Dr Fabio Bernardoni (DESY (DE))
At present there is a tension at the level of 3 \sigma between two exclusive determinations of |Vub|. They are obtained combining the experimental branching ratios of B -> \tau \nu and B -> \pi l \nu (respectively) with a theoretical computation of the hadronic matrix elements f_B and the B to \pi form factor f_+(q^2). To understand the tension, improved precision and a careful analysis of the systematics involved are necessary. We report the results of the ALPHA collaboration for f_B from the Lattice with N_f=2 O(a) improved Wilson fermions. We employ HQET, including 1/m_b corrections, with pion masses ranging down to ~250 MeV. Renormalization and matching were performed non-perturbatively, and three lattice spacings reaching a^-1~4.1 GeV are used in the continuum extrapolation. We also present progress towards a computation of f_+(q^2), to directly compare two independent exclusive determinations of |Vub| with each other and with inclusive determinations. Additionally, we report on preliminary results for f_Bs, which is needed to determine |Vtd| and |Vts|.
Alberto Ramos (CNRS) Antoine Gerardin (Laboratoire de Physique Théorique, Université Paris) Benoit Blossier (DESY) Dr Fabio Bernardoni (DESY (DE)) Mr Felix Bahr (DESY Zeuthen) Georg Matthias Von Hippel Dr Hubert Simma (DESY) Dr Jochen Heitger (Munster University) John Merritt Bulava (CERN) Michele Della Morte (Unknown) Michele Della Morte Nicolas Garron Patrick Fritzsch (H) Rainer Sommer