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ATLAS Higgs Search Update
31 July 2012

On 31 July, 2012, the ATLAS Experiment submitted a scientific paper describing the discovery of a new particle consistent with the Higgs Boson to the journal Physics Letters B.

The paper gives the details of the analyses behind the results presented at the 4 July CERN announcement and the ICHEP conference, and also includes analysis of the H->WW channel with the 2012 data. The significance of observation is thus increased to 5.9 sigma. The mass of the new particle is measured as 126.0 ±0.4±0.4 GeV.

ATLAS concentrated its efforts with the early 2012 data on three complementary decay channels which are each described in the extended letter, with the Higgs decaying to two photons, or to four leptons, or to two leptons with missing energy. The combined result incorporates information from the earlier 2011 data analyses and establishes the discovery of a new fundamental particle.

Result of a statistical analysis of the ATLAS combined Higgs search.

The observed probability (local p0) for background processes to look like the data at mH = 126 GeV corresponds to 1 part in ~600 million. This corresponds to a 5.9 sigma observation of a new particle. The plot also shows that no signal is observed at other masses.

The inset in the low mass range compares the observed probability with the expectation from theory, showing that the observation at mH = 126 GeV is consistent with the Standard Model Higgs boson.

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