We present a search for lepton flavor violation processes at eμ final states with the data collected by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV in 2016 corresponding to the integrated luminosity of 35.9 fb^(-1). No evidence for physics beyond the Standard Model is observed in the eμ invariant mass spectrum, the results are interpreted in terms of three different models, an R-parity violating SUSY model (RPV), a heavy Z’ gauge boson model, and a quantum black hole model (QBH). The lower mass limits at 95\% confidence level (C.L.) are found.We also present a search for new high-mass resonances decaying into electron pair with CMS 2016 data. No evidence of signature beyond the Standard Model prediction in the ee invariant mass spectrum observed, therefore the lower mass limits at 95\% C.L. are found for predictions of sequential standard model, grand unify theory, Randall-Sundrum model.Then we update the results of lower mass limits with the combination of 2016 data in ee and μμ channels and 2017 data in ee channel.Further to these, a study of the vector charmonium-like state Y(4220) is performed by using a combined fit on the cross sections of e^+ e^-→ωχ_c0, e^+ e^-→π^+ π^- h_c, e^+ e^-→π^+ π^- J/ψ and e^+ e^-→D^0 D^(*-) π^++c.c. measured by the BESIII experiment. The mass and width of the Y(4220) are obtained, We find the lower limit of its leptonic decay width to be 30 eV. We also estimate its partial decay width to π^+ π^- J/ψ in different scenarios. These results can be compared with the theoretical expectations of different models, and help the understanding of the nature of the Y(4220) state. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished