M. van Sambeek

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.

The optical properties of the BigBite spectrometer at NIKHEF.

The optical properties of the BigBite spectrometer currently in use at the Internal Target Facility of the AmPS ring at NIKHEF have been determined. The spectrometer, which consists of a single dipole magnet, combines a large solid angle with a large momentum acceptance. The track of a particle is determined from the information of two sets of drift chambers behind the magnet. Tracing this track through the magnetic field to the target yields the position of the scattering vertex and the size and direction of the momentum vector of the scattered particle at the target position. These quantities are calculated using an analytical approximation of the spectrometer, followed by a refinement with the matrix method. The p-resolutions of the reconstruction for 600 MeV electrons are 3 mrad for the angles, 3.2 mm for the vertex position, and 8.4]10~3 for dp/p. ( 1998 Elsevier Science B.V. All rights reserved.

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 Recoil Detector for electron scattering experiments with internal targets

Abstract A Recoil Detector has been constructed for electron-scattering experiments with gas targets internal to the Amsterdam Pulse Stretcher and storage ring (AmPS) at NIKHEF. The detector was designed to detect low-energy (1–10 MeV/nucleon) and low-mass (A ≤ 4) recoiling nuclei emerging from electron-induced reactions. It consists of four sensitive elements: a low-pressure two-step avalanche chamber, two layers of silicon strip detectors of 100 and 475 μm thickness, and a scintillator. The signals from the separate detector elements are processed by custom-made analog and digital electronics. The detector was operated successfully at the AmPS electron scattering facility with a gaseous helium target of 1015 atoms cm−2 internal to the storage ring and beam currents of up to 200 mA.

A recoil detector for the internal target facility of AmPS (NIKHEF)

A recoil detector has been built for internal target experiments with the Amsterdam Pulse Stretcher and storage ring, AmPS, of NIKHEF. The detector was designed to detect low-energy (1-20 MeV/nucleon) and low-mass (A ≤ 4) recoiling nuclei emerging from electron-induced reactions. The detector consists of a low-pressure, two-step avalanche chamber, two layers of silicon strip detectors of 100 and 475 μm thickness and a scintillator. The signals from the separate detector elements are processed by custom-made analog electronics and dedicated VME-based digitizer modules. The detector was operated successfully at the AmPS electron scattering facility with a gaseous He target of 10

Coherent pi0 electroproduction on 4He in the Delta region.

Abstract Coherent π 0 electroproduction on 4 He was studied using the internal target facility of the AmPS electron storage ring at NIKHEF. This 4 He( e , e 14 He π 0 experiment is the first on exclusive π 0 electroproduction on a complex nucleus. The experiment was performed at a luminosity of about 10 33 cm −2 s −1 with a stored beam of about 150 mA 676 MeV electrons and a 4 He gas target of 10 15 atoms/cm 2 . The observation of neutral pions was avoided by detecting in coincidence with scattered electrons the recoiling 4 He nuclei with a dedicated detector. A clear signature for π 0 knockout was achieved and the differential cross sections were measured as a function of the π 0 CM-angle over the full Δ-resonance region at two values of Q 2 of 0.07 and 0.15 (GeV/ c ) 2 .

Study of Proton-Neutron Correlations with the reaction 3,4He(e, e′d)

A 3,4He(e, e′d) experiment has been performed at NIKHEF. The data have been taken in both (q, ω)-constant kinematics and in parallel-kinematics for transferred momenta q of 410, 500 and 600 MeV/c using 576 MeV and 370 MeV electron beams. Preliminary results for 3He at 576 MeV are reported here. The (q, ω) constant results allow to extract the contribution of the structure function W LT from the cross section. The parallel kinematics results show an interesting q-dependence that cannot be described by a cluster-knockout model.