Constraints on Higgs Light Yukawa Couplings with the CMS Detector

TL;DR

The paper addresses measuring the Higgs charm Yukawa coupling $y_c$, a challenging yet essential test of the SM. It combines direct searches in $H\to c\bar{c}$ across $t\bar{t}H$, $VH$, and $cH$ channels with indirect probes from radiative decays such as $H\to J/\psi\gamma$ and $\gamma H$, employing advanced jet-flavor tagging (e.g., ParticleNet) and transformer-based classifiers. The results from CMS Run 2 are consistent with SM expectations and set the most stringent direct constraint to date, $|\kappa_c| < 3.5$ (observed) and $2.7$ (expected), with complementary bounds from other channels. The work demonstrates significant progress in charm-jet discrimination and establishes a foundation for Run 3 and HL-LHC to tighten these limits or observe rare charm-Higgs processes, enhancing our understanding of Yukawa couplings across fermion generations.

Abstract

The discovery of the Higgs boson ten years ago and successful measurement of the Higgs boson couplings to third generation fermions by LHC mark great milestones for HEP. The much weaker coupling to the second generation quarks predicted by the SM makes the measurement of the light Yukawa Higgs couplings, as the Higgs-charm ones, much more challenging. With the latest tagging algorithms capabilities, a lot of progress has been made to constrain these couplings. In this talk, the latest results of direct and indirect measurements by the CMS experiment are presented. Prospects for future improvements are also given.

Figures (4)

• Figure 1: Left: Post-fit discriminator outputs in each category and lepton multiplicity. The signals are represented by the four red and orange histograms HIG24018. Right: dijet invariant mass distribution in a representative $VH$ signal region PRL131.
• Figure 2: Observed and expected limits on $\sigma/\sigma_{SM}$ (left) and likelihood scan for the charm Yukawa coupling modifier $\kappa_c$ (right) for the $VH$ and $t\bar{t}H$, and the combination of the two HIG24018.
• Figure 3: Left: di-photon invariant mass spectrum in the $c H, \, H\to\gamma\gamma$ analysis HIG23010. Right: Weighted distribution of the events in the category with one charm-tagged jet in the $c H, \, H\to WW^*$ analysis HIG24009.
• Figure 4: Left: invariant mass distributions in the search for $H\to J/\Psi \gamma$PLB865. Right: Likelihood scan on $\kappa_c$HIG23011. The black lines represent the case where all couplings except $\kappa_c$ are fixed at their SM values.