Search for a Light CP-odd Higgs Boson and Low-Mass Dark Matter at the Belle Experiment

We report on the first Belle search for a light CP-odd Higgs boson, A(0), that decays into low mass dark matter, chi, in final states with a single photon and missing energy. We search for events produced via the dipion transition (sic)(2S) -> (sic)(1S)pi(+)pi(-), followed by the on-shell process (sic)(1S) -> gamma A(0) with A(0) -> chi chi, or by the off-shell process (sic)(1S) -> gamma chi chi. Utilizing a data sample of 157.3 x 10(6) (sic)(2S) decays, we find no evidence for a signal. We set limits on the branching fractions of such processes in the mass ranges M-A0 < 8.97 GeV/c(2) and M-chi < 4.44 GeV/c(2). We then use the limits on the off-shell process to set competitive limits on WIMP-nucleon scattering in the WIMP mass range below 5 GeV/c(2).