Guy Wilkinson

Abstract:

A sample of 2.2 million hadronic Z decays, selected from the data recorded by the DELPHI detector at LEP during 1994-1995 was used for an improved measurement of inclusive distributions of π+ K+ and p and their antiparticles in gluon and quark jets. The production spectra of the individual identified particles were found to be softer in gluon jets compared to quark jets, with a higher multiplicity in gluon jets as observed for inclusive charged particles. A significant proton enhancement in gluon jets is observed indicating that baryon production proceeds directly from colour objects. The maxima, £*, of the ξ -distributions for kaons in gluon and quark jets are observed to be different.

Abstract:

Lifetime and oscillations of B0s mesons have been studied in events with a large transverse momentum lepton and a Ds of opposite electric charge in the same hemisphere, selected from about, 3.6 million hadronic Z0 decays accumulated by DELPHI between 1992 and 1995. The B0s lifetime and the fractional width difference between the two physical B0s states have been found to be: τB0s = (1.42+0.14-0.13(stat.) ± 0.03(syst.)) ps ΔΓB0s/ΓB0s < 0.46 at the 95% C.L. In the latter result it has been assumed that τB0s = τB0d. Using the same sample, a limit on the mass difference between the physical B0s states has been set: ΔmB0s > 7.4 ps-1 at the 95% C.L. with a corresponding sensitivity equal to 8.1 ps-1.

Abstract:

The fragmentation functions of quarks and gluons are measured in various three-jet topologies in Z decays from the full data set collected with the DELPHI detector at the Z resonance between 1992 and 995. The results at different values of transverse momentum-like scales are compared. A parameterization of the quark and gluon fragmentation functions at a fixed reference scale is given. The quark and gluon fragmentation functions show the predicted pattern of scaling violations. The scaling violation for quark jets as a function of a transverse momentum-like scale is in a good agreement with that observed in lower energy e+e- annihilation experiments. For gluon jets it appears to be significantly stronger. The scale dependences of the gluon and quark fragmentation functions agree with the prediction of the DGLAP evolution equations from which the colour factor ratio CA/CF is measured to be: CA/CF = 2.26 ± 0.09stat. ± 0.06sys. ± 0.12clus.,scale..

Abstract:

A precise measurement of the strange quark forward-backward asymmetry used 3.2M multihadronic events around the Z° peak collected by the DELPHI experiment from 1992 to 1995. The ring imaging Cherenkov detectors in the barrel and end-cap regions identify high energy charged kaons which tag the s quark. The s quark asymmetry was measured at different centre-of-mass energies; m particular at the Z° pole A°ss̄ = 0.1008 ± 0.0113 (stat.) ± 0.0040 (syst.), (1) taking the expected d and u quark asymmetries from the Standard Model. The quark flavour fractions are assumed from the Standard Model and the fragmentation process is modelled by JETSET. From the s quark pole asymmetry the electroweak mixing angle was determined: sin2 θlepteff = 0.2321 ± 0.0029. (2) The parity violating coupling of the s quark to the Z was determined to be: As = 0.909 ± 0.102 (stat.) ± 0.036(syst.). (3).

Abstract:

The partial decay width Rc of the Z into cc̄ quark pair and the number of charm quarks nc per b decay are measured with the DELPHI detector at LEP 1. Particle identification provides clear D0, D+, D+s and Λ+c signatures. The charm hadron production rate is measured in each channel by a fit to the scaled energy, impact parameter information and the invariant mass spectrum. Two measurements of Rc are presented, from the D*+ production rate and from the overall charm counting, including strange charm baryon production, in cc̄ events. The multiplicity nc, which includes hidden cc̄ and strange charm baryon production, is inferred from the charm counting in bb̄ events. The final results are Rc = 0.1665 ± 0.0095 and nc-= 1.166 ± 0.086.