Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC


A search for the Standard Model Higgs boson in proton-proton collisions with the ATLAS detector at the LHC is presented. In the datasets collected at √s = 7 TeV in 2011 and at √s = 8 TeV in 2012 the decay channels H→ZZ(∗)→4ℓ, H→γγ and H→WW(∗)→eνμν have been investigated. Clear evidence for the production of a neutral boson with a measured mass of 126.0 ± 0.4 (stat) ± 0.4 (sys) GeV is presented. This observation, which has a significance of 5.9 standard deviations, is compatible with the production and decay of the Standard Model Higgs boson. This discovery has a fundamental significance for the particle physics theory. Physicists and engineers from the Institute of Physics significantly contributed to the R&D and construction of the Pixel detector which precisely measures coordinates of primary interactions and decay vertices of very short living secondary particles. This is substantial information for the identification of the Higgs boson decay products and for the significant suppression of background of the observed signal.

In the invariant mass spectrum of doublets of electron-positron and muon pairs (left picture) it is clearly seen a peak in the mass region of 126 GeV. Experimental data very well coincide with the signal prediction for the Higgs boson mass of 126 GeV. The similar signal is observed in the invariant mass spectrum of two gammas (right picture).