Determination of the e+e- → γγ(γ) cross-section at centre-of-mass energies ranging from 189 GeV to 202 GeV
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 491:1-2 (2000) 67-80
Abstract:
A test of the QED process e+e- → γγ(γ) is reported. The data analysed were collected with the DELPHI detector in 1998 and 1999 at the highest energies achieved at LEP, reaching 202 GeV in the centre-of-mass. The total integrated luminosity amounts to 375.7 pb-1. The differential and total cross-sections for the process e+e- → γγ were measured, and found to be in agreement with the QED prediction. 95% confidence level (C.L.) lower limits on the QED cut-off parameters of Λ+ > 330 GeV and λ- > 320 GeV were derived. A 95% C.L. lower bound on the mass of an excited electron of 311 GeV/c2 (for λγ = 1) was obtained, s-channel virtual graviton exchange was searched for, resulting in 95% C.L. lower limits on the string mass scale, M(S): M(S) > 713 GeV/c2 (λ = 1) and M(S) > 691 GeV/c2 (γ = -1). (C) 2000 Published by Elsevier Science B.V.Rapidity-rank structure of pp̄ pairs in hadronic Z0 decays
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 490:1-2 (2000) 61-70
Abstract:
The rapidity-rank structure of pp̄ pairs is used to analyze the mechanism of baryon production in hadronic Z0 decay. The relative occurrence of the rapidity-ordered configuration p M p̄, where M is a meson, and that of pp̄ adjacent pairs is compared. The data are found to be consistent with predictions from a mechanism producing adjacent-rank pp̄ pairs, without requiring 'string-ordered' p M p̄ configurations. An upper limit of 15% at 90% confidence is determined for the p M p̄ contribution. (C) 2000 Elsevier Science B.V.Inclusive ∑- and Λ(1520) production in hadronic Z decays
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 475:3-4 (2000) 429-447
Abstract:
Production of ∑- and Λ(1520) in hadronic Z decays has been measured using the DELPHI detector at LEP. The ∑- is directly reconstructed as a charged track in the DELPHI microvertex detector and is identified by its ∑→nπ decay leading to a kink between the ∑- and π-track. The reconstruction of the Λ(1520) resonance relies strongly on the particle identification capabilities of the barrel Ring Imaging Cherenkov detector and on the ionisation loss measurement of the TPC. Inclusive production spectra are measured for both particles. The production rates are measured to beA precise measurement of the τ polarisation at LEP-1
European Physical Journal C 14:4 (2000) 585-611
Abstract:
The τ polarisation has been studied with the e+e- → τ+τ- data collected by the DELPHI detector at LEP in 1993, 1994 and 1995 around the Z resonance firstly through the exclusive decay channels evv̄, μvvμ, πv, ρv, and a1v and secondly with an inclusive hadronic analysis which benefits from a higher efficiency and a better systematic precision. The results have been combined with those previously published on 1990 to 1992 DELPHI data, to produce results which reflect the full LEP-1 statistics. The fit of the τ polarisation dependence on the production angle yielded the polarisation parameters Aτ = 0.1359 ± 0.0096 and Ae = 0.1382 ± 0.0116. From these results the ratio of the vector and axial-vector effective couplings v̄τ/āτ = 0.0683 ± 0.0048 and v̄e/āe = 0.0694 ± 0.0058 have been derived, compatible with e-τ universality. With the assumption of lepton universality, the ratio of vector to axial-vector effective couplings for leptons v̄ι/āι = 0.0687 ± 0.0037 was obtained, implying a value of the effective weak mixing angle sin2 θlepteff= 0.23282 ± 0.00092.A study of the Lorentz structure in tau decays
European Physical Journal C 16:2 (2000) 229-252