Upper limits on branching ratios of the lepton-flavor-violating decays $τ\to \ell γγ$ and $τ\to \ell X$
From analysis of data produced by the BABAR experiment, the first upper bounds (90% C.L.) were obtained on the branching ratios $Br(τ\to e γγ)<2.5 \times 10^{-4}$ and $Br(τ\to μγγ)<5.8 \times 10^{-4}$. In addition, improved upper bounds (95% C.L.) were found on branching ratios $Br(τ\to e X)<1.4 \times 10^{-3}$ and $Br(τ\to μX) <2.0 \times 10^{-3}$, where $X$ is an undetected weakly interacting boson with mass $m_X<1.6$ GeV/$c^2$.
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