Measurement of the Higgs decay width in the diphoton channel

In this note, a projected measurement of the Higgs decay width ($\Gamma_{H}$) is presented, based on interference in the diphoton channel. Two different hypotheses were tested. Hypothesis A assumes that the $H\to\gamma\gamma$ cross-section is proportional to $\Gamma_{H}^{-1}$, whereas hypothesis B assumes that this cross-section is constant and instead uses the overall change in $m_{\gamma\gamma}$ line shape. Events were simulated using Sherpa 2.1, and were used to produce test statistics in order to obtain a 95 % confidence limit of $\Gamma_{H}$. The standard model width was tested using Asimov data sets, which were validated using pseudo-experiments for the integrated luminosities of Run 1, Run 2 and HL-LHC. The obtained limits are significantly improved with respect to previous studies, but further validations of the test are required. The expected limits for 300 fb$^{-1}$ are $1.19\times\Gamma_{H\,SM}$ for hypothesis A and $24\times\Gamma_{H\,SM}$ for hypothesis B.