LHCb

Abstract:

A global event shape analysis of the multihadronic final states observed in neutral current deep inelastic scattering events with a large rapidity gap with respect to the proton direction is presented. The analysis is performed in the range 5 ≤ Q² ≤ 185 GeV² and 160 ≤ W ≤ 250 GeV, where Q² is the virtuality of the photon and W is the virtual-photon proton centre of mass energy. Particular emphasis is placed on the dependence of the shape variables, measured in the γ * -pomeron rest frame, on the mass of the hadronic final state, MX. With increasing MX the multihadronic final state becomes more collimated and planar. The experimental results are compared with several models which attempt to describe diffractive events. The broadening effects exhibited by the data require in these models a significant gluon component of the pomeron. © 1998 Elsevier Science B.V.

Abstract:

This paper presents results on charged Higgs boson production, based on LEP data collected at √s = 172 GeV, that complement the previous DELPHI results obtained at centre of mass energies up to 161 GeV. The charged Higgs bosons are assumed to be pair produced and to decay either into a quark pair or into τVτ. The three different possible final states are included in the analysis. Data from ring imaging Cherenkov and microvertex detectors are used to identify the quarks as a cs pair. The number of candidates found is compatible with the background expected from standard processes. Combining the results of the present analysis with those of the previous analysis at lower energies, a new lower mass limit for the charged Higgs boson is set at 54.5 GeV/c². © 1998 Elsevier Science B.V.

Abstract:

The value of the b quark mass at the M2 scale defined in the MS renormalization scheme, mb(MZ), was determined using 2.8 million hadronic Z decays collected during 1992-1994 by the DELPHI detector to be mb(MZ) = 2.67 ± 0.25 (stat.) ± 0.34 (frag.) ± 0.27 (theo.) GeV/c². The analysis considers NLO corrections to the three-jet production rate including mass effects, and the result obtained agrees with the QCD prediction of having a running b quark mass at an energy scale equal to MZ. This is the first time that such a measurement is performed far above the bb̄ production threshold. The study also verifies the flavour independence of the strong coupling constant for b and light quarks within 1% accuracy. © 1998 Elsevier Science B.V.

Abstract:

The data collected by DELPHI in 1996 have been used to measure the average charged particle multiplicities and dispersions in qq̄ events at centre-of-mass energies of √s = 161 GeV and √s = 172 GeV, and the average charge multiplicity in WW events at √s = 172 GeV. The multiplicities in qq̄ events are consistent with the evolution predicted by QCD. The dispersions in the multiplicity distributions are consistent with Koba-Nielsen-Olesen (KNO) scaling. The average multiplicity of charged particles in hadronic W decays has been measured for the first time; its value, 19.23 ± 0.74(stat + syst), is consistent with that expected for an e⁺e^- interaction at a centre-of-mass energy equal to the W mass. The charged particle multiplicity in W decays shows no evidence of effects of colour reconnection between partons from different W's at the present level of statistics. © 1998 Elsevier Science B.V.

Abstract:

Charged particles (h±) and K0 mesons have been studied in photoproduced events containing at least one jet of ET > 8 GeV n a pseudorapidity interval (-0.5, 0.5) in the ZEUS laboratory frame. Distributions are presented in terms of transverse momentum, pseudorapidity and distance of the particle from the axis of a jet. The properties of h± within the jet are described well using the standard settings of PYTHIA, but the use of the multiparton interaction option improves the description outside the jets.