G. S. Blanpied

Reaction /sup 58/Ni(. pi. /sup +/,2p-italic) at 160 MeV

Data for the /sup 58/Ni(..pi../sup +/,2p-italic) reaction at T-italic..pi.. = 160 MeV were obtained for a number of angle pairs. The resultant angular correlations for T-italic/sub 1/+T/sub 2/>160 MeV (guaranteed pion absorption) peak at a separation angle corresponding to absorption on a deuteron at rest. However, simple estimates of initial- and final-state scatterings suggest that less than 50% of the absorption cross section arises from absorption on nucleon pairs. The data show little evidence for scattering of pions before absorption on nucleon pairs.

Isospin effects in elastic scattering from C12, C13, and C14 at 65 and 80 MeV

Elastic scattering cross sections for ..pi../sup + -/ scattering from /sup 12/C, /sup 13/C, and /sup 14/C are presented for pion energies of 65 and 80 MeV and for scattering angles from 20/sup 0/ to 120/sup 0/. Energy dependent isospin effects are observed. The cross sections were fit with the Kisslinger potential, and the potential strength parameters show an (N-Z)/A dependence similar to that predicted by the impulse approximation at 65 MeV, but not at 80 MeV. Calculations using the Siciliano potential, which contains the explicit isospin dependence of the Lorentz-Lorenz-Ericson-Ericson effect plus isoscalar, isovector, and isotensor terms, indicate the importance and energy dependence of absorption effects. Finally a model independent parametrization of the neutron density suggests a neutron excess at the surface of /sup 13/C but not /sup 14/C.

Analyzing powers for p+d→3He+π0 at 800 MeV

Abstract Analyzing powers for the exclusive pion production reaction p +d→ 3 He+π 0 have been measured at a proton beam energy of 800 MeV. The forward-angle results are in good accord with a microscopic calculation. The analyzing power is determined primarily by the Δ(1232) diagrams at this energy. Possible explanations for the large-angle discrepancies are discussed.

Quasi‐free p↘+n analyzing powers at 800 MeV

The p↘+n analyzing power, Ay(θ), has been measured over the center‐of‐mass angular range 14–75 degrees.

The E2/M1 ratio in Δ photoproduction

New high-precision measurements of p (γ,π) and p (γ,γ) cross sections and beam asymmetries have been combined with other polarisation ratios in a simultaneous analysis of both reactions. The E 2/ M 1 mixing ratio for the N →Δ transition extracted from this analysis is EMR =−3.0%±0.3( stat+sys )±0.2 (model).

The E2/M1 Mixing Ratio in the Excitation of the Δ from Polarized Photo-Reactions

In constituent quark models, a tensor interaction, mixing quark spins with their relative motion, is introduced to reproduce the observed baryon spectrum. This has a consequence completely analogous to the nuclear tensor force between the n and p in deuterium. A D state component is mixed into what would otherwise be a purely S-wave object. The D-wave component breaks spherical symmetry, resulting in a non-vanishing matrix element for the nucleon and a static quadrupole moment and deformation for its first excited state, the Δ resonance, at ∽325 MeV. The magnitude and sign of this D-state component are quite sensitive to the internal structure of the proton and have been of great interest in recent years [1].

Photo-Nuclear Reactions with Polarized Gamma Rays

The Laser Electron Gamma Source (LEGS)[1] has recently begun operations at the National Synchrotron Light Source (NSLS) of Brookhaven National Laboratory. At LEGS, laser light is Compton backscattered from the 2.5 GeV electrons circulating in the X-Ray storage ring of the NSLS. The backscattered photons have gamma ray energies, k < 320 MeV. The corresponding scattered electrons are detected in a tagging spectrometer which is incorporated into the storage ring. This tag provides a determination of the photon energy to ~ 5 MeV [2]. Since the laser light is polarized, and since the spin-flip amplitude in Compton backscattering is very small, the resulting polarization of the gamma-ray beam is very high.

