Magnetic Field Tracking in the Muon g-2 Experiment*

The muon g-2 experiment at Fermilab aims to measure the anomalous magnetic moment of the muon to a precision of 140 parts per billion (ppb). The measurement will shed light on the deviation between Standard Model calculations and the previous measurement at Brookhaven National Laboratory. The experiment measures the difference between the cyclotron and spin precession frequencies of muons in a highly uniform magnetic field, where the magnetic field over a muon's trajectory must be known to 70 ppb. Magnetic field gradients in the storage region are mapped precisely every 3 days by an in-vacuum field mapping system (trolley) carrying an array of 17 nuclear magnetic resonance (NMR) probes. Between trolley runs the time evolution of the field, caused for example by temperature variations in the hall, is monitored by a suite of 378 fixed NMR probes mounted outside of the vacuum chambers. The fixed probes are used to interpolate the field experienced by muons between trolley runs. An overview of the magnetic field interpolation analysis will be presented.