Compton scattering, meson exchange, and the polarizabilities of bound nucleons

Meson-induced correlations of nucleons in nuclear Compton scattering

“…Among the current experimental data for various nuclei contradictions at large angles occur [9,29,3]. As any modification of the energy-dependent part of the mesonic seagull amplitude essentially modifies the angular dependence, a reliable calculation of M may help to clarify this situation.…”

“…At low energies the relative strengths of electromagnetic multipoles were analyzed [1,2,3,4] for comparison with predictions from multipole sum rules. The interesting question, whether the electromagnetic polarizabilities of the nucleon inside the nucleus essentially differ from those of the free nucleon, has been theoretically addressed [5,6,7,8] and experimentally studied with reasonable accuracy [3,9,10].…”

Compton scattering fromC12using tagged photons in the energy range 65–115 MeV

“…This model is based on the work presented in [9]. The Compton-scattering amplitude can be written [15] in terms of the one-and two-body seagull (SG) amplitudes (which are explicitly dependent on the polarizabilities α eff and β eff ) as…”

“…[8] 12 C [9], [10], [11], [12], [13] 16 O [7], [8], [11], [12], [14], [15] 40 Ca [7], [9] It is also reasonable to ask whether the nucleon polarizabilities are modified when the proton or neutron is bound in a nucleus and, if so, to what degree. A multitude of Compton-scattering experiments have been carried out with a variety of light nuclei (see Table I) for the purpose of determining the bound-nucleon polarizabilities (α eff and β eff ) given by α eff = α N + ∆α, β eff = β N + ∆β, (6) where α N and β N are the nucleon-averaged free polarizabilities and ∆α and ∆β represent the nuclear modifications [13] which can be extracted from the scattering data.…”

Electromagnetic polarizabilities of nucleons bound in 40Ca, 16O and 4He

“…In this connection it is of great interest that recently there was the claim [8] that in-medium shifts as large as ∆α = −8 and ∆β = +8 compared to the free-nucleon electromagnetic polarizabilities have been observed in Compton scattering experiments on 16 O. In-medium shifts of this large size would imply that the dominance of the electric multipolarity observed for the free-nucleon electromagnetic polarizabilities is replaced by a dominance of the magnetic multipolarity for the case of bound nucleons. This shift of multipolarity − if confirmed − has the potentiality of being an important discovery, unless it can be traced back to meson exchange currents as tentatively assumed in [8].…”