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

03 February 2019

Abstract: 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 $\Upsilon \left(2S\right)\to \Upsilon \left(1S\right){\pi }^{+}{\pi }^{-}$, followed by the on-shell process $\Upsilon \left(1S\right)\to \gamma {A}^{0}$ with ${A}^{0}\to \chi \chi$, or by the off-shell process $\Upsilon \left(1S\right)\to \gamma \chi \chi$. Utilizing a data sample of $157.3×{10}^{6}$ $\Upsilon \left(2S\right)$ decays, we find no evidence for a signal. We set limits on the branching fractions of such processes in the mass ranges ${M}_{{A}^{0}}<8.97\text{}\text{}\mathrm{GeV}/{c}^{2}$ and ${M}_{\chi }<4.44\text{}\text{}\mathrm{GeV}/{c}^{2}$. We then use the limits on the off-shell process to set competitive limits on WIMP-nucleon scattering in the WIMP mass range below $5\text{}\text{}\mathrm{GeV}/{c}^{2}$.

Published in: Physical Review Letters 122 (2019)