The Standard Model Higgs boson with a mass of ~125 GeV is predicted to have a decay width of ~ 4.1 MeV. Direct ΓH measurements using on-shell Higgs boson production are limited by the experimental energy resolution which is of the order of 1 GeV in the diphoton and four-lepton final states. Hence in order to constrain/measure this crucial parameter we have to rely on different indirect techniques such as global fits to all Higgs boson production modes or cross-section ratios of on-shell to off-shell Higgs boson production. While these methods yield the most competitive results, they have drawbacks in terms of the strong theoretical assumptions that are required in these approaches.
These limitations are not present if one relies on the ΓH dependent interference, in the diphoton decay channel, between on-shell Higgs boson production via gluon fusion (gg→H→γγ) and one of the continuum QCD processes (gg→γγ). This results in a “distorted” diphoton invariant mass distribution that can be translated into a constraint/measurement on ΓH. Such an analysis has been performed for the first time at colliders by CMS using the full Run 2 dataset corresponding to an integrated luminosity of 138 fb−1. The observed (expected) limit on the Higgs boson width is ΓH < 92 (138) MeV at the 95% confidence level.
In this seminar I will present the details of this important study and project the implications therein in Run 3 and beyond.