Fig. 15.

The dimuon invariant mass ($m_{\mathit{\mu }\mathit{\mu }})$ resolutions in $Z\to {\mathit{\mu }}^{+}{\mathit{\mu }}^{-}$ decays in the data and in the MC as a function of $\mathit{\eta }$ region with both decay muons in the same $\mathit{\eta }$ region, for the ID (left) and MS (right). The simulation assumes a perfectly aligned ATLAS detector