Karlsruhe 2024 – scientific programme
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T: Fachverband Teilchenphysik
T 21: BSM Higgs 1 (extended Higgs sectors)
T 21.5: Talk
Monday, March 4, 2024, 17:00–17:15, Geb. 30.41: HS 3
First shot of the smoking gun: probing the electroweak phase transition in the 2HDM with novel searches for A → ZH in ℓ+ ℓ− t t and ν ν b b final states — Thomas Biekötter1, Sven Heinemeyer2, Jose Miguel No2, •Kateryna Radchenko3, and Georg Weiglein3 — 1ITP, Karlsruhe, Germany — 2IFT, Madrid, Spain — 3DESY, Hamburg, Germany
Recently the ATLAS collaboration has reported the first results of searches for heavy scalar resonances decaying into a Z boson and a lighter new scalar resonance, where the Z boson decays leptonically and the lighter scalar decays into a top-quark pair, giving rise to ℓ+ ℓ− t t final states. This had previously been identified as a smoking-gun signature at the LHC for a first-order electroweak phase transition (FOEWPT) within the framework of two Higgs doublet models (2HDMs). We analyze the impact of these new searches on the 2HDM parameter space, with emphasis on their capability to probe currently allowed 2HDM regions featuring a strong FOEWPT. Remarkably, the ATLAS search in the ℓ+ ℓ− t t final state shows a local 2.85 σ excess (for masses of about 650 GeV and 450 GeV for the heavy and light resonance) in the 2HDM parameter region that would yield a FOEWPT in the early universe, which could constitute the first experimental hint of baryogenesis at the electroweak scale. We analyze the implications of this excess, and discuss the detectability prospects for the associated gravitational wave signal from the FOEWPT.
Keywords: EW phase transition; 2HDM; LHC searches; Baryogenesis; Gravitational waves