Constraint on the Higgs boson width in the diphoton final state using signal-background interference in proton-proton collisions at $\sqrt{s}$ = 13 TeV

The standard model Higgs boson, with a mass of 125 GeV, has a predicted decay width, ${\mathrm{\Gamma }}_{\mathrm{H}}$, of 4.1 MeV. This Letter presents the first constraint on ${\mathrm{\Gamma }}_{\mathrm{H}}$ obtained through the interference between the resonant 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 ${\mathrm{\Gamma }}_{\mathrm{H}}$ $<$ 92 (138) MeV at 95% confidence level. This is the most stringent constraint on ${\mathrm{\Gamma }}_{\mathrm{H}}$ from on-shell Higgs boson measurements to date.