Measurement of the WZ production cross section and limits on anomalous triple gauge couplings in proton-proton collisions at sqrt(s) = 7 TeV with the ATLAS detector

TL;DR

This ATLAS study measures WZ production in 7 TeV proton-proton collisions using four leptonic final states, defining a fiducial phase space and extrapolating to the total cross section. With 1.02 fb^-1 of data, 71 WZ candidates are observed against a background of about 12 events, yielding a fiducial cross section of 102 fb and a total cross section of 20.5 pb, both consistent with Standard Model predictions. The analysis also constrains anomalous triple gauge couplings at the WWZ vertex by profiling the likelihood and reweighting simulations, providing limits that incorporate form-factor parametrizations with Λ = 2 TeV and Λ → ∞. Overall, the results affirm SM gauge structure while enhancing bounds on new physics in gauge-boson self-interactions, with sensitivity expected to improve with more data and refined techniques.

Abstract

This Letter presents a measurement of WZ production in 1.02 fb^-1 of pp collision data at sqrt(s) = 7 TeV collected by the ATLAS experiment in 2011. Doubly leptonic decay events are selected with electrons, muons and missing transverse momentum in the final state. In total 71 candidates are observed, with a background expectation of 12.1 +/- 1.4(stat.) +4.1/-2.0(syst) events. The total cross section for WZ production for Z gamma^* masses within the range 66 GeV to 116 GeV is determined to be sigma_WZ^tot = 20.5 +3.1/-2.8(stat.) +1.4/-1.3(syst.) +0.9/-0.8(lumi.)pb, which is consistent with the Standard Model expectation of 17.3 +1.3/-0.8 pb. Limits on anomalous triple gauge boson couplings are extracted.

Figures (3)

• Figure 1: The invariant mass of the lepton pair attributed to the $Z$ boson in candidate events after the full selection. The stacked histograms represent the predictions from simulation or, where applicable, data-driven estimates including the statistical and systematic uncertainty shown by shaded bands. The shape of the top-quark background is taken from simulation.
• Figure 2: The transverse momentum of $Z$ bosons in candidate events after full selection. The stacked histograms represent the predictions from simulation or, where applicable, data-driven estimates including the statistical and systematic uncertainty shown by shaded bands. The last bin includes the overflow. The shape of the top-quark background is taken from simulation.
• Figure 3: 95% C.I. for anomalous couplings from ATLAS and DØ experiments. ATLAS limits are extracted from a fit to the cross section while the DØ D0limits limits are extracted from a fit to the $p_{\mathrm{T}}(Z)$ spectrum. Luminosities, centre-of-mass energy and cut-off $\Lambda$ are shown.