A search for the Standard Model Higgs boson with missing mass final states at center-of-mass energy 188.6 Gev with the ALEPH detector at LEP

Standard Model has been very successful in describing and predicting particle physics phenomena. So far there is no experimental evidence which contradicts the Standard Model. However, the Higgs boson, which gives masses to the weak gauge bosons and fundamental fermions and is predicted by the theory, so far still eludes physicists. The discovery of the Standard Model Higgs boson would be an indispensable proof of the validity of Standard Model. This thesis presents a search for the Standard Model neutral Higgs boson with missing mass final state with the data collected by ALEPH detector at center-of-mass energy 199.6 GeV in 1998. A data set of total integrated luminosity 176.2 pb-1 is used in this search. Neural networks are employed in the selection of missing mass events. When this search is combined with the searches for the Higgs final states, the Standard Model neutral Higgs boson has been excluded below 90.2 GeV /c2 with 95% confidence level.