|Vub | determination in lattice QCD LPHAA Collaboration

The 2012 PDG reports a tension at the level of 3σ between two exclusive determinations of |Vub|. They are obtained by combining the experimental branching ratios of B → τν and B → pilν (respectively) with a theoretical computation of the hadronic matrix elements fB and the B → pi form factor f+(q2). 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 fB from the lattice with 2 flavors of O(a) improved Wilson fermions. We employ HQET, including 1/mb corrections, with pion masses ranging down to ≈ 190 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+(q2), to directly compare two independent exclusive determinations of |Vub | with each other and with inclusive determinations. Additionally, we report on preliminary results for fBs, needed for the analysis of Bs → µ+µ−