Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV

A search for pair-production of supersymmetric particles under the assumption that R-parity is violated via a dominant LQDbar coupling has been performed using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV. The observed candidate events in the data are in agreement with the Standard Model expectation. This result is translated into lower limits on the masses of charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81 GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the 95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure

Search for Bs0B^{0}_{s} oscillations using inclusive lepton events

A search for Bs oscillations is performed using a sample of semileptonic b-hadron decays collected by the ALEPH experiment during 1991-1995. Compared to previous inclusive lepton analyses, the prop er time resolution and b-flavour mistag rate are significantly improved. Additional sensitivity to Bs mixing is obtained by identifying subsamples of events having a Bs purity which is higher than the average for the whole data sample. Unbinned maximum likelihood amplitude fits are performed to derive a lower limit of Dms>9.5 ps-1 at 95% CL. Combining with the ALEPH Ds based analyses yields Dms>9.6 ps-1 at 95% CL.A search for B0s oscillations is performed using a sample of semileptonic b-hadron decays collected by the ALEPH experiment during 1991-1995. Compared to previous inclusive lepton analyses, the proper time resolution and b-flavour mistag rate are significantly improved. Additional sensitivity to B0s mixing is obtained by identifying subsamples of events having a B0s purity which is higher than the average for the whole data sample. Unbinned maximum likelihood amplitude fits are performed to derive a lower limit of Deltam_s>9.5ps^-1 at 95% CL. Combining with the ALEPH D-s based analyses yields Deltam_s>9.6ps^-1 at 95% CL

Measurement of the tau lepton lifetime

The mean lifetime of the tau lepton is measured in a sample of 25700 tau pairs collected in 1992 with the ALEPH detector at LEP. A new analysis of the 1-1 topology events is introduced. In this analysis, the dependence of the impact parameter sum distribution on the daughter track momenta is taken into account, yielding improved precision compared to other impact parameter sum methods. Three other analyses of the one- and three-prong tau decays are updated with increased statistics. The measured lifetime is 293.5+/-3.1+/-1.7 fs. Including previous (1989-1991) ALEPH measurements, the combined tau lifetime is 293.7+/-2.7+/-1.6 fs

Recent Results from the CosmoALEPH Experiment

The ALEPH detector at LEP has been supplemented with five scintillator telescopes. This CosmoALEPH experiment is operating at a depth of 320 m.w.e. under ground measuring the muon component of extensive air showers. The aim of the experiment is to look for the chemical composition of primary cosmic rays and to in vestigate the interaction characteristics of energetic protons and nuclei in the atmosphere in the PeV region. A first look at the cosmic ray data taken in dedicated runs with the CosmoALEPH experiment shows agreement of under ground muon data with gross features based on expectations from the muon content of extensive air showers in the atmosphere

Search for Light Leptoquark Bosons

A search for light leptoquarks decaying into a lepton and a quark has been performed using the CELLO detector at the storage ring PETRA. Decay modes have been looked for where the lepton is either a muon or a neutrino, the latter being detected by a high missing transverse momentum. Except for one event previously reported no further two-jet events with two isolated muons were observed. No evidence for pair production of these particles has been found in other final states configurations. Our results are interpreted within a model where leptoquarks appear as a coloured Goldsone multiplet of charges 2/3.A 95% CL upper limit of 0.30 pb is set on the pair production cross section of such leptoquarks, thus excluding masses between 7 and 20.5 GeV

Measurement of alpha-s from b anti-b production at the CERN p anti-p collider

The UA1 Collaboration has recently improved its measurement of the beauty production cross-section by including explicit measurements of correlations. Using these data we have determined the strong coupling constant alpha(s). The comparison of the measured cross-section for 2-body final states with O(alpha(s)(3)) QCD predictions yields a measurement of alpha(S)(20 GeV) = 0.145(-0.010exp-0.016 th)(+0.012+0.013), corresponding to alpha(S)(M(Z)) = 0.113(-0.006 exp-0.009 th)(+0.007+0.008). This is the first theoretically well-defined measurement of alpha(S) from a purely hadronic production process. Evaluating alpha(S) from cross-sections at different Q(2)-values we find that the running of alpha(S) is needed for internal consistency of the UA1 data

Improved search for B-S(0)-(B)over-bar(S)(0) oscillations

An improved search for Bs oscillations is performed in the ALEPH data sample collected during the first phase of LEP, and reprocessed in 1998. Three analyses based on complementary event selections are presented. First, decays of Bs mesons into hadronic flavour eigenstates are fully reconstructed. This selection yields a small sample of candidates with excellent decay length and momentum resolution and high average Bs purity. Semileptonic decays with a reconstructed Ds- meson provide a second sample with larger statistics, high average Bs purity, but a poorer momentum and decay length resolution due to the partial decay reconstruction. Finally, semileptonic b-hadron decays are inclusively selected and yield the data sample with the highest sensitivity to Bs oscillations, as the much higher statistics compensate for the low average Bs purity and poorer time resolution. A lower limit is set at 10.9 ps-1 at 95% CL, significantly lower than the expected limit of 15.7 ps-1

Study of hadronic final states from double tagged gammagammagammagamma events at LEP

The interaction of virtual photons is investigated using double tagged gammagamma events with hadronic final states recorded by the ALEPH experiment at e^+e^- centre-of-mass energies between 188 and 209 GeV. The measured cross section is compared to Monte Carlo models, and to next-to-leading-order QCD and BFKL calculations.The interaction of virtual photons is investigated using double tagged gammagamma events with hadronic final states recorded by the ALEPH experiment at e^+e^- centre-of-mass energies between 188 and 209 GeV. The measured cross section is compared to Monte Carlo models, and to next-to-leading-order QCD and BFKL calculations