Fourth Generation b-prime decays into b + Higgs

Abstract

If a fourth generation quark exists whose mass is below 255 GeV, then the only two-body charged current decay, b'-->cW, is doubly-Cabibbo suppressed. For this reason, CDF has searched for the one-loop neutral current decay b' --> bZ, assuming that the branching ratio into bZ is 100%; an analysis giving the bounds on m_b' for smaller branching ratios is in preparation. In this Report, we examine the neutral current decay b' --> bH, which will occur if the Higgs mass is less than m_b'-m_b. Four different cases are examined: the sequential case, the non-chiral isosinglet case, the non-chiral isodoublet case, and a two-Higgs model with flavor-changing neutral currents. In the first three of these, the rates for b' --> bZ and b' --> bH are comparable, assuming comparable phase space factors; in the fourth, b' --> bH is completely dominant. Thus, we emphasize the importance of giving b' mass bounds as a function of the branching ratio into bZ, since the assumption of a 100% branching ratio for b' --> bZ may only be valid if the Higgs mass is near or above the b' mass.