Pion scattering to 6- stretched states in Mg24 and Mg26

Inelastic {pi}{sup {plus minus}} cross-section measurements at pion incident energies of 150 and 180 MeV were made on 6{sup {minus}} states in {sup 24,26}Mg. In particular, we have determined the ({ital f}{sub 7/2}{ital d5/2}{sup {minus}1}){sub 6}{sup {minus}} isoscalar {ital Z}{sub 0}=0.21{plus minus}0.02 strength for the strongest {ital T}=0, {ital J} {sup {pi}}=6{sup {minus}} state located at 12.11{plus minus}0.05 MeV in {sup 24}Mg, and the isoscalar {ital Z}{sub 0}=0.17{plus minus}0.04 and isovector {ital Z}{sub 1}=0.21{plus minus}0.02 strength for the strongest {ital T}=1, {ital J} {sup {pi}}=6{sup {minus}} state located at 9.18 MeV in {sup 26}Mg. The distorted-wave impulse-approximation pion cross-section calculations required a multiplicative normalization factor of 1.2{plus minus}0.1 in order to reproduce the pure isovector strength deduced from electron scattering for the well-known {ital T}=1, {sup {pi}}=6{sup {minus}} state at 15.15 MeV in {sup 24}Mg and the {ital T}=2, {ital J} {sup {pi}}=6{sup {minus}} state at 18.05 MeV in {sup 26}Mg.

Pion elastic and inelastic scattering from Mg24 and Mg26

Reported are measurements of angular distributions of resonance-energy positive and negative pions exciting approximately 40 states in {sup 24}Mg and {sup 26}Mg. These include the (ground state, 0{sup +}), (1.36 MeV, 2{sup +}), (4.14, 2{sup +}), (5.93, 4{sup +}), (6.44, 0{sup +}), (7.34), (7.55, 3{sup {minus}}), (8.33, 3{sup {minus}}), (9.32, 4{sup +}), (9.97, 5{sup {minus}}), (11.08, 3{sup {minus}}), (12.06), (13.26), (13.96, 3{sup {minus}}), (15.1, {ital T}=1, 6{sup {minus}}), and (15.4) states in {sup 24}Mg and the (ground state, 0{sup +}), (1.81, 2{sup +}), (2.92, 2{sup +}), (3.59, 0{sup +}), (4.31, 2{sup +}+4{sup +}), (4.90, 4{sup +}), (5.31, 2{sup +}), (5.44, 4{sup +}), (5.69, 4{sup +}), (6.86, 3{sup {minus}}), (7.33, 3{sup {minus}}), (7.79, 3{sup {minus}}), (8.17, 3{sup {minus}}), (9.2, possible 6{sup {minus}}), (10.30, 4{sup +}), and (18.1, {ital T}=2, 6{sup {minus}}) states in {sup 26}Mg. The distorted-wave impulse approximation with a Kisslinger form for the optical potential using a {pi}-nucleon {ital t} matrix at a shifted energy of {minus}25 MeV was found to explain the elastic scattering data from {sup 24,26}Mg in the energy range 116--292 MeV that is spanned by these data. Inelastic distorted-wave impulse approximation calculations employing collective-model deformation parameters were simultaneously fitted to the {pi}{sup +} and {pi}{supmorexa0» {minus}} data for each state.«xa0less

Pion elastic and inelastic scattering from sup 24 Mg and sup 26 Mg

Reported are measurements of angular distributions of resonance-energy positive and negative pions exciting approximately 40 states in {sup 24}Mg and {sup 26}Mg. These include the (ground state, 0{sup +}), (1.36 MeV, 2{sup +}), (4.14, 2{sup +}), (5.93, 4{sup +}), (6.44, 0{sup +}), (7.34), (7.55, 3{sup {minus}}), (8.33, 3{sup {minus}}), (9.32, 4{sup +}), (9.97, 5{sup {minus}}), (11.08, 3{sup {minus}}), (12.06), (13.26), (13.96, 3{sup {minus}}), (15.1, {ital T}=1, 6{sup {minus}}), and (15.4) states in {sup 24}Mg and the (ground state, 0{sup +}), (1.81, 2{sup +}), (2.92, 2{sup +}), (3.59, 0{sup +}), (4.31, 2{sup +}+4{sup +}), (4.90, 4{sup +}), (5.31, 2{sup +}), (5.44, 4{sup +}), (5.69, 4{sup +}), (6.86, 3{sup {minus}}), (7.33, 3{sup {minus}}), (7.79, 3{sup {minus}}), (8.17, 3{sup {minus}}), (9.2, possible 6{sup {minus}}), (10.30, 4{sup +}), and (18.1, {ital T}=2, 6{sup {minus}}) states in {sup 26}Mg. The distorted-wave impulse approximation with a Kisslinger form for the optical potential using a {pi}-nucleon {ital t} matrix at a shifted energy of {minus}25 MeV was found to explain the elastic scattering data from {sup 24,26}Mg in the energy range 116--292 MeV that is spanned by these data. Inelastic distorted-wave impulse approximation calculations employing collective-model deformation parameters were simultaneously fitted to the {pi}{sup +} and {pi}{supmorexa0» {minus}} data for each state.«xa0less