Photoabsorption on nuclei

Abstract

We calculate the total photoabsorption cross section on nuclei in the energy range from 300 MeV to 1 GeV within the framework of a semi-classical phase space model. Besides medium modifications like Fermi motion and Pauli blocking we focus on the collision broadening of the involved resonances. The resonance contributions to the elementary cross section are fixed by fits to partial wave amplitudes of pion photoproduction. The cross sections for $N \, R \to N \, N$, needed for the calculation of collision broadening, are obtained by detailed balance from a fit to $N \, N \to N \, N \, \pi$ cross sections. We show that a reasonable collision broadening is not able to explain the experimentally observed disappearance of the $D_{13}(1520)$-resonance in the photoabsorption cross section on nuclei.Comment: 26 pages Latex including 9 postscript figure

A relativistic two-nucleon model for reaction

“…We do not expect any major change in our results due to these effects. As is pointed out in [47,48,49], the medium correction effects on widths of the s-and p-wave resonances, which make the dominant contribution to the cross sections being investigated here, are not substantial. On the other hand, any medium modification in the width of the d-wave resonance is unlikely to alter our results as their contributions to the cross sections are negligible [46].…”

Proton polarizability contribution to hydrogen hyperfine splitting

“…To obtain correction (3) at the resonance region (W 2 ≤ 4GeV 2 ) we use the Breit-Wigner parameterization for the photoabsorption cross sections in (12), (13), suggested in [20,21,22,23,24,25,26]. There are many baryon resonances that give contribution to photon absorption cross sections.…”

“…We take into account only five important resonances: P 33 (1232), S 11 (1535), D 13 (1520), P 11 (1440), F 15 (1680). Considering the one-pion decay channel of the resonances, the absorption cross sections σ 1/2 and σ 3/2 may be written as follows [23,27]:…”

Proton polarizability contribution to the hyperfine splitting in muonic hydrogen

“…To obtain correction (8) at the resonance region (W 2 ≤ 4GeV 2 ) we use the Breit-Wigner parameterization for the photoabsorption cross sections in (18), (19), suggested in [30][31][32][33][34][35][36]. There are many baryon resonances that give contribution to photon absorption cross sections.…”

“…We take into account only five most important resonances: P 33 (1232), S 11 (1535), D 13 (1520), P 11 (1440), F 15 (1680). Considering the one-pion decay channel of the resonances, the absorption cross sections σ 1/2 and σ 3/2 may be written as follows [33,37]:…”