A. M. Boyarski

D and D meson production near 4 GeV in e+e− annihilation

Abstract We have studied momentum spectra for D0 ( D 0) and D± mesons produced near 4 GeV in e+e− annihilation and find that production is dominated by two-body reactions involving D and D∗ states where the D∗ (charged and neutral) have masses near 2.01 GeV/c2. A detailed study of D momentum spectra near Ecm = 4.028 GeV allows determination of masses and branching ratios of D and D∗ states. Lastly we find that events containing a D0 meson conserve strangeness, thus establishing upper limits on D0- D 0 mixing and on the effects of charm changing neutral currents.

Photoproduction of K+ -hyperon from hydrogen and deuterium at 11 GeV☆

Abstract Using an 11-GeV bremsstrahlung beam and the SLAC 20-GeV spectrometer, we have measured K+ missing mass spectra from hydrogen and deuterium at five angles with momentum transfer squared ranging from 0.025 to 0.46 GeV2. Steps in the spectra as a function of missing mass were found corresponding to production of Λ, Σ, Σ1385 + Λ1405 and Λ1520. The ratio Σ− and Σ0 production is not consistent with pure isotopic spin 1 2 in the t-channel for the reaction γN→K+Σ. The cross sections for γN → K+Σ1385 compared with γN→πΔ violate an SU(3) prediction.

Properties of the proposed τ charged lepton

Abstract The anomalous eμ and 2-prong μx events produced in e + e − annihilation are used to determine the properties of the proposed τ charged lepton. We find the τ mass is 1.90 ± 0.10 GeV/ c 2 ; the mass of the associated neutrino, ν τ , is less than 0.6 GeV/ c 2 with 95% confidence; V - A coupling is favored over V + A coupling for the τ − ν τ current; and the leptonic branching ratios are 0.186 ± 0.010 ± 0.028 from the eμ events and 0.175 ± 0.027 ± 0.030 from the μx events where the first error is statistical and the second is systematic.

Electronics for the BaBar central drift chamber

The central drift chamber for the BaBar detector at the SLAC B-factory is based on a hexagonal cell design with 7104 cells arranged in 40 layers and drift gas helium:isobutane (80%:20%). Performance optimization and integration requirements led to an electronics design that mounts the amplifier-discriminator and digitizing circuitry directly on the endplate. High channel density is achieved using a 4-channel custom amplifier-discriminator IC and an 8-channel custom CMOS TDC/FADC IC on a single circuit board. Data read from the front ends are multiplexed on 4 fiber optic links, and prompt trigger data are sent out continuously on 24 links. Analysis of cosmic ray data demonstrates that the electronics design meets the performance goals for the BaBar drift chamber. The final electronics were installed on the drift chamber in July, 1998. Installation of BaBar on beamline is scheduled for March, 1999.

Automatic Control Program for Spear

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A search for stable particles heavier than the proton and for q = 2/3 quarks produced in e+ e- annihilation

Abstract We have searched 1.4 × 10 6 e + e − annihilation events for particles with 1–3 GeV/ c 2 mass and charge Q = − 2 3 from the processes e + e − →q q X and e + e − → q q . Upper limits of RQ ∼ 10 −4 for each process are presented which improve the previous limits on free quark production in electromagnetic interactions by 2 orders of magnitude.

dE/dx Electronics for Mark II Experiment at SLAC

This paper describes a 100 MHz pulse digitizer for dE/dx measurements on the MARK II drift chamber at SLAC. The electronics provides the read-out of the detectors 5832 sense wires, organized in 336 wires/FASTBUS crate. The system is based on a 16-channel FASTBUS module. The basic element of the module is the TRW 6-bit Flash-ADC.

Operating Results from SPEAR

Initial operating experience with the SLAC electron-positron storage ring SPEAR is described. A luminosity of 1.2 × 1031 cm-2 sec-1 has been achieved and two-beam interaction effects are described. A single-beam coherent instability, which can be suppressed either by control of the ring chromaticity or by feedback, has been observed. Current-dependent bunch lengthening and widening have been observed, and experiments indicate that these phenomena may be associated with an increase in the energy spread of the beam. Procedures to increase the luminosity to the design value are discussed. Plans to increase the maximum beam energy of SPEAR to 4.5 GeV are described.

Measurements on Beam-Beam Interaction at SPEAR

Measurements of luminosity at SPEAR, which were performed at different operational conditions of the storage ring are shown and discussed. The parameters varied are: the current in both beams, the minimum betatron amplitude functions at the collision point, the energy and the vertical betatron frequencies. As a result of these measurements we found that the maximum achievable luminosity is much higher than predicted by the incoherent beam-beam limit using ?v = 0.025. We also found that the maximum achievable luminosity is a strong function of the betatron frequencies. After computing the largest linear tuneshifts, we found that the quarter resonance seems to be the limiting effect for beam-beam collision.