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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.

An updated analysis using about 1.5 million events recorded at s=MZ\\sqrt{s} = M_Zs​=MZ​ with the DELPHI detector in 1994 is presented. Eighteen infrared and collinear safe event shape observables are measured as a function of the polar angle of the thrust axis. The data are compared to theoretical calculations in O(αs2){\\cal O} (\\alpha_s^2)O(αs2​) including the event orientation. A combined fit of αs\\alpha_sαs​ and of the renormalization scale xμx_{\\mu}xμ​ in O(αs2\\cal O(\\alpha_s^2O(αs2​) yields an excellent description of the high statistics data. The weighted average from 18 observables including quark mass effects and correlations is αs(MZ2)=0.1174±0.0026\\alpha_s(M_Z^2) = 0.1174 \\pm 0.0026αs​(MZ2​)=0.1174±0.0026. The final result, derived from the jet cone energy fraction, the observable with the smallest theoretical and experimental uncertainty, is αs(MZ2)=0.1180±0.0006(exp.)±0.0013(hadr.)±0.0008(scale)±0.0007(mass)\\alpha_s(M_Z^2) = 0.1180 \\pm 0.0006 (exp.) \\pm 0.0013 (hadr.) \\pm 0.0008 (scale) \\pm 0.0007 (mass)αs​(MZ2​)=0.1180±0.0006(exp.)±0.0013(hadr.)±0.0008(scale)±0.0007(mass). Further studies include an αs\\alpha_sαs​ determination using theoretical predictions in the next-to-leading log approximation (NLLA), matched NLLA and O(αs2\\cal O(\\alpha_s^2O(αs2​) predictions as well as theoretically motivated optimized scale setting methods. The influence of higher order contributions was also investigated by using the method of Pad\\'{e} approximants. Average αs\\alpha_sαs​ values derived from the different approaches are in good agreement. (arXiv)

A sample of 2.2 million hadronic Z decays, selected from the data recorded by the Delphi detector at Lep during 1994–1995 was used for an improved measurement of inclusive distributions of \\(\\pi^+, K^+\\) and p and their antiparticles in gluon and quark jets. The production spectra of the individual identified particles were found to be softer in gluon jets compared to quark jets, with a higher multiplicity in gluon jets as observed for inclusive charged particles. A significant proton enhancement in gluon jets is observed indicating that baryon production proceeds directly from colour objects. The maxima, \\(\\xi^*\\), of the \\(\\xi\\)-distributions for kaons in gluon and quark jets are observed to be different.

The fragmentation functions of quarks and gluons are measured in various three-jet topologies in Z decays from the full data set collected with the Delphi detector at the Z resonance between 1992 and 1995. The results at different values of transverse momentum-like scales are compared. A parameterization of the quark and gluon fragmentation functions at a fixed reference scale is given. The quark and gluon fragmentation functions show the predicted pattern of scaling violations. The scaling violation for quark jets as a function of a transverse momentum-like scale is in a good agreement with that observed in lower energy \\({\\rm e}^+{\\rm e}^-\\) annihilation experiments. For gluon jets it appears to be significantly stronger. The scale dependences of the gluon and quark fragmentation functions agree with the prediction of the DGLAP evolution equations from which the colour factor ratio \\(C_A/C_F\\) is measured to be:

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 transverse, longitudinal and asymmetric components of the fragmentation function are measured from the inclusive charged particles produced in collisions at LEP. As in deep inelastic scattering, these data are important for tests of QCD. The transverse and longitudinal components of the total hadronic cross section are evaluated from the measured fragmentation functions. They are found to be and respectively. The strong coupling constant is calculated from in next-to-leading order of perturbative QCD, giving Including non-perturbative power corrections leads to The measured transverse and longitudinal components of the fragmentation function are used to estimate the mean charged multiplicity, The fragmentation functions and multiplicities in and light quark events are compared. The measured transverse and longitudinal components of the fragmentation function allow the gluon fragmentation function to be evaluated.

A search for unstable heavy fermions with the DELPHI detector at LEP is reported. Sequential and non-canonical leptons, as well as excited leptons and quarks, are considered. The data analysed correspond to an integrated luminosity of about 48 pb\\(^{-1}\\) at an \\(\\rm e^+e^-\\) centre-of-mass energy of 183 GeV and about 20 pb\\(^{-1}\\) equally shared between the centre-of-mass energies of 172 GeV and 161 GeV. The search for pair-produced new leptons establishes 95% confidence level mass limits in the region between 70 GeV/\\(c^2\\) and 90 GeV/\\(c^2\\), depending on the channel. The search for singly produced excited leptons and quarks establishes upper limits on the ratio of the coupling of the excited fermion to its mass (\\(\\lambda/m_{f^*}\\)) as a function of the mass.

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:

This paper describes a measurement of the Michel parameters, \\(\\eta\\), \\(\\rho\\), \\(\\xi\\), \\(\\xi \\delta\\), and the average \\(\\nu_{\\tau}\\) helicity, \\(h_{\\nu_{\\tau}}\\), in \\(\\tau\\) lepton decays together with the first measurement of the tensor coupling in the weak charged current. The \\(\\tau^{+} \\tau^{-}\\) pairs were produced at the LEP \\(\\mathrm{e^{+} e^{-}}\\) collider at CERN from 1992 through 1995 in the DELPHI detector. Assuming lepton universality in the decays of the \\(\\tau\\) the measured values of the parameters were: \\(\\eta = -0.005 \\pm 0.036 \\pm 0.037\\), \\(\\rho = 0.775 \\pm 0.023 \\pm 0.020\\), \\(\\xi = 0.929 \\pm 0.070 \\pm 0.030\\), \\(\\xi\\delta = 0.779 \\pm 0.070 \\pm 0.028\\), \\(h_{\\nu_{\\tau}} = -0.997 \\pm 0.027 \\pm 0.011\\). The strength of the tensor coupling was measured to be \\(\\kappa^W_\\tau = -0.029 \\pm 0.036 \\pm 0.018\\). The first error is statistical and the second error is systematic in all cases. The results are consistent with the \\(V\\!-\\!A\\) structure of the weak charged current in decays of the \\(\\tau\\) lepton.

Data collected with the DELPHI detector from 1993 to 1995 combined with previous DELPHI results for data from 1991 and 1992 yield the branching fractions \\(B({\\tau \\rightarrow \\mbox{\\rm e} \\nu \\bar{\\nu}}) = (17.877 \\pm 0.109_{stat} \\pm 0.110_{sys} )\\% \\) and \\(B({\\tau \\rightarrow \\mu \\nu \\bar{\\nu}}) = (17.325 \\pm 0.095_{stat} \\pm 0.077_{sys} )\\% \\).