Prospects for measuring the Higgs coupling to light quarks

TL;DR

This paper evaluates the potential to measure light-quark Yukawa couplings to the Higgs boson at current and future colliders, highlighting the challenges and possible sensitivities for charm and strange quarks.

Contribution

It introduces new methods and projections for probing light-quark Yukawa couplings, including inclusive and exclusive approaches at the LHC and future colliders.

Findings

High-luminosity LHC can probe charm Yukawa modifications of a few times the SM value.

Exclusive modes currently have limited sensitivity, around 50 times the SM coupling for charm.

Projected sensitivity for strange Yukawa coupling is around 3000 times the SM value.

Abstract

We discuss the prospects to probe the light-quark Yukawa couplings to the Higgs boson. The Higgs coupling to the charm quark can be probed both via inclusive and exclusive approaches. On the inclusive frontier, we use our recently proposed method together with published experimental studies for the sensitivity of the Higgs coupling to bottom quarks to find that the high-luminosity LHC can be sensitive to modifications of the charm Yukawa of the order of a few times its standard model (SM) value. We also present a preliminary study of this mode for a 100 TeV hadronic machine (with similar luminosity) and find that the bound can be further improved, possibly within the reach of the expected signal in the SM. On the exclusive frontier, we use the recent ATLAS search for charmonia and photon final state. This study yields the first measurement of the background relevant to these modes. Using this background measurement we project that at the high-luminosity LHC, unless the analysis strategy is changed, the sensitivity of the exclusive final state to the charm Yukawa to the charm Yukawa will be rather poor, of the order of 50 times the SM coupling. We then use a Monte-Carlo study to rescale the above backgrounds to the h->phi gamma case and obtain a much weaker sensitivity to the strange Yukawa, of order of 3000 times the SM value. We briefly speculate what would be required to improve the prospects of the exclusive modes.