Measurement of the W mass in e+e−e^+ e^- collisions at 183 GeV

The mass of the W boson is obtained from reconstructed invariant mass distributions in W-pair events. The sample of W pairs is selected from 57 pb$^{-1}$ collected with the ALEPH detector in 1997 at a centre-of-mass energy of 183 GeV. The invariant mass distributions of reweighted Monte Carlo events are fitted separately to the experimental distributions in the $qqbarqqbar$ and all l\nuqqbar channels to give the following W masses: $m_{W}^{hadronic} = 80.461 \pm 0.177(stat.) \pm 0.045(syst.) \pm 0.056(theory) GeV/c^2$, $m_{W}^{semileptonic} = 80.326 \pm 0.184(stat.) \pm 0.040(syst.) GeV/c^2$ where the theory error represents the possible effects of final state interactions. The combination of these two measurements, including the LEP energy calibration uncertainty, gives $m_{W} = 80.393 \pm 0.128(stat.)\pm 0.041(syst.) \pm 0.028(theory)\pm 0.021(LEP) GeV/c^2

Study of Fermion Pair Production in e+e−e^{+}e^{-} Collisions at 130-183 GeV

The cross sections and forward-backward asymmetries of hadronic and leptonic events produced in e+e- collisions at centre-of-mass energies of 130-183 GeV are presented. Results for ee, mumu, tautau, qq, bb and cc production show no significant deviation from the Standard Model predictions. This enable constraints to be set upon physics beyond the Standard Model such as four-fermion contact interactions, leptoquarks, Z' bosons and R-parity violating squarks and sneutrinos. Limits on the energy scale Lambda of eeff contact interactions are typically in the range from 2-10 TeV. Limits on R-parity violating sneutrinos reach masses of a few hundred GeV for large values of their Yukawa couplings

Measurement of the W Mass and Width in e+e−e^+ e^- Collisions at 189 GeV

The mass of the W boson is determined in e+e- collisions at LEP by the direct reconstruction of W decays in WW->qqqq and WW->lvqq events, supplemented by measurements using the kinematic properties of the leptons in the WW->lvlv decay channel. The main sample of W pairs is selected from an integrated luminosity of 174 pb^-1 collected with the ALEPH detector in 1998 at a centre-of-mass energy of 188.63 GeV.The combined result from all channels is mW = 80.432+-0.072(stat.)+-0.041(syst.)+-0.019(FSI)+-0.017(LEP) GeV/c^2, where FSI represents the possible effects of final state interactions in the qqqq channel. In a second two-parameter fit to the qqqq, evqq and mvqq channels, where the W mass and width are decoupled, the average W width is found to be 2.24+-0.20(stat.)+-0.13(syst.) GeV/c^2, consistent with the Standard Model prediction. The combination of the mass measurement presented in this paper together with those derived previously from the W pair cross section at 161 and 172 GeV and direct reconstruction at 172 and 183 GeV gives mW = 80.418+-0.061(stat.)+-0.038(syst.)+-0.019(FSI)+-0.017(LEP) Ge

Search for Gauge-Mediated SUSY Breaking Topologies at s∼\sqrt{s} \sim 189 GeV

Searches for topologies characteristic of Gauge Mediated SUSY Breaking models (GMSB) are performed by analysing 173.6 pb^-1 of data collected at Ecm = 188.6~GeV with the ALEPH detector.These topologies include acoplanar photons, non-pointing single photon, acoplanar leptons, large impact parameter leptons, detached slepton decay vertices, heavy stable charged sleptons and four leptons plus missing energy final states.No evidence for these new phenomena is observed and limits on production cross sections and sparticle masses are derived. A scan of a minimal GMSB parameter space is performed and model dependent lower limits of about 45 GeV/c^2 on the next-to-lightest supersymmetric particle (NLSP) mass and of about 9 TeV on the mass scale parameter Lambda are derived, independently of the NLSP lifetime