W and Z boson production at CMS in pp collisions at $\sqrt s=7$ TeV

We present the first measurements of inclusive W and Z production cross sections in muon and electron decay channels at $\sqrt s = 7~\textrm{TeV}$, obtained using an integrated luminosity of $198~\textrm{nb}^{-1}$ of proton proton collisions recorded by the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC). These production cross-sections at $\sqrt{s}=7~\textrm{TeV}$ have been measured to be $\sigma(W \rightarrow l \nu) = 9.22 \pm 0.24 \mathrm{(stat.)} \pm 0.47 \mathrm{(syst.)} \pm 1.01 \mathrm{(lumi.)}$~nb and $\sigma(Z\rightarrow l^{+}l^{-}) = 0.882 ^{+0.077}_{-0.073} \mathrm{(stat.)} ^{+0.042}_{-0.036} \mathrm{(syst.)} \pm 0.097 \mathrm{(lumi.)}$~nb, limited to the di-lepton invariant mass range: $60 < m_{l^{-} l^{+}} < 120~\mathrm{GeV}/c^2$. The measurement of W cross-section has also been split by charge, obtaining $\sigma(W^{+}\rightarrow l^{+}\nu) = 5.50 \pm 0.18 \mathrm{(stat.)} \pm 0.29 \mathrm{(syst.)} \pm 0.61 \mathrm{(lumi.)} ~\mathrm{nb}$ and $\sigma(W^{-}\rightarrow l^{-} \bar{\nu}}) = 3.60 \pm 0.13 \mathrm{(stat.)} \pm 0.19 \mathrm{(syst.)} \pm 0.40 \mathrm{(lumi.)} ~\textrm{nb}$. The luminosity independent cross section ratios are $\sigma(W\rightarrow l \nu)/\sigma(Z \rightarrow l^{+} l^{-})= 10.46 ^ {+0.99}_{-0.88} \mathrm{(stat.)} ^{+0.65}_{-0.56} \mathrm{(syst.)}$ and $\sigma( W^{+}\rightarrow l^{+}\nu / W^{-}\rightarrow l^{-} \bar{\nu}} ) = 1.51 ^{+0.08}_{-0.07} \mathrm{(stat.)} \pm 0.04 \mathrm{(syst.)}$. All the measurements are in good agreement with NNLO QCD cross section calculations and current parton distribution functions.