Inclusive jet production (e+e−→e+e−+jet+X) is studied in collisions of quasi-real photons radiated by the LEP beams at e+e− centre-of-mass energies see from 189 to 209 GeV. Jets are reconstructed ...using the k⊥ jet algorithm. The inclusive differential cross-section is measured as a function of the jet transverse momentum, pTjet, in the range 5<pTjet<40 GeV for pseudo-rapidities, ηjet, in the range −1.5<ηjet<1.5. The results are compared to predictions of perturbative QCD in next-to-leading order in the strong coupling constant.
Hadronic events produced in e+e- collisions by the LEP collider and recorded by the OPAL detector were used to form distributions based on the number of reconstructed jets. The data were collected ...between 1995 and 2000 and correspond to energies of 91 GeV, 130-136 GeV and 161-209 GeV. The jet rates were determined using four different jet-finding algorithms (Cone, JADE, Durham and Cambridge). The differential two-jet rate and the average jet rate with the Durham and Cambridge algorithms were used to measure in the LEP energy range by fitting an expression in which calculations were matched to a NLLA prediction and fitted to the data. Combining the measurements at different centre-of-mass energies, the value of () was determined to beαS(MZ) = 0.1177 ± 0.0006 (stat.) ± 0.0012 (expt.) ± 0.0010 (had.) ± 0.0032 (theo.).
An investigation of the polar angle distribution of charged hadrons is presented using data taken by the JADE experiment at the PETRA e+e− collider at centre-of-mass energies of 35 and 44 GeV. From ...fits to the polar angle distribution the longitudinal, σL, and transverse, σT, cross-section relative to the total hadronic are determined at an average energy scale of 36.6 GeV. The results are σLσtot=0.067±0.013, σTσtot=0.933∓0.013, where total errors are given and the results are exactly anticorrelated. Using the next-to-leading order QCD prediction for the longitudinal cross-section, the value αS(36.6GeV)=0.150±0.025 of the strong coupling constant is obtained in agreement with the world average value of αS evolved to an energy scale of 36.6 GeV.
The charged particle multiplicities of two- and three-jet events from the reaction e\(^+\)e\(^-\)\(\rightarrow\) Z\(^0\rightarrow hadrons\) are measured for Z\(^0\) decays to light quark (uds) ...flavors. Using recent theoretical expressions to account for biases from event selection, results corresponding to unbiased gluon jets are extracted over a range of jet energies from about 11 to 30 GeV. We find consistency between these results and direct measurements of unbiased gluon jet multiplicity from \(\Upsilon\) and Z\(^0\) decays. The unbiased gluon jet data including the direct measurements are compared to corresponding results for quark jets. We perform fits based on analytic expressions for particle multiplicity in jets to determine the ratio \(r\equiv\mathrm{N}_{g}/\mathrm{N}_{q}\) of multiplicities between gluon and quark jets as a function of energy. We also determine the ratio of slopes, \(r^{(1)}\equiv(\mathrm{d}\mathrm{N}_{g} /\mathrm{d}y) /(\mathrm{d}\mathrm{N}_{q} /\mathrm{d}y)\), and of curvatures, \(r^{(2)}\equiv(\mathrm{d}^2\mathrm{N}_{g} /\mathrm{d}y^2) /(\mathrm{d}^2\mathrm{N}_{q} /\mathrm{d}y^2)\), where y specifies the energy scale. At 30 GeV, we find \(r=1.422\pm0.051,r^{(1)}=1.761\pm0.071\) and \(r^{(2)}=1.98\pm0.13\), where the uncertainties are the statistical and systematic terms added in quadrature. These results are in general agreement with theoretical predictions. In addition, we use the measurements of the energy dependence of \({\mathrm{N}}_{g}\) and \({\mathrm{N}}_{q}\) to determine an effective value of the ratio of QCD color factors, \(C_{\mathrm A}/C_{\mathrm F}\). Our result, \(C_{\mathrm A}/C_{\mathrm F}=2.23\pm0.14 \)(total), is consistent with the QCD value of 2.25.
Measurements of Rb, the ratio of the bb¯ cross-section to the qq¯ cross-section in e+e− collisions, are presented. The data were collected by the OPAL experiment at LEP at centre-of-mass energies ...between 182 and 209 GeV. Lepton, lifetime and event-shape information is used to tag events containing b quarks with high efficiency. The data are compatible with the Standard Model expectation. The mean ratio of the eight measurements reported here to the Standard Model prediction is 1.055±0.031±0.037, where the first error is statistical and the second systematic.
The decay chain \(b \to \bar{\mathrm{B}} \rightarrow \mathrm{D}^{**0} \ell^- \bar{\nu} X , \mathrm{D}^{**0}\rightarrow \mathrm{D}^{*+}\pi^-,\mathrm{D}^{*+} \to \mathrm{D}^0\pi^+, D^0 \to ...(\mathrm{K}\pi\; \mathrm{or} \;\mathrm{K}3\pi)\) is identified in a sample of 3.9 million hadronic Z decays collected with the OPAL detector at LEP. The branching ratio BR \((b \to \bar{B}) \times \mathrm{BR}(\bar{B} \to \mathrm{D}^0_1 \ell^-\bar{\nu} X) \times \mathrm{BR}(\mathrm{D}^0_1 \to \mathrm{D}^{*+}\pi^-)\) is measured to be \((2.64 \pm 0.79 (\mathrm{stat}) \pm 0.39 (\mathrm{syst})) \times 10^{-3}\) for the JP=1+ (D01) state. For decays into the JP=2+ (D2*0) state, an upper limit of 1.4 x 10-3 is placed on the branching ratio at the 95% confidence level.
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