Lattice determination of the muon's anomalous magnetic moment

Project Information

MUON

Grant agreement ID: 101054515

DOI

10.3030/101054515

EC signature date 9 December 2022

Start date 1 October 2023

End date 30 September 2028

Funded under

• European Research Council (ERC)

Total cost

€ 2 085 625,00

EU contribution

€ 2 085 625,00

Coordinated by

FORSCHUNGSZENTRUM JULICH GMBH
Germany

Periodic Reporting for period 1 - MUON (Lattice determination of the muon's anomalous magnetic moment)

Reporting period: 2023-10-01 to 2026-03-31

Summary of the context and overall objectives of the project

The MUON project is designed to span five years, making it a substantial undertaking with well-defined milestones and ambitious objectives. The ultimate goal remained the same as it was in the proposal, namely, significantly improve on the precision of the leading-order hadronic vacuum polarization contribution to the muon's anomalous magnetic moment by reducing its error by approximately 40%. This scientific challenge has far-reaching implications, as it seeks to answer a fundamental question: are there only four forces in nature, or is there yet another unknown interaction at play? To achieve this, a clear plan was necessary for the various computational steps. In fact, both the first year's and the second year's achievements exceeded many of the original milestone expectations.

In year one and year two one of the most crucial and time-consuming tasks is the detailed scientific planning, which involves thorough literature reviews, discussions with international colleagues, and informed decision-making regarding the research steps. In the field of lattice QCD, this last step is particularly critical, as a suboptimal decision about simulation parameters can significantly prolong the project timeline by doubling or tripling it.

A significant amount of time and effort was dedicated to producing a main paper, arXiv:2407.10913 [hep-lat] and to its revised versions, for which I am the corresponding author. The paper spans now close to 100 pages and represents a substantial undertaking. Despite being quite a new paper, it has already generated an impressive 120+ citations.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The main result of the above mentioned paper is a new determination of the leading order hadronic vacuum polarization to the magnetic moment of the muon. The experimental uncertainty is 1.5e-10 and the theoretical one ist 3.3e-10. The two results show perfect agreement within the uncertainties. This means an eleven digit agreement. The theoretical result is based on four major ingredients: (a) the "tree level result of Dirac"; (b) the high loop calculation of quantum electrodynamics (c) the contribution of the weak interaction with spontaneous symmetry breaking; (d) the non-perturbatively formulated and renormalized strong interaction from the lattice. These are very different forms of quantum results and the astonishing agreement between experiment and theory proves that quantum field theory is correct at least up to 11 digits. This is the strongest proof what we have today.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The agreement or non-agreement of theory and experiment is a question of uncertainties. Our theoretical method and result is the most precise one in the literature.