Pair production of the fourth family charged sleptons at e+e- colliders

We study the pair production of $\tilde{l}_{4} $, which is the supersymmetric partner of the fourth family charged lepton, at the e+e− colliders. It is shown that the investigation of this process at ILC/CLIC will give the opportunity to differentiate the MSSM with three and four families. The ILC with $\sqrt{s}=1\,{\rm TeV} $ and Lint = 1 ab−1 has the potential for the observation of the fourth family slepton with mass up to 420 GeV, if the fourth SM family neutrino has a Dirac nature. The CLIC with $\sqrt{s}=3\,{\rm TeV} $ and Lint = 1 ab−1 will enlarge the observation region up to $m_{\tilde{l}_4}=580\,{\rm GeV} $.