[Paper Review] Excesses in the low-mass Higgs-boson search and the $\varvec{W}$-boson mass measurement

Thomas Biekötter, S. Heinemeyer+1 more|arXiv (Cornell University)|Jan 1, 2022

Particle physics theoretical and experimental studies18 citations

TL;DR

This paper proposes that the recently measured W-boson mass by CDF, which significantly exceeds the Standard Model prediction, can be explained within a Two-Higgs-Doublet Model extended with a real singlet (N2HDM) of Yukawa type IV. The same model simultaneously accommodates observed excesses in Higgs searches at ~95 GeV in the γγ, τ⁺τ⁻, and b¯b final states, with the mass splitting between heavy Higgs states generating a large T-parameter contribution that raises MW to match the CDF value.

ABSTRACT

The CDF collaboration recently reported a measurement of the $W$-bososmass, $M_W$, about seven standard deviations above the Standard Model(SM). The question arises whether extensions of the SM exist that canaccomodate such large values, and what further phenomenologicalconsequences arise from this.A different type of deviation from the SM has been observedexperimentally in the searches for light Higgs bosons. CMS has observedtwo $\sim 3\,\sigma$ in the $\gamma\gamma$ and $ au^+ au^-$ final states for ahypothetical Higgs-boson mass of $\sim 95$ GeV. These two excesses arecompatible with the corresponding ATLAS limits. A third excess wasobserved in the $b \bar b$ final state at the $\sim 2\,\sigma$ level at aboutthe same Higgs-boson mass.It was shown recently that the three excesses can be described the the2HDM extended with a real singlet (N2HDM) of Yukawa type~IV, while beingin agreement with all other theoretical and experimental constraints.We demonstrate that the parameter space that accomodates the threeexcesses can also give a large contribution to $M_W$ in agreement withthe recent CDF measurement. We discuss further phenomenologicalconsequences of this scenario

Motivation & Objective

• To investigate whether the large deviation in the CDF W-boson mass measurement (80.4335 GeV) can be explained by new physics within the Standard Model.
• To determine if the same model can simultaneously describe multiple low-mass Higgs boson excesses observed in CMS and LEP data at ~95 GeV.
• To explore the phenomenological consequences of a model that unifies the CDF W-boson mass anomaly with the low-mass Higgs signals.
• To assess the compatibility of the model with theoretical and experimental constraints, including electroweak precision observables and collider limits.

Proposed method

• The study employs a Two-Higgs-Doublet Model extended with a real singlet scalar (N2HDM) of Yukawa type IV, which allows for a singlet-like Higgs boson at ~95 GeV.
• The model's parameter space is scanned numerically to identify regions that simultaneously describe the γγ, τ⁺τ⁻, and b¯b excesses at ~95 GeV with local significances of ~3σ.
• The T parameter is calculated as a function of mass splittings between the heavy Higgs states (h3, A, H±), which directly affects the W-boson mass prediction.
• The model's predictions are tested against experimental constraints from LEP, Tevatron, and LHC, including limits on Higgs couplings and Higgs portal interactions.
• The compatibility of the model with the effective weak mixing angle from SLD and LEP is evaluated to assess consistency with electroweak precision data.
• The possibility of a strong first-order electroweak phase transition is explored, as it is linked to the same mass hierarchy that enhances the T parameter.

Experimental results

Research questions

• RQ1 Can the N2HDM with a real singlet explain the CDF W-boson mass measurement of 80.4335 GeV while remaining consistent with other experimental constraints?
• RQ2 Is there a parameter region in the N2HDM where a single Higgs boson at ~95 GeV can simultaneously explain the γγ, τ⁺τ⁻, and b¯b excesses observed by CMS and LEP?
• RQ3 What is the role of mass splittings between the heavy Higgs states (h3, A, H±) in generating a large T-parameter contribution that raises MW above the SM prediction?
• RQ4 How does the model's compatibility with electroweak precision observables, such as sin²θeff, compare with data from SLD and LEP?
• RQ5 Can the same mass hierarchy that explains the W-boson mass and low-mass Higgs signals also support a strong first-order electroweak phase transition, relevant for baryogenesis and gravitational wave production?

Key findings

• The N2HDM with a real singlet of Yukawa type IV can simultaneously describe the CDF W-boson mass measurement (80.4335 GeV) and the low-mass Higgs excesses at ~95 GeV in γγ, τ⁺τ⁻, and b¯b final states.
• The parameter space that explains the three Higgs excesses also yields a T-parameter enhancement sufficient to raise MW to the CDF value, with mass splittings between h3 and the degenerate A and H± states being key.
• The model remains compatible with all current theoretical and experimental constraints, including electroweak precision data and collider limits.
• The mass hierarchy mh3 < mA ≈ mH±, which favors a strong first-order electroweak phase transition, naturally leads to a large T parameter and thus a high MW prediction.
• The model can also accommodate the 3.5σ excess observed by CMS at ~400 GeV in the di-top final state via the CP-odd Higgs boson A.
• A future world average of MW that includes the CDF result would likely lie between the current PDG average and the CDF central value, and the model remains viable under such a scenario with slightly reduced T-parameter values.