Meanwhile, in 2020 a group of 170 experts known as the Muon g-2 Theory Initiative published a new consensus value of the theoretical value of muon’s magnetic moment, based on three years of workshops and calculations using the Standard Model. That answer reinforced the original discrepancy reported by Brookhaven.
Reached by phone on Monday, Aida X. El-Khardra, a physicist at the University of Illinois and a co-chair of the Muon g-2 Theory Initiative, said she did not know the result that Fermilab would be announcing two days later — and she didn’t want to, lest she be tempted to fudge in a lecture scheduled just before the official unveiling on Wednesday.
“I have not had the feeling of sitting on hot coals before,” Dr. El-Khadra said. “We’ve been waiting for this for a long time.”
On the day of the Fermilab announcement another group, using a different technique known as a lattice calculation to compute the muon’s magnetic moment, concluded that there was no discrepancy between the Brookhaven measurement and the Standard Model.
“Yes, we claim that there is no discrepancy between the Standard Model and the Brookhaven result, no new physics,” said Zoltan Fodor of Pennsylvania State University, one of the authors of a report published in Nature on Wednesday.
Dr. El-Khadra, who was familiar with that work, called it an “amazing calculation, but not conclusive.” She noted that the computations involved were horrendously complicated, having to account for all possible ways that a muon could interact with the universe, and requiring thousands of individual sub-calculations and hundreds of hours of supercomputer time.
These lattice calculations, she said, needed to be checked against independent results from other groups to eliminate the possibility of systematic errors. For now, the Theory Initiative’s calculation remains the standard by which the measurements will be compared.
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