Heavy ion studies/pion studies

The Berkeley research activities of our group center mainly on the study of charged pions or correlated pairs of particles produced in high-energy heavy-ion collisions at the Bevalac. The technical approach involves a large (--4 meter flight path) dipole-dipole magnetic spectrometer (JANUS) and combinations of fast scintillators and wire chambers interfaced with a CAMAC-PDP 11/45 data acquisition system. One major part of the work is the determination of the cross sections (with an exploration of the angular dependence) for pion production in heavy-ion reactions. The authors are also studying the production cross section for low-energy π- and π+ at 900 in the center of mass, where an enhancement in the π+ production has been observed. The authors want to ascertain that this 900 peak does disappear at low energy and to attempt to measure the threshold for its appearance. In addition, they are studying production of charged pions below the single nucleon-nucleon threshold to probe the importance of Fermi momentum in the nucleus. By measuring the center-of-mass angular distribution, the authors want to distinguish between thermal and single particle production modes. The authors have undertaken thick target studies in order to evaluate the practicality of heavy-ion production of useful π- beams. Another major part of our research effort involves pion interferometry studies. In the past ten years theorists have predicted that exotic phenomenon such as pion condensation and quark-gluon plasmas occur in relativistic heavy-ion collisons. One way to obtain information about these phenomena is to measure the radius, lifetime and coherence of the pion-emitting source produced in the collision