The charged particle multiplicity in hadronic three-jet events from Z decays is investigated. The topology dependence of the event multiplicity is found to be well described by a modified leading ...logarithmic prediction. A parameter fit of the prediction to the data yields a measurement of the colour factor ratio CA/CF with the result in agreement with the SU(3) expectation of QCD. The quark-related contribution to the event multiplicity is subtracted from the three-jet event multiplicity resulting in a measurement of the multiplicity of two-gluon colour-singlet states over a wide energy range. The ratios \(r = N_{gg}(s)/N_{q\bar q}(s)\) of the gluon and quark multiplicities and \(r^{(1)} = N_{gg}'(s)/N_{q\bar q}'(s)\) of their derivatives are compared with perturbative calculations. While a good agreement between calculations and data is observed for r(1), larger deviations are found for r indicating that non-perturbative effects are more important for r than for r(1).
Low-energy particle production perpendicular to the event plane in three-jet events produced in Z decays in e+e− annihilation is measured and compared to that perpendicular to the event axis in ...two-jet events. The topology dependence of the hadron production ratio is found to agree with a leading-order QCD prediction. This agreement and especially the need for the presence of a destructive interference term gives evidence for the coherent nature of gluon radiation. Hadron production in three-jet events is found to be directly proportional to a single topological scale function of the inter-jet angles. The slope of the dependence of the multiplicity with respect to the topological scale was measured to be 2.211±0.014(stat.)±0.053(syst.) in good agreement with the expectation given by the colour-factor ratio CA/CF=9/4. This result strongly supports the assumption of local parton–hadron duality, LPHD, at low hadron momentum.
A precise measurement of the tau lifetime Abdallah, J.; Abreu, P.; Adam, W. ...
The European physical journal. C, Particles and fields,
08/2004, Letnik:
36, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The tau lepton lifetime has been measured with the \({\rm e}^ + {\rm e}^- \rightarrow {\rm\tau}^ + {\rm\tau}^-\) events collected by the DELPHI detector at LEP in the years 1991-1995. Three different ...methods have been exploited, using both one-prong and three-prong \(\tau\) decay channels. Two measurements have been made using events in which both taus decay to a single charged particle. Combining these measurements gave \(\tau_\tau \mbox{(1 prong)} = 291.8\pm 2.3_{\mathrm{stat}} \pm 1.5_{\mathrm{sys}} \mathrm{fs}\). A third measurement using taus which decayed to three charged particles yielded \(\tau_\tau \mbox{(3 prong)} = 288.6\pm 2.4_{\mathrm{stat}} \pm 1.3_{\mathrm{sys}} \mathrm{fs}. \) These were combined with previous DELPHI results to measure the tau lifetime, using the full LEP1 data sample, to be \(\tau_\tau = 290.9\pm 1.4_{\mathrm{stat}} \pm 1.0_{\mathrm{sys}} \mathrm{fs}\).
Physics at BES-III Asner, D M; Barnes, T; Bian, J M ...
arXiv.org,
09/2008
Paper, Journal Article
Odprti dostop
This physics book provides detailed discussions on important topics in \(\tau\)-charm physics that will be explored during the next few years at \bes3 . Both theoretical and experimental issues are ...covered, including extensive reviews of recent theoretical developments and experimental techniques. Among the subjects covered are: innovations in Partial Wave Analysis (PWA), theoretical and experimental techniques for Dalitz-plot analyses, analysis tools to extract absolute branching fractions and measurements of decay constants, form factors, and CP-violation and \DzDzb-oscillation parameters. Programs of QCD studies and near-threshold tau-lepton physics measurements are also discussed.
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