Observation of an excess of events in the search for the Standard Model Higgs boson in the gamma-gamma channel with the ATLAS detector

This note reports on a search for the Standard Model Higgs boson in the diphoton decay channel in proton-proton collisions at center-of-mass energies of sqrt(s) = 7 TeV and sqrt(s) = 8 TeV using integrated luminosities of 4.8 fb-1 and 5.9 fb-1, respectively, recorded with the ATLAS detector at the Large Hadron Collider. The search is performed for Higgs boson masses between 110 and 150 GeV. The expected exclusion limit at 95% confidence level varies between 0.8 and 1.6 times the Standard Model cross section over the studied mass range, and results in an expected exclusion range from 110 GeV to 139.5 GeV. The observed exclusion ranges for a Standard Model Higgs boson are found to be (112-122.5) GeV and $(132-143) GeV at 95% confidence level. In between the two excluded regions, an excess of events is observed around the diphoton system invariant mass of about $126.5\GeV$ with a local significance of $4.5\sigma$.