[Paper Review] Has A 125 GeV Pseudoscalar Resonance Been Observed at the LHC?

J. W. Moffat|arXiv (Cornell University)|Apr 20, 2012

Particle physics theoretical and experimental studies11 references3 citations

TL;DR

The paper proposes that the 125 GeV resonance observed at the LHC may be a pseudoscalar quarkonium state ($\zeta^{0}$) rather than the Standard Model Higgs boson, arising from mixing between bottom and top quarkonia. Using the non-relativistic quark model, it shows that the $\gamma\gamma$ and $gg$ decay widths of $\zeta^{0}$ differ significantly from those of the Higgs, and that measuring the production cross sections could distinguish the two particles experimentally.

ABSTRACT

We conjecture that a 125 GeV resonance $ζ^0$ with $J^{PC}=0^{-+}$ composed of a quark-antiquark state may have been observed at the LHC. The decay modes of this pseudoscalar particle are determined using the non-relativistic quark model. The leading order partial decay widths for the decays of the pseudoscalar quarkonium resonance $ζ^0 ightarrow γγ$ and $ζ^0 ightarrow gg$ are compared to the standard model Higgs particle decays $H^0 ightarrow γγ$ and $H^0 ightarrow gg$. An experimental analysis at the LHC of the observed production cross sections for the $ζ^0$ and the Higgs particle could distinguish between a heavy quarkonium $ζ^0$ particle and a light Higgs particle at 125 GeV.

Motivation & Objective

• To investigate whether the 125 GeV resonance observed by ATLAS and CMS could be a pseudoscalar quarkonium state rather than the Standard Model Higgs boson.
• To explore the implications for electroweak symmetry breaking if the resonance is a heavy quarkonium state instead of a fundamental Higgs.
• To distinguish between a $\zeta^{0}$ quarkonium resonance and a light Higgs particle using experimental measurements of production cross sections and branching ratios.
• To analyze the role of mixing between bottom and top quarkonia states in generating a 125 GeV pseudoscalar resonance.

Proposed method

• Uses the non-relativistic quark model to compute leading-order partial decay widths for $\zeta^{0} \rightarrow \gamma\gamma$ and $\zeta^{0} \rightarrow gg$.
• Applies the effective Hamiltonian formalism with a mass matrix $\mathcal{M}$ to describe mixing between $|B\rangle = |b\bar{b}\rangle$ and $|T\rangle = |t\bar{t}\rangle$ states.
• Derives mass eigenstates $m_{\zeta^{0}} \sim 125$ GeV and $m_{\zeta^{0'}} \sim 230$ GeV via diagonalization of the mass matrix using a mixing angle $\phi \sim 36^\circ$.
• Calculates decay widths using the Coulomb approximation, with $|R_0(0)|^2 \propto \alpha_s^3 m_{\zeta^{0}}$ for S-wave quarkonium.
• Compares the production cross section $\sigma(pp \rightarrow \zeta^{0} + X)$ to that of the Higgs using the narrow-width approximation and gluon fusion dominance.
• Defines a ratio $\mu = \sigma_\zeta / \sigma_H$ to compare $\gamma\gamma$ decay rates, where $\mu > 1$ would favor a $\zeta^{0}$ interpretation.

Experimental results

Research questions

• RQ1 Could the 125 GeV resonance observed in the $\gamma\gamma$ channel at the LHC be a pseudoscalar quarkonium state rather than the Standard Model Higgs boson?
• RQ2 How do the decay widths $\Gamma(\zeta^{0} \rightarrow \gamma\gamma)$ and $\Gamma(\zeta^{0} \rightarrow gg)$ compare to those of the Higgs boson at 125 GeV?
• RQ3 Can the production cross sections of the 125 GeV resonance in $gg$ fusion distinguish a $\zeta^{0}$ quarkonium state from a Higgs boson?
• RQ4 What is the role of mixing between bottom and top quarkonia in generating a 125 GeV pseudoscalar state?
• RQ5 Would the absence of significant $WW^*$ and $ZZ^*$ decays in the 125 GeV resonance support a pseudoscalar quarkonium interpretation?

Key findings

• The 125 GeV resonance is interpreted as a $\zeta^{0}$ quarkonium state formed by mixing between $|b\bar{b}\rangle$ and $|t\bar{t}\rangle$ states, with a mixing angle $\phi \sim 36^\circ$.
• The calculated mass of the $\zeta^{0}$ state is $m_{\zeta^{0}} \sim 125$ GeV, consistent with the observed resonance, while the partner state $\zeta^{0'}$ has a mass of $m_{\zeta^{0'}} \sim 230$ GeV.
• The partial decay width $\Gamma(\zeta^{0} \rightarrow \gamma\gamma)$ is proportional to $\alpha^2 \alpha_s^3 m_{\zeta^{0}}$, differing from the Higgs decay width by a factor dependent on coupling constants.
• The ratio $\mu = \sigma_\zeta / \sigma_H$ for $\gamma\gamma$ production is predicted to be greater than unity, indicating a potentially larger production cross section for the $\zeta^{0}$ than for the Higgs.
• The $\zeta^{0}$ state has suppressed couplings to $WW^*$ and $ZZ^*$, unlike the Higgs, which could be tested via branching ratio measurements.
• If the 125 GeV resonance is confirmed as a pseudoscalar quarkonium, it would imply that the Standard Model Higgs does not exist and that electroweak symmetry breaking arises via a new strong dynamics involving fermion condensates.