  When the mass difference between the lightest slepton, the NLSP, and the
lightest neutralino, the LSP, is smaller than the tau mass, the lifetime of the
lightest slepton increases in many orders of magnitude with respect to typical
lifetimes of other supersymmetric particles. These small mass differences are
possible in the MSSM and, for instance, they correspond to the coannihilation
region of the CMSSM for $M_{1/2} \gsim 700$ GeV. In a general gravity-mediated
MSSM, where the lightest supersymmetric particle is the neutralino, the
lifetime of the lightest slepton is inversely proportional to the square of the
intergenerational mixing in the slepton mass matrices. Such a long-lived
slepton would produce a distinctive signature at LHC and a measurement of its
lifetime would be relatively simple. Therefore, the long-lived slepton scenario
offers an excellent opportunity to study lepton flavour violation at ATLAS and
CMS detectors in the LHC and an improvement of the leptonic mass insertion
bounds by more than five orders of magnitude would be possible.

High Energy Physics - Phenomenology