Measurement of Inclusive $W$ and $Z$ Boson Production Cross Sections in $pp$ Collisions at $\sqrt{s}=8\mathrm{TeV}$

A measurement of total and fiducial inclusive $W$ and $\mathrm{Z}$ boson production cross sections in $pp$ collisions at $\sqrt{s}=8\mathrm{TeV}$ is presented. Electron and muon final states are analyzed in a data sample collected with the CMS detector corresponding to an integrated luminosity of $18.2\pm 0.5{\mathrm{pb}}^{-1}$. The measured total inclusive cross sections times branching fractions are $\sigma (pp\to WX)\times \mathcal{B}(W\to \ell \nu )=12.21\pm 0.03(\text{stat})\pm 0.24(\text{syst})\pm 0.32(\mathrm{lum})\mathrm{nb}$ and $\sigma (pp\to \mathrm{Z}X)\times \mathcal{B}(\mathrm{Z}\to {\ell }^{+}{\ell }^{-})=1.15\pm 0.01(\text{stat})\pm 0.02(\text{syst})\pm 0.03(\mathrm{lum})\mathrm{nb}$ for the dilepton mass in the range of 60—120 GeV. The measured values agree with next-to-next-to-leading-order QCD cross section calculations. Ratios of cross sections are reported with a precision of 2%. This is the first measurement of inclusive $W$ and $\mathrm{Z}$ boson production in proton-proton collisions at $\sqrt{s}=8\mathrm{TeV}$.

Figure 1

The missing transverse energy distributions for $W$ boson candidate events in the electron (top) and muon (bottom) final states. The variable $\chi$ shown in the lower plot is defined as $(N_{\mathrm{obs}}-N_{\exp })/\sqrt{N_{\mathrm{obs}}}$, where $N_{\mathrm{obs}}$ is the number of observed events and $N_{\exp }$ is the total of the fitted signal and background yields.

Figure 2

The dilepton mass distributions for $\mathrm{Z}$ boson candidate events in the electron (top) and muon (bottom) final states. The variable $\chi$ shown in the lower plot is defined as $(N_{\mathrm{obs}}-N_{\exp })/\sqrt{N_{\mathrm{obs}}}$, where $N_{\mathrm{obs}}$ is the number of observed events and $N_{\exp }$ is the total of the signal and background yields.

Figure 3

Measured and predicted $W$ versus $\mathrm{Z}$ boson (left column) and $W^{+}$ versus $W^{-}$ boson (right column) production cross sections times branching fractions. The ellipses illustrate the 68% CL coverage for total uncertainties (open) and excluding the luminosity uncertainty (filled). The top row shows the inclusive cross sections times branching fractions and the bottom row shows the results within the fiducial regions. The uncertainties in the theoretical predictions correspond to the PDF uncertainty components only and are evaluated for MSTW 2008 NLO [43], NNPDF 2.3 [47], and CT10 [48].