Measurements of the differential and double-differential Drell-Yan cross sections in proton-proton collisions at 8 TeV

Measurements of the differential and double-differential Drell-Yan cross sections in the dielectron, dimuon and combined channels are presented using an integrated luminosity of $19.7~$fb$^{-1}$ of proton-proton collision data recorded with the CMS detector at the LHC at $\sqrt{s} = 8$~TeV. The measured inclusive cross section in the $Z$-peak region (60--120 GeV) is $\sigma(\textit{l}\textit{l}) = 1139.0 \pm 0.2~\text{(stat.)} \pm 7.9~\text{(exp. syst.)} \pm 25.2~\text{(th. syst.)} \pm 29.6~\text{(lumi.)}~\text{pb}$ for the combination of the dielectron and dimuon channels. The differential cross section $d\sigma/dm$ is measured in the dilepton mass range $15$ to $2000$ GeV and corrected to the full phase space. Results are also presented for the measurement of the double-differential cross section $d^2\sigma/dmd|y|$ over the mass range $20$ to $1500$ GeV and absolute dilepton rapidity from $0$ to $2.4$. In addition the ratios of the normalized differential cross sections measured at 7~TeV and 8~TeV are presented. These measurements are compared to the predictions of perturbative QCD calculations at next-to-leading and next-to-next-to-leading orders using various sets of parton distribution functions. The measurements are found in a good agreement with the NNLO theoretical predictions, as computed with FEWZ~$3.1$ using the CT10 NNLO and NNPDF2.1 NNLO PDFs. The double-differential cross section and the ratio of normalized differential cross sections presented provide sufficient sensitivity to constrain PDFs given the relatively small uncertainties.