L. Bimbot

POLDER: a tensor polarimeter for intermediate energy deuterons

A new deuteron tensor polarimeter (POLDER), based upon the charge exchange reaction 1H(→d, 2p)n, has been constructed and calibrated in the energy range 175–500 MeV for all polarisation signals. The large figures of merit obtained make POLDER a unique instrument in this energy domain. The operation of this polarimeter has been checked in practice in a test experiment on 40Ca(→d, →d′)40Ca elastic scattering performed at Ed = 380 MeV.

The nuclear spin response to intermediate energy protons

Abstract Measurements of the spin-flip probability S nn for inclusive inelastic proton scattering around 300 MeV from nuclei between 12 C and 90 Zr show that an enhanced spin response near 40 MeV excitation at q ∼ 100 MeV/ c is a general feature of nuclear structure. Data for 40 Ca at 800 MeV confirm that the enhancement is not a peculiarity of 300 MeV scattering. In addition, measurements in 44 Ca up to 75 MeV show that the enhancement cannot be attributed solely to a relatively narrow resonance. Continuum RPA calculations suggest that the enhancement is due to the exhaustion of most S = 0 strength at lower energy and a shift of S = 1 strength to higher energy.

Measurement of vector-tensor spin-transfer observables for the reaction between 580 and 1300 MeV

Abstract The three polarization tensor components of the deuteron produced in the H( p , d )π + reaction have been measured for the first time. The experiment was performed using a vertically polarized proton beam produced by the SATURNE accelerator. The deuteron polarization was measured with the POLDER polarimeter. The three polarizing powers t2000, t2100 and t2200 and the three spin-transfer observables t2011, t2211 and t2211 have been extracted at a proton kinetic energy of 580 MeV over a wide angular range and at two fixed center-of-mass angles, 132° and 151°, between 800 and 1300 MeV. The six observables, calculated in the C.M. helicity frame, have been compared with predictions of the most refined partial-wave analyses and also with the predictions of a theoretical coupled-channel model which includes the NN-NΔ transition. The comparison between the data and the theory/partial-wave analyses shows some discrepancies which get worse with increasing proton energy. Adding these data to the world database should improve significantly future partial-wave analyses. The Ay0 analyzing power has also been measured over the same kinematical range. The partial-wave analysis predictions are in good agreement with this observable.

Coherent pion production in 12C(p, nπ) at 800 MeV

Abstract Studies of the production of the Δ resonance in hadronic charge exchange reactions show a shift in the Δ peak position. Measurements looking also at the Δ decay products give some evidence for coherent pion production. We have recently completed a new measurement of the 12 C ( p , n ) reaction leading to the Δ resonance, including a higher resolution coincidence measurement of decay πs in the forward direction. We describe the experiment and some aspects of the preliminary analysis.

Status of the focal plane polarimeter for Hall A at TJNAF

The focal plane polarimeter (FPP) for Hall A at the Thomas Jefferson National Accelerator Facility (TJNAF) is ready for experiments. The ability to calibrate the FPP on-site using elastic scattering of polarized electrons from an unpolarized hydrogen target is demonstrated. The ratio of the proton electric form factor to its magnetic form factor has been measured at Q2=0.810(GeV/c)2.

Physics with a focal plane proton polarimeter for hall A at CEBAF

A focal plane polarimeter intended for the CEBAF Hall A high resolution hadron spectrometer is under construction at Rutgers University and the College of William & Mary. Experiments with focal plane polarimeters are only now beginning at electron accelerators; they play a prominent role in the list of approved experiments for Hall A. Construction of the polarimeter is in progress, it is expected to be brought to CEBAF in spring 1995. Several coincidence (e,e′p) and singles (γ,p) measurements by the Hall A Collaboration are expected to start in 1996. In this paper we describe the polarimeter and the physics program planned for it.

Measurement of tensor polarization observables in the H(p,d)π+ reaction between 580 and 1300 MeV

Abstract During the last decade, our understanding of the πNN system has been improved with the measurement of double polarization observables [1]. In this experiment the recoil deuteron polarization produced in the H ( p , d )π + reaction was measured with the POLDER polarimeter for incident protons of kinetic energies between 580 and 1300 MeV.