Observation of an excess of events in the search for the Standard Model Higgs boson in the H → ZZ(∗) → 4l channel with the ATLAS detector

This note presents an update of the search results and a first measurement of the proper- ties of the newly observed Higgs-like particle in the decay channel H → ZZ(∗) → l+l−l′+l′−, wherel,l′ =eorμ,using4.6fb−1and13.0fb−1ofproton-protoncollisionsat√s=7TeV and 8 TeV, respectively, recorded with the ATLAS detector. An excess of events over back- ground is seen, with a minimum p0 value of 0.0021% (4.1 standard deviations) at mH = 123.5 GeV in the combined analysis of the two datasets. The fitted Higgs mass is measured to be mH = 123.5 ± 0.9 (stat) ± 0.3 (syst) GeV, and the signal strength (the ratio of the ob- served cross-section to the expected SM cross-section) at this mass is found to be μ = 1.3+0.5. −0.4 A spin-parity analysis is performed on the events with 115 GeV < mH < 130 GeV. The 0+ state is found to be favoured over the 0−, 2+ and 2− states with 0− excluded by 2.7 σ when compared to 0+.