Signs of heavy Higgs bosons at CLIC: An $e^+ e^-$ road to the Electroweak Phase Transition

TL;DR

This paper assesses CLIC's potential to detect heavy Higgs bosons, especially through di-Higgs channels, and explores their role in electroweak phase transition scenarios relevant to matter-antimatter asymmetry.

Contribution

It demonstrates CLIC's superior sensitivity over HL-LHC for heavy Higgs searches and investigates the connection between heavy Higgs detection and electroweak phase transition models.

Findings

CLIC can improve sensitivity to heavy Higgses by up to two orders of magnitude over HL-LHC.

Heavy Higgs searches at CLIC can probe parameter regions relevant for a strong first order electroweak phase transition.

Complementarity between CLIC and FCC-ee enhances exploration of singlet extensions of the Standard Model.

Abstract

We analyse the sensitivity of the proposed Compact Linear Collider (CLIC) to the existence of beyond the Standard Model (SM) Higgs bosons through their decays into pairs of massive gauge bosons $H \to VV$ and SM-like Higgses $H \to hh$, considering CLIC centre of mass energies $\sqrt{s} = 1.4$ TeV and $3$ TeV. We find that resonant di-Higgs searches at CLIC would allow for up to two orders of magnitude improvement w.r.t. the sensitivity achievable by HL-LHC in the mass range $m_H \in [250\,\mathrm{GeV},\, 1 \,\mathrm{TeV}]$. Focusing then on a real singlet extension of the SM, we explore the prospects of heavy Higgs searches at CLIC for probing the regions of parameter space yielding a strongly first order electroweak phase transition that could generate the observed matter-antimatter asymmetry of the Universe. Our study illustrates the complementarity between CLIC and other possible future colliders like FCC-ee in probing singlet extensions of the SM, and shows that high-energy $e^+ e^-$ colliders provide a powerful means to unravel the nature of electroweak symmetry breaking in the early Universe.