Abstract
A search for the Zγ decay of the Higgs boson, with Z boson decays into pairs of electrons or muons is presented. The analysis uses proton–proton collision data at s = 13 TeV corresponding to an integrated luminosity of 139 fb−1 recorded by the ATLAS detector at the Large Hadron Collider. The observed data are consistent with the expected background with a p-value of 1.3%. An upper limit at 95% confidence level on the production cross-section times the branching ratio for pp→H→Zγ is set at 3.6 times the Standard Model prediction while 2.6 times is expected in the presence of the Standard Model Higgs boson. The best-fit value for the signal yield normalised to the Standard Model prediction is 2.0−0.9+1.0 where the statistical component of the uncertainty is dominant.
Highlights
IntroductionThe observed properties of the particle, such as its couplings to Standard Model (SM) elementary particles, its spin and its parity, are so far consistent with the predictions for a SM Higgs boson (H) [3,4,5,6,7]
A new boson [1, 2] was discovered in 2012 by the ATLAS and CMS Collaborations
Upper limits are set on the Higgs boson production cross-section at 95% confidence level (CL) using the modified frequentist formalism [116]
Summary
The observed properties of the particle, such as its couplings to Standard Model (SM) elementary particles, its spin and its parity, are so far consistent with the predictions for a SM Higgs boson (H) [3,4,5,6,7] The mass of this boson was determined by the ATLAS and CMS Collaborations to be mH = 125.09 ± 0.21(stat) ± 0.11(syst) GeV using the LHC Run 1 data set [8]. Prior to the present study, the ATLAS Collaboration reported an observed (expected for a SM Higgs boson) upper limit on the production cross-section times branching ratio for pp → H → Zγ of 6.6 (5.2) times the SM prediction at 95% confidence level for a Higgs boson with mH = 125.09 GeV using a sample corresponding to an integrated luminosity of 36.1 fb−1 [20]. A simultaneous fit to the reconstructed Zγ invariant mass distributions in all the categories is performed to extract the overall H → Zγ signal yield
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