Showing papers by "Georges Azuelos published in 1994"
01 Dec 1994
259 citations
TL;DR: In this article, the authors compared the JETSET and HERWIG Monte Carlo models with the OPAL detector at LEP and found that both models agree with the observed data.
Abstract: The inclusive production rates of π±,K± andp\(\bar p\) inZ0 decays have been measured with the OPAL detector at LEP. Using the energy loss measurement in the jet chamber, the momentum range up to the beam energy (45.6 GeV/c) has been covered. Differential cross sections and total particle yields are given. Comparisons of the inclusive momentum spectra and the total rates with predictions of the JETSET and the HERWIG Monte Carlo model are presented. The total single rates are found to be 17.05±0.43 π±, 2.42±0.13K± and 0.92±0.11p\(\bar p\) per hadronic event. Predictions of JETSET for cross sections and total rates agree very well for π±; however, for momenta greater than 4 GeV/c,K± rates are underestimated and\(\bar p\) rates are overestimated. Combined with data of other particle species there is evidence that the peak positions in the ξ=ln(1/x p ) distributions show a different mass dependence for mesons and baryons. However, both JETSET and HERWIG Monte Carlo predictions agree with the observed data.
80 citations
TL;DR: In this paper, a cone-based jet finding algorithm was used to detect hadronic events recorded using the OPAL detector at LEP, and the results showed that the results were significantly narrower than those observed in the CDF experiments.
Abstract: We describe a cone-based jet finding algorithm (similar to that used in
$$\bar p$$
p experiments), which we have applied to hadronic events recorded using the OPAL detector at LEP. Comparisons are made between jets defined with the cone algorithm and jets found by the “JADE” and “Durham” jet finders usually used ine
+
e
− experiments. Measured jet rates, as a function of the cone size and as a function of the minimum jet energy, have been compared with O(α
2
) calculations, from which two complementary measurements
$$\alpha _s \left( {M_{Z^0 } } \right)$$
have been made. The results are
$$\alpha _s \left( {M_{Z^0 } } \right)$$
=0.116±0.008 and
$$\alpha _s \left( {M_{Z^0 } } \right)$$
=0.119±0.008 respectively, where the errors include both experimental and theoretical uncertainties. Measurements are presented of the energy flow inside jets defined using the cone algorithm, and compared with equivalent data from
$$\bar p$$
p interactions, reported by the CDF collaboration. We find that the jets ine
+
e
− are significantly narrower than those observed in
$$\bar p$$
p. The main contribution to this effect appears to arise from differences between quark- and gluon-induced jets.
57 citations
TL;DR: In this article, the B0d meson is reconstructed in final states that contain a D∗− and an l+, where the b flavour of the B 0d at decay time is tagged by the electric charge of the lepton.
49 citations
TL;DR: In this article, a study of forward-backward multiplicity correlations and a measurement of the dependence on charged multiplicity of the mean transverse momentum of charged hadrons, measured with respect to the thrust axis, was performed on a high statistics sample of Z(0) decays to multihadronic final states collected by the OPAL Collaboration at LEP.
28 citations
TL;DR: In this paper, the authors presented an update with increased statistics to their published analysis of hadronic and leptonic cross sections and of the lepton forward-backward asymmetries.
Abstract: We present an update with increased statistics to our published analysis of hadronic and leptonic cross sections and of the leptonic forward-backward asymmetries ine
+
e
−
collisions. The published results were based on a total 454 000 hadronic and 58 000 leptonic events. This analysis adds 733 000 hadronic and 88 000 leptonic events recorded at theZ
0 peak in 1992 by the OPAL experiment at LEP. A model independent analysis ofZ
0 parameters based on an extension of the improved Born approximation leads to tests of lepton universality and gives an interpretation of the results within the Standard Model framework. We also present a model independent test for new physics.
25 citations
TL;DR: In this paper, a search for the Minimal Standard Model Higgs boson (H0) with data from e+e− collisions collected by the OPAL detector at LEP has been performed with data of events of the types e +e−→(e+e −,μ+μ− or νν)H0, H0→qq and was based on approximately 78 pb−1 of data taken at center-of-mass energies between 88 and 95 GeV in the years 1990-1993.
