Study of selection of dimuons in events with more than two muons in the CMS experiment

My work during CERN summer student program was with dimuon selection in events with more than two muons, in the analysis of search for narrow resonances in dimuon invariant mass spectra in the CMS experiment at the LHC. Most of the events selected for this analysis have two muons, but there are some events with more than two muons and we have to choose which pair of muons form the best dimuon candidate in these events. One of the problems of the search for new heavy resonances Z′ is the presence of background processes, for example diboson production WZ and ZZ, in which muons are produced. Dimuons formed from these muons can be misinterpreted as candi-dates for heavy resonances.