2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/207323We report the results of a search for the decay B^0 -> e^+ e^-, mu^+ mu^- and e^{+-} mu^{-+} based on an analysis of 78 fb^{-1} of data collected by the Belle detector at KEKB. No candidate events have been found. Upper limits on the branching fractions are calculated at the 90% confidence level: B(B^0 -> e^+ e^-) < 1.9 x 10^{-7}, B(B^0 -> mu^+ mu^-) < 1.6 x 10^{-7}, and B(B^0 -> e^{+-} mu^{-+})< 1.7 x 10^{-7}. A limit on the Pati-Salam leptoquark mass M_{LQ}> 46 TeV/c^2 is obtained at the 90% confidence level.8 pages, 1 figure, submitted to Phys. Rev. D (RC)High Energy Physics - Experimenttext