24 citations
TL;DR: In this article, the hadronic photon structure function F2γ(x) was measured in twoQ2 ranges with mean values of 5.9 GeV2 and 14.7 GeV 2.
Abstract: We present measurements of the hadronic photon structure functionF2γ(x), in twoQ2 ranges with mean values of 5.9 GeV2 and 14.7 GeV2. The data were taken by the OPAL experiment at LEP, with\(\sqrt s\) close to theZ0 mass and correspond to an integratede+e− luminosity of 44.8 pb−1. In the context of a QCD-based model we find the quark transverse momentum cutoff separating the vector meson dominance (VMD) and perturbative QCD regions to be 0.27±0.10 GeV. We confirm that there is a significant pointlike component of the photon when the probe photon hasQ2>4 GeV2. Our measurements extend to lower values ofx than any previous experiment, and no increase ofF2γ(x) is observed.
24 citations
TL;DR: In this article, the charged particle multiplicity in the hemispheres opposite those containing these jets has been studied as a function of the b purity of the events, and it has been shown to be between 0% and 100% b purity.
Abstract: Using the distance from the average primary vertex to reconstructed secondary vertices in jets, samples of events withb purity varying from about 13% to 89% have been selected. The charged particle multiplicity in the hemispheres opposite those containing these jets has been studied as a function of theb purity of the events. Extrapolating to 0% and 100%b purity, values of the hemisphere charged particle multiplicity inZ0→\(b\bar b\) events and in non-\(b\bar b\) events have been measured to be
$$\begin{gathered} \bar n_b = 11.71 \pm 0.03 \pm 0.18 \pm 0.21, \hfill \\ \bar n_{udsc} = 10.32 \pm 0.01 \pm 0.07 \pm 0.19. \hfill \\ \end{gathered}$$
The first error is statistical, the second systematic and the third is a common systematic error.
23 citations
TL;DR: In this article, the authors discuss the production of new heavy fermions predicted by extensions of the Standard Model at high-energy linear colliders, and analyze in great detail the various signals and corresponding backgrounds for both pair production and single production in association with ordinary Fermions.
Abstract: We discuss the production, at high-energye
+
e
− linear colliders, of new heavy fermions predicted by extensions of the Standard Model. We analyze in great details the various signals and the corresponding backgrounds for both pair production and single production in association with ordinary fermions. Concentrating on new leptons, we use a model detector fore
+
e
− collisions at a center of mass energy of 500 GeV, to illustrate the discovery potential of the next linear colliders.
22 citations
TL;DR: In this paper, the OPAL search for a supersymmetric partner of the top quark (t 1 ) has been performed by OPAL experiment in e + e - collisions at LEP.
TL;DR: In this paper, the authors presented an update of the τ lepton lifetime, using data taken during 1992 and 1993 with the OPAL detector at LEP, and the updated lifetime measurement is: ττ = 288.8 ± 2.2 (stat) ± 1.4 (sys) fs.
TL;DR: In this paper, the OPAL detector at LEP during 1990-1993 was used to measure the time dependence of B d 0 ↔ Bd 0 mixing, which corresponds to an oscillation parameter of xd = ΔmdτBd0 = 0.82±0.09(syst. ps−1.
TL;DR: In this article, the OPAL detector at LEP was used to measure the branching ratios of the τ− → h− π0vτ and τ−→ h− ⩾ 2π0v τ decays.
TL;DR: In this article, a search for rare decays of B hadrons has been performed using approximately two million hadronic Z 0 decays collected by the OPAL experiment between 1990 and 1993.
TL;DR: In this article, an analysis of sub-jet multiplicities, which are expected to be sensitive to the properties of soft gluon radiation, in hadronic decays of the Z 0.
