Model-independent analysis of B → πℓ + ℓ − decays

Abstract

The results obtained by calculating, on the basis of the Standard Model, the branching fractions for the decays B → πℓ + ℓ − (ℓ ± = e ±, µ±) and the invariant-mass spectrum of dileptons for the process B + → π + ℓ + ℓ − are presented. The resulting theoretical estimates depend on the choice of model for the B → π transition form factors f +(q 2), f 0(q 2), and f T (q 2). However, one can get rid of this arbitrariness by employing experimental data or the results of QCD lattice calculations to determine the parameter dependence of the form factors. Data from B-meson factories were used to determine the dependence of the form factor f +(q 2) on the transfer momentum squared. Yet another required form factor, f T (q 2), was extracted from available lattice data on B → π and B → K transitions with allowance for nearly identical effects of the breakdown of flavor SU(3) F symmetry in the respective form factors. The resulting value of the decay branching fraction, B(B + → π +µ+µ−) = (1.88 +0.32−0.21 ) × 10−8, is in good agreement with the results of measurements of the LHCb Collaboration. The branching fraction for the isospin analog of the decay under consideration is B(B + → π +µ+µ−) = (0.94 +0.16−0.11 ) × 10−8. Therefore, this decay can be measured at the Super-B factory under construction.