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An experimental study of the normalized three-jet rate of b quark events with respect to light quarks events (light=ℓ≡u,d,s) has been performed using the CAMBRIDGE and DURHAM jet algorithms. The data used were collected by the DELPHI experiment at LEP on the Z peak from 1994 to 2000. The results are found to agree with theoretical predictions treating mass corrections at next-to-leading order. Measurements of the b quark mass have also been performed for both the b pole mass: Mb and the b running mass: mb(MZ). Data are found to be better described when using the running mass. The measurement yields: \\(m_b(M_Z)=2.85\\pm0.18 (\\text{stat}) \\pm0.13 (\\text{exp}) \\pm0.19 (\\text{had}) \\pm0.12 (\\text{theo}) \\text{GeV}/c^2.\\)for the CAMBRIDGE algorithm.This result is the most precise measurement of the b mass derived from a high energy process. When compared to other b mass determinations by experiments at lower energy scales, this value agrees with the prediction of quantum chromodynamics for the energy evolution of the running mass. The mass measurement is equivalent to a test of the flavour independence of the strong coupling constant with an accuracy of 7 ‰.

Measurements are presented of R_(b), the ratio of the b bbar cross-section to the q qbar cross-section in e+e- collisions, and the forward-backward asymmetry Aᵇ_(F)B at twelve energy points in the range sqrt(s) = 130-207 GeV. These results are found to be consistent with the Standard Model expectations. The measurements are used to set limits on new physics scenarios involving contact interactions.

During 1993 and 1995 LEP was run at 3 energies near the Z\\(^0\\) peak in order to give improved measurements of the mass and width of the resonance. During 1994, LEP operated only at the Z\\(^0\\) peak. In total DELPHI accumulated data corresponding to an integrated luminosity of approximately 116 pb\\(^{-1}\\). Analyses of the hadronic cross-sections and of the cross-sections and forward-backward asymmetries in the leptonic channels used the most precise evaluations of the LEP energies. In the dimuon channel, events with a photon radiated from the initial state have been used to probe the cross-sections and asymmetries down to PETRA energies. Model independent fits to all DELPHI lineshape and asymmetry data from 1990 to 1995 have been carried out giving values of the resonance parameters:These values are significantly more precise than those previously published. The results are interpreted in terms of the Standard Model.

A measurement of the W boson mass and width has been performed by the DELPHI collaboration using the data collected during the full LEP2 programme (1996-2000). The data sample has an integrated luminosity of 660 pb⁻1 and was collected over a range of centre-of-mass energies from 161 to 209 GeV. Results are obtained by applying the method of direct reconstruction of the mass of the W from its decay products in both the W+W- -> lvqq and W+W- -> qqqq channels. The W mass result for the combined data set is M_(W) = 80.336 +/- 0.055 (Stat.) +/- 0.028 (Syst.) +/- 0.025 (FSI) +/- 0.009 (LEP) GeV/c², where FSI represents the uncertainty due to final state interaction effects in the qqqq channel, and LEP represents that arising from the knowledge of the collision energy of the accelerator. The combined value for the W width is Gamma_(W) = 2.404 +/- 0.140 (Stat.) +/- 0.077 (Syst.) +/- 0.065 (FSI) GeV/c². These results supersede all values previously published by the DELPHI collaboration. This paper is dedicated to the memory of Carlo Caso.

Measurements of Zgamma* 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- q qbar, mu+ mu- q qbar, q qbar nu nubar), fully leptonic (l+ l- l'+ l'-) and fully hadronic final states (q qbar q qbar, with a low mass q qbar pair). Measurements of the Zgamma* 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 R_(C)KM=|V_(c)b'/V_(t)b'V_(t)b|, where V_(c)b', V_(t)b' and V_(t)b are elements of the extended CKM matrix.

Double-tagged interactions of photons with virtualities Q2 between 10 GeV2 and 200 GeV2 are studied with the data collected by DELPHI at LEPII from 1998 to 2000, corresponding to an integrated luminosity of 550 pb-1. The γ*γ*→μ+μ- data agree with QED predictions. The cross-section of the reaction γ*γ*→hadrons is measured and compared to the LO and NLO BFKL calculations.

The data collected with the DELPHI detector at centre-of-mass energies between 130 and 172 GeV, during LEP operation in 1995 and 1996, have been used to determine the hadronic and leptonic cross-sections and leptonic forward–backward asymmetries. In addition, the cross-section ratios and forward–backward asymmetries for flavour-tagged samples of light (uds), c and b quarks have been measured. No significant deviations from the Standard Model expectations are found. The results are interpreted by performing S-matrix fits to these data and to the data collected previously at the energies near the \\({\\rm Z}^0\\) resonance peak (88-93 GeV). The results are also interpreted in terms of physics beyond the Standard Model: contact interactions, R-parity violating SUSY particle exchange and of possible Z\\(^{'}\\) bosons.