C.J.G. Onderwater

Evidence for short-range correlations in O-16

Abstract The reaction 16 O( e , e ′ pp ) 14 C has been investigated at three values of the transferred energy ω . The differential cross sections were determined as a function of the missing energy and the missing momentum. Evidence for short-range correlations in 16 O has been obtained from the transition to the ground state of 14 C. The cross sections for this transition are well reproduced by two independent parameter-free microscopic calculations. The results of both calculations show that the reaction is dominated by knockout of a proton pair in a 1 S 0 state, driven by short-range-correlations.

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.

Λb polarization in Z0 decays at LEP

The longitudinal polarization of the Λb baryon is measured at the LEP e+e− collider by DELPHI. It is determined from the charged lepton and neutrino energy spectra in 249±19 Λb semileptonic decays reconstructed in ≈3.5 million hadronic Z0 decays using Λ0-lepton correlations. The measured polarization is: PΛb=−0.49−0.30+0.32(stat.)±0.17(syst.)

The 4He(e, e′p) cross section at large missing energy

Abstract The ( e , e ′ p ) reaction on 4 He nuclei was studied in kinematics designed to emphasize effects of nuclear short-range correlations. The measured cross sections display a peak in the kinematical regions where two-nucleon processes are expected to dominate. Theoretical models incorporating short-range correlation effects agree reaconably with the data.

Alpha-cluster knockout in the 16O(e,e' alpha)12C reaction.

Abstract The knockout of α-clusters induced by electrons has been used to study four-nucleon correlations in 16O. For the transition to the ground state of 12C the (e,e′α) cross section has been measured for three values of the momentum transfer and four values of the missing momentum. The momentum-transfer dependence gives evidence for a quasi-elastic α-knockout mechanism. The shape of the measured missing-momentum distribution is reasonably well described by shell-model and cluster-model calculations, but the theoretical curves overshoot the data by a factor three to four.

Alpha-cluster knockout in the O-16(e,e 'alpha)C-12 reaction

Abstract The knockout of α-clusters induced by electrons has been used to study four-nucleon correlations in 16O. For the transition to the ground state of 12C the (e,e′α) cross section has been measured for three values of the momentum transfer and four values of the missing momentum. The momentum-transfer dependence gives evidence for a quasi-elastic α-knockout mechanism. The shape of the measured missing-momentum distribution is reasonably well described by shell-model and cluster-model calculations, but the theoretical curves overshoot the data by a factor three to four.

High Missing-Momentum Components in 4He studied with the e,e'p reaction

The nucleon-nucleon (N N) interaction in the nuclear medium is of fundamental importance for the description of nuclear properties. In particular its short-range part is still poorly known. High-momentum components of the nuclear wave function are sensitive to short range correlations (SRC). Measurement of high momenta will therefore yield information on the N N-interaction at short internucleon distances [1]. Because of the availability of realistic calculations of the wave function of few-body systems, a light nucleus is preferred for such a study. Since the effects of short range correlations are expected to be enhanced in dense nuclei we choose for 4He.

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.