Limits on the production of scalar leptoquarks from Z (0) decays at LEP

A search has been made for pairs and for single production of scalar leptoquarks of the first and second generations using a data sample of 392000 Z0 decays from the DELPHI detector at LEP 1. No signal was found and limits on the leptoquark mass, production cross section and branching ratio were set. A mass limit at 95% confidence level of 45.5 GeV/c2 was obtained for leptoquark pair production. The search for the production of a single leptoquark probed the mass region above this limit and its results exclude first and second generation leptoquarks D0 with masses below 65 GeV/c2 and 73 GeV/c2 respectively, at 95% confidence level, assuming that the D0lq Yukawa coupling alpha(lambda) is equal to the electromagnetic one. An upper limit is also given on the coupling alpha(lambda) as a function of the leptoquark mass m(D0)

A Measurement of the b anti-b forward backward asymmetry using the semileptonic decay into muons

0info:eu-repo/semantics/publishe

A Measurement of the mean lifetimes of charged and neutral B hadrons

The decays of B-hadrons have been reconstructed using the charged particles recorded in the DELPHI silicon microstrip detector. The sum of the charges of the secondaries determines the charge of the B-hadron parent. Some 232 114 multihadronic Z0 decays recorded during the 1991 run of LEP at centre-of-mass energies between 88.2 GeV and 94.2 GeV yield 253 B-hadron candidates with well-measured charge. From these the mean lifetimes of neutral and charged B-hadrons are found to be 1.44 ± 0.21 (stat.) ± 0.14(syst.) ps and 1.56 ± 0.19(stat.) ± 0.13(syst.) ps respectively. The ratio of their lifetimes is 1.09+0.28 -0.23(stat.) ± 0.11 (syst.). Under some assumptions on the abundance and lifetime of the Λ0 b and B0 s states, the B0 and B+ lifetimes are inferred.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Experimental study of the triple gluon vertex

In four-jet events from e+e-→Z0→multihadrons one can separate the three principal contributions from the triple-gluon vertex, double gluon-bremsstrahlung and the secondary quark-antiquark production, using the shape of the two-dimensional angular distributions in the generalized Nachtmann-Reiter angle 0NR* and the opening angle of the secondary jets. Thus one can identify directly the contribution from the triple-gluon vertex without comparison with a specific non-QCD model. Applying this new method to events taken with the DELPHI-detector we get for the ratio of the colour factor NC to the fermionic Casimir operator CF: NC/C F=2.55±0.55(stat.)±0.4(fragm.+models)±0.2(error in bias) in agreement with the value 2.25 expected in QCD from NC=3 and CF=4/3.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Production of strange particles in the hadronic decays of the Z0

An analysis of the production of strange particles from the decays of the Z0 boson into multihadronic final states is presented. The analysis is based on about 90 000 selected hadronic Z0 decays collected by the DELPHI detector at LEP in 1990. KS 0, K*±, Λ(Λ̄) and Ξ- (Ξ̄+) have been identified by their characteristic decays. The measured production cross sections are compared with predictions of the Lund Monte Carlo tuned to data at PEP/PETRA energies.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)

Improved measurements of cross-sections and asymmetries at the Z0 resonance

During the 1992 running period of the LEP e+e- collider, the DELPHI experiment accumulated approximately 24 pb-1 of data at the Z0 peak. The decays into hadrons and charged leptons have been analysed to give values for the cross sections and leptonic forward-backward asymmetries which are significantly improved with respect to those previously published by the DELPHI collaboration. Incorporating these new data, more precise values for the Z0 resonance parameters are obtained from model-independent fits. The results are interpreted within the framework of the Standard Model, yielding for the top quark mass mt = 157-48 +36 (expt.) -20 +19 (Higgs) GeV, and for the effective mixing angle sin2 θeff lept = 0.2328 ± 0.0013(expt.)-0.0003 +0.0001(Higgs), where (Higgs) represents the variation due to Higgs boson mass in the range 60 to 1000 GeV, with central value 300 GeV.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

J / psi production in the hadronic decays of the Z

J/ψ mesons have been reconstructed from their decay to μ+μ- and e+e-, using the data collected by the DELPHI experiment during 1991 and 1992 at the LEP collider. From about 1 million hadronic Z decays 153 ± 17 J/ψ were found, 5.4 ± 2.3 ψ′ were obtained in the channel J/ψ (→μ+μ-)π+π- and 6.4 ± 2.7 χc in the channel J/ψ ( → μ+μ-)γ. As the dominant source of Jψ mesons is from bquarks, the following branching ratios: Br(b → J/ψ X) = (1.12 ± 0.12 (stat) ± 0.10 (syst.))%, Br(b → ψ′ X) = (0.48 ± 0.22 (stat.± 0.10 (syst.))%, Br(b → χc1 X) = (1.4 ± 0.6 (stat.)-0.2+0.4 (syst.))% were measured. From the proper time distribution of the J/ψ sample, the average lifetime of b-hadrons decaying into J/ψ was found to be: τB = 1.50-0.21+0.24 (stat.) ± 0.03 (syst.) ps. A search for completely reconstructed B meson decays to final states including a J/ψ gave a signal of 15 ± 5 events.0info:eu-repo/semantics/publishe

Determination of alpha-s from the scaling violation in the fragmentation functions in e+ e- annihilation

A determination of the hadronic fragmentation functions of the Z0 boson is presented from a study of the inclusive hadron production with the DELPHI detector at LEP. These fragmentation functions were compared with the ones at lower energies, thus covering data in a large kinematic range: 196 ≤ Q2 ≤ 8312 GeV2 and x (= Ph Ebeam) > 0.08. A large scaling violation was observed, which was used to extract the strong coupling constant in second order QCD: αs(MZ) = 0.118 ± 0.005. The corresponding QCD scale for five quark flavours is: Λ (5) MS = 230 ± 60 MeV.0info:eu-repo/semantics/publishe