Inclusive distributions of charged particles in hadronic W decays are experimentally investigated using the statistics collected by the DELPHI experiment at LEP during 1997, 1998 and 1999, at centre-of-mass energies from 183 to around 200 GeV. The possible effects of interconnection between the hadronic decays of two Ws are not observed. Measurements of the average multiplicity for charged and identified particles in q qbar and WW events at centre-of-mass energies from 130 to 200 GeV and in W decays are presented. The results on the average multiplicity of identified particles and on the position xi^* of the maximum of the xi_p = -log(2p/sqrt(s)) distribution are compared with predictions of JETSET and MLLA calculations.
Corrected multiplicites and dispersions of charged particles produced in hadronic decays from QQBAR events. The 200 GeV results are a weighted average fromthe 192, 196 and 200 GeV data.
Average multiplicities of identified hadrons produced in hadronic decays from QQBAR events.
Corrected multiplicites and dispersions of charged particles produced in fully hadronic W decays from two W 4Q and 2Q events.
The total hadronic cross section in e + e − annihilation has been measured at s = 57.77 GeV using 290 pb −1 data sample collected with the VENUS detector at KEK TRISTAN. The cross section obtained is 140.3 ±1.8 pb for s ′/ s ≥0.5, where s ′ is the square of the invariant mass of the final state hadrons. The present result together with the recent results from the LEP collaborations is used to determine the hadronic γ − Z 0 interference parameter, j tot had , to be 0.196±0.083. The result is in good agreement with the Standard Model prediction of 0.220.
The statistical and systematic errors are added in quadrature.
No description provided.
The complete charge distribution of products from Au nuclei fragmenting in nuclear emulsion at 10.7A GeV has been measured. Multiplicities of produced particles and particles associated with the targe
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The reaction e+e−→μ+μ− has been measured at s=57.77GeV, based on 289.6±2.6 pb−1 data collected with the VENUS detector at TRISTAN. The production cross section is measured in bins of the production angle within an angular acceptance of |cosθ|<~0.75, according to a model-independent definition. The result is consistent with the prediction of the standard electroweak theory. Although a trend in measurements at lower energies that the total cross section tends to be smaller than the prediction remains, the discrepancy is not significant. The model-independent result is converted to the differential cross section in the effective-Born scheme by unfolding photon-radiation effects. This result can be extrapolated to quantities for the full solid angle as σtotEB=30.05±0.59 pb and AFBEB=−0.350±0.017, by imposing an ordinary assumption on the production-angle dependence. The converted results are used to set constraints on extensions of the standard theory. S-matrix parametrization, and possible contributions from contact interactions and heavy neutral-scalar exchanges are examined.
Primary model-independant results.
Differential cross section in the effective-Born scheme.
Total cross section and forward backward asymmetry results in the effective-Born scheme.
The cross section of the γγ → p p reaction was measured at two-photon center-of-mass energy ( W γγ ) between 2.2 and 3.3 GeV, using the two-photon process at an e + e − collider, TRISTAN. The W γγ dependence of the cross section integrated over a c.m. angular region of | cos θ ∗ | < 0.6 is in good agreement with the previous measurements and the theoreticalv prediction based on diquark model in the high W γγ region.
Numerical values supplied by Hirhoshi Hamasaki.
Angular distributions.
The polarization of tau leptons in the reaction e+ e- --> tau+ tau- has been measured using a e+e- collider, TRISTAN, at the center-of-mass energy of 58 GeV. From the kinematical distributions of daughter particles in tau --> e nu nu-bar, mu nu nu-bar, rho nu or pi(K) nu decays, the average polarization of tau- and its forward-backward asymmetry have been evaluated to be 0.012 +- 0.058 and 0.029 +- 0.057, respectively.
Charged-conjugated states are included. The polarization is measured from final charged-particle energy spectrum. The last value is the combination of the results for all decay modes. The systematic error is not given.
Charged-conjugated states are included. The forward-backward asymmetry of the polarization is defined as (SIG(F)*POL-SIG(B)*POL)/(SIG(F)*POL+SIG(B)*POL). The last value is the combination of the results for all decay modes. The systematic error is not given.
Using the VENUS detector at TRISTAN we have investigated the charm-quark production by detecting D*+ - mesons in the two-photon process of e+et - collisions. The study has confirmed that the charm-quark production rate is larger than that predicted from direct cc̅ production alone. The distribution of the transverse momentum of the D*+ t- mesons and the forward energy flow associated with the D*+ - production suggest that the main part of the observed excess comes from the contribution of a resolved photon process.
D* production cross section in the given kinematic ranges under the anti-tagging condition |cos(theta(e+-))|>0.990.
Bhabha scattering at a center-of-mass energy of 57.77 GeV has been measured using the VENUS detector at KEK TRISTAN. The precision is better than 1% in scattering angle regions of |cosθ|⩽0.743 and 0.822⩽cosθ⩽0.968. A model-independent scattering-angle distribution is extracted from the measurement. The distribution is in good agreement with the prediction of the standard electroweak theory. The sensitivity to underlying theories is examined, after unfolding the photon-radiation effect. The q2 dependence of the photon vacuum polarization, frequently interpreted as a running of the QED fine-structure constant, is directly observed with a significance of three standard deviations. The Z0 exchange effect is clearly seen when the distribution is compared with the prediction from QED (photon exchanges only). The agreement with the standard theory leads us to constraints on extensions of the standard theory. In all quantitative discussions, correlations in the systematic error between angular bins are taken into account by employing an error matrix technique.
Cross section is integrated over the cos(theta ) bin.
An analysis of theA-dependence of the target-diffractive cross-section is presented. Data on thet-dependence of the cross section are fitted in the usual exponential form. The mean multiplicity of negative particles produced diffractively is found not to be sensitive to the nuclear mass. TheA-dependence of the emitted proton multiplicity and the angular distributions of the produced charged particles suggest re-scattering of the emitted particles on other nucleons of the nucleus. All these facts are compared with results obtained by Monte-Carlo simulation according to a two-component Dual Parton Model.
For target-diffractive cross-section.
For target-diffractive cross-section.
Multiplicities for the diffractive system.
Cross-sections are obtained for coherent interactions of π+ and K+-mesons with Al and Au nuclei at 250 GeV/c, leading to three, five and seven charged mesons. The total coherent cross-section is (4.3 ± 0.5)% of the inelastic cross-section for each of the four meson-nucleus interactions. In 85% of the coherent events, the charged meson production is accompanied by neutral mesons. Effective mass distributions are presented for coherently produced particles, including charged mesons and photons, carrying total measured energy of more than 85% of the initial energy. Charged particle and γ spectra are analysed. No charge asymmetry is observed within the coherently produced cluster.
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