Simulations of QCD using Physical Up, Down, Strange, and Charm Twisted Mass Fermions

High-intensity particle physics experiments, such as those at MAMI in Mainz and at Jefferson Lab and Fermi Lab, are providing precision nucleon structure results in the search for new physics.

A major challenge at this so-called precision frontier, is to determine accurately the contributions due to the strong interaction component of the Standard Model, governed by the theory of Quantum Chromodynamics (QCD). In this project, we propose a large-scale lattice QCD simulation that will enable the ab initio calculation of hadronic contributions to key nucleon quantities being measured in these precision experiments as well as planned within the Electron-Ion Collider.

The proposed simulation will be carried out using degenerate up and down quarks, a strange, and a charm quark (Nf=2+1+1) tuned to their physical mass values (physical point). We will use the twisted mass fermion formulation, with a lattice spacing of a=0.07 fm and spatial extent L=108a=7.6 fm. With these parameters, this simulation will be the largest lattice volume ever simulated using twisted mass fermions and therefore the most computationally demanding, crucially relying on resources of the scale of Lumi-C.

Combined with four existing ensembles available at three values of a and two values of L, this simulation will enable a first combined continuum and infinite volume limit study of key hadronic observables directly at the physical point.

Quantities that will be targeted using these simulations are connected to fundamental questions of hadron structure, such as the muon anomalous magnetic moment, the nucleon σ-terms, scalar, axial, and tensor charges, nucleon electromagnetic and axial form factors, and moments of PDFs. These quantities are of crucial importance in advancing our theoretical understanding of QCD, such as how the nucleon mass and spin arise from its constituent quarks and gluons, as well as in providing input into new physics searches.