T. Botto

Measurement of T20 in Elastic Electron-Deuteron Scattering

The authors report on a measurement of the tensor analyzing power T{sub 20} in elastic electron-deuteron scattering in the range of four-momentum transfer from 1.8 to 3.2 fm{sup {minus}1}. Electrons of 704 MeV were scattered from a polarized deuterium internal target. The tensor polarization of the deuterium nuclei was determined with an ion-extraction system, allowing an absolute measurement of T{sub 20}. The data are described well by a non-relativistic calculation that includes the effects of meson-exchange currents.

Performance of a Polarized Deuterium Internal Target in a Medium-Energy Electron Storage Ring.

Abstract A polarized deuterium target internal to a medium-energy electron storage ring is described in the context of spin-dependent (e,e′d) and (e,e′p) experiments. Tensor polarized deuterium was produced in an atomic beam source and injected into a storage cell target. A Breit-Rabi polarimeter was used to monitor the injected atomic beam polarization. An electrostatic ion-extraction system and a Wien filter were utilized to measure on-line the atomic fraction of the target gas (71 ± 2%) in the storage cell. A target thickness t ⋍ 2 × 10 13 2 H/cm 2 was achieved. The target tensor polarization was varied from P zz + = 0.49(3) to P zz − = −0.89(6) while keeping the vector polarization P z at zero. The luminosity was ∼ 2 × 10 31 e − · 2 H · cm −2 s −1 at a beam current of 120 mA. The performance was stable over a fiv running period. A large acceptance non-magnetic detector system was used for the electron-proton (deuteron) coincidence measurement. It is demonstrated that these techniques result in low backgrounds due to scattering from species other than the polarized target gas and allow for fast and flexible orientation of the target spin. Specific issues such as interfacing the experiment to the storage ring and monitoring the performance of the target system are discussed in detail.

Tensor Analyzing Powers for Quasielastic Electron Scattering from Deuterium

We report on a first measurement of tensor analyzing powers in quasi-elastic electron-deuteron scattering at an average three-momentum transfer of 1.7 fm{sup -1}. Data sensitive to the spin-dependent nucleon density in the deuteron were obtained for missing momenta up to 150 MeV/c with a tensor polarized {sup 2}H target internal to an electron storage ring. The data are well described by a calculation that includes the effects of final-state interaction, meson-exchange and isobar currents, and leading-order relativistic contributions.

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.

Supersonic gas jets as internal targets at NIKHEF

Abstract We investigated a gas jet issued from a rectangular slit nozzle. Such jets can be made to dynamically converge by interacting with the residual, lower density, gas inside the accelerator vacuum vessel. Densities of up to few times 10 15 atoms cm −2 were achieved. We describe the experimental facility, the diagnostics used and present the result of our data analysis.

Spin-dependent electromagnetic response of few-body systems.

We report on the experimental program with polarized electrons and polarized few-body systems at the internal target facility of the NIKHEF electron storage ring. With a polarized deuterium internal target, absolute measurements of unprecedented accuracy have been performed for the analyzing powers T20 and T22 in elastic electron-deuteron scattering at transferred four-momenta 1.1 < Q < 2.8 fm−1. Results for a first measurement of the tensor analyzing power in quasi-elastic scattering are also presented. These data provide new constraints for descriptions of the deuteron spin structure and for reaction mechanism effects. Quasi-elastic electron scattering from polarized 3He may provide precise information on the S′ and the D-wave parts of the 3He ground-state wave function, the neutron form factors, and the role of spin-dependent reaction mechanism effects. We have started an experimental program at NIKHEF where polarized 3He and polarized electrons are used, in combination with large acceptance electron and hadron detectors. Data were taken for the transverse (Ay0) and longitudinal (A′z) asymmetries at Q ⋍ 2 fm−1. We outline the performance of the target and detectors.

Electron scattering at NIKHEF with polarized beam and targets

We present the Internal Target Facility of the NIKHEF 900 MeV polarized electron storage ring. We give some results which illustrate the presently unique opportunity offered by this facility to study the spin structure of the nucleon, 2-body and 3-body system by the measurement of spin-dependent electron scattering observables.

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.

SPIN EFFECTS IN MEDIUM-ENERGY ELECTRON-3HE SCATTERING

Abstract New physics can be accessed by scattering polarized electrons from a polarized 3He internal gas target. It is discussed how the asymmetries for the reactions 3 He ( e , e′), 3 He ( e , e′p) 3 He ( e , e′n) 3 He ( e , e′d) and 3 He ( e , e′pn) may provide precise information of the S′ and the D-wave parts of the 3He ground-state wave function, the neutron form factors, and the role of spin-dependent reaction mechanism effects. The experiment uses up to 900 MeV (polarized) electrons from the AmPS storage ring in Amsterdam, Netherlands, in combination with large acceptance electron and hadron detectors.

A large-acceptance detector system for electron scattering from polarized internal targets

Abstract The design and the performance of a non-magnetic detector setup for internal target physics at the NIKHEF electron-scattering facility is described. The detector setup, used in the first internal-target experiment at the AmPS ring, measures the spin dependence in the elastic and break-up reaction channels from tensor polarized deuterium. It has been established that the detector setup can operate adequately in an internal target environment at luminosities up to 10 32 e − atoms cm −2 s −1 . Results and measured resolutions are presented.