Search Strategy for Sleptons and Dark Matter Using the LHC as a Photon Collider.

We propose a search strategy using the LHC as a photon collider to open sensitivity to scalar lepton (slepton ℓ[over ˜]) production with masses around 15 to 60 GeV above that of neutralino dark matter χ[over ˜]{1}^{0}. This region is favored by relic abundance and muon (g-2){μ} arguments. However, conventional searches are hindered by the irreducible diboson background. We overcome this obstruction by measuring initial state kinematics and the missing momentum four-vector in proton-tagged ultraperipheral collisions using forward detectors. We demonstrate sensitivity beyond LEP for slepton masses of up to 200 GeV for 15≲Δm(ℓ[over ˜],χ[over ˜]_{1}^{0})≲60  GeV with 100  fb^{-1} of 13 TeV proton collisions. We encourage the LHC collaborations to open this forward frontier for discovering new physics.