Abstract (data abstract)

Results are presented from a search for the Higgs boson decay $\mathrm{H}\to\mathrm{Z}\gamma$, where $\mathrm{Z}\to\ell^+\ell^-$ with $\ell=\mathrm{e}$ or $\mu$. The search is performed using a sample of proton-proton ($\mathrm{pp}$) collision data at a center-of-mass energy of $13~\mathrm{TeV}$, recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of $138~\mathrm{fb}^{-1}$. Events are assigned to mutually exclusive categories, which exploit differences in both event topology and kinematics of distinct Higgs production mechanisms to enhance signal sensitivity. The signal strength $\mu$, defined as the product of the cross section and the branching fraction [$\sigma(\mathrm{pp}\to\mathrm{H})\mathcal{B}(\mathrm{H}\to\mathrm{Z}\gamma)$] relative to the standard model prediction, is extracted from a simultaneous fit to the \llg invariant mass distributions in all categories and is found to be $\mu= 2.4\pm0.9$ for a Higgs boson mass of $125.38~\mathrm{GeV}$. The statistical significance of the observed excess of events is 2.7 standard deviations. This measurement corresponds to $\sigma(\mathrm{pp}\to\mathrm{H})\mathcal{B}(\mathrm{H}\to\mathrm{Z}\gamma)=0.21\pm0.08~\mathrm{pb}$. The observed (expected) upper limit at 95% confidence level on $\mu$ is $4.1$ ($1.8$). The ratio of branching fractions $\mathcal{B}(\mathrm{H}\to\mathrm{Z}\gamma)/\mathcal{B}(\mathrm{H}\to\gamma\gamma)$ is measured to be $1.5^{+0.7}_{-0.6}$, which agrees with the standard model prediction of $0.69 \pm 0.04$ at the 1.5 standard deviation level.

Figure 2a

Data from Figure 2 (upper left).

10.17182/hepdata.127896.v1/t1

The $\mathcal{D}_{\mathrm{VBF}}$ distributions for signal, simulated background, and data. The $\mathcal{D}_{\mathrm{VBF}}$ distribution includes only dijet-tagged events. The sum of contributions...
Figure 2b

Data from Figure 2 (upper right).

10.17182/hepdata.127896.v1/t2

The $\mathcal{D}_{\mathrm{kin}}$ distributions for signal, simulated background, and data. The $\mathcal{D}_{\mathrm{kin}}$ distribution includes only untagged events. The sum of contributions...
Figure003-a

Upper left plot of Figure 3

10.17182/hepdata.127896.v1/t3

Fits to the $m_{\ell^+\ell^-\gamma}$ data distribution in the lepton-tagged categories. In the upper panel, the red solid line shows the...
Figure003-b

Upper right plot of Figure 3

10.17182/hepdata.127896.v1/t4

Fits to the $m_{\ell^+\ell^-\gamma}$ data distribution in the dijet-1 categories. In the upper panel, the red solid line shows the...
Figure003-c

Lower left plot of Figure 3

10.17182/hepdata.127896.v1/t5

Fits to the $m_{\ell^+\ell^-\gamma}$ data distribution in the dijet-2 categories. In the upper panel, the red solid line shows the...
Figure003-d

Lower right plot of Figure 3

10.17182/hepdata.127896.v1/t6

Fits to the $m_{\ell^+\ell^-\gamma}$ data distribution in the dijet-3 categories. In the upper panel, the red solid line shows the...
Figure004-a

Upper left plot of Figure 4

10.17182/hepdata.127896.v1/t7

Fits to the $m_{\ell^+\ell^-\gamma}$ data distribution in the untagged 1 categories. In the upper panel, the red solid line shows...
Figure004-b

Upper right plot of Figure 4

10.17182/hepdata.127896.v1/t8

Fits to the $m_{\ell^+\ell^-\gamma}$ data distribution in the untagged 2 categories. In the upper panel, the red solid line shows...
Figure004-c

Lower left plot of Figure 4

10.17182/hepdata.127896.v1/t9

Fits to the $m_{\ell^+\ell^-\gamma}$ data distribution in the untagged 3 categories. In the upper panel, the red solid line shows...
Figure004-d

Lower left plot of Figure 4

10.17182/hepdata.127896.v1/t10

Fits to the $m_{\ell^+\ell^-\gamma}$ data distribution in the untagged 4 categories. In the upper panel, the red solid line shows...
Figure006

Data from Figure 6

10.17182/hepdata.127896.v1/t11

Observed signal strength ($\mu$) for a SM Higgs boson at 125.38 GeV. The labels untagged combined,dijet combined and combined represent...
Figure007

Data from Figure 7

10.17182/hepdata.127896.v1/t12

Upper limit (95% CL) on the signal strength ($\mu$) relative to the SM prediction, as a function of the assumed...

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