A Search for the Standard Model Higgs Boson in Four-jet Final States at Center-of-mass Energies near 183 GeV with the ALEPH Detector at LEP

The center-of-mass energies available at the upgraded Large Electron Positron collider (LEP2) at CERN provide an opportunity to search for the Higgs boson, the fundamental scalar boson predicted by the Standard Model of electroweak interactions. A search is performed using data gathered by the ALEPH experiment at LEP during 1997. The data sample consists of an integrated luminosity of 57 pb<super >&minus; 1</super> at center-of-mass energies near 183 GeV. Possible signals from production of the Standard Model Higgs boson in the reaction e<super>+</super>e<super>&minus; </super> &rarr; HZ &rarr; bb &macr; qq&macr; are searched for using a cut-based analysis as well as a neural network approach. The main component of this search is a b- tagging algorithm utilizing neural network techniques. Results including other possible final states (i.e., H&ell; <super>+</super >&ell; <super>&minus; </super>, H&nu; <overline> &nu; </overline>, H&tau; <super>+</super>&tau; <super>&minus; </super> and &tau; <super> +</super>&tau; <super>&minus; </super>qq&macr; ) are also presented. No evidence of a signal is found in the data: seven events are selected, in agreement with the expectation of 7.2 events from standard processes. This results in a lower limit on the mass of the Higgs boson: MH > 87.9 GeV/<italic>c</italic><super> 2</super> at a 95donfidence level.