Two-step processes and short-range correlations in the reactionC12(γ,p)

Abstract

One-nucleon knockout calculations have been performed for the reaction ' C(y, p )" B at incident photon energies of 60, 80, and 100 MeV. Both two-step processes and high-momentum components in the single-nucleon wave function due to short-range correlations have been included. It is shown that direct knockout leading to the "B ground state followed by inelastic excitation of the -, ' state at 6.743 MeV in "B exceeds the direct excitation of this state by 1 to 2 orders of magnitude. For the ground-state transition the influence of high-momentum components becomes increasingly important going from Ey =60 to 100 MeV. Constraining the parameters entering the calculation by recently measured quasielastic "C(e,e'p) "B data a discrepancy is found between the calculations and the data, particularly at low photon energies, which is attributed to exchange currents and randomphase approximation correlations.

Comparison of the quasielastic (e,e’p) and the (γ,p) reactions

“…The data for this peak are enhanced by a factor of 2 compared to other transitions. The observation that this peak has apparently enhanced strength when missing energy spectra from the two reactions are compared has been the subject of previous publications [36,51,50,52]. The DKO calculation represents the incoherent sum of contributions of knockout f'rom the I f7g2, 2aiy2, and 1dsg2 shells.…”

“…[50], the application of both the OA and nonlocality corrections would amount to double counting. Furthermore, the correction due to the coupling of the photon to the current of the A -1 system is not applied (10) The complex at 7 MeV in C(p, p) is a special case, and is treated as an incoherent sum of the three (s,~,~) states We have u. sed the t;, values from Ref.…”

“…[50]), because it represents a contribution in addition to DKO. As the aim of this study is to make a consistent comparison of (e, e'p) and (p, p) reactions within a quasielastic DKO framework, it must be omitted.…”

“…[50], where it was shown that two-step processes in the excitation of the 2 state contribute significantly to the magnitude of the cross section. The value of these two-step calculations was recently dexnonstrated in a dedicated~C (e, e'p) experiment at low p [57].…”

Two-body currents in the reaction 12C(e, e′p)11B at high missing momenta

“…This calculation is similar to that of Refs. [23,32] using the same spectroscopic factors and /32 values. After adding the contributions of the l/2+ and 5/2+ states, the corresponding dashed-plus curve is about a factor of ten larger than the DWIA curves.…”