A. Bonissent

Heavy flavour production in Z decays

Abstract From an analysis of inclusive leptons in data collected by the ALEPH detector at LEP, we measure the fractions of b b and c c events in hadronic Z decays. The b b fraction times semileptonic branching ratio is measured to be Br ( b → e )·Γ b b /Γ had = 0.0224 ± 0.0016 ± 0.0010 . Assuming a b semileptonic branching ratio of 0.102 ± 0.010 gives Γ b b /Γ had = 0.220 ± 0.016 ± 0.024 , in good agreement with the standard model prediction of 0.217. The c c fraction times semileptonic branching ratio is measured to be Br ( c → e )·Γ c c /Γ had = 0.0133 ± 0.0040 −0.0031 +0.0038 . Assuming a c semileptonic branching ratio of 0.090 ± 0.013 gives Γ c c /Γ had = 0.148 ± 0.044 −0.038 +0.045 , in agreement with the standard model prediction of 0.171.

A precise determination of the number of families with light neutrinos and of the Z boson partial widths

More extensive and precise results are reported on the parameters of Z decay. On the basis of 20 000 Z decays collected with the ALEPH detector at LEP we find Mz=91.182±0.026 (exp.) ±0.030 (beam) GeV, Γz=2.541±0.056 GeV and σhad0=41.4±0.8 nb. The partial widths for the hadronic and leptonic channels are Γhad=1804±44 MeV, Γe+e−=82.1±3.4 MeV, Γμ+μ−=87.9±6.0 MeV and Γτ+τ−=86.1±5.6 MeV, in good agreement with the standard model. On the basis of the average leptonic width Γl+l−=83.9±2.2 MeV, the effective weak mixing angle is found to be sin2θw(Mz)=0.231±0.008. Usin g the partial widths calculated in the standard model, the number of light neutrino families is Nν=3.01±0.15 (exp.)±0.05 (theor.).

Search for the Neutral Higgs Boson from Z0 Decay

Abstract A search for the neutral Higgs boson, using the processes Z 0 → H 0 e + e − , Z 0 → H 0 μ + μ − , Z 0 → H 0 τ + τ − , Z 0 → H 0 v v and Z 0 → H 0 q q , is performed on data collected by the ALEPH detector corresponding to about 11 550 events of Z0 → hadrons. Combining all these processes, the mass range excluded is 32 MeV−15 GeV at 95% CL and 40 MeV−12 GeV at 99% CL. The result from this experiment is unambiguous in the context of the standard model.

First results of XPAD3, a new photon counting chip for X-ray CT-scanner with energy discrimination

XVAD3 is a single photon counting chip based on hybrid pixel counters, with low noise, high dynamics and high speed readout. Its features have been improved to provide an high counting rate capability, a very low threshold, an energy discrimination and a fast image readout. The chip is designed in 0.25 mum IBM technology, and contains 9600 pixels (130 mum times 130 mum) distributed into 80 columns of 120 elements each. An innovative architecture has been designed in order to prevent the digital circuits from disturbing the very sensitive analogue cells. XPAD3 was realized into two versions. The XPAD3-S version accepts positive input charges and offers an energy range from 4 keV to 40 keV with a single threshold. The XPAD3-C version accepts negative input charge and has an energy range from 6 keV to 60 keV with a windowed energy selection set by two independent thresholds. This last feature will be quite useful for experimentations where high contrast resolution is needed. The XPAD3 circuits can be bump-bonded with Si, CdTe or GaAs sensors to match detection efficiency with increasing photon energy. The aim of this development is to combine several XPAD3 circuits to build an 7.5 cm x 12 cm sensitive area for the development of a small animal micro-CT scanner, PIXSCAN and synchrotron X-ray scattering experiments. First prototypes of single chip detectors bump- bonded with a Si sensor and double chip detectors bump-bonded with a CdTe sensor have been produced and tested and preliminary results are presented.

