### Résumé du preprint Irfu-12-296

Irfu-12-296
Search for a Standard Model Higgs Boson decaying into two photons at CMS
S. Ganjour
A search for a Higgs boson decaying into two photons in proton-proton collisions at centre-of-mass energies of 7~TeV and 8~TeV is reported. The data analysed correspond to an integrated luminosity of 5.1 fb$^{-1}$, recorded in 2011 at $\\sqrt{s}=7$ TeV and of 5.3 fb$^{-1}$, recorded in 2012 at $\\sqrt{s}=8$ TeV by the CMS experiment at the LHC. The Higgs boson mass range explored is 110--150 GeV. Limits are set on the cross section of the Standard Model Higgs boson decaying to two photons. An excess of events above the expected background is observed for a Higgs boson mass hypothesis of 125~GeV, with a local significance of 4.1$\\sigma$. The global significance of observing such an excess anywhere in the search range is estimated to be 3.2$\\sigma$. This result constitutes evidence for the existence of a new state that decays into two photons. A fit to this signal gives a mass of $125.1 \\pm 0.4 (\\rm stat) \\pm 0.6 (syst)$~GeV. The decay to two photons indicates that the new particle is a boson with spin different from one.