Evidence for a new boson in the search for the Standard Model Higgs particle decaying to four leptons at CMS

One of the most important analyses of CMS is presented: the search for the Higgs boson in the “four-lepton” channel. This is one of the analyses providing the best chances of discovery: it uses the excellent performances of CMS in terms of particle reconstruction and identification, particle detection efficiency and its capability to trigger hard scattering events. The dataset used for this study comprises data collected during 2011 (with the LHC working at a center of mass energy of 7 TeV) and 2012 (at 8 TeV), for a statistics of 5 + 12 fb−1 . The search leads to an evidence for a signal presence with a statistical significance of more than four standard deviations. The excess of data, with respect to the background-only expectations, indicates the presence of a new boson, with a mass of about 126 GeV, decaying to two Z bosons, whose characteristics are compatible with the SM Higgs ones. The work presented in this thesis can be seen as a cross check to the official CMS analysis.