Guy Wilkinson

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 mw 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.

Abstract:

From data recorded by DELPHI between 1991 and 1994, which corresponds to 3.2 million hadronic Z0 decays, a measurement of the Bd0 meson lifetime, based on the inclusive reconstruction of 3520 ± 150 semileptonic decays of the type Bd0 → D*+ X ℓ νℓ, has been performed. The result is: τ(Bd0) = 1.532 ± 0.041(stat.) ± 0.040(syst.)ps. The contribution to the systematic uncertainty which depends on external errors is ±0.015. © Springer-Verlag 1997.