Search For Heavy Neutral Particles With Different Flavor Di-lepton Decay In Proton-proton Collisions At (?)=13TeV With The ATLAS Detector At The LHC

Since the discovery of the Higgs boson,the Standard Model(SM)theory has been almost completed and searching for new physics beyond the SM has been one of the most important topics in the field of current particle physics.In the SM,all decays should obey the conservation of lepton number.Observation of any process of Lepton Flavor Violation(LFV)would be a clear signature of new physics.The experiment of neutrino oscillation indicates that leptons without charge participate in LFV process.This thesis report a search for the possibility of LFV with charged leptons via the pro-cess qq ?X?e?/e?/?? based on ATLAS experiment in the LHC as a probe of new physics.There are several characteristics in this process:1.There are only 2 opposite charged leptons with different flavors in the final states which is helpful to suppress the background from SM and improve the possible signal to noise ratio of new physics.2.In these models,the final state leptons are from a heavy neutral particle.The invariant mass of the heavy neutral particle can be fully reconstructed(for the final states with ?,a collinear neutrino approximation method can help to have a reasonable reconstruction.)to search for new physics.This thesis used the proton-proton(pp)collision data at(?)=13 TeV with an inte-grated luminosity of 36.1 fb-1 recorded in 2015 and 2016 by the ATLAS detector at the LHC.Three possible models are assumed:a scalar v? particle in SUSY,a vector Z' par-ticle in Sequential SM and a tensor Quantum Black Hole in QBH model.No evidence of such heavy neutral particles is found.The 95%CL lower limits on the invariant mass and 95%CL upper limits on cross section times branching ratio are set for the 3 models.