Muon g-2
In measuring g − 2 with high precision and comparing its value to the theoretical prediction, physicists will discover whether the experiment agrees with theory.
[19] Fermilab is continuing the experiment conducted at Brookhaven[20] to measure the anomalous magnetic dipole moment of the muon.
[21] The goal is to make a more accurate measurement (smaller σ) which will either eliminate the discrepancy between Brookhaven's results and theory predictions or confirm it as an experimentally observable example of physics beyond the Standard Model.
New efforts at Fermilab have resulted in a three-fold improved overall uniformity, which is important for the new measurement at its higher precision goal.
[10] Data-taking came to an end on July 9, 2023, when the collaboration shut off the muon beam, concluding the experiment after six years of data collection.
The difference from 2 (the "anomalous" part) depends on the lepton, and can be computed quite precisely based on the current Standard Model of particle physics.
[25] The computation of the Standard Model prediction of the muon's g factor is extremely complicated, and several different approaches exist.
Subsequent works by the Coordinated Lattice Simulations (CLS) group[31][32] and the European Twisted Mass Collaboration (ETMC)[33][34] have come closer each to the theoretical value, suggesting there could be systematical errors in the estimation of the R-ratio of the hadronic vacuum polarization used by Fermilab.
The move traversed 3,200 miles (5,100 km) over 35 days,[36] mostly on a barge down the East Coast and through Mobile, Alabama, to the Tennessee–Tombigbee Waterway and then briefly on the Mississippi.
The magnetic moment measurement is realized by 24 electromagnetic calorimetric detectors, which are distributed uniformly on the inside of the storage ring.
Thus, the magnetic field curls it inward where it hits a segmented lead(II) fluoride (PbF2) calorimeter read out by silicon photo-multipliers (SiPM).
The experimental goal of g − 2 is to achieve an uncertainty level on the magnetic field to 70 ppb averaged over time and muon distribution.
Calibration of the trolley is referenced to the Larmor frequency of a proton in a spherical water sample at a reference temperature (34.7 °C), and is cross-calibrated to a novel helium-3 magnetometer.
This is accomplished by employing parallel data-processing architecture using 24 high-speed GPUs (NVIDIA Tesla K40) to process data from 12 bit waveform digitisers.
The DAQ system processes data from 1296 calorimeter channels, 3 straw tracker stations, and auxiliary detectors (e.g. entrance muon counters).
