Measurement of the WW cross section in sqrt(s) = 7 TeV pp collisions with the ATLAS detector and limits on anomalous gauge couplings

TL;DR

This ATLAS study measures the WW production cross section in dilepton final states at $\sqrt{s}=7$ TeV with 1.02 fb$^{-1}$, reporting a total cross section of $\sigma(pp\rightarrow WW)=54.4\pm4.0\text{(stat)}\pm3.9\text{(syst)}\pm2.0\text{(lumi)}$ pb, consistent with the SM prediction. A fiducial cross section is provided for the detector-level region, and the analysis achieves precise background estimation via MC and data-driven methods, including a data-driven jet-veto correction using Z data. The paper also derives limits on anomalous gauge couplings by fitting the leading-lepton $p_T$ distribution under three EFT-inspired coupling scenarios, finding no significant deviations from the SM and placing competitive constraints on $WWV$ interactions. Overall, the results validate SM predictions at the LHC energy scale and enhance constraints on new physics in the electroweak sector, with implications for Higgs-related backgrounds and future TGC studies.

Abstract

This Letter reports a measurement of the WW production cross section in sqrt(s) = 7 TeV pp collisions using data corresponding to an integrated luminosity of 1.02/fb collected with the ATLAS detector. Using leptonic decays of oppositely charged W bosons, the total measured cross section is sigma(pp -> WW) = 54.4 +/- 4.0 (stat.) +/- 3.9 (syst.) +/- 2.0 (lumi.) pb, consistent with the Standard Model prediction of sigma(pp -> WW) = 44.4 +/- 2.8 pb. Limits on anomalous electroweak triple-gauge couplings are extracted from a fit to the transverse-momentum distribution of the leading charged lepton in the event.

Figures (5)

• Figure 1: The multiplicity distribution of jets with $p_T > 25$ GeV for the combined dilepton channels, after all $WW$ selection cuts except the jet veto requirement. The systematic uncertainties shown in the $>$0-jet bins include only those on the integrated luminosity and the theoretical cross sections.
• Figure 2: The $E_{\mathrm{T}}^{\mathrm{miss}}$ (top left), $m_{\mathrm T}$ (top right), $\Delta\phi(l,l)$ (bottom left) and $m_{\ell\ell}$ (bottom right) distributions for the combined dilepton channels after all selection requirements. The data (dots) are compared to the expectation from $WW$ and the backgrounds (histograms). The $W$ + jet and dijet backgrounds are estimated using data. The hashed region shows the $\pm 1\sigma$ uncertainty band on the expectation.
• Figure 3: The $p_{\mathrm{T}}$ distribution of the highest-$p_{\mathrm{T}}$ charged lepton in $WW$ final states. Shown are the data (dots), the background (shaded histogram), SM $WW$ plus background (solid histogram), and the following $WW$ anomalous couplings added to the background: $\Delta k_Z = 0.1$ (dashed histogram), $\lambda_Z=\lambda_{\gamma}=0.15$ (dotted histogram), and $\Delta g_1^Z=0.2$ (dash-dotted histogram). The last bin corresponds to $p_{\mathrm{T}}\xspace > 120$ GeV.
• Figure 4: Two-dimensional fits to the anomalous couplings in the LEP scenario: $\Delta k_Z$ vs. $\lambda_Z$ (left), $\Delta k_Z$ vs. $\Delta g_1^Z$ (middle), and $\lambda_Z$ vs. $\Delta g_1^Z$ (right).
• Figure 5: Anomalous TGC limits from ATLAS, D0 and LEP (based on the LEP scenario) and CDF and CMS (based on the HISZ scenario), as obtained from $WW$ production measurements.