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A precise measurement of the strange quark forward-backward asymmetry used 3.2M multihadronic events around the Z\\(^0\\) peak collected by the DELPHI experiment from 1992 to 1995. The ring imaging Cherenkov detectors in the barrel and end-cap regions identify high energy charged kaons which tag the s quark. The s quark asymmetry was measured at different centre-of-mass energies; in particular at the Z\\(^0\\) poletaking the expected d and u quark asymmetries from the Standard Model. The quark flavour fractions are assumed from the Standard Model and the fragmentation process is modelled by JETSET. From the s quark pole asymmetry the electroweak mixing angle was determined:The parity violating coupling of the s quark to the Z was determined to be:

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 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.

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.

The production of single photons has been studiedin 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 multi-photonfinal states accompanied by missing energy has been updated with 189 GeV data.The data were collected with the DELPHI detector and correspondto integrated luminosities of about 51 pb⁻1and 158 pb⁻1at thetwo energies.The number of light neutrino families is measured to be2.860.13(stat)0.14(syst). The absence ofan excess of events beyond that expected from Standard Modelprocesses is used to set limits on new physicsas described by supersymmetric and composite models.A limit on the gravitational scale is also determined.

Double-tagged interactions of photons with virtualities Q² between 10GeV² and 200GeV² are studied with the data collected by DELPHI at LEP2 from 1998 to 2000, corresponding to an integrated luminosity of 550pb⁻1. The gamma*gamma* -> mu+mu- data agree with QED predictions. The cross-section of the reaction gamma*gamma* -> hadrons is measured and compared to the LO and NLO BFKL calculations.

A search for excited lepton production in e+e- collisions was performed using the data collected by the DELPHI detector at LEP at centre-of-mass energies ranging from 189 GeV to 209 GeV, corresponding to an integrated luminosity of approximately 600 pb⁻1. No evidence for excited lepton production was found. In searches for pair-produced excited leptons, lower mass limits were established in the range 94 - 103 GeV/c², depending on the channel and model assumptions. In searches for singly-produced excited leptons, upper limits on the parameter f/Lambda were established as a function of the mass.

An experimental study of the normalized three-jet rate of b quark events with respect to light quark 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: M_(b) and the b running mass: m_(b)(M_(Z)). Data are found to be better described when using the running mass. The measurement yields: m_(b)(M_(Z)) = 2.95 +- 0.18(stat) +- 0.13(exp) +- 0.19(had) +- 0.12(theo) GeV/c2 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 determination 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 independance of the strong coupling constant with an accuracy of 7 per mille