Precision magnetometry in the Muon g-2 storage ring at Fermilab

The Muon g-2 experiment at Fermilab is the fifth generation measurement of the Muon’s anomalous magnetic moment with improved precision to reduce the current uncertainty between measurement and Standard Model prediction. This requires a simultaneous determination of the muon’s anomalous precession frequency and the magnetic field along its trajectory. The upgraded  field measurement system is described in detail including compatibility with shimming techniques for improved field homogeneity around the 50 foot diameter storage ring. Outside the storage region 378 probes continuously monitor the field where more than 350 have precisions of 50 parts per billion (ppb). A mini version of this system periodically samples the field seen by muons. We show field variations over the last running period and discuss the implications of temperature dependence and other effects from the magnet itself. The data are used to interpolate between measurements in the storage volume and when convoluted with muon trajectories comprise field measurements for this phase of the experiment.