J.A. McGill

Evidence for Δ− components in nuclei

Abstract Ratios of double-differential cross sections for incident 500-MeV pions are presented for ( π + , π + p) and ( π + , π − p) reactions on 12,13 C, 90 Zr, and 208 Pb. A comparison with intra-nuclear cascade-model calculations suggest that the outgoing pion spectra show a feature consistent with quasi-free scattering from the Δ − component of the nuclear ground state wave function.

Pion double charge exchange above the Δ(1232) resonance

Abstract First measurements of exclusive cross sections for the ( π + , π − ) reaction at incident energies of 300–500 MeV are reported. For the analog-state transitions in 14 C and 18 O the 5° cross sections are found to remain nearly constant in this energy interval. This behavior is in disagreement both with predictions based on six-quark cluster models and with simple expectations based on recent single-charge-exchange measurements.

Energy dependence of the total 12C(π+, 2p) cross section

Abstract Measurements have been made of the excitation function for π + absorption on 12 C at energies from 19 to 140 MeV using a large solid angle bismuth germanate multi-element detection system. These measurements show a smooth energy dependence of the pion absorption cross sections contradicting a previously reported dip in the energy dependence at 28 MeV.

Polarization observables for the reaction pp→ppπ0 at 800 MeV

Abstract The Wolfenstein polarization observables DNN, D SΩ and D LΩ , where Ω denotes a mixture of S and L polarization components, the induced polarization P, and the analysing power A have been measured for the reaction pp→ppπ0 at 800, 733, and 647 MeV. Comparisons are made to theoretical predictions of the model of Dubach, Kloet and Silbar.

A superconducting radio-frequency cavity for manipulating the phase space of pion beams at LAMPF

Abstract The SCRUNCHER is a superconducting radio-frequency cavity for manipulating the longitudinal phase space of the secondary pion beam from the low energy pion channel at LAMPF. Test results of the cavity performance and initial results from in-beam tests are presented.

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.

Pion-nucleus elastic scattering on {sup 12}C, {sup 40}Ca, {sup 90}Zr, and {sup 208}Pb at 400 and 500 MeV

Pion-nucleus elastic scattering at energies above the Delta(1232) resonance is studied using both pi+ and pi- beams on 12C, 40Ca, 90Zr, and 208Pb. The present data provide an opportunity to study the interaction of pions with nuclei at energies where second-order corrections to impulse approximation calculations should be small. The results are compared with other data sets at similar energies, and with four different first-order impulse approximation calculations. Significant disagreement exists between the calculations and the data from this experiment.

Pion - nucleus elastic scattering on C-12, Ca-40, Zr-90, and Pb-208 at 400-MeV and 500-MeV

Pion-nucleus elastic scattering at energies above the Delta(1232) resonance is studied using both pi+ and pi- beams on 12C, 40Ca, 90Zr, and 208Pb. The present data provide an opportunity to study the interaction of pions with nuclei at energies where second-order corrections to impulse approximation calculations should be small. The results are compared with other data sets at similar energies, and with four different first-order impulse approximation calculations. Significant disagreement exists between the calculations and the data from this experiment.

Pion elastic scattering from polarized 13C in the energy region of the P33 resonance.

Analyzing powers [ital A][sub [ital y]] were measured for [pi][sup +] and [pi][sup [minus]] elastic scattering from polarized [sup 13]C at incident pion energies [ital T][sub [pi]] near the [ital P][sub 33] [pi]-nucleon resonance. At [ital T][sub [pi]]=130 MeV, the values of [ital A][sub [ital y]] are significantly different from zero for [pi][sup [minus]] scattering. For [pi][sup +] at [ital T][sub [pi]]=130 MeV and for both [pi][sup [minus]] and [pi][sup +] at all other energies, the [ital A][sub [ital y]] are mostly consistent with zero. Elastic differential cross sections were measured using an unpolarized [sup 13]C target. Both the analyzing-power and cross-section data were compared with predictions using a variety of nuclear structure and reaction models. The analyzing power was found to be strongly sensitive to the quadrupole spin-flip part of the transition. The data of this work complement measurements of the magnetic form factor by electron scattering. The pion [ital A][sub [ital y]] data are not reproduced by calculations using wave functions that fit the magnetic form factor at low momentum transfers.

Pion elastic scattering from polarized [sup 13]C in the energy region of the [ital P][sub 33] resonance

Analyzing powers [ital A][sub [ital y]] were measured for [pi][sup +] and [pi][sup [minus]] elastic scattering from polarized [sup 13]C at incident pion energies [ital T][sub [pi]] near the [ital P][sub 33] [pi]-nucleon resonance. At [ital T][sub [pi]]=130 MeV, the values of [ital A][sub [ital y]] are significantly different from zero for [pi][sup [minus]] scattering. For [pi][sup +] at [ital T][sub [pi]]=130 MeV and for both [pi][sup [minus]] and [pi][sup +] at all other energies, the [ital A][sub [ital y]] are mostly consistent with zero. Elastic differential cross sections were measured using an unpolarized [sup 13]C target. Both the analyzing-power and cross-section data were compared with predictions using a variety of nuclear structure and reaction models. The analyzing power was found to be strongly sensitive to the quadrupole spin-flip part of the transition. The data of this work complement measurements of the magnetic form factor by electron scattering. The pion [ital A][sub [ital y]] data are not reproduced by calculations using wave functions that fit the magnetic form factor at low momentum transfers.