Search for composite and exotic fermions at LEP 2

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 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 fermio

Search for neutral heavy leptons produced in ZZ decays

Weak isosinglet Neutral Heavy Leptons (νm) have been searched for using data collected by the DELPHI detector corresponding to 3.3 × 106 hadronic Z0 decays at LEP1. Four separate searches have been performed, for short-lived νm production giving monojet or acollinear jet topologies, and for long-lived νm giving detectable secondary vertices or calorimeter clusters. No indication of the existence of these particles has been found, leading to an upper limit for the branching ratio BR(Z0 → νmν̄) of about 1.3 × 10-6 at 95% confidence level for νm masses between 3.5 and 50 GeV/c2. Outside this range the limit weakens rapidly with the νm mass. The results are also interpreted in terms of limits for the single production of excited neutrinos. © Springer-Verlag 1997

Measurement of the Mass of the Z-Boson and the Energy Calibration of Lep

Contains fulltext : 26847___.PDF (publisher's version ) (Open Access

Electroweak parameters of the z0 resonance and the standard model

Contains fulltext : 124399.pdf (publisher's version ) (Open Access

Lifetime and production rate of beauty baryons from Z decays

The production and decay of beauty baryons (b-baryons) have been studied using 1.7 x 10(6) Z hadronic decays collected by the DELPHI detector at LEP. Three different techniques were used to identify the b-baryons. The first method used pairs of a Lambda and a lepton to tag the b-baryon decay. The second method associated fully reconstructed Lambda(c) baryons with leptons. The third analysis reconstructed the b-baryon decay points by forming secondary vertices from identified protons and muons of opposite sign. Using these methods the following production rates were measured: f(b --> b-baryon) x BR(b-baryon --> Lambda l nu(l)X) = (0.30 +/- 0.06 +/- 0.04)%, f(b --> b-baryon) x BR(b-baryon --> Lambda(c)l nu(l)X) = (1.18 +/- 0.26(-0.21)(+0.31)%, f(b --> b-baryon) x BR(b-baryon --> p mu nu(mu)X) = (0.49 +/- 0.11 +/- (+0.15)(-0.11)%. The average b-baryon lifetime was determined to be: tau = 1.21(-0.18)(+.21)(stat.) +/- 0.04(exp.syst.)(-.07)(+.02)(th.syst,) ps

A measurement of B+^{+} and B0^{0} lifetimes using D‾\overline{D}l+^{+} events

A measurement of B meson lifetimes is presented using data collected from 1991 to 1993 by the DELPHI detector at the LEP collider. Samples of events with a D meson and a lepton in the same jet are selected where \overline{\mathrm{D}}^0 \ell^+ and \mathrm{D}^{*-} \ell^+ events originate mainly from the semileptonic decays of B^+ and B^0 mesons, respectively. From the reconstructed B decay length and the estimated B momentum, taking into account the dilution due to B decays into \overline{\mathrm{D}}^{**} \ell^+ \nu, the following B meson lifetimes and lifetime ratio are measured: \begin{eqnarray*} \tau(\mathrm{B}^+) &=& 1.61^{+0.16}_{-0.16} \;(\mathrm{stat}.) \pm 0.12 \;(\mathrm{syst.}) \;\mathrm{ ps} \\ \tau(\mathrm{B}^0) &=& 1.61^{+0.14}_{-0.13} \;(\mathrm{stat}.) \pm 0.08 \;(\mathrm{syst.}) \;\mathrm{ ps} \\ \tau(\mathrm{B}^+) / \tau(\mathrm{B}^0) &=& 1.00^{+0.17}_{-0.15} \;(\mathrm{stat.}) \pm 0.10 \;(\mathrm{syst.}) \end{eqnarray*} and an average lifetime of B^+ and B^0 mesons is obtained: \begin{eqnarray*} \tau(\mathrm{B}) = 1.61^{+0.08}_{-0.07} \;\mathrm{(stat.)} \pm 0.05 \;\mathrm{(syst.) \;ps} \end{eqnarray*