Search for the neutral Higgs Boson from Z0 decay in the Higgs mass range between 11 and 24 GeV

Abstract A search for the neutral Higgs boson in the mass range above 11 GeV (above the H 0 →b b threshold), using the process Z0→H0e+e−, Z0→H0μ+μ− and Z 0 → H 0 v v , is performed on data collected by the ALEPH detector corresponding to about 25 000 events of Z0→ hadrons. Combining all these processes, the mass range excluded is 11 GeV at 95% CL. Together with a previously published result from ALEPH, the mass range excluded is 32 MeV to 24 GeV at 95% CL. This result also extends the excluded mass region for neutral Higgs bosons from supersymmetry.

Measurement of the charged particle multiplicity distribution in hadronic Z decays

The charged particle multiplicity distribution of hadronic Z decays was measured on the peak of the Z resonance using the ALEPH detector at LEP. Using a model independent unfolding procedure the distribution was found to have a mean 〈n〉=20.85±0.24 and a dispersion D=6.34±0.12. Comparison with lower energy data supports the KNO scaling hypothesis in the energy range GeV. At GeV the shape of the multiplicity distribution is well described by a log-normal distribution, as predicted from a cascading model for multi-particle production. The same model also successfully describes the energy dependence of the mean and width of the multiplicity distribution. A next-to-leading order QCD prediction in the framework of the modified leading-log approximation and local parton-hadron duality is found to fit the energy dependence of the mean but not the width of the charged multiplicity distribution, indicating that the width of the multiplicity distribution is a sensitive probe for higher order QCD or non-perturbative effects.

SEARCHES FOR THE STANDARD HIGGS BOSON

Abstract A data sample corresponding to about 100 000 hadronic Z decays collected by ALEPH at LEP has been used to search for the standard Higgs boson produced in the reaction e + e − → H 0 Z 0∗ . No indication for any signal was found, and a 95% CL lower limit on the Higgs boson mass has been set at 41.6 GeV.

Properties of hadronic events in e+e− annihilation at s=91 GeV

We report on properties of hadronic events from e+e− annihilation observed by the ALEPH detector at the large Electron Positron Collider at CERN. The center-of-mass energy was . Measured distributions of the global event-shape variables sphericity, aplanarity, thrust and minor value, and of the inclusive variables xp, p⊥in, p⊥out and y are presented. We measure a mean charged multiplicity in hadronic events of 〈Nch〉=21.3±0.1 (statistical)±0.6 (systematic). The data are in good agreement with QCD-based models which use the leading-logarithm approximation, and are less well described by a model using O(αs2) QCD.

Search For Neutral Higgs Bosons From Supersymmetry In Z-decays

The light scalar Higgs boson h and the pseudoscalar Higgs boson A of the minimal supersymmetric standard model have been searched for in the processes e+e−→hff and e+e−→hA using data collected by ALEPH at the LEP e+e− collider, with center of mass energies at and near the Z peak. Using a variety of signatures adapted to various mass ranges for h and A, we have excluded a large domain in the parameter space. For large values of ν2ν1, the ratio of the vacuum expectation values of the two Higgs fields, the whole range from 0 to 38.8 GeV is excluded for Mh and MA at 95% CL.

Search for the neutral Higgs bosons of the MSSM and other two-doublet models

The aim of this paper is to present the French approach to Information and Communication, and to sketch out some arguments pro and con for their amalgamation into a unique scientific body. Since its creation in 1975, the French academic field of Information-Communication has proved several advantages in the development of a new scientific corpus, but also some drawbacks. These are going to be reviewed and the question will be posed on the opportunity to generalize that model or to abandon it. The research concludes that a dichotomy between information and communication is certainly not representative of the French field of information and communication; it would rather be a continuum or a multi-polar space. Furthermore it is suspected that Anglo-Saxon separation of information science from communication science is not clear either. International comparison and research program in information – communication are advocated.