Measurements of Inclusive W/Z Production Cross Sections at CMS and W/Z as a Luminometer

Leptonic decays of W/Z bosons provide the first electroweak precision measurements at the Large Hadron Collider (LHC). The results of measurements of inclusive W and Z boson production cross sections in pp collisions at $\sqrt{s}=7 \mathrm{TeV}$ are presented, based on 2.9 pb$^{-1}$ of data recorded by the Compact Muon Solenoid (CMS) detector at the LHC. The measurements, performed in the electron and muon decay channels, are combined to give $\sigma(\mathrm{pp} \rightarrow \mathrm{W}X) \times {\cal{B}}(\mathrm{W} \rightarrow \ell \nu)$ = $9.95\pm0.07\,{\textrm{(stat.)}}\pm 0.28\,{\textrm{(syst.)}}\pm1.09\,{\textrm{(lumi.)}} \mathrm{nb}$ and $\sigma(\mathrm{pp} \rightarrow \mathrm{Z}X) \times {\cal{B}}(\mathrm{Z} \rightarrow \ell^+ \ell^-)$ = $0.931\pm0.026\,{\textrm{(stat.)}}\pm 0.023\,{\textrm{(syst.)}}\pm0.102\,{\textrm{(lumi.)}} \mathrm{nb}$, where $\ell$ stands for either $\mathrm{e}$ or $\mu$. Theoretical predictions, calculated at the next-to-next-to-leading order (NNLO) in QCD using recent parton distribution functions (PDFs), are in agreement with the measured cross sections. Hence copious production of these well understood and clean signatures suggest the use of W/Z as a "standard candle" for measuring the luminosity at the LHC alongside the current Van der Meer (VdM) separation scan method.