0000000000826196
AUTHOR
J.-c Brient
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 art: 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/c(2), assuming it decays totally invisibly and for a production cross section equal to that of the Standard Model. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Single- and multi-photon production in e+e− collisions at a centre-of-mass energy of 183 GeV
The production of final states involving one or more energetic photons from e(+)e(-) collisions is studied in a sample of 58.5 pb(-1) of data recorded at a centre-of-mass energy of 183 GeV by the ALEPH detector at LEP. The e(+)e(-) --> v (v) over bar gamma(gamma) and e(+)e(-) --> gamma gamma(gamma) cross sections are measured. The data are in good agreement with predictions based on the Standard Model and are used to set upper limits on the cross sections for anomalous photon production in the context of two supersymmetric models and for various extensions to QED. In particular, in the context of a super-light gravitino model a cross section upper limit of 0.38 pb is placed on the process e…
Absolute mass lower limit for the lightest neutralino of the MSSM from $e^{+}e^{-}$ data at $\sqrt{s}$ up to 209 GeV
Charginos and neutralinos are searched for in the data collected by the ALEPH experiment at LEP for centre-of-mass energies up to 209 GeV. The negative result of these searches is combined with those from searches for sleptons and Higgs bosons to derive an absolute lower limit of 43.1 GeV/c(2) on the mass of the lightest supersymmetric particle (LSP), assumed to be the,lightest neutralino. This limit is obtained in the framework of the MSSM with R-parity conservation and with gaugino and sfermion mass unification at the GUT scale and assuming no mixing in the stau sector. The LSP limit degrades only slightly to 42.4 GeV/c(2) if stau mixing is considered. Within the more constrained framewor…
Four-jet final state production in $e^+ e^-$ collisions at centre-of-mass energies ranging from 130 to 184 GeV
The four jet topology is analysed in the ALEPH data taken between November 1995 and November 1997, at centre-of-mass energies ranging from 130 to 184 GeV. While an unexpected accumulation of events with a dijet mas sum around 105 GeV/c**2 had been observed during the first run in 1995 at 130/136 GeV, corresponding to an integrated luminosity of 5.7 pb-1, no significant differences between data and standard model prediction is noticed, either in the high energy runs (81.1 pb-1 taken at centre-of-mass energies from 161 to 184 GeV) or in the 7.1 pb-1 recorded during a new short run at 130/136 GeV in 1997. We have found no other explanation for the earlier reported ``four jet anomaly'' than a s…