[Paper Review] Measurement of the Higgs-boson CP properties using decays into WW and ZZ at the Photon Collider

P. Nieżurawski, A. F. Żarnecki+1 more|ArXiv.org|Jul 14, 2003

Particle physics theoretical and experimental studies1 references5 citations

TL;DR

This paper investigates the measurement of Higgs boson CP properties at the TESLA Photon Collider using $\gamma\gamma \to h \to WW/ZZ$ decays. By combining invariant-mass and angular correlation analyses of $W^+W^-$ and $ZZ$ decay products, it demonstrates that CP-violating couplings can be probed with 1–2% statistical precision after one year of running, enabling discrimination between SM-like and extended Higgs models including 2HDM II and generic CP-violating couplings.

ABSTRACT

Higgs-boson production at the Photon Collider at TESLA is studied for masses from 180 to 350 GeV, using realistic luminosity spectra and detector simulation. Parity of the SM Higgs-boson can be verified from the measurement of the interference effects in the W+ W- decay channel and of the angular correlations in the decays of W+ W- and ZZ pairs. SM-like Two Higgs Doublet Model (2HDM II) and model with the generic higgs couplings are considered.

Motivation & Objective

• To assess the feasibility of measuring Higgs boson CP properties at the Photon Collider using $\gamma\gamma \to h \to WW/ZZ$ decays.
• To determine the sensitivity of invariant-mass and angular correlation distributions to CP-violating couplings in extended Higgs models.
• To evaluate the precision of measuring $\tan\beta$, $H$–$A$ mixing angle, and generic CP-violating parameters in the 2HDM II and generic models.
• To establish a model-independent method for probing Higgs CP parity using angular distributions of decay products.
• To quantify the improvement in coupling precision when combining invariant-mass and angular distribution measurements.

Proposed method

• Uses realistic luminosity spectra and detector simulation (SIMDET v3.01) for the TESLA Photon Collider, based on Compton backscattering of laser photons on electron beams.
• Performs event generation with PYTHIA 6.152 for $\gamma\gamma \to h \to W^+W^-$ and $\gamma\gamma \to h \to ZZ$ processes, including interference with SM backgrounds.
• Applies selection cuts to isolate $W^+W^- \to q\bar{q}q\bar{q}$ and $ZZ \to l^+l^-q\bar{q}$ final states ($l = e, \mu$) for analysis.
• Analyzes invariant-mass distributions of $W^+W^-$ and $ZZ$ pairs to extract $\Gamma_{\gamma\gamma}$ and $\phi_{\gamma\gamma}$, and combines with angular correlations for CP sensitivity.
• Conducts simultaneous fits to invariant-mass and angular distributions to constrain parameters $\lambda_A$ and $\lambda_H$ in a generic CP-violating model.
• Imposes relative normalization between $ZZ$ and $W^+W^-$ samples based on cross-section predictions, while allowing overall luminosity normalization to vary.

Experimental results

Research questions

• RQ1 Can the CP properties of the Higgs boson be determined independently of the production mechanism using angular correlations in $W^+W^-$ and $ZZ$ decay products?
• RQ2 What is the precision of measuring the $H$–$A$ mixing angle in a CP-violating Two Higgs Doublet Model (2HDM II) at the Photon Collider?
• RQ3 How does combining invariant-mass and angular distribution measurements improve the sensitivity to CP-violating couplings in the Higgs sector?
• RQ4 What statistical precision can be achieved in measuring $\tan\beta$ and generic CP-violating parameters ($\lambda_A$, $\lambda_H$) in extended Higgs models?
• RQ5 To what extent do interference effects in $W^+W^-$ production enhance sensitivity to the phase of the $h \to \gamma\gamma$ coupling?

Key findings

• For Higgs masses between 180 and 350 GeV, the $\gamma\gamma$ partial width and phase of the Higgs coupling can be measured with 3–8% and 30–100 mrad precision, respectively, after one year of Photon Collider running.
• In the SM-like 2HDM II model, $\tan\beta$ can be determined with approximately 10% statistical precision after one year of data-taking.
• For the CP-violating 2HDM II model, the $H$–$A$ mixing angle can be measured with a statistical precision of 20 to 90 mrad in the small-mixing approximation.
• In a generic CP-violating model, the parameters $\lambda_A$ and $\lambda_H$ describing CP-violating couplings to vector bosons can be determined with 10% statistical uncertainty.
• Combining invariant-mass and angular distribution measurements reduces the statistical uncertainty in Higgs coupling determinations to 1–2%, significantly improving sensitivity.
• The $W^+W^-$ invariant-mass distribution is the dominant constraint on $\lambda_A$, while the $ZZ$ invariant-mass distribution primarily constrains $\lambda_H$, with expected errors of ~0.01 and ~0.01–0.02, respectively.