Abstract: This paper describes an analysis of sub-jet multiplicities, which are expected to be sensitive to the properties of soft gluon radiation, in hadronic decays of theZ0. Two- and three-jet event samples are selected using thek⊥ jet clustering algorithm at a jet resolution scaley1. The mean sub-jet multiplicity as a function of the sub-jet resolution,y0, is determined separately for both event samples by reapplying the same jet algorithm at resolution scalesy0
TL;DR: In this article, the neutral Higgs bosons h0 and A0, predicted by the Minimal Supersymmetric Extension of the Standard Model (MSSM), have been performed by the OPAL Collaboration at LEP.
Abstract: A search for the neutral Higgs bosons h0 and A0, predicted by the Minimal Supersymmetric Extension of the Standard Model (MSSM), has been performed by the OPAL Collaboration at LEP. The analysis was based on approximately 75 pb−1 of data taken at centre-of-mass energies in the vicinity of the Z0 resonance. No Higgs boson signals have been detected. Using, in addition, an upper limit on the contribution of non-Standard Model processes to the Z0 boson width, almost the entire MSSM parameter space that can be reached at present LEP energies has been excluded. In particular, at the 95% confidence level, our results imply that\(m_{h^0 } > 44.5\) GeV/c2 and\(m_{A^0 } > 24.3\) GeV/c2, for tan β≥1. The sensitivity to this assumption is discussed and the search results are also interpreted in the context of general two-doublet models.
TL;DR: In this article, the authors describe measurements of the tau lepton to K S 0 and charged K ∗ (892) using Z 0 → τ + τ − candidates collected with the OPAL detector at LEP during 1990-1992.
TL;DR: In this paper, the OPAL data collected during 1990-1992 were used to study exclusive decays of B mesons, and the authors measured the mass of the B s 0 meson to be 5.359 ± 0.007 GeV/ c 2.
TL;DR: In this paper, a mixed tag method involving the identification of (Z^0 \to b\bar b\) events by two different techniques is presented using a “mixed tag” method involving identification of events by using the large impact parameter of tracks emerging from the decay of b-flavoured hadrons and the semi-leptonic decay.
Abstract: A measurement of\(\Gamma _{b\bar b} /\Gamma _{had} \equiv \Gamma (Z^0 \to b\bar b)/\Gamma (Z^0 \to hadrons)\) is presented using a “mixed tag” method involving the identification of\(Z^0 \to b\bar b\) events by two different techniques. The first uses the large impact parameter of tracks emerging from the decay ofb-flavoured hadrons and the second their semi-leptonic decay. The identification efficiencies are measured from the data using all possible combinations of the two tags in opposite hemispheres. The method is therefore insensitive to Monte Carlo modelling of bottom quark production and ofb-flavoured hadron production and decay properties, and depends only weakly on the simulation of the detector. The data sample collected by OPAL at LEP in 1990 and 1991 is considered. The result is:
$$\frac{{\Gamma _{b\bar b} }}{{\Gamma _{had} }} = 0.218 \pm 0.006(stat) \pm 0.007(syst) \pm 0.007(\Gamma _{c\bar c} /\Gamma _{had} ),$$
where the systematic uncertainty due to the charm quark partial width has been separated from the other systematic uncertainties. Combination with previous OPAL measurements gives:
$$\frac{{\Gamma _{b\bar b} }}{{\Gamma _{had} }} = 0.220 \pm 0.004(stat) \pm 0.006(syst) \pm 0.006(\Gamma _{c\bar c} /\Gamma _{had} ),$$
21 Apr 1994-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: A large scale prototype of a liquid argon accordion calorimeter, conceived as a sector of a full LHC Barrel detector and consisting of an electromagnetic and a hadronic section, has been constructed and tested at the CERN SPS with electron and pion beams in the energy range 10 −287 GeV as discussed by the authors.
Abstract: A large scale prototype of a liquid argon accordion calorimeter, conceived as a sector of a full LHC Barrel detector and consisting of an electromagnetic and a hadronic section, has been constructed and tested at the CERN SPS with electron and pion beams in the energy range 10–287 GeV.