Observation of $W\gamma \gamma$ triboson production in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract

This letter reports the observation of $W(\ell \nu )\gamma \gamma$ production in proton-proton collisions. This measurement uses the full Run 2 sample of events recorded at a center-of-mass energy of $\sqrt{s}=13$ TeV by the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb${}^{-1}$. Events with a leptonically-decaying $W$ boson and at least two photons are considered. The background-only hypothesis is rejected with an observed and expected significance of $5.6$ standard deviations. The inclusive fiducial production cross section of $W(e\nu )\gamma \gamma$ and $W(\mu \nu )\gamma \gamma$ events is measured to be ${\sigma }_{\mathrm{fid}}=13.8\pm 1.1(\mathrm{stat})\begin{array}{c}+2.1\\ -2.0\end{array}(\mathrm{syst})\pm 0.1(\mathrm{lumi})$ fb, in agreement with the Standard Model prediction.

36 pages in total, author list starting page 19, 3 figures, 2 tables, published in PLB. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2018-33/

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• Muon reconstruction and identification efficiency in ATLAS using the full Run 2 $pp$ collision data set at $\sqrt{s}=13$ TeV
• Performance of the ATLAS muon triggers in Run 2
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• Electroweak, QCD and flavour physics studies with ATLAS data from Run 2 of the LHC
• Observation of WZ$\gamma$ production and constraints on new physics scenarios in proton-proton collisions at $\sqrt{s}$ = 13 TeV
• Evidence of ZZ$\gamma$ production and observation of $4\ell \gamma$ in proton-proton collisions at $\sqrt{s}$ = 13 TeV
• Observation of tWZ production at the CMS experiment
• Gluon-gluon fusion contribution to the productions of three gauge bosons at the LHC