E. Matsinos

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.

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.

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 a very light Higgs boson in Z decays

A search has been made for a very light Higgs boson in the processes e+e- → e+e-H and e+e- →μ+μ-H using data collected by ALEPH at the LEP e+e- collider at centre of mass energies close to the Z peak. The mass range between 0 and 57 MeV is unambigously excluded at the 95% confidence level. If we combine this with our previously published analysis, the complete range from 0 to 24 GeV is excluded at 95% CL. The search is extended to light Higgs bosons of the minimal supersymmetric standard model, with the result that all possibilities of coupling are excluded for Higgs masses below 3 GeV.

Search for neutralino production in Z decays

Limits on Z decay branching ratios into neutralinos are reported. They were obtained from searches for monojets, acoplanar jets, acoplanar lepton pairs, single photons and acoplanar photon pairs as signaturs for the reactions e+e- → χχ′ and e+e- → χχ′, where χ is the lightest neutralino and χ′ any heavier one. The data sample used for these searches corresponds to about 23 000 events of Z decay into multihadrons, collected at LEP by the ALEPH detector for centre of mass energies at and near the Z peak. The results obtained are used to restrict the parameter space of the minimal supersymmetric standard model.

A search for pair-produced charged Higgs bosons in Z0 decays

The utilitarian representation of sport in Rumania, a brake in the development of leisure practice. Since the countries of central Europe entered the liberal sphere influence, the consumptions of possessions and services develop there. We observe a movement of tutellaire and ideological emancipation of the sports organizations, but the practice of popular physical activities delays developing. If, on the ground, we notice the appearance of an structured professionally offer, contrary to all expectations, it does not pull a real increase of consumption. This situation which rises in inferred paradox a cultural interrogation on the previous history of these brakes. Historically, the sport during the influence of communist sphere was enpreint of elitist and nationalist ideologies. An inquiry, made with the professionals of the forming in physical and sports education, moves closer to this weak development of the popular sports with the cultural inheritance of the country. The frame of sports of leisure in the representation that builds itself the professional actors, as the consumers, always revet a strongly utilitarian dimension which hinders its development. To develop the sports of leisure implies to integrate this peculiarity into the professionals of sports forming programme.

SEARCH FOR EXCITED LEPTONS IN Z0 DECAY

We have looked for evidence of excited lepton production in Z0 decay observed in the ALEPH detector at LEP. We find no llγγ events and set new limits at 95% CL on l∗ masses at 44.6, 44.6 and 41.2 GeV/c2 for respectively. Observed events in the llγ channels are consistent with radiative effects and we set limits for the first time on the coupling for l∗ masses in the range up to 86 GeV/c2.