Abstract
A search for heavy resonances decaying into a pair of Z bosons leading to ell ^+ell ^-ell '^+ell '^- and ell ^+ell ^-nu {{bar{nu }}} final states, where ell stands for either an electron or a muon, is presented. The search uses proton–proton collision data at a centre-of-mass energy of 13 TeV collected from 2015 to 2018 that corresponds to the integrated luminosity of 139 mathrm {fb}^{-1} recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. Different mass ranges spanning 200 GeV to 2000 GeV for the hypothetical resonances are considered, depending on the final state and model. In the absence of a significant observed excess, the results are interpreted as upper limits on the production cross section of a spin-0 or spin-2 resonance. The upper limits for the spin-0 resonance are translated to exclusion contours in the context of Type-I and Type-II two-Higgs-doublet models, and the limits for the spin-2 resonance are used to constrain the Randall–Sundrum model with an extra dimension giving rise to spin-2 graviton excitations.
Highlights
ATLAS detectorThe ATLAS experiment is described in detail in Ref. [20]. ATLAS is a multipurpose detector with a forward–backward symmetric cylindrical geometry and a solid-angle coverage of nearly 4π
Background estimationThe main background source in the H → Z Z → + − + − final state is non-resonant SM Z Z production, accounting for 97% of the total background events in the inclusive category
It arises from quark–antiquark annihilation qq → Z Z (86%), gluon-initiated production gg → Z Z (10%), and a small contribution from EW vector-boson scattering (1%). The last of these is more important in the vector-boson fusion (VBF)-enriched category using the deep neural networks (DNN)-based categorisation, where it accounts for 20% of the total background events
Summary
The ATLAS experiment is described in detail in Ref. [20]. ATLAS is a multipurpose detector with a forward–backward symmetric cylindrical geometry and a solid-angle coverage of nearly 4π. The inner detector is surrounded by a thin superconducting solenoid providing a 2 T magnetic field, and by a finely segmented lead/liquid-argon (LAr) electromagnetic calorimeter covering the region |η| < 3.2. A steel/scintillator-tile hadron calorimeter provides coverage in the central region |η| < 1.7. The endcap and forward regions, covering the pseudorapidity range 1.5 < |η| < 4.9, are instrumented with LAr electromagnetic and hadron calorimeters, with steel, copper, or tungsten as the absorber material. Three layers of precision wire chambers provide muon tracking in the range. The first stage, implemented with custom hardware, uses information from the calorimeters and muon chambers to select events from the 40 MHz bunch crossings at a maximum rate of 100 kHz. The second stage, called the high-level trigger (HLT), reduces the data acquisition rate to about 1 kHz on average. The HLT is software-based and runs reconstruction algorithms similar to those used in the offline reconstruction
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