Search for scalar quarks in Z0 decays

A search has been made for pairs of scalar quarks (squarks) produced in e+e- annihilations at LEP (√s≃MZ0), and decaying into a standard quark and a neutral, non-interacting, stable, massive particle (the lightest supersymmetric particle, LSP). The search has been conducted for differences in the mass of the squark and LSP of 2 GeV/c2 and above. Up squarks with masses below 42 GeV/c2 and down squarks below 43 GeV/c2 were excluded. Six squark flavours degenerate in mass were excluded below 45 GeV/c2.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

A Search for sleptons and gauginos in Z0 decays

Using a data sample corresponding to 10 000 hadronic Z0 decays, we have searched for the production of sleptons and gauginos in the two-prong decays of Z0. No candidate remains after straightforward selections. For neutralinos, we use selection methods developed in our previous search for neutral Higgs particles. The negative results are translated into improved mass limits and parameter constraints on the minimal supersymmetric extension of the standard model

A Comparison of jet production rates on the Z0 resonance to perturbative QCD

The production rates for 2-, 3-, 4- and 5-jet hadronic final states have been measured with the DELPHI detector at the e+e- storage ring LEP at centre of mass energies around 91.5 GeV. Fully corrected data are compared to O(αs 2) QCD matrix element calculations and the QCD scale parameter ΛMS is determined for different parametrizations of the renormalization scale μ2. Including all uncertainties our result is αs(MZ 2)=0.114±0.003[stat.]±0.004[syst.]±0.012[theor.] .0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Measurement of the Mathematical expression branching ratio of the z by double hemisphere tagging

Two measurements of Mathematical expression are presented. Both measurements use 250000 Z decays taken with the DELPHI detector in 1991 and rely mainly on the precision of the microvertex detector. One tagging method is as simple as possible so that background rates can be reliably predicted by simulation. The other one uses a more involved tagging technique and reduces the dependence on simulation as much as possible. Combining both results, Mathematical expression is found to be 0.2209±0.0041(stat.)±0.0042(syst.)±0.0018 Mathematical expression. © 1995 Springer-Verlag

Lifetime of charged and neutral B hadrons using event topology

The lifetimes of charged and neutral B hadrons have been measured using data collected by the DELPHI experiment at LEP between 1991 and 1993. B hadrons are tagged as jets with a secondary vertex and the charge of the B candidate is taken to be the sum of the charges of the particles in the secondary vertex. Approximately 1,434,000 multihadronic Z0 decays yielded 1817 B hadron candidates. The B purity was estimated to be around 99.1±0.3%, and 83% (70%) of the events measured as neutral (charged) came from neutral (charged) B's. The mean lifetimes of charged and neutral B hadrons were found to be 1.72±0.08 (stat.) ±0.06 (syst.) ps and 1.58±0.11 (stat.)±0.09 (syst.) ps respectively. The ratio of their lifertimes, τcharged/τneutral, was 1.09-0.10+0.11 (stat.)±0.08 (syst.). By making assumptions about the Bs0 and Λb0 states, the B+ and B0 meson lifetimes were determined to be τB+ = 1.72 ± 0.08 (stat.) ±0.06 (syst.) ps and τB+ = 1.63 ± 0.14 (stat.)±0.13 (syst.) ps and the ratio of their lifetimes was: τB+/τB0 = 1.06-0.11+0.13 ±0.10. The mean B lifetime was also deduced to be < τ > = 1.64 ±0.06 (stat.)±0.04 (syst.) ps. © 1995 Springer-Verlag

A Study of intermittency in hadronic Z0 decays

The correlations in rapidity in hadron production from e+e- annihilation near the Z0 resonance were studied by means of the method of factorial moments, using data taken with the DELPHI detector at LEP. The parton shower hadronization model was found to be in quantitative agreement with the data, in contrast with previous results at lower energies. © 1990.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Charged particle multiplicity in e(+)e(-) interactions at root s=130 GeV

From the data collected by DELPHI at LEP in autumn 1995, the multiplicity of charged particles at a hadronic energy of 130 GeV has been measured to be = 23:84 0:51(stat) 0:52(syst). When compared to lower energy data, the value measured is consistent with the evolution predicted by QCD with corrections at next-to-leading order, for a value s(130GeV) = 0:105 0:003(stat) 0:008(syst)

Search for pair produced heavy scalars in Z0 decays

A search for charged Higgs bosons decaying into quarks is described, based on statistics of around 1.7 million hadronic Zo decays detected in DELPHI. Despite the very high background from standard hadronic decays of the Zo, masses in the range up to 43.5 GeV/c2 are excluded at the 95% confidence level. After combination with a search for leptonic decays, this mass limit is extended to cover all branching ratios. A similar analysis sets new limits on the possible production of any pair-produced heavy scalar decaying into a pair of jets, such as neutral Higgs bosons in a two doublet scheme and diquarks. © 1994 Springer-Verlag.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Search for high mass gamma gamma resonances in e+ e ---> lepton+ lepton- gamma gamma, neutrino anti-neutrino gamma gamma and q anti-q gamma gamma at LEP-1

A search for high mass photon pairs from the processes e(+)e(-) --> l(+)l(-)gamma gamma, e(+)e(-) --> <q(q)over bar gamma gamma> and e(+)e(-) --> nu nu gamma gamma with the DELPHI detector at LEP I is reported. From a data sample containing 3.5 million hadronic Z(0) decays, collected by DELPHI during the years 1991 to 1994, 79 events with two charged leptons and two isolated photons were selected with photon pair masses above 10 GeV/c(2), where 76 +/- 6 events were predicted from standard sources. In the same data sample, no <nu(nu)over bar gamma gamma> candidates were found and no accumulation of events was visible for gamma gamma masses above 10 GeVlc2 in the q<q(q)over bar gamma gamma> channel. Upper limits at 95% confidence level on the Z(0) branching ratios for the three different channels were extracted from the data. In the mass region m(gamma gamma) > 30 CeV/c(2) the limits obtained are between 3x10(-6) and 4x10(-6)