# Topological susceptibility and $\eta'$ meson mass from $N_f=2$ lattice QCD at the physical point

## TL;DR

This study calculates the topological susceptibility and $ ext{η'}$ meson mass in $N_f=2$ lattice QCD at the physical pion mass, demonstrating consistent results and a linear pion mass dependence of the susceptibility.

## Contribution

It provides a lattice QCD analysis of topological susceptibility and $ ext{η'}$ mass at the physical point with new insights into their pion mass dependence.

## Key findings

- $ ext{η'}$ mass is approximately 772 MeV with small uncertainty.
- Topological susceptibility shows linear dependence on $M_ ext{π}^2$ with lattice artifacts.
- Physical point can be reached without increased statistical noise.

## Abstract

In this paper we explore the computation of topological susceptibility and $\eta'$ meson mass in $N_f=2$ flavor QCD using lattice techniques with 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 $\eta'$ 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 $\eta'$ mass being flat we arrive at $M_{\eta'}= 772(18)\ \mathrm{MeV}$ without an explicit continuum limit. For the topological susceptibility we observe a linear dependence on $M_\pi^2$, however, with an additional constant stemming from lattice artifacts.