In 2020, a group of 170 experts published what is known as the Muon g-2 Theory Initiative a new consensus value of the theoretical value of the magnetic moment of muon, based on three-year workshops and calculations using the standard model. That answer compounded the original discrepancy that Brookhaven reported.
Reached by phone on Monday, Aida X. El-Khardra, a physicist at the University of Illinois and co-chair of the Muon g-2 Theory Initiative, said she didn’t know what result Fermilab would announce two days later – and she didn’t want to so she is not tempted to fumble in a lecture scheduled shortly before the official unveiling on Wednesday.
“I’ve never felt like I’m on hot coals,” said Dr. El-Khadra. “We have waited a long time for this.”
On the day Fermilab announced, another group, using a technique known as lattice computation to compute the muon’s magnetic moment, concluded that there was no discrepancy between the Brookhaven measurement and the Standard Model.
“Yes, we claim 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, familiar with this work, called it an “amazing calculation, but inconclusive”. She found that the calculations involved were excruciatingly complex, had to take into account all possible ways a muon could interact with the universe, and required thousands of individual sub-calculations and hundreds of hours of supercomputer time.
These grid calculations would have to be compared with independent results from other groups in order to rule out the possibility of systematic errors. For the time being, the calculation of the theory initiative remains the standard against which the measurements are compared.
