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| CMS-HIG-25-004 ; CERN-EP-2026-211 | ||
| Constraint on the Higgs boson width in the diphoton final state using signal-background interference in proton-proton collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 1 September 2026 | ||
| Submitted to Physical Review Letters | ||
| Abstract: The standard model Higgs boson, with a mass of 125 GeV, has a predicted decay width, $ \Gamma_{\mathrm{H}} $, of 4.1 MeV. This Letter presents the first constraint on $ \Gamma_{\mathrm{H}} $ obtained through the interference between the resonant $ \mathrm{H} \to \gamma\gamma $ process and the continuum $ \gamma\gamma $ production, both produced via gluon-gluon fusion. The analysis is performed using proton-proton collision data at $ \sqrt{s}= $ 13 TeV, collected by the CMS experiment between 2016 and 2018, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. The observed (expected) limit on the Higgs boson width is $ \Gamma_{\mathrm{H}} < 92 (138) \text{MeV} $ at 95% confidence level. This is the most stringent constraint on $ \Gamma_{\mathrm{H}} $ from on-shell Higgs boson measurements to date. | ||
| Links: e-print arXiv:2609.01385 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Diphoton invariant mass spectrum after full detector simulation, for the $ \mathrm{g}\mathrm{g}\mathrm{H} $ signal component of Eq. (1), denoted $ \mathcal{S}_{\mathrm{g}\mathrm{g}\mathrm{H}} $ (blue points), for the interference contribution of Eq. \eqrefeq:sigmaI, denoted $ \mathcal{I} $ and amplified by a factor 5 for better visualization (orange points), and their sum (black points), for samples with $ m_{\mathrm{H}}= $ 125 GeV and $ \Gamma_{\mathrm{H}}=\Gamma_{\mathrm{H}}^\mathrm{SM} $. |
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Figure 2:
The nominal signal shape in $ m_{\gamma\gamma} $ for $ \Gamma_{\mathrm{H}}=\Gamma_{\mathrm{H}}^\mathrm{SM} $, shown with the 68% CL envelope of all the experimental shape systematic uncertainties (grey band), together with the $ \Gamma_{\mathrm{H}} = $ 0 and 25 $ \Gamma_{\mathrm{H}}^\mathrm{SM} $ hypotheses (blue and red lines, respectively). The shown shapes are obtained as the weighted sum of each process and category. The weight for each category is proportional to $ S/(S+B) $, where $ S $ and $ B $ are, respectively, the expected signal and background yields in a narrow window around the $ \mathrm{H}\to\gamma\gamma $ mass peak. |
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Figure 3:
Weighted $ m_{\gamma\gamma} $ distribution in data, after background subtraction, with weights proportional to $ S/(S+B) $, in a zoomed range around the observed $ m_{\mathrm{H}} $. The best fit signal model (red line) is superimposed on the data, together with signal predictions in which all parameters except $ \lambda = \sqrt{\smash[b]{\Gamma_{\mathrm{H}}/\Gamma_{\mathrm{H}}^\mathrm{SM}}} $ are set to their best fit values. The parameter $ \lambda $ is evaluated at several different values of $ \lambda=0, 1, $ 5 (blue, gray, purple lines). In the inset plot, the data and fitted distributions are shown before background subtraction in the full fit range. |
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Figure 4:
Distribution of 1 $ - \text{CL} $ as a function of $ \Gamma_{\mathrm{H}} $, constructed using the Feldman--Cousins approach as defined in the text. The vertical bars on the points represent the statistical uncertainty in 1 $ - \text{CL} $ due to the limited number of pseudo-experiments. The dashed horizontal lines indicate the 68% and 95% confidence levels. |
| Summary |
| In summary, a constraint on the Higgs boson width $ \Gamma_{\mathrm{H}} $ is presented, using for the first time the interference between the resonant $ \mathrm{H} \to \gamma\gamma $ and continuum $ \gamma\gamma $ processes, both produced via gluon-gluon fusion. The observed (expected) limit is $ \Gamma_{\mathrm{H}} < 92 (138) \text{MeV} $ at 95%confidence level. This is the most stringent constraint on $ \Gamma_{\mathrm{H}} $ from on-shell Higgs boson measurements to date. |
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