Jan Kallne

Pion double charge exchange on 3He and 4He

Abstract We have measured the differential cross section d 2 σ/ d Ω d T for the double charge exchange reactions 4He(π+, π−)4p and 3He(π−, π+)3n at 140, 200 and 295 MeV. By fitting this data with a simple phase-space model we have estimated the integrated cross section d σ/ d Ω and the total cross section. The 4He data agree qualitatively with the predictions of a meson exchange calculation and with one version of the successive single charge exchange model. The 3He cross sections are considerably larger than those of 4He and in some cases the missing mass plot shows a strong enhancement, which resembles a broad three-nucleon resonance.

Two-nucleon pion absorption in 3,4He

Abstract Results are presented for π+NN → Np yields in 3,4He relative to πd → pp from (π, p) measurements at energies between 50 and 295 MeV and estimates are given for total cross sections. These yields are nearly proportional to the number of target NN pairs, which is not true for 6Li and heavier nuclei. This is believed to indicate that πNN → Np is sensitive to the NN short-range behavior which is deuteron-like for 3,4He but not always so for NN pairs in other nuclei.

Quasi-free nucleon scattering on 16O☆

The 16O(p, 2p)15N and 16O(p, pn)15O reactions have been observed using the MRS facility and a 505 MeV proton beam at TRIUMF. Data were acquired for sixteen pairs of angles of the emitted nucleons leading to the mirror 1p12 ground and 1p32 excited states of the residual nuclei over a broad range of recoil momenta. Cross sections and cross-section ratios were extracted from the data. The results are compared with DWIA calculations in which microscopic optical potentials, with medium effects included, are used in the calculation of the scattering wave functions. The amplitudefactorized form of the cross section is used rather than the usual cross-section factorized form. Comparisons of the (p, 2p)/(p, pn) cross-section ratios are made for calculations with and without the spin-orbit optical potential, and with the free nucleon-nucleon elastic scattering cross-section ratios. The experimental cross sections and ratios are generally smaller than any of the calculations, and these differences remain to be clarified.

Elastic π± + 3He scattering

Abstract Differential cross sections have been measured at θ ≈20–120° at 50, 100 and 200 MeV. Salient features of the angular distributions are Coulomb interference effects at 50 MeV and clear spin-flip contributions to π − compared to π + scattering in the angular region of θ ≈80° dominated by the πN p-wave minimum. Comparison with optical model calculations account for the data up to 200 MeV while this first-order scattering theory misses conspicuous features of data at 295 MeV.

Elastic scattering of π+ and π− mesons from 3He and 4He at energies from 300 TO 475 MeV

Abstract The cross section for elastic scattering of pions from 3 He and 4 He was measured for incident energies from 300 to 475 MeV. The pions were detected in a magnetic spectrometer at scattering angles from 30° to 130°. Results on angular distributions are presented. A particularly interesting feature is that a deep minimum at 110°, previously observed at 295 MeV, is found to persist up to 400 MeV. The minimum is fixed in angle and is therefore not a simple function of q 2 .

The (π±,p) reactions and nuclear pp and pn correlations

The authors have measured ( pi +or-, p) spectra for 3,4He and 27Al at theta =20 degrees and report on the two-nucleon pion absorption over the energy range 50-300 MeV. The pi +NN to Np and pi -pp to pn yields for T=0 NN systems in 3,4He are found to be larger than expected relative to pi +d to pp while they are smaller for T=1 systems and show a significant difference between 3He and 4He.

Pion single charge exchange scattering fromHe3at 285, 428, and 525 MeV

We have measured the cross section of /sup 3/He(..pi../sup -/,..pi../sup 0/)/sup 3/H at T = 285, 428, and 525 MeV for angles in the range of 60/sup 0/< or approx. =theta< or approx. =135/sup 0/ covering the momentum transfer range 0.5< or approx. =q< or approx. =1.0 GeV/c. Comparison is made with Glauber model calculations to discuss the sensitivity to nuclear structure and pion-nucleus interaction effects.