# Probe Charm Yukawa at the future $e^{-}p$ and $e^{+}e^{-}$ colliders

## TL;DR

This paper evaluates the potential of future electron-proton and electron-positron colliders to measure the charm Yukawa coupling, which is challenging at the LHC due to background, and finds that CEPC offers significantly better sensitivity than LHeC.

## Contribution

It compares the sensitivity of future colliders LHeC and CEPC for measuring the charm Yukawa coupling, highlighting the advantages of electron-positron colliders for this purpose.

## Key findings

- LHeC can reach 2σ significance for κ_c ≈ 1 with 3 ab^{-1}.
- CEPC can reach 8σ significance for κ_c ≈ 1 with 2 ab^{-1}.
- CEPC provides a more promising avenue for charm Yukawa measurement.

## Abstract

Large Hadron Collider (LHC) has provided direct evidence of Yukawa couplings between the third generation charged fermions and the 125 GeV Higgs boson. Whether the first two generation charged fermions arise from exactly the same mechanism becomes the next interesting question. Therefore, direct measurements of charm or muon Yukawa couplings will be crucial to answering this puzzle. The charm Yukawa measurement at the LHC suffers from severe QCD background and it is extremely difficult to reach the sensitivity. In this paper, we compare the potential of probing charm Yukawa coupling at the two proposed future "Higgs Factory" experiments, the Large Hadron electron Collider (LHeC) and Circular electron positron collider (CEPC). At the LHeC, Higgs bosons will be produced via weak boson fusion and the energetic forward jet may suppress the background significantly. However, due to huge $\gamma-g$ scattering background, the potential of LHeC search is still limited. With $-80\%$ polarized electron beam of 60 GeV, the signal significance can only reach $2\sigma$ for $ \kappa_{c}\simeq 1$ with a 3 ab$^{-1}$ integrated luminosity. In comparison, measurement at the CEPC can then reach $8.0\sigma$ for $\kappa_{c}\simeq 1$ with a 2 ab$^{-1}$ of data.