CMSHIG21016 ; CERNEP2022151  
Search for exotic Higgs boson decays H $ \to \mathcal{A} \mathcal{A} \to 4\gamma$ with events containing two merged diphotons in protonproton collisions at $ \sqrt{s} = $ 13 TeV  
CMS Collaboration  
13 September 2022  
Phys. Rev. Lett. 131 (2023) 101801  
Abstract: The first direct search for exotic Higgs boson decays H $ \to \mathcal{A} \mathcal{A} $, $ \mathcal{A} \to\gamma\gamma$ in events with two photonlike objects is presented. The hypothetical particle $ \mathcal{A} $ is a lowmass spin0 particle decaying promptly to a merged diphoton reconstructed as a single photonlike object. Data collected by the CMS experiment at $ \sqrt{s} = $ 13 TeV corresponding to an integrated luminosity of 136 fb$^{1}$ are analyzed. No excess above the estimated background is found. Upper limits on the branching fraction $\mathcal{B}( \mathrm{H} \to \mathcal{A} \mathcal{A} \to 4\gamma)$ of (0.93.3)$ \times $10$^{3}$ are set at 95% confidence level for masses of $ \mathcal{A} $ in the range 0.11.2 GeV.  
Links: eprint arXiv:2209.06197 [hepex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; Physics Briefing ; CADI line (restricted) ; 
Figures  
png pdf 
Figure 1:
Mass distributions from selected events in data. Center: the 2D$ m_{\Gamma} $ distribution for data events in the $ m_{ \mathrm{H} } $SR. The red dashed lines indicate the $m_{ \mathcal{A} } $SR boundaries. The contours of simulated H $ \to \mathcal{A} \mathcal{A} \to 4\gamma$ events for $ m_{ \mathcal{A} }= $ 0.4 GeV are plotted for 75% (solid contour) and 50% (dotted contour) of the distribution maximum. The corresponding $m_{\Gamma_1}$ (left) and $m_{\Gamma_2}$ (right) projections for the overlap of the $ m_{ \mathrm{H} } $SR and $m_{ \mathcal{A} } $SR are also shown. The data distributions (black points) are plotted against the total predicted background distributions (blue curves). The statistical uncertainties in the former are negligible and the total uncertainties in the latter are barely visible as green bands. The spectra of simulated H $ \to \mathcal{A} \mathcal{A} \to 4\gamma$ events for $ m_{ \mathcal{A} }= $ 0.1 (purple dashed curve), 0. 4 (gray dotted curve), and 1.0 GeV (orange dashdotted curve) are also provided. They are each normalized to the value of $\mathcal{B}( \mathrm{H} \to \mathcal{A} \mathcal{A} \to 4\gamma)$ that is expected to be excluded by the background model (described under the CL$ _\text{s} $ criterion in our results) times 10$^ 3$. The black points in the lower panels of the left and right plots give the ratios of the data to the predicted background distributions. The vertical bars represent the statistical uncertainties in the former, and the green bands represent the total uncertainty in the latter. 
png pdf 
Figure 1a:
$m_{\Gamma_1}$ projection for the overlap of the $ m_{ \mathrm{H} } $SR and $m_{ \mathcal{A} } $SR. The data distribution (black points) is plotted against the total predicted background distribution (blue curve). The statistical uncertainties in the former are negligible and the total uncertainties in the latter are barely visible as a green band. The spectra of simulated H $ \to \mathcal{A} \mathcal{A} \to 4\gamma$ events for $ m_{ \mathcal{A} }= $ 0.1 (purple dashed curve), 0.4 (gray dotted curve), and 1.0 GeV (orange dashdotted curve) are also provided. They are each normalized to the value of $\mathcal{B}( \mathrm{H} \to \mathcal{A} \mathcal{A} \to 4\gamma)$ that is expected to be excluded by the background model (described under the CL$ _\text{s} $ criterion in our results) times 10$^ 3$. The black points in the lower panel give the ratios of the data to the predicted background distributions. The vertical bars represent the statistical uncertainties in the former, and the green bands represent the total uncertainty in the latter. 
png pdf 
Figure 1b:
2D$ m_{\Gamma} $ distribution for data events in the $ m_{ \mathrm{H} } $SR. The red dashed lines indicate the $m_{ \mathcal{A} } $SR boundaries. The contours of simulated H $ \to \mathcal{A} \mathcal{A} \to 4\gamma$ events for $ m_{ \mathcal{A} }= $ 0.4 GeV are plotted for 75% (solid contour) and 50% (dotted contour) of the distribution maximum. 
png pdf 
Figure 1c:
$m_{\Gamma_2}$ projection for the overlap of the $ m_{ \mathrm{H} } $SR and $m_{ \mathcal{A} } $SR. The data distribution (black points) is plotted against the total predicted background distribution (blue curve). The statistical uncertainties in the former are negligible and the total uncertainties in the latter are barely visible as a green band. The spectra of simulated H $ \to \mathcal{A} \mathcal{A} \to 4\gamma$ events for $ m_{ \mathcal{A} }= $ 0.1 (purple dashed curve), 0.4 (gray dotted curve), and 1.0 GeV (orange dashdotted curve) are also provided. They are each normalized to the value of $\mathcal{B}( \mathrm{H} \to \mathcal{A} \mathcal{A} \to 4\gamma)$ that is expected to be excluded by the background model (described under the CL$ _\text{s} $ criterion in our results) times 10$^ 3$. The black points in the lower panel give the ratios of the data to the predicted background distributions. The vertical bars represent the statistical uncertainties in the former, and the green bands represent the total uncertainty in the latter. 
png pdf 
Figure 2:
Observed (black solid curve with points) and median expected (blue dashed curve) 95% CL upper limit on $\mathcal{B}( \mathrm{H} \to \mathcal{A} \mathcal{A} \to 4\gamma)$ as a function of $m_{ \mathcal{A} }$ for prompt $ \mathcal{A} $ decays. The 68% (green band) and 95% (yellow band) CIs are plotted around the expected limit. The 95% CL upper limit from the CMS measurement [1] of $\mathcal{B}( \mathrm{H} \to\gamma\gamma)$ is also shown (red band, where the width represents the uncertainty in the measurement). 
Summary 
In summary, the results of a search for the exotic Higgs boson decay H $ \to \mathcal{A} \mathcal{A} \to 4\gamma$ for a Higgs boson mass of 125 GeV are presented. Events reconstructed with two photonlike objects are used, where each photonlike object is assumed to be a merged $ \mathcal{A} \to\gamma\gamma$ candidate. A method is developed to measure the invariant mass of merged diphoton candidates to discriminate a potential signal from the standard model background. This is the first search of its kind at CMS and made possible by a novel endtoend reconstruction technique of merged diphotons. No excess of events above the estimated background is found. An upper limit on the branching fraction $\mathcal{B}( \mathrm{H} \to \mathcal{A} \mathcal{A} \to 4\gamma)$ of (0.93.3)$ \times $10$^{3}$ is set at 95% CL for masses of $ \mathcal{A} $ in the range 0.11.2 GeV, assuming prompt $ \mathcal{A} $ decays. These are the current best constraints on H $ \to \mathcal{A} \mathcal{A} \to 4\gamma$ in this $m_{ \mathcal{A} }$ range. 
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