| Summary: | We establish improved upper limits on branching fractions for B[superscript 0] 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 471×10[superscript 6] BB̅ pairs collected at the Υ(4S) resonance by the BABAR experiment at the PEP-II e[superscript +]e[superscript -] storage ring at the SLAC National Accelerator Laboratory, we establish upper limits at the 90% confidence level of 2.4×10-5 for the branching fraction of B[superscript 0]→invisible and 1.7×10[superscript -5] for the branching fraction of B[superscript 0]→invisible+γ.
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