Search for fourth generation quarks and leptons at the Fermilab Tevatron and CERN large hadron collider

If the next generations of heavy quarks and leptons exist within the standard model (SM), they can manifest themselves in Higgs boson production at the Fermilab Tevatron and the CERN LHC, before being actually observed. This generation leads to an increase of the Higgs boson production cross section via gluon fusion at hadron colliders by a factor 6-9. So, the study of this process at the Tevatron and LHC can finally fix the number of generations in the SM. Using the WW* Higgs boson decay channel, the studies at the upgraded Tevatron will answer the question about the next generation for mass values 135 GeV less than or similar to M-H less than or similar to 190 GeV. Studying the tau<(tau)over bar> channel we show its large potential for the study of the Higgs boson at the LHC even in the standard case of three generations. At the Tevatron, studies in this channel could explore the mass range 110-140 GeV. [S0556-2821(99)08319-8].