|V_ub| and Constraints on the Leading-Twist Pion Distribution Amplitude from B->pi l nu

Abstract

Using new experimental data on the leptonic mass spectrum of B->pi l nu, we simultaneously determine |V_ub| and constrain a_2^pi and a_4^pi, the first two Gegenbauer moments of the pion's leading-twist distribution amplitude. We find |V_ub| = (3.2\pm 0.1\pm 0.1\pm 0.3) 10^-3, where the first error is experimental, the second comes from the shape of the form factor in q^2 and the third is a 8% uncertainty from the normalisation of the form factor. We also find a_2^pi(1 GeV)=0.19\pm 0.19 and a_4^pi(1 GeV)\geq -0.07.