Search for B0 Decays to Invisible Final States and to nu nubar gamma
  We establish 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 B0 decays to nu nubar gamma. Within the Standard Model, these decays have branching fractions that are below current experimental sensitivity, but various models of physics beyond the Standard Model predict significant contributions from these channels. Using 88.5 million B Bbar pairs collected at the Y(4S) resonance by the BaBar experiment at the PEP-II e+e- storage ring at the Stanford Linear Accelerator Center, we establish upper limits at the 90% confidence level of 22 x 10^-5 for the branching fraction of B0 -> invisible and 4.7 x 10^-5 for the branching fraction of B0 -> nu nubar gamma. 
B. Aubert, et al, BABAR Collaboration