  The recent result of the higgs search at the LHC experiment has lead to more
attention to the supersymmetric standard models with heavy sfermions. Among
them, the models with the almost pure wino being the lightest supersymmetric
particle (LSP) have been widely discussed due to their success in providing a
consistent dark matter candidate. The notable phenomenological feature of the
wino LSP is the degeneracy with its charged SU(2)_L partner (the charged wino)
in mass. The tiny mass splitting makes the charged wino long-lived, which
allows us to detect the wino production at the LHC experiment by searching for
the disappearing charged tracks inside the detectors. Since the reach of the
experiment is sensitive to the mass splitting, it is mandatory to estimate it
very precisely. We therefore perform a full calculation of the mass splitting
at two-loop level, and find that the splitting is reduced by a few MeV compared
to the one-loop calculation. This reduction leads to about a 30 % longer
lifetime of the charged wino, with which the current constraint on the wino
mass by the ATLAS experiment is improved by about 10 %.
