Fourth generation b ' decays into b+Higgs boson - art. no. 057303

In a fourth generation quark exists whose mass is below 255 GeV, then the o nly two-body charged current decay, b'-->c+W, is doubly Cabibbo suppressed. For this reason, CDF has searched for the one-loop neutral current decay b '-->b+Z, assuming that the branching ratio into b+Z is 100%; an analysis gi ving the bounds on m(b') for smaller branching ratios is in preparation. in this Brief Report, we examine the neutral current decay b'-->b+H, which wi ll occur if the Higgs boson mass is less than m(b')-m(b). Four different ca ses are examined: the sequential case, the non-chiral isosinglet case, the non-chiral isodoublet case, and a two-Higgs-doublet model with flavor-chang ing neutral currents. In the first three of these, the rates for b'-->b+Z a nd b'-->b+H are comparable, assuming comparable phase space factors: in the fourth, b'-->b+H is completely dominant. Thus, we emphasize the importance of giving b' mass bounds as a function of the branching ratio into b+Z, si nce the assumption of a 100% branching ratio for b'-->b+Z may only be valid if the Higgs boson mass is near or above the b' mass.