Non-Leptonic Decays Op Beauty Hadrons – From Phenomenology to Theory

Abstract

In the last few years considerable progress has been achieved in our understanding of the decays of heavy flavour hadrons. One can now calculate inclusive transition rates in QCD proper through an expansion in inverse powers of the heavy flavour quark mass without recourse to phenomenological assumptions. The non-perturbative contributions are treated systematically in this way; they are found to produce corrections of order a few percent in beauty decays, i.e. typically somewhat smaller than the perturbative corrections. One finds, among other things: (a) The lifetime of B − mesons is predicted to be longer than that of B 0 mesons by several percent. (b) The QCD prediction for the semileptonic branching ratio of B mesons appears to exceed present experimental values. We discuss the implications of this discrepancy. The phenomenological engineering that has been developed for the description of exclusive two-body modes of B mesons has reached a mature stage and awaits more precise and detailed experimental tests. First steps towards a genuine QCD treatment of these modes are being made. 'Anyone who keeps the ability to see beauty never grows old'Franz Kafka 1 To appear in the second edition of the book 'B Decays', S.Stone (ed.), World Scientific 2 Permanent address

Lifetimes of heavy-flavour hadrons—whence and whither?

“…Quantitative predictions [16] for the lifetime ratios of beauty hadrons through order 1/m 3 b are given in Table 2 together with present data. The predictions follow the same general pattern as in charm decays.…”

Higher-order perturbative corrections to b → c transitions at zero recoil

“…where ∆m ∼ Λ QCD is the renormalon ambiguity in the pole mass of a heavy quark [24,27]. As previously, the upper (lower) sign refers to the vector (axial vector) current.…”

Measurements of the b baryon lifetime

“…Deviations from this picture could arise from non-perturbative QCD corrections or the presence of non-spectator e ects such a s Wexchange or W-annihilation. In contrast to the diversity observed in the lifetimes of charm hadrons, the di erences among various b hadron species have been estimated to be not much larger than 10% [1], due to the larger b quark mass. Non-spectator e ects should be small in the case of b mesons, but could be larger in b baryon decays due to the absence of helicity suppression in the nal state; thus a comparison of the lifetimes of b mesons and b baryons is of special interest.…”

“…To calculate the product branching ratio, a detection e ciency of (7:5 0:6)% is determined using a Monte Carlo simulation [16] of process (1) in which a b baryon polarization of 30% [17] is assumed. Applying this e ciency, the product branching ratio is …”