Neutral pion photoproduction at high energies

Abstract

A Regge model with absorptive corrections is employed in a global analysis of the world data on the reactions γp→π 0 p and γn→π 0 n for photon energies from 3 to 18 GeV. In this region resonance contributions are expected to be negligible so that the available experimental information on differential cross sections and single-and double polarization observables at −t≤2 GeV 2 allows us to determine the non-resonant part of the reaction amplitude reliably. The model amplitude is then used to predict observables for photon energies below 3 GeV. A detailed comparison with recent data from the CLAS and CB-ELSA Collaborations in that energy region is presented. Furthermore, the prospects for determining the π 0 radiative decay width via the Primakoff effect from the reaction γp→π 0 p are explored. PACS. 11.55.Jy Regge formalism -13.60.Le Meson production -13.60.-r Photon and charged-lepton interactions with hadrons -25.20.Lj Photoproduction reactions

Nuclear incoherent photoproduction ofπ0andηfrom 4 to 12 GeV

“…would certainly provide plausible interpretations of the proton data both for π 0 and η photoproduction. A detailed analysis of the elementary amplitude for π 0 photoproduction from 3 to 18 GeV was recently published by Sibirtsev et al [39]. This work used a Regge model with pole and cut amplitudes for ω, ρ, and b 1 exchanges and reproduced quite satisfactorely a larger data set of the differential cross sections and single and double polarization observables for π 0 photoproduction.…”

“…Nevertheless, as presented in Table 3 of Ref. [39], the model uses 17 free parameters in order to achieve a global fitting to the data. Furthermore, the F 1 amplitude was obtained without the Coulomb term and omitting the interference region |t| < 0.04 GeV 2 of the differential cross section; a crucial region included in our analysis.…”

“…Such restriction of the analysis from Ref. [39] is strong evidence of the poor experimental scenario of the differential cross sections of π 0 photoproduction at extreme forward angles, making it difficult to establish one unambiguous Regge model for the interpretation of the data. This scenario is even more critical for η photoproduction, where data at extreme forward angles is provided only up to 6 GeV (Fig.…”

“…It is worth mentioning, however, that the predictions from Ref. [39] for the neutron cross section are extremely useful for possible improvements in the analysis, since one can disentangle the isoscalar and isovector contributions of the amplitudes.…”

Incoherent photoproduction of pseudoscalar mesons off nuclei at forward angles

“…In the coherent photoproduction off spinless nuclei only the spin nonflip ampli tude survives. As for the incoherent photoproduction, this amplitude is the dominant one [11], though all four amplitudes are involved in the process. 3 For instance, the incoherent cross section would be strongly suppressed as a result of the Pauli exclusion principle, which is not the case in [14] (see, for instance, expression (33b)).…”