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Search Capability for $η\to ν_{e,τ}\barν_{e,τ}$ Decays in Cubic Kilometer Neutrino Detectors

We investigate the discovery potential of cubic kilometer neutrino observatories such as IceCube to set stringent limits on the forbidden decays $η\toν_e\barν_e$ and $η\toν_τ\barν_τ$. The signatures for these decays are cascade events resulting from the charged-current reactions of $ν_e, ν_τ$, $\barν_e$ and $\barν_τ$ on nuclei in such detectors. Background cascade events are mainly due to $ν_e$'s from atmospheric $μ$, $K^+$, and $K^{0}_S$ decays and to a lesser extent from atmospheric $ν_μ$ neutral current interactions with nuclei. A direct upper limit for the branching ratio $η\to ν_{e,τ} \barν_{e,τ}$ of $4.5\times10^{-4}$ at 90% CL can be achieved.