Electroweak parameters of the z0 resonance and the standard model

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

Study of final state photons in hadronic Z0 decay and limits on new phenomena

The differential cross section for final state radiation from primary quarks is obtained from a study of isolated energetic photons produced in the reaction e+ e- --> Z0 --> hadrons + gamma, as measured in the DELPHI detector at the CERN LEP collider. When combined with the measurement of the total hadronic width of the Z0, the observed rate determines the electroweak coupling constants of up and down type quarks, i.e., upsilon(1/3)2 + a(1/3)2 = 1.13 +/- 0.29 and upsilon(2/3)2 + a(2/3)2 = 1.65 +/- 0.43. No evidence is seen for additional photon production from anomalous decays of the Z0 or from decays of new particles. This measurement leads to upper limits on the production cross section times branching fraction of (a) the Higgs boson in the reaction e+ e- --> Z0 --> H +gamma, H --> hadrons, (b) an excited quark, q* --> q + gamma, and (c) the contribution of an anomalous decay of the Z0 into a photon and hadrons. These limits, all at the 95% confidence level, vary from 3 to 10 pb as the mass of the intermediate state (H, q* or Z*) varies from 10 GeV/c2 to 80 GeV/c2

Search for excited charged leptons in Z0 decays

Using a data sample of 115000 hadronic Z0 decays, a search was performed for the production of excited charged leptons decaying into an ordinary lepton and one photon. Pair production of excited leptons of mass below 45 GeV/c2 is excluded. From an analysis of the lepton-photon mass spectra this experiment is also able to exclude single production of these particles for masses that reach up to 85 GeV/c2, if the compositeness scale is below 1 TeV. © 1992 Springer-Verlag0SCOPUS: ar.jinfo:eu-repo/semantics/publishe