# Heavy-quark physics with a tmQCD valence action

## TL;DR

This paper presents a mixed-action lattice QCD approach combining twisted mass valence quarks with Wilson sea quarks, demonstrating automatic O(a) improvement and introducing a Gradient Flow smearing technique to improve signal quality.

## Contribution

It introduces a novel mixed-action setup with maximally twisted valence quarks and a new Gradient Flow smearing method for better signal-to-noise ratio.

## Key findings

- Automatic O(a) improvement holds up to sea quark mass effects.
- Gradient Flow smearing effectively improves signal quality.
- The approach is compatible with CLS ensembles.

## Abstract

We introduce a mixed-action approach based on CLS ensembles, where a valence $N_f$=2+1+1 Twisted Mass QCD action is combined with the $N_f$=2+1 non-perturbatively O$(a)$-improved Wilson sea sector. We show that for maximally twisted valence quarks, the automatic O$(a)$-improvement of this set-up holds up to lattice artifacts coming from sea quark mass effects. Furthermore, we introduce a three-dimensional Gradient Flow smearing in order to tame the signal to noise ratio problem.