R.R. Johnson

The interaction between positive pions and deuterons at 47.5 MeV

Abstract The interaction of 47.5 (±0.5) MeV positive pions with douterons was studied using a scintillation counter telescope as the pion spectrograph. With an energy resolution sufficient to separate the elastic from inelastically scattered pions, the system was used to measure the cross sections for these reactions as well as the non-radiative pion capture process over the angular range of 22.5°–157.5°. The scattering results are well-fitted by recent theoretical calculations provided appropriate pion-nucleon phase shifts are used. The protons from the non-radiative capture reaction are fitted by a differential cross section of the form: d σ/ d Ω ∝ A + cos 2 θ , with A = 0.31 ± 0.03.

Elastic scattering of positive pions from 12C at 30, 40 and 50 MeV

Abstract We have measured the angular distribution of π + elastically scattered from 12 C at E π = 28.4, 38.6 and 48.9 MeV . The angular range was between 13° and 165° lab. Scattered pions were detected with two counter telescopes which required pion identification through the observation of the decay muon. Data agree well with calculations derived from the free πn scattering amplitudes when absorption effects have been included.

Study of isobaric analog ground states for several nuclei using the (3He, t) reaction

Abstract The ( 3 He, t) reaction was used at 37.7 MeV to investigate the isobaric analogs of the ground states of 46 Ti, 54 Fe, 62 Ni, 64 Ni, 89 Y, 90 Zr, 91 Zr, 92 Zr and 93 Nb. Differential cross sections were measured from 5° to 50°. The angular distributions were described adequately by a macroscopic distorted wave theory. The effect of variations in the optical-model parameters and in the form of the interaction potential was investigated. The strengths of the interaction potentials extracted from the data are compared with values of the asymmetry potential obtained from a recent analysis of 3 He and t elastic scattering data. Certain nucleus dependent effects are noted. Coulomb displacement energies were determined for nuclei with A around 90.

Pion production by pions in the 16O(π+,π+π−) reaction at Tπ+ = 280 MeV

The results of an experiment of pion-induced pion production on 16O at a laboratory energy of 280 MeV are reported. The four-fold-differential cross section, d4σdΩπ+dΩπ+dEπ+dEπ, was measured, and the missing mass, Mx, for the reaction 16Ofs(π+,π+π−) at laboratory angles of 50°, 80° and 115° for the π−, and from 22° to 128° for the π+ was deduced. The angular and energy distributions of the many-fold differential cross sections are compared with an A(π+,π+π−) model for the reaction. The observed cross sections are reproduced in magnitude and shape when the theoretical calculations consider a proper pion dispersion relation, gw(q), inside the nuclear medium. The total cross section, deduced by integrating the four-fold differential cross sections, is compared with the available theoretical predictions for the 16O(π+, π+π−) reaction.

Pion production from hydrogen bombarded by polarized protons at intermediate energies

Abstract Angular distributions of differential cross sections and polarization analyzing powers are presented for the 1 H ( p , π + ) 2 H reaction for incident proton energies between 305 and 425 MeV. The pions were detected in a single-arm configuration employing a magnetic spectrograph. Pions associated with both bound (deuteron) and unbound final nucleon states were detected simultaneously. These data provide the first indication of the contribution of d-wave pions in this energy region. Some data concerning the analyzing power for the inclusive pions from the 1 H ( p , π + ) pn reaction are also presented. An interesting feature of these results is the similarity of the analyzing power for the 1 H ( p , π + ) pn reaction (when the relative kinetic energy in the pn system is 10–20 MeV) to that for 1 H ( p , π + ) 2 H .

1H(π, 2π) cross sections with ππ scattering derived from chiral lagrangians

Abstract Pion induced pion production cross sections have been calculated in an isobar model that includes pion-pion scattering amplitudes as derived from higher order chiral lagrangians. The results agree with data in all the isospin channels and indicate that after a full understanding of the isobar role in the reaction a precise (π, 2π) experiment could constrain the parameters of such pion-pion lagrangians.

Total reaction cross sections for 20–30 MeV pions and the anomaly of pionic atoms

Abstract Total reaction cross sections of 20 MeV π− and 30 MeV π+ and π− have been measured for carbon and nickel targets. The experimental results are in very good agreement with calculations based on commonly accepted pion-nucleus potentials but disagree with calculations based on the potentials associated with the so-called pionic atom anomaly.

Integral cross sections for π+p interactions at low energies

Abstract Integral cross sections for the elastic scattering of π+ by protons into angles greater than 20° or 30° (lab) have been measured by the beam-attenuation technique over the energy range of 45–126MeV. The measurements are aimed at providing independent checks on the absolute normalization of differential cross sections, where discrepancies exist between different data sets. Comparisons with predictions made with existing phase shifts show very good agreement with the dispersion-relation constrained phase shifts of the Karlsruhe group.

Pion-induced pion production on deuterium: a quasifree process

Abstract A detailed experimental analysis of the π + d → π + π − pp in-plane coincidence data first presented by Rui et al. is compared to an expanded version of the Oset and Vicente-Vacas model for pion-induced pion production on a free nucleon. This extended model averages over Fermi motion to describe the assumed quasifree nature of the process occurring on the deuteron and includes nine additional diagrams to account for the N ∗ → N (ππ) p-wave reaction channels. Experimental effects such as pion energy loss in the target and in the detectors, pion decay and muon detection are investigated and incorporated into the comparison of experimental data and theory. Inclusion of Fermi motion was found to be essential to provide good agreement between data and model confirming the quasifree nature of the reaction. When compared to the total-cross-section measurements of Manley et al. , the free-reaction model yields a model-dependent estimate of the overall strength of the diagram containing the N ∗ → N (ππ) s-wave vertex.

π+π− coincidence measurement in the 4He(π+, π+π−) reaction at Tπ+ = 280 MeV

Abstract The pion induced pion production (π, 2π) reaction on deuterium has been studied at an incident pion energy of 280 MeV. The outgoing pions were detected in coincidence and the measured four-fold cross sections were compared with a πN → ππ N microscopic model, and, upon integration, with the available experimental total cross sections from the same reaction on H and 2 H. Finally, the results were directly compared with recent data from the 16 O(π + , π + π − ) reaction at the same incident energy.