Speaker
Description
The Muon g-2 Experiment at Fermi National Accelerator Laboratory was designed to measure the anomalous magnetic moment of the muon, $𝑎_𝜇$, with a target precision of 140 parts-per-billion (ppb); a four-fold improvement over the former measurement at Brookhaven National Laboratory. The experiment was motivated by the ~3.5 standard deviation between the BNL result and the Standard Model prediction of $𝑎_𝜇$; which could be a hint of new physics. The first result at Fermilab from the Run-1 data taking period has achieved an uncertainty of 460 parts-per-billion and confirmed the BNL discrepancy, further increasing the tension with the Standard Model.
The experimental concept uses a polarized muon beam stored in an extremely homogeneous storage ring magnetic field. Parity violation in the weak decay is used as a spin analyzer; the detected rate of the decay electrons oscillates with the frequency, $𝜔_𝑎$, in the magnetic field expressed in terms of the Larmor frequency of protons shielded in a spherical water sample, $𝜔_𝑝$. Since $𝑎_𝜇$ is derived from the ratio of $𝜔_𝑎$ and $𝜔_𝑝$, both are equally important and systematic uncertainties must be kept below 70 ppb for each observable. The magnetic field measurement system to determine $𝜔_𝑝$ consists of 378 new Nuclear Magnetic Resonance probes that constantly monitor the field, an upgraded in-vacuum field mapping system that scans the muon storage region over the full azimuth, and a special water-based probe to calibrate the probes of the field mapping system. The talk will give a short experimental overview and then focus on the details of the magnetic field measurement.