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

The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC ✩ .ATLAS Collaboration This paper is dedicated to the memory of our ATLAS colleagues who did not live to see the full impact and significance of their contributions to the experiment. a r t i c l e i n f o a b s t r a c t A search for the Standard Model Higgs boson in proton–proton collisions with the ATLAS detector at the LHC is presented. The datasets used correspond to integrated luminosities of approximately 4.8 fb −1 collected at b and τ + τ − in the 7 TeV data and results from improved analyses of the H → Z Z (*) → 4 and H → γ γ channels in the 7 TeV data. 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, corresponding to a background fluctuation probability of 1.7 × 10 −9 , is compatible with the production and decay of the Standard Model Higgs boson. The Standard Model (SM) of particle physics [1–4] has been tested by many experiments over the last four decades and has been shown to successfully describe high energy particle interactions. However, the mechanism that breaks electroweak symmetry in the SM has not been verified experimentally. This mechanism [5–10], which gives mass to massive elementary particles, implies the existence of a scalar particle, the SM Higgs boson. The search for the Higgs boson, the only elementary particle in the SM that has not yet been observed, is one of the highlights of the Large Hadron Collider [11] (LHC) physics programme. Indirect limits on the SM Higgs boson mass of m H < 158 GeV at 95% confidence level (CL) have been set using global fits to precision electroweak results [12]. Direct searches at LEP [13], the Tevatron [14–16] and the LHC [17,18] have previously excluded, at 95% CL, a SM Higgs boson with mass below 600 GeV, apart from some mass regions between 116 GeV and 127 GeV. Both the ATLAS and CMS Collaborations reported excesses of events in their 2011 datasets of proton–proton (pp) …