Researchers Achieve High-precision QED Corrections for Muon G-2 with GeV and MeV Data

The persistent discrepancy between theoretical predictions and experimental measurements of the muon’s anomalous magnetic moment, known as the muon g-2, demands increasingly precise calculations of quantum electrodynamic (QED) corrections, particularly those arising from the complex interactions within the hadronic vacuum polarization. Christoph Lehner, Julian Parrino, and Andreas Völklein, all from Universität Regensburg, address a significant challenge in these calculations, the long-distance contributions which are notoriously difficult to model accurately. Their work introduces a novel method for reconstructing these contributions by focusing on exclusive finite-volume states, effectively building up a precise picture of the underlying physics. This approach represents a crucial step towards matching the precision of the recent results from the Fermilab E989 experiment and resolving the long-standing puzzle surrounding the muon g-2.

This work introduces a method for achieving this precision by reconstructing contributions from individual, exclusive states within a finite volume. Researchers establish relationships between the contributions from pion-photon interactions in different diagrams, and demonstrate the method using lattice QCD+QED data. This advancement is crucial because lattice QCD+QED calculations are now providing the Standard Model prediction for the hadronic vacuum polarization contribution to the muon g-2, enabled by progress in both theoretical understanding and computational resources, allowing for a more accurate determination of this crucial quantity. Accurate calculation of the hadronic vacuum polarization is essential for precisely predicting the muon’s anomalous magnetic dipole moment and comparing it with experimental measurements, potentially revealing new physics beyond the Standard Model.

Improving Hadronic Vacuum Polarization Calculations

This paper details a method to enhance the precision of calculations related to the muon’s anomalous magnetic moment, addressing the muon g-2 anomaly where experimental measurements deviate from Standard Model predictions. A major source of uncertainty in the Standard Model prediction is the hadronic vacuum polarization (HVP), a quantum effect arising from virtual particles. Accurately calculating HVP is extremely difficult, particularly modeling its behavior at long distances. The authors employ high-precision Lattice QCD to calculate HVP, focusing specifically on pion-photon contributions which dominate at long distances.

They identify relationships between different operators describing particle interactions, simplifying calculations and reducing the number of quantities needing determination. They demonstrate relationships between the pion-photon contributions of different diagrams and achieve significant noise reduction, exceeding a factor of five in some cases. The team incorporates techniques to simulate quantum electrodynamics (QED) in an infinite volume, crucial for accurately modeling long-distance behavior, and utilizes a powerful software library for performing the lattice QCD calculations. The method promises to significantly improve the precision of the HVP calculation, particularly at long distances, and reduce statistical noise, making the calculations more reliable. By reducing uncertainty in the HVP calculation, researchers aim to provide a more accurate Standard Model prediction for the muon g-2, helping determine whether the observed discrepancy is due to new physics or calculation inaccuracies.

Hadronic Vacuum Polarization via Exclusive States

Researchers have developed a new method for calculating a challenging contribution to the precise determination of the muon’s magnetic moment, a quantity vital for testing the Standard Model of particle physics. This calculation concerns the long-distance effects of quantum electrodynamics (QED) on the hadronic vacuum polarization, a limiting factor in matching the precision of recent experimental results from the Fermilab E989 experiment. The team successfully reconstructed this contribution by focusing on exclusive finite-volume states, offering a pathway to higher precision calculations. The method involves carefully analyzing how different diagrams contribute to the overall calculation, specifically those involving pion and photon interactions.

By establishing relationships between these diagrams, scientists were able to reconstruct the long-distance contribution with improved accuracy. Demonstrating the technique, the team performed calculations using lattice QCD+QED data. This approach allows for a more systematic and controlled calculation of the QED corrections, addressing challenges previously encountered with direct calculations or reliance on phenomenological models. Results demonstrate the feasibility of reconstructing the long-distance contribution, paving the way for more accurate theoretical predictions of the muon’s magnetic moment.

The team’s calculations account for various diagrams, including those involving pion-photon interactions and contributions from states like the rho meson and pion pairs, while also incorporating necessary renormalization procedures. This advancement is crucial for reducing the theoretical uncertainty surrounding the muon g-2 value, enabling a more stringent test of the Standard Model and potentially revealing hints of new physics beyond it. The method promises to significantly improve the precision of future calculations, bringing theory and experiment into closer agreement and furthering our understanding of fundamental particles and forces.

Pion and Photon Contributions to Muon g-2

This research presents a new method for calculating the long-distance contribution of quantum electrodynamic (QED) corrections to the hadronic vacuum polarization, a quantity important for precisely determining the muon’s magnetic moment. The team developed a technique to reconstruct contributions from individual states, allowing for a more precise first-principles calculation of these corrections. Results demonstrate relationships between contributions from pions and photons within different diagrams, enabling individual analysis of the dominant diagrams. The method successfully reduces statistical noise in calculations, with a noise reduction exceeding a factor of five observed for the most challenging diagram. These calculations were performed at a pion mass approximately twice the physical value, demonstrating the potential of the approach for high-precision results. Future work will extend these studies to different computational setups, including calculations with physical pion masses and the inclusion of additional diagrams.