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On The Expected Photon Spectrum in B -> X_s + gamma and Its Uses

Ikaros Bigi·Nikolai Uraltsev
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Abstract

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 \ellνpromises 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 + γ. A method is proposed to incorporate 1/m_b corrections into this relation. The low-E_γtail 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 \ellνwidth with a too high value of the lower cut on q^2 in alternative approaches to |V_ub|.

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Ikaros Bigi, Nikolai Uraltsev. 2002-04-17. On The Expected Photon Spectrum in B -> X_s + gamma and Its Uses. https://doi.org/10.1142/s0217751x02010856

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