First Physics Results at the Physical Pion Mass from $N_f = 2$ Wilson Twisted Mass Fermions at Maximal Twist

TL;DR

This paper reports on lattice QCD simulations at the physical pion mass using $N_f=2$ Wilson twisted mass fermions with a clover term, achieving accurate results for meson and baryon properties and lepton magnetic moments.

Contribution

Introduction of a clover term in twisted mass fermion simulations to reduce isospin breaking and obtain physical hadron and lepton properties at the physical pion mass.

Findings

Pion mass splitting due to isospin breaking is minimized.

Computed meson decay constants and quark masses agree with continuum results.

Nucleon and $ riangle$ baryon masses are consistent with physical values.

Abstract

We present physics results from simulations of QCD using $N_f = 2$ dynamical Wilson twisted mass fermions at the physical value of the pion mass. These simulations were enabled by the addition of the clover term to the twisted mass quark action. We show evidence that compared to previous simulations without this term, the pion mass splitting due to isospin breaking is almost completely eliminated. Using this new action, we compute the masses and decay constants of pseudoscalar mesons involving the dynamical up and down as well as valence strange and charm quarks at one value of the lattice spacing, $a \approx 0.09$ fm. Further, we determine renormalized quark masses as well as their scale-independent ratios, in excellent agreement with other lattice determinations in the continuum limit. In the baryon sector, we show that the nucleon mass is compatible with its physical value and that the masses of the $\Delta$ baryons do not show any sign of isospin breaking. Finally, we compute the electron, muon and tau lepton anomalous magnetic moments and show the results to be consistent with extrapolations of older ETMC data to the continuum and physical pion mass limits. We mostly find remarkably good agreement with phenomenology, even though we cannot take the continuum and thermodynamic limits.