Fermilab scientists have published the final results of a long-term muon G-2 experiment under the US Department of Energy, achieving unprecedented accuracy when measuring the magnetic anomalies of Moon.
This conclusive result, delivered with an accuracy of 127 parts per billion percent, exceeds the project’s original design goals and reviews previous findings released in 2021 and 2023.
The Muon G-2 experiment investigates the basic properties of electron-like subatomic particles, but is 200 times heavier. Like electrons, the moon has spin and acts like a small magnet wobbling in a magnetic field.
Measurement of this wobble or precession velocity gives a value known as a magnetic anomaly. This is important for testing the limitations of standard modeling in particle physics.
Muon G-2: A legacy of precision and innovation
The origin of the Muon G-2 returned to previous experiments at Brookhaven National Laboratory in the 1990s and early 2000s, suggesting a potential contradiction between experimental results and theoretical predictions.
This led to appetite questions about the existence of unknown particles or forces. This is a window into “new physics” that goes beyond the standard model.
To more accurately solve these questions, Brookhaven’s magnetic storage rings were transported nationwide in 2013 to Fermilab, Illinois.
After a comprehensive upgrade, the experiment was officially resumed in 2017, with the aim of dramatically improving accuracy.
The final result is confirmed, but the gap will be narrowed
The latest results from Fermilab drawn from data collected between 2021 and 2023 integrate the benefits from previous datasets and important improvements to experimental design.
The updated values for Muon magnetic anomalies are:
Aμ=(g-2)/2(Muon, experiment)=0.001 165 920 705 +-0.000 000 000 114 (stat.)
+-0.000 000 000 091 (syst.)
This measurement exists as the most accurate determination of this amount to date. This dataset was more than three times larger than that used in the 2023 release, and incorporated enhanced beam quality and reduced uncertainty.
The final values match previous experimental results, but complicate the broader narrative. Initially, the contradiction between experimental and theoretical values strongly suggested new physics.
However, recent theoretical recalculation using advanced computational methods published by the Muon G-2 Theoretical Initiative approached the experimental results and reduced the gap.
Theory: Evolving landscape
Theoretical physicists have worked in parallel to improve predictions of Moon’s magnetic anomalies.
In 2020, major updates based on data from other experiments deepened the inconsistency with Fermilab’s initial measurements. However, new calculations that rely heavily on computational methods have reorganized theories that are close to the observed data.
Despite this constriction of contradiction, the situation remains unresolved. Currently, there are two competing theoretical models (one data-driven, one calculation) that have different influences on new physics.
The Muon G-2 experiments currently serve as an important benchmark for evaluating these approaches, and future theoretical research aims to adjust them.
International collaboration promotes success
The Muon G-2 collaboration, consisting of 176 scientists from 34 institutions in seven countries, reflects the extraordinary convergence of expertise.
Unlike most high-energy physics experiments, Muon G-2 portrayed a diverse range of experts, not just particle physicists, but also accelerators, atom and nuclear physics experts.
This interdisciplinary teamwork helped us achieve technical refinement and ultimate success in our experiments.
The comprehensive and international features of the project demonstrate the global nature of modern scientific discoveries and the importance of collaborative innovation in answering some of the most fundamental questions of physics.
What’s next for Muon Research?
Fermilab’s Muon G-2 experiment concludes a major analysis, but the legacy of the data continues.
Future studies will investigate other properties of Muon, such as electric dipole moments and potential violations of charge, parity, and time inversion symmetry.
Follow-up experiments at the Japanese Proton Accelerator Research Complex (J-PARC) in the early 2030s aim to revisit the Muon magnetic anomaly. However, it initially works with a lower accuracy than the Fermilab benchmark settings results.
Meanwhile, theoretical initiative resolves discrepancies between competing predictions and ensures that the accuracy achieved by Muong G-2 will remain a central test of the theoretical model for the next few years.
Muon G-2: Future benchmarks
The final results of the Muon G-2 experiment are more than just numbers. It is the culmination of decades of scientific research, a model of international cooperation, and a new standard of experimental accuracy.
The narrow gap between theory and experiments eases early excitement about potential new physics, but it strengthens Muon as a powerful probe into real structures, confirming the resilience of the standard model in the face of unprecedented scrutiny.
The story of Muon G-2 doesn’t end here. It only enters a new chapter in quest to understand the universe at the most basic level.
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