Double Blinding Procedure for Muon g-2

The Fermi National Accelerator Laboratory Muon g-2 Experiment measures the muon's anomalous magnetic moment a_μ = (g-2)/2 in order to reassess its tension with the Standard Model based on the original result from Brookhaven National Laboratory. To protect final results from personal biases, we double-blind the key observable ω_a (the anomalous precession frequency) in both hardware and software until the collaboration finalizes their results and unanimously agrees to unblind. We implement hardware-level blinding in the form of a offset to the primary 40-MHz clock which drives the experiment's calorimeters. During data collection, we monitor deviations in this primary clock from its nominal value to ensure its long-term stability whilst remaining unaware of its blinded set point. We add an additional layer of software-level blinding to prevent influence amongst the multiple analysis groups. Each analyzer picks a unique string which is hashed into a new offset value R that replaces ω_a in their analysis. We applied this blinding procedure successfully to the earliest dataset and continue its application to all subsequent datasets.