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

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+(q2), f0(q2), and fT (q2). 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+(q2) on the transfer momentum squared. Yet another required form factor, fT (q2), 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−) = (1.88−0.21+0.32) × 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−) = (0.94−0.11+0.16) × 10−8. Therefore, this decay can be measured at the Super-B factory under construction.