Electron performance studies for the Higgs→ 4 lepton search in proton-proton collisions at √s = 7 TeV, with the ATLAS detector at the Large Hadron Collider

The Standard Model of the electroweak and strong interactions is an, extremely successful, effective theory that describes the electromagnetic, weak, and strong forces at the quantum level. One of the key elements of the SM is the Higgs mechanism, that generates the masses of the weak vector bosons, of the charged quarks and of the leptons. The Higgs mechanism predicts the existence of a massive scalar particle, the Higgs boson, which is the only particle of the SM not yet experimentally observed. For this reason, its discovery or exclusion is one of the main goals of the ATLAS experiment in the Large Hadron Collider. The experimentally cleanest signature for the discovery of the Higgs boson at the Large Hadron Collider is its “golden” decay to four leptons, Higgs→ZZ(∗) →4ℓ. The ability to efficiently identify electrons, while retaining a high rejection against QCD-jets and electrons, is of high importance to the Higgs searches using its “golden” decay channel. Furthermore, the prediction of the background normalisation, shape and their uncertainties in the signal-region from early measurements is vital, given the low signal statistics expected in the first years of LHC running. The key contributions of this work are: the first observation of p0 →gg events at √s = 900 GeV proton-proton collisions with the ATLAS experiment and subsequent studies of the ATLAS electromagnetic calorimeter performance; the first observation of J/y → e+e− events in proton-proton collisions at √s = 7 TeV with the ATLAS experiment; studies of the ATLAS electron identification performance using J/y →e+e− and Z →e+e− decays in proton-proton collision data at √s = 7 TeV; a data driven method for extracting the pp→Z+X background in the low mass Higgs→ZZ(∗) →4ℓ region. i