A. Bross

Tests of models for quark and gluon fragmentation ine+e− annihilation at\(\sqrt s = 29 GeV\)

Three currently used fragmentation models are tested by studying the distribution of particles between jet axes in the 3-jet events ofe+e− annihilation, using data collected by the Time Projection Chamber at PEP. These three models — the Lund String model, the Webber Cluster model and an Independent Fragmentation model (IF) — each implement different Lorentz-frame structures for the fragmentation process of quarks and gluons into hadrons. The Lund model provides a good description of the data, while the IF model does not. The Webber model, which is untuned, does not describe the absolute particle densities between jets, but correctly predicts the ratios of those densities, which are less sensitive to the tuning.

Properties of new scintillator glasses and scintillating fibers

We present data on the light output and optical properties of new scintillation glasses. Data on light (¿ ¿ 2.6g/cm3) and heavy (¿ > 3.4g/cm3) glasses are presented. In addition, the performance of scintillating glass fibers fabricated using a new light glass is discussed.

Prompt electron production ine+e− annihilations at 29 GeV

We have measured the inclusive prompt electron cross section over a wide momentum range (P>0.5 GeV/c) with the PEP-4 TPC detector. The semielectronic branching fractions of thec andb quarks are (9.1±0.9 (stat.)±1.3 (syst.))% and (11.0±1.8±1.0)%, respectively. Theb quark fragmentation function peaks at highz with 〈zb〉=0.74±0.05±0.03. The axial couplings to the neutral current areac=2.3±1.4±1.0 for thec quark andab=−2.0±1.9±0.5 for theb quark.

Spatial Resolution of the PEP-4 Time Projection Chamber

The spatial resolution and response of the segmented cathode pads of the PEP-4 TPC have been measured with data taken at 8.5 atmospheres of 80% Argon-20% Methane gas with a 4kG magnetic field. The dependence of the spatial resolution and pad response on drift distance and track-anode crossing angle is presented.

Measurement of Ionization Loss in the Relativistic Rise Region with the Time Projection Chamber

We present here some results obtained with the LBL Time Projection Chamber (TPC) regarding the particle identification by the measurement of the ionization losses in the relativistic rise region. This includes the method of calibration using 55Fe sources, the measurement of the resolution using cosmic rays, which shows an equivalent K-¿ separation of 4.8 standard deviations at 3.5 GeV/c, and the preliminary results obtained with multihadronic events from e+e- annihilations.

Performance of radiation hard CCDs as tracking devices

We present data on the operation of radiation hard CCDs used as tracking devices. The system consisted of 5 Texas Instruments CCDs with a total number of cells equal to 2.7 × 106. The tracking resolution for minimum ionizing particles was measured to be σx = 4.8 ± 0.2 μm and σy = 5.0 ± 0.3 μm. Two track separation of better than 40 μm in space was also obtained.

Inclusive γ and π0 production cross sections and energy fractions ine+e− annihilation at 29 GeV

Inclusive production cross sections for photons and π0s ine+e− annihilation at a center of mass energy of 29 GeV have been measured. The π0 production spectrum agrees with a corresponding measurement for π±. The ratio of the π0 inclusive rate to the average for π± is 0.92±0.14. The fractions of the total energy carried by photons and π0s are 0.244±0.016 and 0.217±0.033, respectively. The fraction of total energy carried by all stable hadrons, prompt leptons and photons is determined to be 0.938±0.045, leaving 0.062±0.045 for neutrinos.

Properties of New Scintillation Glasses and Scintillating Fibers

We present data on the light output and optical properties of new scintillation glasses. Data on light (? ? 2.6g/cm3) and heavy (? > 3.4g/cm3) glasses are presented. In addition, the performance of scintillating glass fibers fabricated using a new light glass is discussed.

Geiger Mode Calorimeter for PEP-4

The PEP-4 hexagonal barrel calorimeter, with lead-laminate layers and 5×lOmm2 Geiger-mode discharge cells, has demonstrated excellent stability and uniformity in operation. The use of projective geometry in half degree-wide cathode strips at ±60 degrees to the sense wire channels provides excellent spatial resolution and reconstruction capability. The electronic noise-to-signal ratio without preamplification is sufficiently low that individual 50 pC Geiger discharges are accurately measured and used for energy calibration. Measurements made at 14.5 GeV e± beam energy have provided preliminary spectra of Bhabhas and of photon-photon invariant mass. The latter show that ¿os can be reconstructed.

Performance of the Signal Processing System for the Time Projection Chamber

The Time Projection Chamber has operated in the PEP colliding beams at SLAC since January 1982. Its signal processing system, containing 16020 channels, has been calibrated and monitored using a computer-controlled test pulser system. We describe the test system and review measurements made with the system of signal processing electronics.