17][18]. Note that an open circle is overlaid on top of a filled circle for the overlapping data point at E lab = 4 GeV.…”

Evidence for a backward peak in the γd → π0d cross section near the η threshold

“…In this work, we present the first systematic evidence for a similar phenomenon (the first indication was found in Ref. [11]) in the coherent photoproduction of a neutral pion on the deuteron, γd → π 0 d. All of the above phenomena take place because η-meson production in hadron-hadron collisions near threshold is enhanced. This is because the cross section for excitation of the nearby baryonic resonance N (1535)S 11 is large and this resonance is strongly coupled to the ηN channel.…”

“…Thus, the experimentally observed enhancement in the excitation functions near E γ ∼ 0.7 GeV needs no exotic explanation such as was done, for instance, in Ref. [11].…”

“…The structure near 0.7 GeV and its magnitude persists. Both of the measurements [11,23] were done at the same accelerator facility and used an untagged bremsstrahlung beam, which might introduce large systematic uncertainties in the determination of the photon flux. (2)).…”