Improved Limits on B⁰ Decays to Invisible (+γ) Final States

We establish improved upper limits on branching fractions for B⁰ decays to final states where the decay products are purely invisible (i.e., no observable final state particles) and for final states where the only visible product is a photon. Within the Standard Model, these decays have branching fractions that are below the current experimental sensitivity, but various models of physics beyond the Standard Model predict significant contributions for these channels. Using 471 x 10⁶ BB̅ pairs collected at the Υ(4S) resonance by the BABAR experiment at the PEP-II e⁺e⁻ storage ring at the SLAC National Accelerator Laboratory, we establish upper limits at the 90% onfidence level of 2.4 x 10⁻⁵ for the branching fraction of B⁰ → invisible and1.7 x 10⁻⁵ for the branching fraction of B⁰ → invisible + γ.