Measurement of the Inclusive W and Z Production Cross Sections in pp Collisions at sqrt(s) = 7 TeV

Abstract: A measurement of inclusive W and Z production cross sections in pp collisions at sqrt(s)=7 TeV is presented. The electron and muon decay channels are analyzed in a data sample collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 36 inverse picobarns. The measured inclusive cross sections are sigma(pp-> WX) B(W-> l nu) = 10.30 +/- 0.02 (stat.) +/- 0.10 (syst.) +/- 0.10 (th.) +/- 0.41 (lumi.) nb and sigma(pp -> ZX) B(Z-> l^+l^-) = 0.974 +/- 0.007 (stat.) +/- 0.007 (syst.) +/- 0.018 (th.) +/- 0.039 (lumi.) nb, limited to the dilepton invariant mass range 60 to 120 GeV. The luminosity-independent cross section ratios are [sigma(pp->WX) B(W-> l nu)]/[sigma(pp-> ZX) B(Z->l^+l^-)] = 10.54 +/- 0.07 (stat.) +/- 0.08 (syst.) +/- 0.16 (th.) and [sigma(pp->W^+X) B(W^+ -> l^+nu)] / [sigma(pp->W^- X) B(W^- -> l^- nu)] = 1.421 +/- 0.006 (stat.) +/- 0.014 (syst.) +/- 0.029 (th.). The measured values agree with next-to-next-to-leading order QCD cross section calculations based on recent parton distribution functions.

• The paper measures the inclusive production cross sections of W and Z bosons in proton-proton collisions at 7 TeV using 36 pb⁻¹ of data collected by the CMS detector at the LHC.
• The study reports precise measurements of W and Z cross sections and their ratios (W/Z and W⁺/W⁻) in electron and muon decay channels, achieving high experimental accuracy.
• These results provide stringent tests of Standard Model predictions at NNLO QCD and constrain potential new physics scenarios, establishing a foundation for future analyses.

Measurement of the Inclusive W and Z Production Cross Sections in pp Collisions at $\sqrt{s} = 7 \text{TeV}$

The paper from the CMS Collaboration presents a detailed analysis of the inclusive production cross sections of W and Z bosons in proton-proton (pp) collisions at the Large Hadron Collider (LHC) with a center-of-mass energy of 7 TeV. This study utilizes data collected by the CMS detector corresponding to an integrated luminosity of 36 pb$^{-1}$. The paper is meticulous in presenting measurements carried out in the electron and muon decay channels, enabling a comprehensive exploration of electroweak (EWK) processes as a test of the Standard Model (SM) predictions.

Data Analysis and Methodology

The analysis focuses on the decay modes of W and Z bosons into electrons and muons. The inclusive cross section for W production is measured as $$\sigma(\text{pp} \rightarrow \text{WX}) \times \mathcal{B}(\text{W} \rightarrow \ell\nu) = 10.30 \pm 0.02 \text{ (stat.)} \pm 0.10 \text{ (syst.)} \pm 0.10 \text{ (th.)} \pm 0.41 \text{ (lumi.)} \text{ nb}$$, and for Z production as $$\sigma(\text{pp} \rightarrow \text{ZX}) \times \mathcal{B}(\text{Z} \rightarrow \ell^{+}\ell^{-}) = 0.974 \pm 0.007 \text{ (stat.)} \pm 0.007 \text{ (syst.)} \pm 0.018 \text{ (th.)} \pm 0.039 \text{ (lumi.)} \text{ nb}$$, emphasizing the high precision achieved in the results.

The methodology involves advanced techniques for event selection, detectors' efficiency calibration, and background subtraction. For instance, the missing transverse energy ($E_{\text{T}}^{\text{miss}}$) is a critical observable for isolating W boson candidates, while a precise invariant mass window is used for selecting Z boson candidates. Additionally, a tag-and-probe method is employed on Z events to determine lepton efficiencies, reflecting robust calibration techniques.

Results and Implications

The observed cross section ratios, $\frac{\sigma(W)}{\sigma(Z)}$ and $\frac{\sigma(W^+)}{\sigma(W^-)}$, are used as benchmarks for the SM, providing agreement with theoretical predictions at the next-to-next-to-leading order (NNLO) in quantum chromodynamics (QCD) augmented by recent parton distribution functions (PDFs). The measured ratio for the W to Z production cross sections is 10.54 $$\pm 0.07 \text{ (stat.)} \pm 0.08 \text{ (syst.)} \pm 0.16 \text{ (th.)}$$, and for W$^+$ to W$^-$ it is 1.421 $$\pm 0.006 \text{ (stat.)} \pm 0.014 \text{ (syst.)} \pm 0.029 \text{ (th.)}$$. These findings reinforce the robustness of the SM while setting constraints on potential new physics scenarios.

Theoretical and Practical Considerations

The study includes extensive discussion of theoretical uncertainties, notably from PDFs and higher-order corrections. The analysis employs multiple theoretical frameworks to evaluate uncertainties and quantify acceptance corrections, indicative of the detailed consideration given to theoretical inputs.

Practically, this research is integral for precision measurement at the LHC, establishing a foundation for exploring deviations that might suggest physics beyond the SM. The approach also lays out a clear path for future data analyses as integrated luminosity increases. With advances in detector technology and data analysis techniques, future research could probe more subtle effects, potentially revealing new phenomena.

In summary, this paper provides a rigorous demonstration of the CMS detector's capabilities in precision measurements of fundamental interactions, confirming the SM predictions within experimental uncertainties. It highlights the collaborative effort in advancing high-energy physics research, paving the way for deeper investigations into the fundamental forces of nature.