Search For New Physics With Dijets And Large E_T^misswith The ATLAS Detector At LHC

This thesis presents two studies searching for new physics in the experimental final state composed of large missing transverse energy and dijets.Both of the two searches use the Large Hadron Collider 13 TeV proton-proton collision data recorded by the ATLAS detector in 2015 and 2016,corresponding to an integrated luminosity of 36.1 fb-1.The first study searches for heavy resonances that decay into ZZ or ZW in the final state of vvqq.The neutrino pair comes from the decay of a Z boson and the quarks are the decay products of the other vector boson,either a Z or a W boson.The analysis searches for several different models,a spin-0 high mass Higgs boson,a spin-1 Wf from heavy vector triplet model,and a spin-2 graviton from the Randall-Sundrum model.Different production mechanisms are considered in this study,gluon-gluon fusion,vector boson fusion,Drell-Yan process,depending on signal models.Heavy resonances within a mass range of 300 GeV to 5 TeV are searched,no evidence of their existence is observed.Upper limits on the production cross section are set for these signals,at 95%confidence level.The corresponding exclusion region of signal masses are significant improved,compared with previous studies.The second study is searching for dark matter in association with a hadronically de-caying vector boson.The final state contains dark matter particles and a pair of quarks decayed from the vector boson(W or Z).In this channel,the simplified vector mediator dark matter model is studied.No evidence of the production of dark matter is found.However,with larger dataset and new analysis strategy,this study largely improves pre-vious results from searches and provides an exclusion region on the dark matter mass and the mediator mass in this channel for the first time.