η and η' mesons from lattice QCD

Area of Science:

• Quantum Chromodynamics (QCD)
• Particle Physics
• Hadron Spectroscopy

Background:

• The mass of the ninth pseudoscalar meson (η') is significant in understanding quantum chromodynamics (QCD).
• Its large mass is hypothesized to stem from the axial anomaly and gauge field topology in QCD.

Purpose of the Study:

• To perform a realistic lattice QCD calculation of the η and η' meson masses and their mixing.
• To confirm the role of axial anomaly and gauge field topology in determining the η' meson mass.

Main Methods:

• A 2+1-flavor lattice QCD calculation was employed.
• The study focused on calculating meson masses and mixing properties.
• Extrapolation to physical light quark mass was performed.

Main Results:

• The calculation confirmed the hypothesized picture of η' mass origin.
• Small octet-singlet mixing was observed with a mixing angle of θ=-14.1(2.8)°.
• Extrapolated masses were mη=573(6) MeV and mη'=947(142) MeV, consistent with experimental values.

Conclusions:

• The lattice QCD results validate the combined effects of axial anomaly and gauge field topology in generating the η' meson's large mass.
• The calculated masses and mixing parameters align with experimental observations.
• This study provides strong evidence for the theoretical understanding of pseudoscalar meson properties within QCD.