Hadronic events from the data collected with the DELPHI detector at LEP within the energy range from 89 GeV to 209 GeV are selected, their jet rates are determined and compared to predictions of four ...different event generators. One of them is the recently developed APACIC++ generator which performs a massive matrix element calculation matched to a parton shower followed by string fragmentation. The four-jet rate is used to measure alpha(s) in the next-to-leading-order approximation yielding alpha(s)(M-Z(2)) = 0.1175 +/- 0.0030. The running of alpha(s) determined by using four-jet events has been tested. The logarithmic energy slope is measured to be dalpha(s)(-1)/d log E-cm = 1.14 +/- 0.36. Since the analysis is based on four-jet final states it represents an alternative approach to previous DELPHI alpha(s) measurements using event shape distributions.
Measurements of Zγ* production are presented using data collected by the DELPHI detector at centre-of-mass energies ranging from 183 to 209 GeV, corresponding to an integrated luminosity of about 667 ...pb-1. The measurements cover a wide range of the possible final state four-fermion configurations: hadronic and leptonic (e+e-qq̄, μ+μ-qq̄, qq̄νν̄), fully leptonic (l+l-l’+l’-) and fully hadronic final states (qq̄qq̄, with a low mass qq̄ pair). Measurements of the Zγ* cross-section for the various final states have been compared with the Standard Model expectations and found to be consistent within the errors. In addition, a total cross-section measurement of the l+l-l’+l’- cross-section is reported, and found to be in agreement with the prediction of the Standard Model.
A search for the pair production of fourth generation b’-quarks was performed using data taken by the DELPHI detector at LEP-II. The analysed data were collected at centre-of-mass energies ranging ...from 196 to 209 GeV, corresponding to an integrated luminosity of 420 pb-1. No evidence for a signal was found. Upper limits on BR(b’→bZ) and BR(b’→cW) were obtained for b’ masses ranging from 96 to 103 GeV/c2. These limits, together with the theoretical branching ratios predicted by a sequential four generations model, were used to constrain the value of , where Vcb′, Vtb′ and Vtb are elements of the extended CKM matrix.
A novel high precision method measures the b-quark forward-backward asymmetry at the Z pole on a sample of 3,560,890 hadronic events collected with the DELPHI detector in 1992 to 2000. An enhanced ...impact parameter tag provides a high purity b sample. For event hemispheres with a reconstructed secondary vertex the charge of the corresponding quark or anti-quark is determined using a neural network which combines in an optimal way the full available charge information from the vertex charge, the jet charge and from identified leptons and hadrons. The probability of correctly identifying b-quarks and anti-quarks is measured on the data themselves comparing the rates of double hemisphere tagged like-sign and unlike-sign events. The b-quark forward-backward asymmetry is determined from the differential asymmetry, taking small corrections due to hemisphere correlations and background contributions into account. The results for different centre-of-mass energies are: A_{FB}^b (89.449 GeV) = 0.0637 \pm 0.0143(stat.) \pm 0.0017(syst.) A_{FB}^b (91.231 GeV) = 0.0958 \pm 0.0032(stat.) \pm 0.0014(syst.) A_{FB}^b (92.990 GeV) = 0.1041 \pm 0.0115(stat.) \pm 0.0024(syst.) Combining these results yields the b-quark pole asymmetry A_{FB}^{b,0} = 0.0972 \pm 0.0030(stat.) \pm 0.0014(syst.)
Lifetime and oscillations of B-s(0) mesons have been studied in events with a large transverse momentum lepton and a D-s of opposite electric charge in the same hemisphere, selected from about 3.6 ...million hadronic Z(0) decays accumulated by DELPHI between
The production of single photons has been studied in the reaction e(+)e(-) --> gamma +invisible particles at centre-of-mass energies of 183 GeV and 189 GeV. A previously published analysis of ...events with multiphoton final states accompanied by missing ene
Measurements of the Xi- and anti-Xi+ masses, mass differences, lifetimes and lifetime differences are presented. The anti-Xi+ sample used is much larger than those used previously for such ...measurements. In addition, the Xi production rates in Z -> b anti-b and Z -> q anti-q events are compared and the position xi* of the maximum of the xi distribution in Z -> q anti-q events is measured.
The partial decay width of the Z to b (b) over bar quark pairs has been measured by the DELPHI detector at LEP using data taken in the years 1992 to 1995. Decays of b-hadrons were tagged by several ...methods using tracks with large impact parameters and/or
The ratio of the CKM quark-mixing matrix elements \V-ub\/\V-cb\ has been measured using B hadron semileptonic decays. The analysis uses the reconstructed mass M-X of the secondary hadronic system ...produced in association with an identified lepton. Since B
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