NEAR-THRESHOLD PROTON-INDUCED NEUTRAL PION PRODUCTION FROM DEUTERIUM.

摘要

In an attempt to learn about reaction mechanisms involved in nucelon induced single pion production near threshold, an experiment investigating the reaction pd (--->) ('3)He(pi)('0) was performed in a region closer to threshold than has ever been investigated before for any few nucleon system. The measurement was made by detecting the recoil ('3)He in coincidence with the decay gamma rays from the associated (pi)('0). Total cross sections, differential cross sections, and analyzing powers were measured at pion center of mass energies ranging from 0.1 to 2.7 MeV.;The relative roles of s and p wave pion emission in the threshold region for this nuclear system are discussed. It is demonstrated that there is a direct connection between emission from this final state nucleus and emission from a nucleon pair in that nucleus. This provides the basis for establishing the role played by nonresonant modes of production, that is, modes that are not dominated by an intermediate (DELTA), in the threshold region. The experiment provides evidence that nonresonant modes of production, as evinced by s wave emission, dominate in pd (--->) ('3)He(pi)('0) for (eta) as high as (TURN) 0.5, and appear to remain significant for (eta) at least as large as 1.0. It is also demonstrated that there is good reason to expect a similar result in heavier nuclear systems. The impact of these developments on present experimental and theoretical efforts is discussed.