In 2021, the combined Fermilab and Brookhaven measurements of the muon's anomalous…
PHYSICS · Subjective · Fermi University Physics · Scientific Practice & Experimental Methods · Uncertainty in measurement · Records, communication and the epistemology of evidence
Measurement and Method, Ch Models, idealisation and what a measurement is evidence for
Problem
In 2021, the combined Fermilab and Brookhaven measurements of the muon's anomalous magnetic moment differed from one Standard-Model prediction by about z=4.2. A commentary states: 'This measurement refutes the Standard Model outright, since the discrepancy is far past z=3.'Which of the following is the correct assessment of this claim? (a) The claim is correct: any z beyond 3 refutes the theory it is tested against, without further qualification. (b) The claim is wrong in the opposite direction: a large z can safely be ignored because instruments always have unlisted systematic effects. (c) The discrepancy shows that something in the full chain linking the theory to the measured number is false, which could be the Standard-Model prediction itself, the input hadronic-vacuum-polarisation calculation used to compute it, the storage ring's magnetic-field calibration, or another auxiliary assumption; which one is false is not settled by the z value alone. (d) Because the result was published, it must already have been checked and the anomaly accepted as confirmed new physics. State the letter of the correct assessment and give one sentence for why each of the other three fails.