Measurement of the electric field correction to the muon spin precession frequency in the E989 Muon g-2 experiment at Fermilab*

The E989 Muon g-2 experiment at Fermilab aims to measure the anomalous magnetic moment of the muon to an unprecedented precision of 140 ppb to solve the tantalizing 3-4 standard deviation discrepancy between the previous  measurement at Brookhaven in 2001 and the Standard Model prediction. The E989 experiment has completed its first physics run and collected a dataset roughly two times larger than the Brookhaven experiment's. The measurement of the anomalous magnetic moment relies on measuring the muon spin precession frequency and the storage magnetic field to a precision of 120 and 70 ppb, respectively. Electrostatic quadrupoles provide vertical focusing for the beam circulating in the muon storage ring. The quadrupole electric fields affect the precession frequency of off momentum muons. We will discuss in this talk the measurement of the anticipated O(100) ppb correction to the spin precession frequency using data from the 2018 run, and the challenge of achieving the uncertainty budget of 20 ppb.