LHCb

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.

Abstract:

Dijet cross sections are presented using photoproduction data obtained with the ZEUS detector during 1994. These measurements represent an extension of previous results, as the higher statistics allow cross sections to be measured at higher jet transverse energy (E ). Jets are identified in the hadronic final state using three different algorithms, and the cross sections compared to complete next-to-leading order QCD calculations. Agreement with these calculations is seen for the pseudorapidity dependence of the direct photon events with E > 6 GeV and of the resolved photon events with E > 11 GeV. Calculated cross sections for resolved photon processes with 6 GeV < E < 11 GeV lie below the data. T T T T jet jet jet jet