Did this signal disappear with more data? [Muons: 'Strong' evidence found for a new force of nature 7 April 2021 https://www.bbc.com/news/56643677]
You’re referring to the Muon g-2 experiment and the intriguing results reported on April 7, 2021, suggesting potential evidence for a new force of nature due to a discrepancy in the muon’s magnetic moment (the "g-2" value) compared to predictions from the Standard Model of particle physics. The question is whether this signal—indicating possible new physics—held up as more data was analyzed. As of April 4, 2025, the Muon g-2 experiment, conducted at Fermilab, has indeed collected and analyzed significantly more data since that initial 2021 announcement. The first result was based on just 6% of the planned dataset (Run 1). Subsequent updates, including results from Runs 2 and 3, have been released, with the most recent major update in 2023 doubling the precision of the initial findings. The anomaly persisted in these later analyses, with the discrepancy between the experimental measurement and the Standard Model prediction remaining statistically significant—around 4.2 sigma, just shy of the 5-sigma threshold physicists typically require to claim a definitive discovery. However, the signal hasn’t "disappeared" in the sense of being washed out by more data. Instead, it’s become more precisely measured, and the tension with the Standard Model has held steady. That said, the interpretation of this signal remains under intense scrutiny. A key factor complicating the story is the theoretical prediction itself. The Standard Model’s expected value for the muon’s g-2 relies on complex calculations involving quantum contributions from known particles. In 2021, a significant debate emerged when a new lattice QCD (quantum chromodynamics) calculation suggested the Standard Model might actually align closer to the experimental result, reducing the apparent anomaly. This contrasted with the traditional "data-driven" method endorsed by the Muon g-2 Theory Initiative, which showed the larger discrepancy reported in the BBC article. As more experimental data has come in (with Runs 4, 5, and 6 still being analyzed as of 2025), the focus has shifted somewhat to resolving this theoretical uncertainty. If the lattice QCD approach is correct, the "signal" for new physics might indeed weaken or vanish, not because the experimental data changed dramatically, but because the baseline prediction adjusted. Conversely, if the data-driven method holds, the anomaly could strengthen with the full dataset—potentially reaching or exceeding 5 sigma once all runs are included (expected around 2026–2027). So, to answer directly: No, the signal hasn’t disappeared with more data as of now. The experimental discrepancy persists and has been reinforced by additional runs, but its significance as evidence for a new force hinges on ongoing debates about the theoretical prediction. The jury’s still out, and physicists are eagerly awaiting the final analysis of the complete dataset to see if this tantalizing hint solidifies into a breakthrough—or fades into a quirk of calculation. Stay tuned, as the original announcement suggested!
