J. Hylen

Determination of ±s from a differential-jet-multiplicity distribution in e+e- collisions at ss =29 and 91 GeV

We measured the differential jet-multiplicity distribution in {ital e}{sup +}{ital e}{sup {minus}} annihilation with the Mark II detector. This distribution is compared with the second-order QCD prediction and {alpha}{sub {ital s}} is determined to be 0.123{plus minus}0.009{plus minus}0.005 at {radical}{ital s}{approx}{ital M}{sub {ital Z}} (at the SLAC Linear Collider) and 0.149{plus minus}0.002{plus minus}0.007 at {radical}{ital s}=29 GeV (at the SLAC storage ring PEP). The running of {alpha}{sub {ital s}} between these two center-of-mass energies is consistent with the QCD prediction.

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.

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.

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 hexagonal calorimeter at PEP-4

Abstract A Geiger-mode electromagnetic shower calorimeter has been constructed for PEP-4. Six trapezoidal modules cover 75% of 4 π solid angle in a hexagonal array. Each module contains 40 sense wire planes between 0.25 radiation-length thick lead-laminates, and is divided electrically into submodules of 27 and 13 layers. Half-degree wide hodoscopic channels in projective geometry provide excellent spatial resolution. In each gap three stereo views using the sense wires as well as strips on both cathodes at ±60° to the wires provide good shower reconstruction capabilities in multi-track jet events. Calibration and data analysis procedures are outlined. The performance of the calorimeter in the measurement of Bhabha events and the reconstruction of π 0 s in jet events is in excellent agreement with Monte Carlo simulations. The π 0 mass resolution is MeV (rms).

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.

Performance of a Drift Chamber System for the Time Projection Chamber Detector Facility at PEP

A svstem of two cylindrical drift chambers has been designed and constructed to trigger the Time Projection Chamber and to assist in tracking and momentum reconstruction. Performance of these chambers has been studied with data collected from cosmic rays and actual e+e-collisions during recent experimental runs.

A Muon Detection System for the PEP4 Facility

A large muon detection system has been constructed and is fully operational in the PEP 4 facility. It is more than 99.6% efficient. The system is rugged and reliable. It is possible to verify the integrity of all the chambers in a few minutes. Associated software for identifying muons has been written and is working.

Determination of. alpha. sub s from a differential-jet-multiplicity distribution in e sup + e sup minus collisions at radical s =29 and 91 GeV

We measured the differential jet-multiplicity distribution in {ital e}{sup +}{ital e}{sup {minus}} annihilation with the Mark II detector. This distribution is compared with the second-order QCD prediction and {alpha}{sub {ital s}} is determined to be 0.123{plus minus}0.009{plus minus}0.005 at {radical}{ital s}{approx}{ital M}{sub {ital Z}} (at the SLAC Linear Collider) and 0.149{plus minus}0.002{plus minus}0.007 at {radical}{ital s}=29 GeV (at the SLAC storage ring PEP). The running of {alpha}{sub {ital s}} between these two center-of-mass energies is consistent with the QCD prediction.