Electroproduction of Associated Two-Body Final States.

Deep inelastic electron scattering is a valuable tool for studying the behavior of elementary particles and their constituent partons. Electron scattering is linked to photoproduction by treating the scattering of the electron as the production of a virtual photon which then interacts with the target. Vector meson dominance then explains many of the observed final states, as it does in photoproduction. Other two-body reactions might also be expected to contribute to the total cross section, as they do in hadronic collisions. The non-resonant interactions are thought to reflect the properties of the constituents of the target nucleon. The Large Aperture Magnet Experiment at the Cornell Electron Synchrotron measured electron scattering in the region 2.98 < s < 13.69 GeV('2) and 0.5 < Q('2) < 3.0 GeV('2). The 11.5 GeV extracted electron beam struck a liquid hydrogen target in an eight kilogauss magnetic field. The charged particles in the final state were tracked through the field by a multiwire proportional chamber system of 34 planes. A lead-scintillator shower counter triggered the experiment on detection of a scattered electron. Time-of-flight and water Cherenkov counters identified some of the final state hadrons. The data recorded on tape was then passed through computer programs which linked proportional chamber strikes into tracks, fit momenta to the tracks, applied particle identification algorithms, selected interesting events, and plotted histograms of invariant masses. All of this is described here in detail, with special attention to the front-end electronics and the track-finding program. Many specific final states were observed. The analysis presented here concentrates on the reaction (gamma)(,v)p (--->) p(pi)('+)(pi)('-)(pi)('0), with the final hadrons resulting from the decay of a two-body state. The states p(omega)('0) and p(eta)('0) are measured. Limits are set for the production of (DELTA)('++)(rho)('-), (DELTA)('+)(rho)('0), and (DELTA)('0)(rho)('+). There is no convincing evidence for any other state decaying into p(pi)('+)(pi)('-)(pi)('0), to p(pi)('+)(pi)('+)(pi)('-)(pi)('-)(pi)('0), to n(pi)('+)(pi)('+)(pi)(' -), or to n(pi)('+)(pi)('+)(pi)('+)(pi)('-)(pi)('-). The conclusion we draw is that hadron-like two-body processes are almost completely absent in virtual photon scattering in this kinematic region. Vector meson production, excitation of the nucleons, and the scattering of the photons directly from individual partons are the important processes.