Multihadronic e+e− annihilation events at a center-of-mass energy of 29 GeV have been studied with both the original (PEP 5) Mark II and the upgraded Mark II detectors. Detector-corrected distributions from global shape analyses such as aplanarity, Q2-Q1, sphericity, thrust, minor value, oblateness, and jet masses, and inclusive charged-particle distributions including x, rapidity, p⊥, and particle flow are presented. These distributions are compared with predictions from various multihadron event models which use leading-logarithmic shower evolution or QCD matrix elements at the parton level and string or cluster fragmentation for hadronization. The new generation of parton-shower models gives, on the average, a better description of the data than the previous parton-shower models. The energy behavior of these models is compared to existing e+e− data. The predictions of the models at a center-of-mass energy of 93 GeV, roughly the expected mass of the Z0, are also presented.
Aplanarity distribution.
QX Distribution(QX=SQRT(3)*(Q3-Q2)).
The (Q2-Q1) distribution.
Inclusive momentum and energy spectra of neutral and charged D-mesons produced in e + e − annihilation at energies near 7 GeV are presented. The slope of the energy spectrum is similar to the charged pion spectrum at the same energy. The inclusive cross section σ(e + e − → D or D + anything) at 7 GeV is 4.8±1.3 nb.
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SCALING VARIABLE IS X(P=3,DEF=2*E(P=3)/SQRT(S)) > 0.54.
The production of Λ hyperons in e+e− annihilation has been measured as a function of their total momenta, transverse momenta, and the event thrust. The total production rate is 0.213±0.012±0.018 Λ or Λ¯ per hadronic event. The observation of correlations in rapidity and angles for events with two detected Λ decays supports fragmentation models with local baryon-number compensation.
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We have measured the differential cross section for p¯p and pp elastic scattering at s=53 GeV in the interval 0.5<|t|<4.0 (GeV/c)2 at the CERN intersecting storage rings using the split-field magnet detector. The shape of the differential cross section differs significantly between p¯p and pp scattering in the region 1.1<|t|<1.5 (GeV/c)2, with p¯p data showing a less pronounced dip structure than pp data.
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We have measured inclusive distributions for charged particles in hadronic decays of the Z boson. The variables chosen for study were charged-particle multiplicity, scaled momentum, and momenta transverse to the sphericity axes. The distributions have been corrected for detector effects and are compared with data from e+e− annihilation at lower energies and with the predictions of several QCD-based models. The data are in reasonable agreement with expectations.
Mean corrected charged particle multiplicity.
Corrected charged particle X distributions. Errors are statistical and systematic combined.
Corrected charged particle PTIN distributions. Errors are statistical and systematic combined.
Inclusive Ω− production in e+e− annihilation at 29 GeV has been measured with the Mark II detector. From an integrated luminosity of 207 pb−1, we determine a production rate of 0.014±0.006±0.004 Ω−, Ω¯+ per hadronic event. This is roughly 35 times the Lund-model prediction of 0.0004 Ω−, Ω¯+ per hadronic event, but comparable to the Webber-model prediction of 0.006 Ω−, Ω¯+ per hadronic event. The large rate of Ω− production, compared with production rates for other baryons, and with theoretical predictions based on diquark models, indicates that spin suppression does not hold for Ω− production.
Radiatively corrected inclusive cross section.
Extrapolation to full momentum range.
Inclusive Ξ− production in e+e− annihilation at 29 GeV has been measured with the Mark II detector. From an integrated luminosity of 207 pb−1, we determine a production rate of 0.017±0.004±0.004 Ξ−+Ξ¯+ per hadronic event. A search for Ξ*0(1530)→Ξ−π+ leads to an upper limit of N(Ξ*0)/N(Ξ−)<0.35 at a 90% confidence level.
Numerical values supplied by S. Klein.
Extrapolation over full x range using LUND Monte Carlo.
Distributions of the Bjorken scaling variables x and y, and the structure function F+(x), are presented both for neutral-current and for charged-current νμ interactions. The data were obtained by use of the Fermilab 15-ft neon bubble chamber exposed to a narrow-band νμ beam. Results are based on 151 neutral-current and 683 charged-current events. An important feature of the neutral-current analysis is the event-by-event reconstruction of the outgoing neutrino.
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DATA REQUESTED FROM C.BALTAY ON 20/9/91.
DATA REQUESTED FROM C.BALTAY ON 20/9/91.
We have studied D* production mechanisms using data from a photoproduction experiment at the Fermilab Tagged Photon Spectrometer. A large sample of charged D*’s was selected via the clean signature of the cascade decay D*→D0π+ and subsequently D0→K−π+ or D0→K−π+π0. The cross section for the process γp→(D*++anything)p at an average energy of 105 GeV was measured to be 88±32 nb. Only (11±7)% of D*’s were found to be consistent with being accompanied solely by a D¯* or a D¯; the remaining events contain additional particles. The distribution of the production angle of the D* in the photon-fragmentation-system center of mass is strongly anisotropic and consistent with the form f(θ*)=cos4θ*. We set a limit on the associated-production-process cross section σ(γp→(D¯*−+anything)Λc) x)<60 nb (90% C.L.).
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We have measured the K0+K¯ 0 inclusive cross section in e+e− annihilation at 29 GeV with the Mark II detector SLAC PEP. We find 1.27±0.03±0.15 K0+K¯ 0 per hadronic event. We have also used time-of-flight particle identification to measure the K± rate over the momentum range 300–900 MeV/c.
Extrapolated to full momentum range by Monte-Carlo.
Statistical errors only.
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