Search for R-Parity Violating Decays of Supersymmetric Particles in e+e−e^{+}e^{-} Collisions at Centre-of-Mass Energies near 183 GeV

Searches for pair-production of supersymmetric particles under the assumption that R-parity is violated via a single dominant $LL{\bar E}$, $LQ{\bar D}$ or ${\bar U} {\bar D} {\bar D}$ coupling are performed using the data collected by the \ALEPH\ collaboration at centre-of-mass energies of 181--184~\gev. The observed candidate events in the data are in agreement with the Standard Model expectations. Upper limits on the production cross-sections and lower limits on the masses of charginos, sleptons, squarks and sneutrinos are de rived

Search for charginos and neutralinos in e+e−e^+ e^- collisions at center-of-mass energies near 183-GeV and constraints on the MSSM parameter space

Searches for charginos and neutralinos are performed with the data collected by the ALEPH detector at LEP at centre-of-mass energies near 183 GeV. In these searches, it is assumed that R-parity is conserved and that the lightest neutralino is the LSP. No evidence of a signal is observed in the 57 pb −1 accumulated, which excludes chargino and associated neutralino production up to the kinematic limit over large regions of the MSSM parameter space. Under the assumptions of common gaugino and common sfermion masses at the unification scale, the interplay between the chargino, neutralino and slepton exclusion limits allows a lower bound of 27 GeV/ c2 to be set on the mass of the lightest neutralino. Tighter constraints on the MSSM parameter space are obtained using in addition exclusions in the Higgs sector. Finally, the results are interpreted within the framework of minimal supergravity

Search for invisible Higgs boson decays in e+ e- collisions at center-of-mass energies up to 184-GeV

In a data sample of 78.3 pb^-1 collected in 1996 and 1997 by the ALEPH detector at centre-of-mass energies from 161 to 184 GeV, invisible decays of a Higgs boson have been searched for in the reaction e+e- --> hZ, where the Z can decay into e+e-, mu+mu- or qqbar. No evidence for a signal is found and limits on the production cross section are derived as a function of the Higgs boson mass. These results are combined with those obtained in an update of the analyses of the ALEPH data taken at LEP 1. For a production cross section equal to that of the minimal standard model Higgs boson, masses below 80 GeV/c^2 are excluded at 95% C.L

Measurement of the W mass in 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 qq\uafqq\uaf and all l\u3bdqq\uaf channels to give the following W masses:where the theory error represents the possible effects of final state interactions. The combination of these two measurements, including the LEP energy calibration uncertainty, give

Search for an invisibly decaying Higgs boson in e+ e- collisions at 189-GeV

The data collected in 1998 by ALEPH at LEP at a centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 176.2 pb-1, are analysed to search for invisible decays of a Higgs boson produced in the reaction e+e- -> hZ. The number of events found in the data and their properties are in agreement with the Standard Model expectation. This search results in an improved 95% C.L. lower limit on the Higgs boson mass of 95.4 GeV/c2, assuming it decays totally invisibly and for a production cross section equal to that of the Standard Model

Search for charged Higgs bosons in e+e−e^+ e^- collisions at S(1/2)S^(1/2) = 181-GeV - 184-GeV

Data collected at centre-of-mass energies of 181-184 GeV by ALEPH at LEP, corresponding to an integrated luminosity of 56.9 pb^-1, are analysed in a search for pair-produced charged Higgs bosons H+-. Three analyses are employed to select the tau nu tau nu, tau nu c s and c s c s final states. No evidence for a signal is found. Mass limits are set as a function of the branching fraction B( H+ -> tau+ nu ). Under the assumption that the decay modes considered cover the totality of the possible final states, charged Higgs bosons with masses below 59 GeV/c^2 are excluded at 95% C.L. independently of B( H+ -> tau+ nu )