Searches for gauge mediated supersymmetry breaking at ALEPH with centre-of-mass energies up to 209 GeV

Abstract

A total of 628 pb-1 of data collected with the ALEPH detector at centre-of-mass energies from 189 to 209 GeV is analysed in the search for gauge mediated supersymmetry breaking (GMSB) topologies. In this framework, a novel search for six-lepton final states when the stau is the next-to-lightest supersymmetric particle (NLSP) and has negligible lifetime is performed. Other possible signatures at LEP are studied and the ALEPH final results described for two acoplanar photons, non-pointing single photons, acoplanar leptons, large impact parameter leptons, detached slepton decay vertices, heavy stable charged sleptons and multi-leptons plus missing energy final states. No evidence is found for new phenomena, and lower limits on the masses of the relevant supersymmetric particles are derived. A scan of a minimal GMSB parameter space is performed and lower limits are set for the NLSP mass at 54 GeV and for the mass scale parameter Lambda at 10 TeV, independent of the NLSP lifetime. Including the results from the neutral Higgs boson searches, a NLSP mass limit of 77 GeV is obtained and values of Lambda up to 16 TeV are excluded.Comment: PhD thesis Royal Holloway University of London, September 2002 111 pages, with 55 figures and 22 table