Abstract
Differential cross-section measurements are presented for the electroweak production of two jets in association with a Z boson. These measurements are sensitive to the vector-boson fusion production mechanism and provide a fundamental test of the gauge structure of the Standard Model. The analysis is performed using proton–proton collision data collected by ATLAS at sqrt{s}=13 hbox {TeV} and with an integrated luminosity of 139 hbox {fb}^{-1}. The differential cross-sections are measured in the Zrightarrow ell ^+ell ^- decay channel (ell =e,mu ) as a function of four observables: the dijet invariant mass, the rapidity interval spanned by the two jets, the signed azimuthal angle between the two jets, and the transverse momentum of the dilepton pair. The data are corrected for the effects of detector inefficiency and resolution and are sufficiently precise to distinguish between different state-of-the-art theoretical predictions calculated using Powheg+Pythia8, Herwig7+Vbfnlo and Sherpa 2.2. The differential cross-sections are used to search for anomalous weak-boson self-interactions using a dimension-six effective field theory. The measurement of the signed azimuthal angle between the two jets is found to be particularly sensitive to the interference between the Standard Model and dimension-six scattering amplitudes and provides a direct test of charge-conjugation and parity invariance in the weak-boson self-interactions.
Highlights
The analysis presented in this article measures differential cross-sections of EW Z j j production in the Z → + − decay channel ( = e, μ) and as a function of four observables; the transverse momentum of the dilepton pair, the dijet invariant mass (m j j ), the absolute rapidity1 separation of the two jets (| y j j |), and the signed azimuthal angle between the two jets ( φ j j )
The differential cross-sections for EW Z j j production as a function of m j j, | y j j |, pt, and φ j j are shown in Fig. 7 and are compared with theoretical predictions produced by Herwig7+Vbfnlo, Powheg+Py8 and Sherpa
parton distribution functions (PDF) uncertainties on the EW Z j j predictions are estimated by reweighting the nominal sample to reproduce the 100 variations of the NNPDF3.0nnlo PDF sets and taking the RMS of these variations; the impact of PDFrelated uncertainties on the EW Z j j predictions are found to be much smaller than the impact of scale uncertainties
Summary
The ATLAS detector [25] at the LHC covers nearly the entire solid angle around the collision point It consists of an inner tracking detector surrounded by a thin superconducting solenoid, electromagnetic and hadronic calorimeters, and a muon spectrometer incorporating three large superconducting toroidal magnets. The high-granularity silicon pixel detector covers the vertex region and typically provides four measurements per track, the first hit normally being in the insertable B-layer (IBL) installed before the start of Run 2 [26,27]. The electroweak Z j j process is defined by the t-channel exchange of a weak boson and at tree level is calculated at. The strong Z j j process has no weak boson exchanged in the t-channel and at tree level is (a). The HLT further reduces the rate in order to write events to disk at about 1 kHz
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