Study Of Electroweak Physics In The L~±vl±vjj Final State With The ATLAS Detector

The electroweak theory in the Standard Model(SM)is a non-Abelian gauge field theory based on the SU(2)×U(1)gauge symmetry,it uniformly describes the elec-tromagnetic interaction and the weak interaction.The electroweak theory predicts four vector bosons:the massive W± and Z0 rgauge bosons are the weak force carriers,and the massless photon y is the electromagnetic force carrier.The non-Abelian nature of the electroweak symmetry group in the SM predicts the interactions between bosons.The electroweak symmetry breaking mechanism in the SM gives rise to mass for the W±andZ0 gauge bosons.The multiple-boson production is of great significance to crucially test the SM non-Abelian gauge structure.The vector boson scattering process is sensitive to the electroweak symmetry breaking mechanism.Besides,the multiple-boson production and the vector boson scattering process often constitute important and irreducible backgrounds to searches for new physics beyond the SM at the high colli-sion energy.Therefor,the studied of those two electroweak processes are salient for the physics program of searching for new physics beyond the SM.Using the 13 TeV proton-proton collision data collected by the ATLAS detector,two rare electroweak processes of vector boson scattering and multiple-boson production are studied in the l±vl±vjj final state.The electroweak production of W±W±jj is a process predicted by the SM,and one of its main production mechanisms is called vector boson scattering.Vector boson scattering is sensitive to the electroweak symmetry breaking mechanism as well as new phenomena beyond the SM.The electroweak production of W±W±jj has been mea-sured using 36.1 fb-1 of proton-proton collision data that is recorded at a center-of-mass energy of(?)= 13 TeV.The study was proceeded with the final state which includes a pair of same sign leptons(e or ?)in association with two jets with a large invariant mass and rapidity difference.A total of 122 candidate events are observed with the expected background of 69±7 events.The electroweak production of W±W±jj is observed with an observed(expected)signal significance of 6.9(4.6)standard deviations.The mea-sured fiducial cross section is 2.91-0.47+0.57(stat.)-0.29+0.28(syst.)fb.It is compatible with the Standard Model prediction of 2.01-0.23+0.33fb.The triboson W±W±W(?)production is a SM process that has never been observed.Due to the non-Abelian nature of the electroweak symmetry group in the SM,gauge bosons are allowed to interact with each other.Investigations of gauge boson self-interaction provide crucial tests of the SM non-Abelian gauge structure.The triboson W±W±W± production has been searched for using 79.8 fb-1 of proton-proton colli-sion data recorded at a center-of-mass energy of(?)=13 TeV.The study was proceeded with the final state which includes two same sign leptons(e or ?)in association with two jets with an invariant mass consistent with a hadronically decaying W boson.A total of 798 candidate events are observed with the expected background of 691 ±23 events.The measured signal strength for W±W±W(?)?l?±vl±vjj is 2.24-0.57+0.62,the corre-sponding observed(expected)signal significance is 4.3(1.7)standard deviations.After combining with W±W±W(?)?l±vl±vl(?)v channel,the measured signal strength(?)is 1.37-0.42+0.46,the observed(expected)signal significance is 3.3(2.4)standard deviations.The W±W±jj electroweak production was first observed in the ATLAS experi-ment.It demonstrates the existence of the vector boson scattering process.Besides,the ATLAS experiment found the first evidence of W±W±W(?)production.Studies of those two analyses test the SM electroweak theory at the energy frontier of the LHC.Two analyses are statistically limited.With more collision data,these two rare electroweak processes can be measured more accurately.