Electroweak precision measurements with the CMS detector

We report on a precision measurement of the effective weak mixing angle using the forward-backward asymmetry of Drell-Yan ($ee$ and $\mu\mu$) events in pp collisions at $\sqrt{s}=8~\mathrm{TeV}$ at CMS. The data sample corresponds to an integrated luminosity of $18.8~\mathrm{fb}^{-1}$ and $19.6~\mathrm{fb}^{-1}$ for muon and electron channels, respectively. The sample consists of 8.2 million dimuon and 4.9 million dielectron events. With new analysis techniques and large samples the statistical and systematic uncertainties are reduced by a factor of two compared to previous measurements at the LHC. The extracted value of the effective weak mixing angle from the combined $ee$ and $\mu\mu$ data samples is $sin^2\theta^{lept}_{eff}=0.23101\pm 0.00036(stat)\pm 0.00018(syst)\pm 0.00016(theory)\pm 0.00030(pdf)$ or $sin^2\theta^{lept}_{eff}=0.23101\pm0.00052$.