Semileptonic Decays of Heavy Quarks

The presence of hadrons containing heavy quarks is deduced by the observation of their decay products. In a first approximation of fc-fiavored hadron decays, only the beauty quark participates in the transition while the other quark acts as a specta- 

The table shows the quark content, the mass, the lifetime and the decay length [30] 

The universality of the weak decay is reflected in the unitarity of the CKM matrix. Hence, the CKM matrix can be parametrized by three mixing angles and one irreducible phase which accounts for the Cf -violation intrinsic to the weak decay in the Standard Model. The decay width is proportional to the squared CKM matrix element. Measurements of semileptonic decays of B mesons have shown that the matrix elements relevant for the weak decay of the b quark are very small compared to other elements Vcb = 0.0412 0.0011 and Vub = 0.00393 0.00036 [30]. Consequently, the b quark decay is highly suppressed and the b quark has a relatively large lifetime of r 10 s. Since Vcb is about an order of magnitude larger than I Vub the preferred decay is ft cW with a branching ratio of almost 100%. 

The W boson originating If om the weak decay of the b quark decays either hadron-ically or leptonicaUy. Within this analysis the semileptonic decay of b quarks into muons is studied since the muon provides a clean signature which is relatively easy 

In addition, about 10% of the subsequent charm decays also have a muon and a neutrino in the final state. The Feynman diagrams of the semileptonic decay of a Z -hadron with a muon in the final state are illustrated in Fig. 3.10. 

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