Upper limits on branching ratios of the lepton-flavor-violating decays τ → ℓ γ γ and τ → ℓ X

TLDR: In this article, the first 90% C.L.L upper bound on branching ratios was obtained for weakly interacting boson with mass (X) l1.6.

Abstract: From analysis of data produced by the BABAR experiment, the first upper bounds (90% C.L.) were obtained on the branching ratios $\mathrm{Br}(\ensuremath{\tau}\ensuremath{\rightarrow}e\ensuremath{\gamma}\ensuremath{\gamma})l2.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and $\mathrm{Br}(\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}\ensuremath{\gamma})l5.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. In addition, improved upper bounds (95% C.L.) were found on branching ratios $\mathrm{Br}(\ensuremath{\tau}\ensuremath{\rightarrow}eX)l1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ and $\mathrm{Br}(\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}X)l\phantom{\rule{0ex}{0ex}}2.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, where $X$ is an undetected weakly interacting boson with mass ${m}_{X}l1.6\text{ }\text{ }\mathrm{GeV}/{c}^{2}$.