Evidence for the production of three massive vector bosons with the ATLAS detector

Abstract

A search for the production of three massive vector bosons in proton–proton collisions is performed using data at s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider in the years 2015–2017, corresponding to an integrated luminosity of 79.8 fb −1 . Events with two same-sign leptons ℓ (electrons or muons) and at least two reconstructed jets are selected to search for W W W → ℓ ν ℓ ν q q . Events with three leptons without any same-flavour opposite-sign lepton pairs are used to search for W W W → ℓ ν ℓ ν ℓ ν , while events with three leptons and at least one same-flavour opposite-sign lepton pair and one or more reconstructed jets are used to search for W W Z → ℓ ν q q ℓ ℓ . Finally, events with four leptons are analysed to search for W W Z → ℓ ν ℓ ν ℓ ℓ and W Z Z → q q ℓ ℓ ℓ ℓ . Evidence for the joint production of three massive vector bosons is observed with a significance of 4.1 standard deviations, where the expectation is 3.1 standard deviations.