W boson polarization measurement in the ttbar dilepton channel using the CDF II Detector

We present a measurement of $W$ boson polarization in top-quark decays in $t\bar{t}$ events with decays to dilepton final states using $5.1 {\rm fb^{-1}}$ of integrated luminosity in $p\bar{p}$ collisions collected by the CDF II detector at the Tevatron. A simultaneous measurement of the fractions of longitudinal ($f_0$) and right-handed ($f_+$) $W$ bosons yields the results $f_0 = 0.71 ^{+0.18}_{-0.17} {\rm (stat)} \pm 0.06 {\rm (syst)}$ and $f_+ = -0.07 \pm 0.09 {\rm (stat)} \pm 0.03 {\rm (syst)}$. Combining this measurement with our previous result based on single lepton final states, we obtain $f_0 = 0.84 \pm 0.09 {\rm (stat)} \pm 0.05 {\rm (syst)}$ and $f_{+} = -0.16 \pm 0.05 {\rm (stat)} \pm 0.04 {\rm (syst)}$. The results are consistent with standard model expectation.Comment: Published in Phys. Lett.

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

A search for the neutral Higgs boson in the mass range above 11 GeV (above the threshold), using the process Z0→H0e+e−, Z0→H0μ+μ− and , 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 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

A Study of single and multi - photon production in e+ e- collisions at center-of-mass energies of 130-GeV and 136-GeV

The production of final states involving one or more energetic photons from e+e- collisions at high energies is studied using data collected by the ALEPH detector at LEP. The data consist of two samples of 2.9 pb-1 each, recorded at centre-of-mass energies of 130 GeV and 136 GeV. The data are in agreement with the predictions of the Standard Model. From an analysis of two-photon final states new limits are placed on the parameters of models involving contact interactions and excited electrons. The 95% confidence level lower limits on the QED cut-off parameters are found to be 169 and 132 GeV respectively

Measurement of charge asymmetry in hadronic Z decays

A significant charge asymmetry is observed in the hadronic Z decays with the ALEPH detector at LEP. The asymmetry expressed in terms of the difference in momentum weighted charges in the two event hemispheres is measured to be −= −0.0084±0.0015 (stat.) ±0.0004 (exp. sys.). In the framework of the standard model this can be interpreted as a measurement of the effective electroweak mixing angle, sin2Ow (Mz2=0.2300±0.0034 (stat.) ±0.0010 (exp. sys.) ±0.0038 (theor. sys.) or of the ratio of the vector to axual- vector coupling costants of the electron, gvegAe=+0.073±0.024

Updated measurement of the tau lepton lifetime

A new measurement of the mean lifetime of the tau lepton is presented. Three different analysis methods are applied to a sample of 90000 tau pairs, collected in 1993 and 1994 with the ALEPH detector at LEP. The average of this measurement and those previously published by ALEPH is tau_tau = 290.1 +- 1.5 +- 1.1 fs.Comment: 17 pages, Latex; to be published in Physics Letters

Searches for scalar top and scalar bottom quarks at LEP-2

Searches for scalar top and bottom quarks have been performed with data collected by the ALEPH detector at LEP. The data sample consists of 21.7 pb^-1 taken at sqrt{s} = 161, 170, and 172~GeV and 5.7 pb^-1 taken at sqrt{s} = 130 and 136~GeV. No evidence for scalar top quarks or scalar bottom quarks was found in the channels stop --> c chi, stop --> b l snu, and sbottom --> b chi. For the channel stop --> c chi a limit of 67 GeV/c^2 has been set on the scalar top quark mass, independent of the mixing angle between the supersymmetric partners of the left and right-handed states of the top quark. This limit assumes a mass difference between the stop and the chi of at least 10 GeV/c^2. For the channel stop --> b l snu the mixing-angle independent scalar top limit is 70 GeV/c^2, assuming a mass difference between the stop and the snu of at least 10 GeV/c^2. For the channel sbottom --> b chi, a limit of 73 GeV/c^2 has been set on the mass of the supersymmetric partner of the left-handed state of the bottom quark. This limit is valid if the mass difference between the sbottom and the chi is at least 10 GeV/c^2.Comment: Latex (epsfig): 16 pages including 6 figure

A Measurement of R(b) using mutually exclusive tags

A measurement of Rb using five mutually exclusive hemisphere tags has been performed by ALEPH using the full LEP1 statistics. Three tags are designed to select the decay of the Z0 to b quarks, while the remaining two select Z0 decays to c and light quarks, and are used to measure the tagging efficiencies. The result, Rb = 0.2159 ± 0.0009(stat) ±0.0011(syst), is in agreement with the electroweak theory prediction of 0.2158 ± 0.0003

A Measurement of R(b) using a lifetime mass tag

ALEPH's published measurement of using a lifetime tag is updated using the full LEP 1 data sample. Considerable effort has been devoted to understanding systematic effects. Charm background is better controlled by combining the lifetime tag with a tag based on the hadron mass difference. Furthermore, the algorithm used to reconstruct the event primary vertex is designed so as to reduce correlations between the two hemispheres of an event. The value of Rb is measured to be 0.2167 ± 0.0011(stat) ± 0.0013(syst)

Search for heavy lepton pair production in e+ e- collisions at center-of-mass energies of 130-GeV and 136-GeV

A search for pair production of new heavy leptons has been performed assuming different scenarios for the mixing of the new particles with Standard Model leptons. No candidate events were found in a data sample corresponding to an integrated luminosity of 5.6 pb−1 collected by the ALEPH detector at centre-of-mass energies of 130 and 136 GeV. New limits on production cross-sections and on masses of sequential leptons were obtained which significantly extend the mass regions excluded at LEP1. For instance, charged heavy leptons with masses below 63.5 GeV/c2 are excluded at 95% C.L. for mass differences to the associated neutral lepton of more than 7 GeV/c2