Abstract : A ﬂavour independent search for the neutral Higgs boson is performed in the four jets chanel, e+e− -> h(hadrons)Z(qqbar), in the chanel with missing energy, e+e− -> h(hadrons)Z(nu nubar) and in the leptonic chanel e+e− -> h(hadrons)Z(e+e−, µ+µ−).
The analysed data have been collected by the ALEPH detector at LEP during the years 1998, 1999 and 2000, at center of mass energies from 189 to 210 GeV.
Selections in four jets and missing energy chanels are based on artiﬁcial neural networks multivariate method. This allows to combine non linearly the signal informations. To obtain a selection independent of the Higgs boson decay products, these informations are purely kinematic and topologic variables.
The selection in the leptonic chanel is performed by a set of cuts, and uses the very good electron and muon identiﬁcation.
No evidence of signal has been seen in the data collected by ALEPH up to 189 GeV. This allows to restrict the allowed values of the mass, cross section and branching ratio of the Higgs boson. The result is expressed by a excluded region at 95% of conﬁdence level in a two dimensions space. With this, it's possible to verify if a particular model is excluded or not by the experience.
This result is interpreted in the Standard Model and the MSSM. In the Standard Model, a lower limit is derived on the Higgs boson mass, Mh > 109.5 GeV/c2, with a 95% of conﬁdence level.