pn-Pair Coupling in the(γ,pn)Reaction at 72 MeV

Abstract

The 16 O͑g, pn͒ reaction was measured at E g ϳ 72 MeV with resolution sufficient to distinguish the low-lying states of the residual 14 N nucleus. Cross sections averaged over the acceptance of the detector system were determined for each of the resolved states. The relative population of residual states indicates that proton-neutron pairs coupled to ͑J p , T ͒ ͑0 1 , 1͒ play a minor role in the photon absorption process compared to ͑1 1 , 0͒ pairs and that both L 0 and L 2 pairs participate in the reaction.

First measurements of the 16O(e, e'pn)14N reaction

“…There have been several measurements of real-photon two-nucleon knockout reactions on 16 O [26,27,28]. The first measurement [26], carried out at the Mainz 180 MeV electron Microtron MAMI-A, measured both reaction channels and covered the photon energy range 80-131 MeV.…”

“…The study of ref [27] [27] which both have strong L = 2 components. The low recoil momentum range sampled in [28] therefore favoured excitation of the 3.95 MeV (1 + ) state.…”

Knockout of proton-neutron pairs from 16O with electromagnetic probes

“…For the particular case of super-parallel kinematics, which were used in the measurement of the 16 O(e,e ′ pn) 14 N reaction [9], they enhance the contribution to the cross section which arises from the one-body currents. This effect is dramatic at low missing momentum and fully accounts for the previously observed [9] 14 N reaction [9] was made at the electron scattering facility (3-spectrometer facility [30]) at MAMI, Mainz [31,32]. Data were taken with an incoming electron beam of energy 855 MeV at currents of 10-20 µA.…”

“…The 16 O nucleus is of particular interest regarding the study of correlated behaviour. Various theoretical models exist which attempt to describe these reactions [6,7,8] and there have been numerous measurements of twonucleon knockout reactions using both real and virtual photons [9,10,11,12,13,14,15]. In [9] the results from the first measurement of the 16 O(e,e ′ pn) 14 N reaction were reported and compared with theory.…”

First measurements of the 16O(e, e'pn)14N reaction

“…The real photon studies of the 16 O(γ,pn) reaction [27,28] 14 N marked in figure 6 [44]. The calculations were carried out in the same super-parallel kinematics as the measurement; again these calculations predict cross sections roughly an order of magnitude smaller than the data.…”