M.H. Wang

LARGE-SOLID-ANGLE STUDY OF PION ABSORPTION ON 3HE

Measurements have been made of [pi][sup +] absorption on [sup 3]He at [ital T][sub [pi]][sup +]=118, 162, and 239 MeV using the Large Acceptance Detector System. The nearly 4[pi] solid angle coverage of this detector minimizes uncertainties associated with extrapolations over unmeasured regions of phase space. The total absorption cross section is reported. In addition, the total cross section is divided into components in which only two or all three nucleons play a significant role in the process. These are the first direct measurements of the total and three nucleon absorption cross sections.

A LARGE ACCEPTANCE DETECTOR SYSTEM (LADS) FOR STUDIES OF PION ABSORPTION

Abstract A Large Acceptance Detector System (LADS) has been designed and built at the Paul Scherrer Institute to study multiparticle final states following pion-nucleus absorption. It consists of a 28-sector cylinder of plastic scintillators of 1.6 m active length and 1.4 m diameter, two cylindrical wire chambers, and two 14-sector plastic scintillator end-caps which close each end. The nearly 4π solid angle coverage of this detector minimizes uncertainties associated with extrapolations over unmeasured regions of phase space. The design and the performance of the LADS detector are presented.

Contribution of initial state interactions to the three-nucleon absorption of pions by 3He

Abstract The distributions of protons after the absorption of positive pions by 3 He at 118, 162 and 239 MeV are presented. A decomposition of the three-nucleon cross section in terms of initial state interactions and other processes is given, based upon simple models. A clear signal of initial state interactions is visible in the data, diminishing at the lower energies.

New perspectives in multi-nucleon pion absorption on light nuclei

Multinucleon absorption cross sections have been measured in 3He and 4He with three unbound, energetic nucleons in the final state. The ratios of the different 3NA cross sections are difficult to understand in terms of only two-step processes. Similar difficulties appear in the decomposition of the 3NA yield into mechanisms. Although a part of this yield is identified to be due to two-step processes, a large fraction is well described by a simple phase space model. (AIP)