Fourth Generation b-prime decays into b + Higgs

TL;DR

This paper explores the decay modes of a hypothetical fourth-generation b' quark, focusing on the neutral current decay b' --> bH, and discusses how Higgs mass influences decay branching ratios and experimental bounds.

Contribution

It analyzes the decay channels of b' quarks into bH across different models, highlighting the significance of Higgs mass in decay branching ratios and experimental searches.

Findings

b' --> bH decay can dominate if Higgs mass is low

Branching ratios depend on the specific model and Higgs mass

Importance of setting mass bounds based on variable branching ratios

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.