| We report a search for a light CP-odd Higgs boson A 0, which can be produced in U decays and decay to low mass dark matter, chi. We search for evidence of the on-shell process, Y(1S) → gamma A0,A0 → chichi, and the off-shell process, Y(1S) → gammachichi, via the dipion transition Y(2S) → Y(1S)pi+pi--. We present the first Belle search for final states with a single photon and missing energy in the mass range of MA0 < 9.0 GeV/c2 and Mchi < 4.5 GeV/c2 with a data sample of 157.3 x 106 Y(2S) decays. We find no evidence for a signal and set limits on branching fractions for such processes. We also use the limit on the off-shell process to set competitive limits on WIMP-nucleon scattering cross sections. |
