The reaction e+ e- ---> gamma gamma (gamma) at Z0 energies

The total and differential cross-sections for the reaction e+e- → γγ(γ) are measured at centre of mass energies around 91 GeV using an integrated luminosity of 4.7 pb-1. The aggreement with QED prediction is good. Consequently there is no evidence for non-standard channels which would have the same experimental signature. The lower limits on the QED cuttoff parameters are Λ+ > 113 GeV and Λ- > 95 GeV. An upper limit on the effective coupling between a possible excited electron and the gamma is derived. At 95% confidence level the branching ratios for Z0 decay into π0γ, ηψ and γγγ are below 1.5 × 10-4, 2.8 × 10-4 and 1.4 × 10-4 respectively.0info:eu-repo/semantics/publishe

A measurement of B+ and B-0 lifetimes using (D)over-bar-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 ($) over bar D(0)l(+) and D*(-)l(+) events originate mainly from the semileptonic decays of B+ and B-0 mesons, respectively. From the reconstructed B decay length and the estimated B momentum, taking into account the dilution due to B decays into ($) over bar D**l(+)v, the following B meson lifetimes and lifetime ratio are measured: tau(B+) = 1.61(-0.16)(+0.16) (stat.) +/- 0.12 (syst.) ps tau(B-0) = 1.61(-0.13)(+0.14) (stat.) +/- 0.08 (syst.) ps tau (B+)/tau(B-0) = 1.00(-0.15)(+0.17) (stat.) +/- 0.10 (syst.) and an average lifetime of B+ and B-0 mesons is obtained: tau(B) = 1.61(-0.07)(+0.08) (stat.) +/- 0.05 (syst.) p

MEASUREMENT OF THE AVERAGE LIFETIME OF B-HADRONS

The average lifetime of B hadrons produced in hadronic Z0 decays has been measured with the DELPHI detector at LEP. The measurement is based on the analysis of the impact parameter distribution of high p(t) muons and hadrons. The resulting mean B lifetimes are tau(B) = (1.30 +/- 0.10 +/- 0.08) ps and tau(B) = (1.27 +/- 0.04 +/- 0.12) ps respectively, giving a combined value of tau(B) = (1.28 +/- 0.10) ps. The hadronic sample was also used to measure the partial Z0 width GAMMA(bbBAR)/GAMMA(h) and gave a value of 0.222(-0.031)+0.033 +/- 0.017

STUDY OF ORIENTATION OF 3-JET EVENTS IN Z(0) HADRONIC DECAYS USING THE DELPHI DETECTOR

The study of the orientation of three-jet events from e+ e- –> Z0 –> multi-hadrons is presented, in particular the polar angle distributions of the thrust axis and of the normal to the three-jet plane, and the azimuthal correlations between the hadron plane and the one defined by the beam and thrust axes. The data are compared with results at lower energy and with QCD predictions. Good agreement with QCD predictions is observed. The scalar gluon theory is excluded by the data

Measurement of the transverse spin correlation in Z→τ+τ−Z \to \tau^+\tau^- decays

The measurement of the correlation between the transverse spin components of $\tau^+\tau^-$ pairs collected during 1992 to 1994 with the DELPHI detector at LEP1 is presented. A value \begin{center} $C_{TT}$~=~0.87~$\pm$~0.20~(stat.)~$^{+~0.10}_{-~0.12}$~(syst.) \end{center} was obtained for the correlation parameter, in agreement with the Standard Model expectation

First measurement of the strange quark asymmetry at the Z(0) peak

A measurement of the strange quark forward-backward asymmetry at the Z(0) peak was performed using 718,000 multihadronic Z(0) decays collected by the DELPHI detector at LEP in 1992. The s-quark was tagged by the presence of high momentum charged kaons identified by the Ring Imaging Cherenkov detector and by Lambda(0)'s decaying into p pi(-). The s-quark purity obtained was estimated for the two hadrons to be 43%. The average s-quark asymmetry was found to be 0.131 +/- 0.035 (stat.) +/- 0.013 (syst.). The forward-backward asymmetry was measured for unresolved d- and s-quarks, tagged by the detection of a high energy neutron or neutral kaon in the Hadron Calorimeter. The combined d- and s-quark purity was 69% and their asymmetry was found to be 0.112 +/- 0.031 (stat.) +/- 0.054 (syst.)