Search for charged lepton flavor violating decays of ϒ (1S)

We present a search for the charged lepton-flavor-violating decays $\Upsilon(1S)\rightarrow\ell\ell^\prime$ and radiative lepton-flavour-violating $\Upsilon(1S)\rightarrow\gamma\ell\ell^\prime$ [$\ell,\ell^\prime = e, \mu, \tau$] using 158 million $\Upsilon(2S)$ sample collected by Belle detector at KEKB collider. This uses $\Upsilon(1S)$ mesons produced in $\pi^+\pi^-\Upsilon(1S)$ transitions. do not find any significant signal, so we provide upper limits on branching fractions 90% confidence level.