  The minimal supersymmetric (SUSY) standard model (MSSM) augmented by right
chiral sneutrinos may lead to one such sneutrino serving as the lightest
supersymmetric particle and a non-thermal dark matter candidate, especially if
neutrinos have Dirac masses only. In such cases, if the lightest MSSM particle
is a stau, the signal of SUSY at the LHC consists in stable charged tracks
which are distinguishable from backgrounds through their time delay between the
inner tracker and the muon chamber. We show how to determine in such scenarios
the mass hierarchy between the lightest neutralino and right sleptons of the
first two families. The techniques of neutralino reconstruction, developed in
earlier works, are combined with the endpoint of the variable $M_{T2}$ in smuon
(selectron) decays for this purpose. We show that one can thus determine the
mass hierarchy for smuons (selectrons) and neutralinos up to 1 TeV, to the
level of 5-10\%.
