Rare decays of the Z and the standard model, 4th generation, and beyond
Several issues in rare decays of the Z are addressed. The rate for flavor-changing Z decay grows as the fourth power of the fermion masses internal to the quantum loop, and so offers a window to the existence of ultraheavy (m > M{sub W}) fermions. In the standard model, with three generations, BR(Z {yields} bs) < 10{sup -7} and BR(Z{yields}tc)<10{sup -13}. With four generations, BR(Z {yields} bb{sub 4}) may be as large as 10{sup -5} if m{sub b4} < M{sub Z}; and similarly for BR(Z {yields} N{sub 4}v), where N{sub 4} is the possibly heavy fourth generation neutrino. In supersymmetric and other two Higgs doublet models, BR(Z {yields} tc) may be as large as 5 {times} 10{sup -6} in the three generation scheme. With minimal supersymmetry, the reaction Z {yields} H{gamma} is guaranteed to go, with a parameter-dependent branching ratio of 10{sup -6 {plus minus} 3}. With mirror fermions or exotic E{sub 6} fermions, the branching ratios for Z {yields} ct (70 GeV), Z {yields} {mu}{tau}, and Z {yields} bb{sub 4} (70 GeV) are typically 10{sup -4}, 10{sup -4}, and 10{sup -3} respectively, clearly measurable at LEP. Depending on unknown quark masses, the Z may mix with vector (b{sub 4}{bar b}{sub 4}) and the W may mix with vector (t{bar b}) or (t{bar s}). CP violating asymmetries in flavor-changing Z decay are immeasurably small in the standard model, but may be large in supersymmetric and other nonstandard models. 28 refs.
- Research Organization:
- Vanderbilt Univ., Nashville, TN (USA). Dept. of Physics and Astronomy
- Sponsoring Organization:
- DOE/ER
- DOE Contract Number:
- FG05-85ER40226
- OSTI ID:
- 7273802
- Report Number(s):
- CONF-8902110-5; ON: DE90007182; TRN: 90-006612
- Resource Relation:
- Conference: 2. international symposium on the 4th family of quarks and leptons, Santa Monica, CA (USA), 23-25 Feb 1989
- Country of Publication:
- United States
- Language:
- English
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Z NEUTRAL BOSONS
WEAK PARTICLE DECAY
BRANCHING RATIO
CP INVARIANCE
HIGGS BOSONS
STANDARD MODEL
SUPERSYMMETRY
BOSONS
DECAY
ELEMENTARY PARTICLES
INTERMEDIATE BOSONS
INTERMEDIATE VECTOR BOSONS
INVARIANCE PRINCIPLES
MATHEMATICAL MODELS
PARTICLE DECAY
PARTICLE MODELS
POSTULATED PARTICLES
SYMMETRY
UNIFIED GAUGE MODELS
645203* - High Energy Physics- Particle Interactions & Properties-Theoretical- Weak Interactions & Properties