A. R. Clark

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.

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.

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.

Search for the decay b→Xsμ+μ−

Abstract We have searched for the flavor-changing neutral current decay b → X s μ + μ − in p p collisions at s = 1.8 TeV with the DO detector at Fermilab. We determine the 90% confidence level limit for the branching fraction to be B ( b → X s μ + μ − ) −4 . We argue that this limit is more stringent than the best published limit on this decay rate.We have searched for the flavor-changing neutral current decay b ->s mu+ mu- in p pbar collisions at sqrt(s) = 1.8 TeV with the DO detector at Fermilab. We determine the 90% confidence level limit for the branching fraction to be B(b ->X_s mu+ mu-)<3.2 x 10^{-4}. We argue that this limit is more stringent than the best published limit on this decay rate.

Study of χc2 production in photon-photon collisions☆

Abstract Two-photon production of the charmonium state χ c has been studied by the TPC/Two-Gamma experiment at the SLAC e + e − collider PEP. We observe evidence of the χ c 2 state in the channel γγ → χ c 2 , χ c 2 → γJ / ψ , J / ψ → l + l − and obtain a value of Γ γγ ( χ c 2 )=3.4±1.7±0.9 keV. This is the first observation of the two-photon production of a χ c state. Comparison is made with previous experimental results and QCD predictions for Γ γγ ( χ c 2 ).

The central tracking detectors for D

Abstract Three types of drift chambers are being constructed for the Fermilab Do experiment. The construction and readout of these chambers stress good spatial resolution, good two hit separation, and d E /d x measurement. A 106 MHz FADC system with hardware zero suppression is being constructed to read out this system.

tt̄ production cross section in pp̄ collisions at √s = 1.8 TeV

Results are presented on a measurement of the t (t) over bar pair production cross section in p (p) over bar collisions at roots=1.8 TeV from nine independent decay channels. The data were collected by the D empty set experiment during the 1992-1996 run of the Fermilab Tevatron Collider. A total of 80 candidate events is observed with an expected background of 38.8+/-3.3 events. For a top quark mass of 172.1 GeV/c(2), the measured cross section is 5.69+/-1.21(stat)+/-1.04(syst) pb.Results are presented on a measurement of the ttbar pair production cross section in ppbar collisions at sqrt{s} = 1.8 TeV from nine independent decay channels. The data were collected by the Dzero experiment during the 1992-1996 run of the Fermilab Tevatron Collider. A total of 80 candidate events are observed with an expected background of 38.8 +- 3.3 events. For a top quark mass of 172.1 GeV/c^2, the measured cross section is 5.69 +- 1.21 (stat) +- 1.04 (sys) pb.

Test results from a precision drift chamber vertex detector prototype using dimethylether

Abstract Results of beam tests of a prototype drift chamber vertex detector developed for the D-Zero experiment at the Fermilab collider are reported. The chamber design emphasizes dual goals of high accuracy position measurement and excellent two track resolution. These requirements are met by using a slow gas, dimethyl ether, in a jet chamber geometry with a double plane of field-shaping wires near the anodes. Resolution of nearby hits is facilitated by 100 MHz flash digitization of the signal pulses. The prototype tested consisted of a full-length (97 cm) model of one azimuthal sector of the innermost layer of the detector, with 8 anode wires. Position measurement accuracy of 30–80 μm for drift distances of 2–11 mm and pulse pair resolution of 0.7 mm (for 90% of all pulses) is achieved.

D0 vertex drift chamber construction and test results

A jet-cell based vertex chamber has been built for the D{O} experiment at Fermilab and operated in a test beam there. Low drift velocity and diffusion properties were achieved using CO{sub 2}(95%)-ethane(5%) at atmospheric pressure. The drift velocity is found to be consistent with (9.74+8.68( E -1.25)) {mu}m/nsec where E is the electric field strength in (kV/cm < E z 1.6 kV/cm.) An intrinsic spatial resolution of 60 {mu}m or better for drift distances greater than 2 mm is measured. The track pair efficiency is estimated to be better than 90% for separations greater than 630 {mu}m. 8 refs., 6 figs., 1 tab.

Quark fragmentation functions and long-range correlations ine+e− annihilation at 29 GeV

AbstractWe study long-range correlations between hadrons in opposite jets ine+e− annihilation events at