Flavour singlet pseudoscalar masses in N_f = 2 QCD

TL;DR

This study uses lattice QCD simulations to estimate the eta' meson mass in two-flavor QCD, confirming the role of topological gauge configurations in the mass gap.

Contribution

First lattice QCD analysis of flavour singlet pseudoscalar masses with dynamical Wilson fermions at this lattice spacing and quark mass extrapolation.

Findings

Estimated m_eta' = 3.7(+8)(-4) m_pi at physical light quark masses.

Mass gap between eta' and pion linked to topologically non-trivial gauge configurations.

Crude phenomenological extrapolation suggests m_eta' ≈ 5.1 m_pi for N_f=2.

Abstract

We perform a lattice mass analysis in the flavour singlet pseudoscalar channel on the SESAM and TXL full QCD vacuum configurations, with 2 active flavours of dynamical Wilson fermions at beta = 5.6. At our inverse lattice spacing, a^-1 = 2.3 GeV, we retrieve by a chiral extrapolation to the physical light quark masses the value m_eta' = 3.7(+8)(-4) m_pi. A crude extrapolation from (N_f = 3) phenomenology would suggest m_eta' \approx 5.1 m_pi for N_f = 2 QCD. we verify that the mass gap between the singlet state eta' and the pi flavour triplt state is due to gauge configurations with non-trivial topology.