Speaker
Description
The Belle and Belle II experiment have collected samples of $e^+e^-$ collision data at center-of-mass energies near the $\Upsilon(nS)$ resonances. These data have constrained kinematics and low multiplicity, which allow searches for dark sector particles in the mass range from a few MeV to 10 GeV. We present new searches in a $600~\mathrm{fb}^{-1}$ sample collected by Belle II, including searches for a light dark photon decaying to a pair of muons, an axion-like particle decaying to two photons, and a $Z^{\prime}$ boson that decays invisibly. Using a $711~\mathrm{fb}^{-1}$ sample collected by Belle, we search for $B\to h + \mathrm{invisible}$ decays, where $h$ is a $\pi$, $K$, $D$, $D_{s}$ or $p$, and $B\to Ka$, where $a$ is an axion-like particle.
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