F.T. Baker

The nuclear spin response to intermediate energy protons and deuterons at low momentum transfer

Abstract Measurements of polarization transfer in the inelastic scattering of intermediate energy protons and deuterons have yielded a wealth of data on the spin response of nuclei. This work complements the well-known studies of Gamow-Teller strength in charge-exchange reactions. The emphasis here is on a consistent determination of the S = 1, T = 0 response, practical only with deuterons, and on the proper separation of S = 0 and S = 1 strength in proton spectra for appropriate comparison with sum rules. We concentrate on two nuclei, 40 Ca and 12 C, at momentum transfers below about 1 fm −1 and on excitations up to about 50 MeV. The continuum second random phase approximation provides the primary theoretical tool for calculating and interpreting the response in terms of properties of the nucleon-nucleon force inside the nuclear medium. The reaction mechanism is described by the DWIA, applied here to continuum proton scattering almost as rigorously as it is usually applied to low energy excitations. A new DWIA formalism for the description of spin observables in deuteron scattering is used. Comparison of the proton and deuteron data with each other and with RPA/DWIA calculations yields interesting insights into the current state of understanding of collectivity and the nuclear spin response.

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.

Recent results on the isoscalar spin response in 40Ca and 12C

Abstract A signature S d y of isoscalar spin-transfer strength has been tested in the inelastic scattering of 400 MeV deuterons from 12 C. It was applied to search for ΔS =1 ΔT =0 strength in 40 Ca and 12 C. In 40 Ca, spin excitations were found in the 9 MeV region and over a broad range in the continuum with a cluster of strength around 15 MeV. In 12 C, ΔS=1 ΔT =0 levels were observed at 12.7 MeV (well known T =0 1 + level), 18.3 MeV (2 − T =0 level) and 20.4 MeV. Resonances were found at 20 MeV and at 30 MeV. Beyond 35 MeV the ΔS =1 ΔT =0 response is similar to the one observed in 40 Ca. Microscopic DWIA calculations agree nicely with the 12 C data.

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.

Isoscalar spin strength in 12C and 40Ca

The isoscalar spin‐transfer signature Syd has been used in inelastic scattering of 400 MeV polarized deuterons to search for ΔS=1 ΔT=0 strength in 40Ca and 12C. In 40Ca, spin excitations were found in the 9 MeV region and over a broad range in the continuum with a cluster strength around 15 MeV. In 12C, a previously unknown ΔS=1 ΔT=0 level was observed at 20.5 MeV; ΔS=1 ΔT=0 resonances were also found at 20 MeV and 30 MeV. Microscopic DWIA calculations agree nicely with 12C data.

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.