D. G. Ireland

Comparison of the quasielastic ([ital e],[ital e][prime][ital p]) and the ([gamma],[ital p]) reactions

Recent data obtained with the quasielastic ([ital e],[ital e][prime][ital p]) reaction, and the ([gamma],[ital p]) reaction at photon energies of about 60 MeV, on [sup 12]C, [sup 16]O, [sup 27]Al, [sup 40]Ca, and [sup 51]V are examined. Comparisons are made using disorted-wave impulse-approximation calculations. The ([ital e],[ital e][prime][ital p]) data are used to determined the values of spectroscopic factors and root-mean-square radii of the overlap wave function for each transition considered. These parameters constrain the direct-knockout (DKO) calculations for the ([gamma],[ital p]) reactions which have been performed within the same framework. While the calculations give a very good description of the ([ital e],[ital e][prime][ital p]) data, a discrepancy of typically a factor of six is observed between the DKO calculations and the ([gamma],[ital p]) data. The discrepancy is largely removed when meson exchange current contributions in the ([gamma],[ital p]) reaction are estimated on the basis of the Siegert theorem.

Investigation of the ExclusiveH3e(e,e′pp)nReaction

Cross sections for the 3 He(e,e8 pp )n reaction were measured over a wide range of energy and threemomentum transfer. At a momentum transfer q5375 MeV/c, data were taken at transferred energies v ranging from 170 to 290 MeV. At v5220 MeV, measurements were performed at three q values ~305, 375, and 445 MeV/c). The results are presented as a function of the neutron momentum in the final state, as a function of the energy and momentum transfer, and as a function of the relative momentum of the two-proton system. The data at neutron momenta below 100 MeV/c, obtained for two values of the momentum transfer at v5220 MeV, are well described by the results of continuum-Faddeev calculations. These calculations indicate that the cross section in this domain is dominated by direct two-proton emission induced by a one-body hadronic current. Cross section distributions determined as a function of the relative momentum of the two protons are fairly well reproduced by continuum-Faddeev calculations based on various realistic nucleonnucleon potential models. At higher neutron momentum and at higher energy transfer, deviations between data and calculations are observed that may be due to contributions of isobar currents.

Photon-induced proton knockout from 208Pb

Abstract Cross sections have been measured for the reaction 208Pb(γ,p) leading to the low-lying ( 1 2 + , 3 2 + ) and ( 11 2 − , 5 2 + ) doublets and 7 2 + state in 207Tl using a high energy-resolution tagged photon beam of 41 to 57 MeV. The data are compared with results obtained with the reaction 208Pb(e,e′p) in the same recoil-momentum range. The recoil-momentum distributions derived from the (γ,p) data do not coincide with those obtained from the (e,e′p) data. Distorted-wave impulse-approximation (DWIA) calculations of which the input is constrained by the (e,e′p) data underestimate the (γ,p) data by typically one order of magnitude. An estimate of meson-exchange currents (MEC) effects using the Siegert theorem brings the DWIA-calculations close to the data. Random-phase approximation calculations also give a fair account of the data, but in this case MEC-effects are predicted to be less important.

Photon-induced proton knockout from 208Pb and 12C

Abstract Cross sections have been measured for the reactions 208Pb(γ,p) and 12C(γ,p) leading to the low-lying and continuum states in 207Tl and 11B using a high energy-resolution tagged photon beam of 41 to 57 MeV. The data are compared with results obtained with the (e,e′p) reaction in the same recoil-momentum range and with various theoretical calculations. A comparison of the (e,e′p) and (γ,p) data in terms of a reduced cross section versus momentum does not show a systematic overlap of the (e,e′p) and (γ,p) results, i.e. no scaling is observed. Distorted-wave impulse-approximation (DWIA) calculations, of which the input is constrained by the (e,e′p) data, and random-phase approximation calculations (RPA) underestimate the 12C(γ,p) data by typically a factor five depending on angle and missing energy. For 208Pb the difference between the calculations and the data for the low-lying states is much less, but an increasing discrepancy between the data and the calculations is found in the continuum. The inclusion of meson-exchange currents (MEC) brings the calculations for both nuclei on average closer to the data, but MEC effects are considerably less important for 208Pb as compared to 12C. Finally, a remarkable similarity is observed between the continuum response of the (γ,p) and (e,e′p) reactions on 208Pb despite the difference in the electromagnetic couplings involved.

N* resonances from K\(\Lambda\) amplitudes in sliced bins in energy

Abstract.The two reactions

Tensor analyzing powers for Li induced transfer breakup reactions

\gamma p\rightarrow K^{+}\Lambda

The 4He(γ,n) reaction: a potential testing ground for the alpha-particle wavefunction

γp→K+Λ and

Electron-induced two-proton knockout from 3He

\pi^{-} p\rightarrow K^{0}\Lambda

A Regge-plus-resonance approach to kaon production on the nucleon

π-p→K0Λ are analyzed to determine the leading photoproduction multipoles and the pion-induced partial wave amplitudes in slices of the invariant mass. The multipoles and the partial-wave amplitudes are simultaneously fitted in a multichannel Laurent+Pietarinen model (L+P model), which determines the poles in the complex energy plane on the second Riemann sheet close to the physical axes. The results from the L+P fit are compared with the results of an energy-dependent fit based on the Bonn-Gatchina (BnGa) approach. The study confirms the existence of several poles due to nucleon resonances in the region at about 1.9 GeV with quantum numbers

Measurement of theHe4(γ,n)reaction from23<Eγ<70MeV

J^{P} = 1/2^{+}, 3/2^{+}, 1/2^{-}, 3/2^{-}, 5/2^{-}