G. van der Steenhoven

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.

Charge-exchange processes in the quasi-elastic (e, e′p) and (e, e′n) reactions

Abstract Calculations of charge-exchange processes in the final state of the quasi-elastic (e, e′N) reaction have been performed employing the Lane formalism. The Lane equations were decoupled by means of a transformation to the isospin representation. It is found that charge exchange has a small effect on the (e, e′p) cross section, but may play an appreciable role in the (e, e′n) reaction.

Search for nucleon-nucleon correlations in the proton spectral function of 208Pb

Abstract Cross sections for the reaction 208Pb(e,e′p) have been measured with the continuous electron beam from the Amsterdam Pulse-Stretcher facility at NIKHEF-K. The spectral function has been extracted for protons with initial momenta of 300 to 500 MeV/c and binding energies up to 26 MeV. The data are compared to calculations with and without inclusion of nucleon-nucleon correlations. Mean-field predictions significantly underestimate the data and the discrepancy increases with binding energy. For transitions to the valence states the discrepancy is removed by introducing long-range correlations. Above the two-nucleon emission threshold long-range and short-range correlations reduce the discrepancy, but are insufficient to fully account for the measured strength.

LARGE-SOLID-ANGLE STUDY OF PION ABSORPTION ON 3HE

Measurements have been made of [pi][sup +] absorption on [sup 3]He at [ital T][sub [pi]][sup +]=118, 162, and 239 MeV using the Large Acceptance Detector System. The nearly 4[pi] solid angle coverage of this detector minimizes uncertainties associated with extrapolations over unmeasured regions of phase space. The total absorption cross section is reported. In addition, the total cross section is divided into components in which only two or all three nucleons play a significant role in the process. These are the first direct measurements of the total and three nucleon absorption cross sections.

Electroproduction of neutral pions on the proton

Abstract The double-differential coincidence cross section for the reaction 1 H(e,e′π 0 )p has been measured at Q 2 = 0.1 (GeV/ c ) 2 for a range in the invariant energy W of 1 to 14 MeV above threshold in order to determine the s-wave multipoles E 0+ and L 0+ . The experiment was performed with a 525 MeV electron beam of the Amsterdam Pulse Stretcher and a cryogenic hydrogen target. The scattered electron and the recoiling proton were detected in two high-resolution magnetic spectrometers. By using a recent LET prediction for the relevant combinations of p-wave multipoles, values for E 0+ and L 0+ were extracted from the cos ϑ π ∗ and cos φ π ∗ dependent terms in the cross section. The data are compared to calculations from Chiral Perturbation Theory and from several Lagrangian models. All models give a fair to good description of L 0+ . ChPT gives also a good description of E 0+ , but the Lagrangian models tend to underestimate its value. The data for the angle-independent part of the cross section indicate that the value for the 2 M 1+ + M 1− combination of p-wave multipoles is overestimated by a recent ChPT prediction.

A LARGE ACCEPTANCE DETECTOR SYSTEM (LADS) FOR STUDIES OF PION ABSORPTION

Abstract A Large Acceptance Detector System (LADS) has been designed and built at the Paul Scherrer Institute to study multiparticle final states following pion-nucleus absorption. It consists of a 28-sector cylinder of plastic scintillators of 1.6 m active length and 1.4 m diameter, two cylindrical wire chambers, and two 14-sector plastic scintillator end-caps which close each end. The nearly 4π solid angle coverage of this detector minimizes uncertainties associated with extrapolations over unmeasured regions of phase space. The design and the performance of the LADS detector are presented.

Fragmentation of the 1f-hole strength in 90Zr studied with the (e,e′p) reaction

Abstract The proton-hole spectral function of 90 Zr has been measured up to 20 MeV excitation energy by means of the (e,e′p) coincidence reaction. The deduced spectroscopic factors and fragmentation of the 1f-hole states are compared with results from hadronic reactions and with mean-field theory.

Contribution of 2h̷ω transitions to the excitation of 0+ states in 58Ni and 26Mg in inelastic electron scattering

Abstract The excitation of 0+ states in 58Ni and 26Mg has been investigated by inelastic electron scattering. Shell model calculations in a 1&ℏ;ω model space are not able to reproduce the data, which clearly show contributions from 2&ℏ;ω, i.e. giant monopole resonance-like, excitations.

Relativistic effects in the electrodisintegration of deuterium

Abstract The structure function R LT and the cross-section asymmetry A φ with respect to the direction of the momentum transfer in the reaction 2 H( e , e ′ p ) have been measured at a four-momentum transfer squared of 0.2 (GeV/c) 2 , for missing momenta between 160 and 220 MeV/c at an invariant mass of 1050 MeV. For a proper description of these data calculations that include a relativistic form of the nucleon current operator are favoured. The absolute 2 H( e , e ′ p ) cross-section data favour a covariant calculation over non-relativistic calculations with relativistic corrections.

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.