R. Tschirhart

Production cross section and electroweak asymmetry of D* and D mesons produced in e+e- annihilations at 29 GeV

Abstract The production of D * and D mesons has been studied in e + e − annihilations at √s = 29GeV. The data, corresponding to an integrated luminosity of 300 pb −1 , were obtained using the HRS detector at PEP. The cross section is measured to be R (D 0 + D + ) = 2.40±0.35 and we determine the electroweak asymmetry to be −9.9 ± 2.7%, which corresponds to an axial vector coupling constant product g e g c = 0.26 ± 0.07.

Evidence for the decay τ+→π+ηντ

Abstract The inclusive production of η mesons in tau lepton decay has been studied using the High Resolution Spectrometer at the PEP e + e - facility. The data sample corresponds to an integrated luminosity of 300 pb −1 and the storage ring was operated at GeV. The η production appeaars to be only compatible with the decay τ + →π + η ν , which violates isospin and G -parity conservation. The branching ratio of 5.1±1.5% explains much of the current discrepancy between the one-prong topological branching ratio and the sum of the individual one-prong modes.

Measurement of the D0→K−π+ branching fraction

Abstract The D 0 →K − π + branching fraction has been measured by tagging a sample of D ∗+ → D 0 π + decays, independent of the D 0 decay mode. The D ∗ mesons were obtained in e + e − annihilations at √ s =29 GeV using data obtained with the HRS detector at PEP. The result iss Br(D 0 →K − π + ) = 4.5±0.8±0.5%.

THE PERFORMANCE OF 'VIRTUAL PHASE' CCDs AS DETECTORS OF MINIMUM IONIZING PARTICLES

Abstract The Texas Instruments “Virtual Phase” CCD has been the basis of an ambitious design for a precision vertex detector to be used at the Stanford Linear Collider. The performance of this chip shows promise for future use in electron linear colliders. Experimental results are reported in addition to description of the electronic readout and preliminary mechanical design.

Charged K∗ production in e+e− annihilations at 29 GeV

Abstract We report a measurement of the charged K ∗ (892) production in e + e − annihilations at 29 GeV center-of-mass energy. The 300 pb −1 data sample used for this analysis is obtained with the High Resolution Spectrometer at the SLAC storage ring PEP. The total mean multiplicity is measured to be 〈n K ∗± (892) 〉=0.62±0.045±0.04 per hadronic event. Evidence is also given for the production of a charged K 2 ∗ (1430) tensor meson.

Measurement of the spin density matrix of D∗ mesons produced in e+e− annihilations

Abstract Vector mesons produced in the reaction e+e−→V+X at √s=29 GeV were isolated by observing D∗ mesons through the D ∗+ → D 0 π + decay. The D0 decay modes used are D0→K3π, Kπ, Kπ, and Kπ(π0). The data, which correspond to an integrated luminosity of 300 pb−1, were collected by the High Resolution Spectrometer at PEP. Spin density matrix elements for the D∗ meson are measured as a function of the energy sharing variable ZD∗. There is no evidence for alignment of D∗ mesons produced in e+e− annihilation at our energy.

Measurement of upper limits for the decay widths of D∗+ and D∗0

Abstract Upper limits for the decay widths of the D ∗+ and D ∗0 mesons have been measured using data from e + e − annihilations at √ s =29 GeV obtained with the High Resolution Spectrometer at PEP. We find Γ D ∗+ MeV /c 2 at 90% CL from an analysis of the mass difference distribution for the decay mode D ∗+ → D 0 π + . The D ∗+ − D 0 mass difference is also measured to be ((45.40±0.05±0.10) MeV/ c 2 . We determine Γ D ∗0 MeV /c 2 at 90% CL for a D ∗0 mass of 2007.2 MeV /c 2 , from a search for the decay mode D ∗0 → D + π − which could occur if the width were sufficiently large.

Production of η mesons in e+e− annihilations at √s=29 GeV

Abstract Data from e + e − annihilations at 29 GeV have been used to measure the production cross section and fragmentation function of η mesons. The signal is observed in the η → γγ decay channel. The fragmentation for p η >1.5 GeV/ c agrees well with the prediction of the Lund model, whereas the prediction of the Webber model lies above the data. The mean multiplicity is measured to be 〈 n η 〉=0.58±0.10 η mesons per hadronic event, of which 0.51 represents the direct production of η and η ′ mesons in the fragmentation chain.

Charged particle multiplicity distributions in e+e- annihilation at 29 GeV: a comparison with hadronic data

The charged particle multiplicity distributions for two-jet events ine+e− annihilation at 29 GeV have been measured using the High Resolution Spectrometer at PEP. A Poisson distribution describes the data for both the complete event and for the single jets. In addition, no correlation is observed between the multiplicities in the two jets of an event. For fixed values of the prong number of the complete event, the multiplicity sharing between the two jets is in good agreement with a binomial distribution. The rapidity gap distribution is exponential with a slope equal to the mean rapidity density. These observations, which are consistent with a picture of independent emission of single particles, are contrasted to the results from soft hadronic collisions and conclusions are drawn about the nature of clusters.

Inclusive η production in τ decays

Abstract We have searched for inclusive η production in τ decays using a data sample of 2553 events of e + e - →τ + τ - in the one-three topology. The data were obtained using the High Resolution Spectrometer at √ s =29 GeV. A 90% confidence level upper limit on the process τ ± →π ± ηX of 2.1% is found. Using τ decays to five charged particles limits of 0.5% on τ ± →π ± ηηX and 0.3% on τ ± →π ± π + π - ηX are also obtained.