Probing light quark Yukawa couplings through angularity distributions in Higgs boson decay

TL;DR

This paper proposes using angularity distributions in Higgs decay to quarks and gluons at electron-positron colliders to constrain light quark Yukawa couplings, achieving sensitivity down to about 7-15% of the bottom quark Yukawa.

Contribution

It introduces a novel method employing angularity event shapes and SCET predictions to probe light quark Yukawa couplings in Higgs decays at colliders.

Findings

Potential to constrain light quark Yukawa couplings to 7-15% of bottom quark Yukawa.

Angularity distributions differ significantly between quark and gluon jets.

Improved control of nonperturbative effects can enhance sensitivity.

Abstract

We propose to utilize angularity distributions in Higgs boson decay to probe light quark Yukawa couplings at $e^+e^-$ colliders. Angularities $\tau_a$ are a class of 2-jet event shapes with variable and tunable sensitivity to the distribution of radiation in hadronic jets in the final state. Using soft-collinear effective theory (SCET), we present a prediction of angularity distributions from Higgs decaying to quark and gluon states at $e^+e^-$ colliders to ${\rm NNLL}+\mathcal{O}(\alpha_s)$ accuracy. Due to the different color structures in quark and gluon jets, the angularity distributions from $H\to q\bar{q}$ and $H\to gg$ show different behaviors and can be used to constrain the light quark Yukawa couplings. We show that the upper limit of light quark Yukawa couplings could be probed to the level of $\sim15\%$ of the bottom quark Yukawa coupling in the Standard Model in a conservative analysis window far away from nonperturbative effects and other uncertainties; the limit can be pushed to $\lesssim 7-9\%$ with better control of the nonperturbative effects especially on gluon angularity distributions and/or with multiple angularities.