Abstract
A search for the decay of the Standard Model Higgs boson into a bb¯ pair when produced in association with a W or Z boson is performed with the ATLAS detector. The data, corresponding to an integrated luminosity of 79.8fb−1 were collected in proton–proton collisions during Run 2 of the Large Hadron Collider at a centre-of-mass energy of 13TeV. For a Higgs boson mass of 125GeV, an excess of events over the expected background from other Standard Model processes is found with an observed (expected) significance of 4.9 (4.3) standard deviations. A combination with the results from other searches in Run 1 and in Run 2 for the Higgs boson in the bb¯ decay mode is performed, which yields an observed (expected) significance of 5.4 (5.5) standard deviations, thus providing direct observation of the Higgs boson decay into b-quarks. The ratio of the measured event yield for a Higgs boson decaying into bb¯ to the Standard Model expectation is 1.01±0.12(stat.)−0.15+0.16(syst.). Additionally, a combination of Run 2 results searching for the Higgs boson produced in association with a vector boson yields an observed (expected) significance of 5.3 (4.8) standard deviations.
Highlights
The Higgs boson [1,2,3,4] was discovered in 2012 by the ATLAS and CMS Collaborations [5,6] with a mass of approximately 125 GeV from the analysis of proton–proton collisions produced by the Large Hadron Collider (LHC) [7]
The analysis of data collected at centre-of-mass energies of 7 TeV, 8 TeV and 13 TeV in Runs 1 and 2 of the LHC has led to the observation of many of the production modes and decay channels predicted by the Standard Model (SM)
The background prediction in all post-fit distributions is obtained by normalising the backgrounds and setting the nuisance parameters according to the results of the signal extraction fit
Summary
The Higgs boson [1,2,3,4] was discovered in 2012 by the ATLAS and CMS Collaborations [5,6] with a mass of approximately 125 GeV from the analysis of proton–proton (pp) collisions produced by the Large Hadron Collider (LHC) [7]. As well as probing the dominant decay of the Higgs boson, this measurement allows the overall Higgs boson decay width [25,26] to be constrained and provides the best sensitivity to the Z H and W H production modes, which are (for instance) important elements in the interpretation of Higgs boson measurements in effective field theories [27] Searches in this channel at the Tevatron by the CDF and D0 Collaborations showed an excess of events with a significance of 2.8 standard deviations for a Higgs boson with a mass of 125 GeV [28]. An observation of the bbdecay of the Higgs boson by the CMS Collaboration [31] was submitted for publication at the same time as this Letter
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