Topological susceptibility and $η ′$ meson mass from $N_f = 2$ lattice QCD at the physical point

In this paper we explore the computation of topological susceptibility and $η′$ meson mass in $N_f=2$ flavor QCD using lattice techniques with a physical value of the pion mass as well as larger pion mass values. We observe that the physical point can be reached without a significant increase in the statistical noise. The mass of the $η′$ meson can be obtained from both fermionic two point functions and topological charge density correlation functions, giving compatible results. With the pion mass dependence of the $η′$ mass being flat we arrive at $M_{η′}=772(18) MeV$ without an explicit continuum limit. For the topological susceptibility we observe a linear dependence on $M^2_π$, however, with an additional constant stemming from lattice artifacts