An experimental investigation of the absorption reaction ⁴He(π⁺,ppp) has been undertaken on the M11 beamline at the TRIUMF cyclotron. Positive pions at an average kinetic energy of 165 MeV were directed onto a cylindrical liquid 4He target and the outgoing protons were measured by a combination of two time-of-flight arrays and two plastic scintillator telescopes. A description of the apparatus, experimental technique and calibration is presented. Results from triple proton coincidences at a single orientation of three of the detectors are discussed. Their angular settings with respect to the pion beam were 40°, 136° and —55°. Comparisons are made with Monte-Carlo simulations of three and four body phase spaces. Identification of a quasi-free three nucleon absorption mode is made for the first time at this energy. An integrated cross-section for this process is determined (σQ₃N = 4.4 ± 0.6mb). The quantitative agreement between these results and those of another recent experiment¹ indicate that a small fraction(≈10%) of the coincidences could be due to a two step absorption mechanism. ¹Backenstoss et al. Phys. Rev. Lett 61:923(1988) / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Graduation date: 1996

We introduce a relativistic model for pion-nucleon scattering which includes an elementary delta dressed by its decay. Crossing-symmetric single-particle exchange is augmented by parametrized multiple-scattering interactions, with covariant sideways form factors in both 3- and 4-field vertices. Causality is enforced by dispersion relations. Unitary fits to observed on-shell amplitudes are obtained; a modest number of parameters precisely reproduce all 6 S- and P-wave ��-N amplitudes up to 1.36 GeV invariant mass. / Graduation date: 1995

A first coincident measurement of the pion induced pion production reaction cross-section on a complex nucleus (A > 2) has been successfully performed. In particular, the reaction ¹⁶O(π⁺,π⁺,π⁻) was measured at 280 MeV incident pion energy. The only previous published measures of this reaction on nuclei consisted of a dated measurement done on emulsion nuclei [BBD*69] and did not provide very stringent limits to the nuclear cross section. Single arm experiments have previously been done elsewhere on the proton [BJK*80] and the deuteron [PGM*84]. The reaction was measured at TRIUMF using the QQD magnetic spectrometer in coincidence with the CARUZ [RGR88], a total absorption scintillator range telescope. The measured four-fold differential cross sections were extrapolated to the unmeasured portions of the phase-space to extract the total reaction cross-section at 280 MeV, which was found to be σtot = 2.250 ± .350m6. The (π,2π) cross-section is thus observed to provide approximately 40% of the inclusive double charge exchange cross section [Woo84] at this energy. The model of [OV86] is found to explain many of the features of the data, including σtot. The present data do not preclude effects due to pion condensate precursor phenomena as proposed by [CE83] but they do not support the existence of a strong effect. The data are also compared to kinematical Monte Carlo simulations of some possible reaction mechanisms and it is found that the presence of an intermediate ∆ can aid the explanation of the low energy features of the π⁺ energy spectrum. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

We used recent phenomenological form factors to calculate the effect of on-shell two-pion exchange in nucleon-nucleon scattering below the two-pion production threshold. As expected, the contributions of partial wave amplitudes are all negligible. We also noticed that the relativistic spin-operator decomposition of the scattering amplitude is not unique at certain momenta and angles. / Graduation date: 2000

Thesis (Ph. D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1991. / Includes bibliographical references (leaves 135-146).

Thesis (Ph. D.)--Ohio University, August, 2004. / Includes bibliographical references (p. 113-117).

Thesis (Ph.D.)--Ohio University, August, 2004. / Title from PDF t.p. Includes bibliographical references (p. 113-117)

No description available.

This thesis describes measurements of the pion induced pion production reaction π⁺d → π⁺π⁻p p performed with a 280 MeV incident π⁺ beam at TRIUMF. The data are compared with an improved version of the Oset and Vicente-Vacas theoretical model [12]. The goal of the experiment and of the analysis was to provide a larger body of data for the free reaction and to test the validity of theoretical models. In the process, the ability to determine the values of the coupling constants C, f∆ , gN*∆π within such a model framework would be explored. The knowledge of the precise value of these coupling constants would constrain N* decay branching ratios and other pion induced reaction mechanisms like Double Charge Exchange. A previous experiment [23] had indicated that the pion induced pion production on deuterium is essentially a quasifree process with the reaction occurring on the neutron leaving the proton merely a spectator. The main difference with respect to the free reaction is the effect of Fermi motion of the neutron. Although we were interested in studying the free reaction (π⁻p → π⁺π⁻n), we chose a deuterium target so that the experiment could be run with a π⁺beam, since the π⁻ beam flux is about 6 times lower than the flux of the positive pion beam at 280 MeV, the energy at which our experiment was performed. Such a flux would have required a much longer running time for the experiment in order to achieve the same statistical accuracy. The quasifree nature of the process was also confirmed in our experiment. This experiment involved a coincidence measurement of the quasifree process and as such provided four-fold differential cross section spectra of the reaction thus allowing for a microscopic comparison between data and theoretical models. In the theoretical description we incorporated additional amplitudes for the N* → N(ππ)p-wave diagrams required to describe the reaction cross section at Tπ = 280 MeV. We also added the Fermi motion of the nucleon to the model to account for the deuterium environment. The 'free' parameters of the model are the largely unknown coupling constants listed above. We fixed C to be -2.08 by requiring the energy dependence of the model to be that of the measurement of [22] and compared the energy and angular distributions of the model to our data for several values of the f∆ and gN*∆π coupling constants ranging between 0 and 2 (where the units are 4/5 fNNπ) and between 1.08 and 1.53 respectively. We found reasonable sensitivity of the model to the f∆ variation, but only limited sensitivity to the value of the gN*∆π coupling constant. Overall we achieved a very good agreement between data and the theoretical predictions for f∆ values smaller than 0.5 and gN*∆π values closer to its lower limit. Improved statistical accuracy of the data would however be needed to better constrain the values of the coupling constants. On the basis of our results we feel that this model is a useful tool for planning future experiments and that a more extensive (π, 2π) experimental program, where differential cross sections are measured for differing isospin channels, would provide a further, more stringent test on the model allowing for a more precise determination of the coupling constants. / Science, Faculty of / Physics and Astronomy, Department of / Graduate