[en] The τ polarisation has been studied with the e⁺e^-→τ⁺τ^- data collected by the DELPHI detector at LEP in 1993, 1994 and 1995 around the Z resonance firstly through the exclusive decay channels eν anti ν, μν anti ν, πν, ρν and a₁ν and secondly with an inclusive hadronic analysis which benefits from a higher efficiency and a better systematic precision. The results have been combined with those previously published on 1990 to 1992 DELPHI data, to produce results which reflect the full LEP-1 statistics. The fit of the τ polarisation dependence on the production angle yielded the polarisation parameters A_τ=0.1359±0.0096 and A_e=0.1382±0.0116. From these results the ratio of the vector and axial-vector effective couplings anti v_τ/ anti a_τ=0.0683±0.0048 and anti v_e/ anti a_e=0.0694±0.0058 have been derived, compatible with e-τ universality. With the assumption of lepton universality, the ratio of vector to axial-vector effective couplings for leptons anti v_l/ anti a_l=0.0687±0.0037 was obtained, implying a value of the effective weak mixing angle sin²θ^lept_eff=0.23282±0.00092. (orig.)

[en] The preliminary results of two different methods for the search of colour reconnection effects (CR), used in the DELPHI experiment at LEP are presented. The methods were found to be largely uncorrelated, and a combined likelihood for values of the κ strength parameter in the SK-I model is given

[en] The average charged multiplicity and the dispersion of the charged multiplicity distribution are among the basic observables characterizing hadronic final states. A summary of the measurements made with data collected at LEP2 at centre of mass energies equal to 130, 136, 161, 172 and from the recent run at 183 GeV, is presented. Emphasis will be given to the comparison with QCD predictions and to the test of the Koba-Nielesen-Olesen scaling

[en] From the data collected by DELPHI in 1997 and 1998, respectively at 183 and 189 GeV in the centre of mass, the average multiplicities of charged particles in qq events (Z,γ* → qq-bar), from the hadronic of the W boson and in bb-bar events are presented. The differences of multiplicities in bb-bar events to the multiplicities in light quark events were also measured to be: δ_bl(183GeV) = 5.07 ± 1.28(stat.) ± 1.07(syst.) δ_bl(189GeV) = 3.97 ± 0.83(stat.) ± 0.68(syst.) and consistent with the constant value predictions from QCD

[en] The average charged multiplicity and the dispersion of the charged multiplicity distribution are among the basic observables characterizing hadronic final states. A summary of the measurements made with data collected at LEP2 at centre of mass energies equal to 130, 136, 161, 172 and from the recent run at 183 GeV, is presented. Emphasis is given to the comparison with QCD predictions and to the test of the Koba-Nielsen-Olesen scaling. (orig.)

[en] The weak mixing angle has been measured from the charge asymmetry of hadronic events with two different approaches using the DELPHI detector at LEP. Both methods are based on a momentum-weighted charge sum to determine the jet charge in both event hemispheres. In a data sample of 247300 multihadronic Z⁰ decays a charge asymmetry of < Q_F>-< Q_B>=-0.0076±0.0012(stat.)±0.0005(exp. syst.)±0.0014(frag.) and a raw forward-backward asymmetry of A_FB^raw=-0.0109±0.0020(stat.)±0.0010(exp. syst.)±0.0017(frag.) have been measured. This result corresponds to a value of sin²θ_eff=0.2345±0.0030(exp.)±0.0027(frag.), sin²θ sub(anti MS)=0.2341±0.0030(exp.)±0.0027(frag.) and to sin²θ_w=1-m_w²/m_Z²=0.2299±0.0030(exp.)±0.0027(frag.)±0.0028(theor.). The experimental error is the quadratic sum of the statistical and the experimental systematic error and the theoretical error originates from a value of m_t=130±40 GeV/c² and a range of m_H from 45 GeV/c² to 1000 GeV/c². (orig.)

[en] The search in DELPHI data for neutral Higgs bosons is described. No candidate for the Standard Model Higgs is seen in Z⁰ decays to H⁰νanti ν, H⁰μ⁺μ^- or H⁰τ⁺τ^- after selections that proved efficient for finding simulated H⁰. One remaining candidate for Z⁰→H⁰e⁺e^- is consistent with background. Together with our earlier studies, these results restrict the H⁰ mass to be above 38 GeV/c² at the 95% confidence level. No signal is found for decays of Minimal Supersymmetric Standard Model neutral Higgs bosons to τ⁺τ^-. Limits are obtained for their decays to produce four jets. (orig.)

[en] A search for charged Higgs bosons decaying into quarks is described, based on statistics of around 1.7 million hadronic Z⁰ decays detected in DELPHI. Despite the very high background from standard hadronic decays of the Z⁰, masses in the range up to 43.5 GeV/c² are excluded at the 95% confidence level. After combination with a search for leptonic decays, this mass limit is extended to cover all branching ratios. A similar analysis sets new limits on the prossible production of any pair-produced heavy scalar decaying into a pair of jets, such a neutral Higgs bosons in a two doublet scheme and diquarks. (orig.)

[en] A new measurement of α_s is obtained from the distributions in thrust, heavy jet mass, energy-energy correlation and two recently introduced jet broadening variables following a method proposed by Catani, Trentadue, Turnock and Webber. This method includes the full calculation of O(α_s²) terms and leading and next-to-leading logarithms resummed to all orders of α_s. The analysis is based on data taken with the DELPHI detector at LEP during 1991. It its found that the inclusion of the resummed leading and next-to-leading logarithms reduces the scale dependence of α_s and allows an extension of the fit range towards the infrared limit of the kinematical range. The combined value for α_s obtained at the scale μ²=M_Z² is: α_s(M_Z²)=0.123±0.006. (orig.)

[en] DELPHI results are presented on the inclusive production of two (KK-bar π)⁰ states in the mass region 1.2-1.6 GeV/c² in hadronic Z decays at LEP I. The measured masses (widths) are 1274±6 MeV/c² (29±12 MeV/c²) and 1426±6 MeV/c² (51±14 MeV/c²), respectively. A partial-wave analysis of the (KK-bar π)⁰ system shows that the first peak is consistent with the I^G(J^PC)=0⁺(1⁺⁺)/(0^-+)a₀(980)π and the second with the I^G(J^PC)=0⁺(1⁺⁺)K*(892)K-bar+c.c. assignments. The total hadronic production rates per hadronic Z decay are (0.165±0.051) and (0.056±0.012), respectively. These measurements are consistent with the two states being the f₁(1285) and f₁(1420) mesons