Evidence for the Higgs boson decay to a $Z$ boson and a photon at the LHC
The first evidence for the Higgs boson decay to a $Z$ boson and a photon is presented, with a statistical significance of 3.4 standard deviations. The result is derived from a combined analysis of the searches performed by the ATLAS and CMS Collaborations with proton-proton collision data sets collected at the CERN Large Hadron Collider (LHC) from 2015 to 2018. These correspond to integrated luminosities of around 140 fb$^{-1}$ for each experiment, at a center-of-mass energy of 13 TeV. The measured signal yield is $2.2\pm0.7$ times the Standard Model prediction, and agrees with the theoretical expectation within 1.9 standard deviations.
7 September 2023
Contact: Higgs conveners
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Figures
Figure 02
The Zγ invariant mass distribution. Events from all categories in the ATLAS and CMS analyses are shown. As different ranges in mZγ are used in the two analyses, only the common subrange is visualized here. The data (points with error bars) in each category are weighted by ln(1 + S/B), where S and B are the observed signal and background yields in that category, in the 120–130 GeV interval. The S and B values are derived from the fit to data. The error bars are invisible because of their small values. The fitted signal-plus-background (background) probability density functions (pdfs) in each category are also weighted in the same way and summed, and represented by a red solid (blue dashed) line. The lower panel shows the background-subtracted results with the same data and pdfs.
png (157kB) pdf (36kB)
Figure 03
The negative profile log-likelihood test statistic, where Λ represents the likelihood ratio, as a function of the signal strength μ derived from the ATLAS data (blue line), the CMS data (red line), and the combined result (black line). The different Higgs boson masses assumed by ATLAS and CMS have a negligible impact on the results.
png (129kB) pdf (45kB)
