Search for long-lived resonance decaying to a dilepton pair in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

A search for a long-lived neutral massive particle decaying to a $\mu\mu$, $ee$, or $e\mu$ pair is presented with 32.8 $\mathrm{fb^{-1}}$ of $pp$ collisions at $\sqrt{s}=13$ TeV taken by the ATLAS detector at the LHC. Upper limits are presented on the production cross section times branching ratio for resonances decaying to a lepton pair. Also presented is the detection efficiency as a function of $p_{T}$ and $\eta$ for a resonance with mass of 0.1$-$2.0 TeV and lifetime ($c\tau$) of 100$-$500 mm to allow for an estimate of the upper limit on the cross section for any model of interest.