Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
2002-02-18
Int.J.Mod.Phys.A17:4709-4732,2002
Physics
High Energy Physics
High Energy Physics - Phenomenology
24 pages, 6 figures, LaTeX. Revised: Complete version. Numerical predictions are improved and the estimate for the decay fract
Scientific paper
10.1142/S0217751X02010856
Measuring the photon energy spectrum in radiative B decays provides essential help for gaining theoretical control over semileptonic B transitions. The hadronic recoil mass distribution in B -> X_u \ell\nu promises the best environment for determining |V_ub|. The theoretical uncertainties are largest in the domain of low values of the lepton pair mass q^2. Universality relations allow to describe this domain reliably in terms of the photon spectrum in B -> X_s + \gamma. A method is proposed to incorporate 1/m_b corrections into this relation. The low-E_\gamma tail in radiative decays is important in the context of extracting |V_ub|. We argue that CLEO's recent fit to the spectrum underestimates the fraction of the photon spectrum below 2 GeV. Potentially significant uncertainties enter in the theoretical evaluation of the integrated end-point lepton spectrum or the B -> X_u \ell\nu width with a too high value of the lower cut on q^2 in alternative approaches to |V_ub|.
Bigi Ikaros I.
Uraltsev Nikolai
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