A search for heavy long-lived sleptons using 16 fb$^{-1}$ of pp collisions at $\sqrt{s} = 8$ TeV with the ATLAS detector

A search for heavy long-lived scalar leptons (sleptons) through a measurement of the mass of slepton candidates is presented in this note. The search is performed on a data sample of 15.9 fb$^{-1}$ of proton-proton collisions at a centre-of-mass energy $\sqrt{s} = 8$ TeV collected by the ATLAS detector at the LHC in 2012. Such sleptons are expected to interact as if they were heavy muons, charged and penetrating. Their mass is estimated from a measurement of their speed, $\beta$, and their momentum, $\it{p}$, using the relation $m=p/\beta\gamma$, based on their interactions in the inner detector, the calorimeters and the muon spectrometer. No excess is observed above the estimated background. Results are interpreted in the context of gauge-mediated supersymmetry breaking (GMSB) models where the $\tilde{\tau}_1$, supersymmetric partner of the $\tau$ lepton, is the next to lightest supersymmetric particle and decays outside the ATLAS volume. Lower limits, at 95% confidence level, are set on the mass of the long-lived sleptons. Long-lived $\tilde{\tau}_1$s in the GMSB model considered are excluded at 95% confidence level at masses below 425-385 GeV, for $\tan\beta = $5-50. Exclusion limits on the $\tilde{\tau}_1$ mass up to 395 (365) GeV are set in the hypothesis that $\tilde{\tau}_1$ are produced directly or via light slepton ($\tilde{e}$, $\tilde{\mu}$) pair production, assuming a mass splittings between light slepton and stau of 1 (90) GeV. In decoupled scenarios, where $\tilde{\tau}_1$ pair production is the only SUSY signature, exclusion limits up to 327 GeV are set on the $\tilde{\tau}_1$ mass. Finally, indirect constraints are placed on the mass of charginos and neutralinos.