Higgs Discovery before Lhc ?

The standard model (SM) of fundamental interactions, has been the successful theory over the last 25 years. The overall success of the SM in describing the elementary interactions, the discovery of gauge bosons at CERN in the eighties as well as the top discovery at Fermilab in 1995, strengthened the expectation that the Higgs mechanism is the one that gives mass to all particles. At the moment the Higgs particle is the only missing pieces of the puzzle. The sensitivity of parameters of the electroweak theory to the mass of the top quark and of the W boson has been exploited to provide limits on the mass of the Higgs particle (MH). Due to the logarithmic dependence of MH to the ratio of MW/Mtop, a small change in the central values translates into a large change in the limit on MH . At present (Spring 2001), the current 95% CL lower bound is 212 GeV/c while the upper limit from LEP experiments is 113.5 GeV/c with the additional hint of a possible signal at 115 GeV/c[1]. Due to its coupling Higgs decays into the heaviest possible pair of particles, therefore for MH below 130 GeV/c 2 (low mass region) the most important channels are b or τ pairs, while for heavier masses, the branching fraction into vector boson pairs becomes dominant. A hadron collider provides excellent chances to discover the Higgs given that (in the low mass region) tagging of b-jets would be available. The tool became a reality at the Tevatron during the search for top and is now taken for granted in any experiment at hadron colliders. In fig. 1 Higgs production cross section at 2 TeV is shown. While the gluon fusion mechanism is by large the dominating generating process, the signal over background ratio is such that at low mass the associated production of Higgs particle and vector boson (W,Z) is better suited for a discovery. At the Tevatron the interaction cross section is about 70 mb. About 70% of it provides events that are visible in the experiments while the Higgs cross section is in the order of 1 pb or less. Therefore an efficient trigger