Guy Wilkinson

Abstract:

Two-particle angular correlations in jet cones have been measured in e⁺e^- annihilation into hadrons at LEP energies (√s =91 and 183 GeV) and are compared with QCD predictions using the LPHD hypothesis. Two different functions have been tested. While the differentially normalized correlation function shows substantial deviations from the predictions, a globally normalized correlation function agrees well. The size of a α^effS (and other QCD parameters) and its running with the relevant angular scale, the validity of LPHD, and problems due to non-perturbative effects are discussed critically. © 1998 Elsevier Science B.V. All rights reserved.

Abstract:

Decays of W^± bosons, produced at LEP2, have been used to measure the |Vcs| element of the Cabibbo-Kobayashi-Maskawa matrix. Values for |Vcs| were extracted both from the measured hadronic branching ratio of W^± decays and by tagging the flavour of hadronic jets produced in W^± decays. Applying the two methods to the data collected during 1996 at energies of 161 and 172 GeV, DELPHI obtains |Vcs| = 0.091^+0.15-0.14(stat) ± 0.05(syst). © 1998 Elsevier Science B.V. All rights reserved.

Abstract:

The total and the differential cross-sections for the reaction e⁺e^- → γγ(γ) have been measured with the DELPHI detector at LEP at centre-of-mass energies from 130 to 183 GeV for an integrated luminosity of 78.19 pb^-1. The results agree with the QED predictions. The lower limits (obtained including previously published results at the Z⁰ energies) on the QED cutoff parameters are Λ+ > 253 GeV and Λ-> 225 GeV and the lower bound on the mass of an excited electron with an effective coupling constant λγ = 1 is 231 GeV/c². All the limits are at the 95% confidence level. © 1998 Published by Elsevier Science B.V. All rights reserved.

Abstract:

The hadronic structure of the decay of the τ lepton to three charged particles, τ → 3πντ, is studied using data collected by the DELPHI detector at LEP between 1992 and 1995. The invariant mass of the 3π system, m3π, is fitted using the models of Kühn and Santamaria, Isgur Morningstar and Reader, and Feindt. The 3π and π⁺π^- mass spectra are compared with each model. Below m²3π = 2.3 GeV², all are in good qualitative agreement. Above m²3π = 2.3 GeV², anomalous behaviour is observed, consistent with the existence of a hitherto unseen decay mode of the τ through a radial excitation of the a1 meson. © 1998 Published by Elsevier Science B.V. All rights reserved.

Abstract:

Using D *+ mesons exclusively reconstructed in the DELPHI detector at LEP, an excess of 66 ± 14(stat.) events is observed in the D *+π+ π- final state with a mass of 2637 ± 2(stat.) ± 6(syst.) MeV/c2 and a full width smaller than 15 MeV/c2 (95% C.L.). This signal is compatible with the expected decay of a radially excited D *′ (JP = 1-) meson. © 1998 Published by Elsevier Science B.V. All rights reserved.