Guy Wilkinson

Abstract:

The hadronic fragmentation functions of the various quark flavours and of gluons are measured in a study of the inclusive hadron production from Z⁰ decays with the DELPHI detector and are compared with the fragmentation functions measured elsewhere at energies between 14 GeV and 91 GeV. A large scaling violation is observed, which is used to extract the strong coupling constant from a fit using a numerical integration of the second order DGLAP evolution equations. The result is αs(Mz) = 0.1241^+0.006-0.007(exp) ±0.009(theory) where the first error represents the experimental uncertainty and the second error is due to the factorization and renormalization scale dependence. © 1997 Elsevier Science B.V.

Abstract:

In a sample of 3.02 million hadronic Z⁰ decays collected by the DELPHI detector, 270 J/ψ → l⁺l^- candidates have been selected. A search for fully reconstructed B^±c mesons has yielded one B^±c → J/ψ π^± candidate, no B^±c → J/ψ l^± Vl candidates, and one B^±c → J/ ψ π⁺ π^- π^± candidate, consistent with expected background in each channel. The following 90% confidence level upper limits are determined: Br(Z⁰ → B^±c X) × Br(B^±c → J/ψ π^±) < (1.05 to 0.84) × 10^-4 and Br(Z⁰ → B^±c X) × Br(B^±c → J/ψ l^± Vl) < (5.8 to 5.0) × 10^-5, where the ranges quoted correspond to the range of predicted B^±c lifetimes from 0.4 to 1.4 ps, and Br(Z⁰ → B^±c X) × Br(B^±c → J/ψ π⁺ π^- π^±) < 1.75 × 10^-4, constant over the range of predicted B^±c lifetimes. © 1997 Elsevier Science B.V.

Abstract:

In 1996 LEP ran at a centre-of-mass energy of 161 GeV, just above the threshold of W-pair production. DELPHI accumulated data corresponding to an integrated luminosity of 9.93 pb^-1, and observed 29 events that are considered as candidates for W-pair production. From these, a cross-section for the doubly resonant e⁺e^- → WW process of 3.67^+0.97-0.85 ± 0.19 pb has been measured. Within the Standard Model, this cross-section corresponds to a mass of the W-boson of 80.40 ± 0.44(stat.) ±0.09(syst.) ±0.03(LEP) GeV/c². Alternatively, if m^w is held fixed at its current value determined by other experiments, the observed cross-section is used to obtain limits on trilinear WWV(V ≡ γ, Z) couplings. © 1997 Elsevier Science B.V.

Abstract:

A search for stable or long-lived heavy charged particles in e⁺e^- interactions at energies of 130-136, 161 and 172 GeV has been performed using the data taken by the DELPHI experiment at LEP. The search is based on particle identification provided by the Time Projection Chamber and the Ring Imaging Cherenkov detector. Upper limits at 95% confidence level are derived on the cross-section for heavy long-lived pair-produced charge ±e and ±2/3e particles in the range of 0.4-2.3 pb for masses from 45 to 84 GeV/c². Within supersymmetric extensions of the Standard Model, long-lived charginos with masses from 45 to 84 (80) GeV/c² for high (low) sneutrino masses can be excluded at 95% confidence level. Left-handed (right-handed) long-lived or stable smuons and staus with masses between 45 and 68 (65) GeV/c² can be excluded at 95% confidence level. © 1997 Elsevier Science B.V.

Abstract:

A search with the DELPHI detector at LEP for excited leptons (e*, μ*, τ* and v*) decaying through γ, W or Z transitions is reported. The data used correspond to an integrated luminosity of 10 pb^-1 at an e⁺e^- centre-of-mass energy of 161 GeV. The search for pair produced excited leptons established the limits me* > 79.6 GeV/c², mμ* > 79.6 GeV/c², mτ* > 79.4 GeV/c² and mv* > 56.4 GeV/c² at 95% confidence level, assuming that the SU(2) and U(1) couplings of excited leptons are in the same ratio as for normal leptons and considering both left and right-handed components. Limits corresponding to other assumptions are also given. The search for single excited lepton production established upper limits on the ratio λ/mℓ* of the coupling of the excited lepton to its mass.