Semi-leptonic flavour-changing neutral-current decays of the fourth generation b′-quark
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Abstract:

AbstractWe study the decay modes b′ → bℓ+ℓ−, b′ → bνν for minb′ ⪅MZ including virtual γ, Z0, and box diagram contributions, the latter complicating the computation considerably. Due to the effect of the Z0 propagator and the finite Z0 width, these decay rates are substantial. The box diagram is subleading but also not negligible. As a consequence, the lepton pair mass distribution is rather flat and high mass ℓ+ℓ− or νν pairs are much more abundant than suggested from phase space. It is found that b′ → bZ∗ (loosely denoting the sum of ifb′ → bℓ+ℓ−, b′ → νν and b′ → bqq) is of similar order as the b′ → bg decay mode, and is likely to dominate in case mt′ is very heavy. With three light neutrinos, the decay b′ → bνν is similar order as b′ → b γ, however, the b′ → bℓ+ℓ− mode are relatively suppressed. The flavour-changing neutral-current b′ decay scenario is thus shown to be quite rich. A comprehensive, but theoretical, discussion is given regarding b′ discovery potentials at present and future colliders.

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