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 text {TeV} corresponding to an integrated luminosity of 36.1 hbox {fb}^{-1} collected with the ATLAS detector during 2015 and 2016 at the Large Hadron Collider. Different mass ranges for the hypothetical resonances are considered, depending on the final state and model. The different ranges span between 200 and 2000 text {GeV}. 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, while those 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. [23]. ATLAS is a multi-purpose detector with a forward–backward symmetric cylindrical geometry and a solid-angle coverage of nearly 4π
Background estimationThe main background component in the H → Z Z → + − + − final state, accounting for 97% of the total expected background events, is non-resonant Z Z production
The selection used combines the likelihood with the number of track hits and defines two working points (WP) which are used in the analyses presented here
Summary
The ATLAS experiment is described in detail in Ref. [23]. ATLAS is a multi-purpose 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/scintillatortile hadronic calorimeter provides coverage in the central region |η| < 1.7. The end-cap and forward regions, covering the pseudorapidity range 1.5 < |η| < 4.9, are instrumented with electromagnetic and hadronic LAr calorimeters, with steel, copper or tungsten as the absorber material. Three layers of precision wire chambers provide muon tracking in the range |η| < 2.7, while dedicated fast chambers are used for triggering in the region |η| < 2.4. The first stage, implemented with custom hardware, uses information from calorimeters and muon chambers to reduce the event rate from about 40 MHz to a maximum 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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