Abstract
This article presents results on measurements of the signal strength, mass, and spin of the recently discovered Higgs-like boson in the H → ZZ(*) → 4ℓ decay channel using the ATLAS detector. The results are based on the combined dataset of the 2011 and 2012 LHC runs consisting of 4.6 fb−1 of ps √s = 7 TeV and 20.7 fb−1 of √s = 8 TeV proton-proton collision data. An excess of events is observed corresponding to mH = 124.3 GeV with a p0 value of 2.7 × 10−11 (6.6 standard deviations). The fit at this mass point yields a signal strength relative to the SM of 1.7−0.4+0.5 with mH = 124.3−0.5+0.6 (stat)−0.3+0.5 (syst) GeV. Tests of various spin-parity hypotheses are also presented, with the 0− and 1+ hypotheses being excluded versus the 0+ hypothesis at >97% confidence level.
Highlights
The recent observation of a Higgs-like boson [1, 2] was a major success for the ATLAS and CMS experiments at the LHC
An unbinned maximum-likelihood fit of signal and background models to the observed m4 distribution was performed and the best fit point corresponds to mH = 124.3 GeV with a signal strength μ = 1.7+−00
The significance of an excess is given by the probability p0, that a background-only experiment is more signal-like in terms of the test statistic than the observed data
Summary
The recent observation of a Higgs-like boson [1, 2] was a major success for the ATLAS and CMS experiments at the LHC. Determining whether this newly-discovered particle is compatible with the Standard Model (SM) predictions for the Higgs boson or not is of utmost importance. The H → ZZ(∗) → 4 ( = e, μ) decay channel is important in these measurements due to the small wellconstrained backgrounds and full reconstruction of all decay products of the Higgs boson.
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