Speaker
Description
The well-known Dirac's relativistic quantum mechanics prediction of $g=2$ for the magnetic dipole moment of a point particle, e.g., an electron, breaks down at the $10^{-3}$ level. The resulting magnetic anomaly, $a_e = (g − 2)/2$, is due to couplings to virtual particles excited in the vacuum. Due to its greater mass, the muon probes significantly deeper into the high-mass excitations of the vacuum than does the better studied electron. For this reason, the efforts to measure the muon magnetic anomaly, $a_\mu$, have persisted over decades. The most recent such effort to report results is Fermilab Muon $g-2$ experiment, E989.
E989 follows closely in the footsteps of its predecessor, the Brookaven National Lab E821, having transported the BNL 821 muon storage to a dedicated muon beam line at Fermilab, and implemented a number of critical improvements. In July 2023 E989 concluded data taking in its last run cycle, Run-6, and a month later unblinded and published analysis results of data from Runs 2 and 3, that add to the Run 1 results published in 2021. The new results have brought about an improvement by a factor of two in the precision of the world average of $a_\mu$. In parallel, recent theoretical and experimental developments regarding the hadronic vacuum polarization (HV) have led to a reexamination of the context for the interpretation of the measured value of $a_\mu$.
This talk will examine the new results of Fermilab E989, discussing the experimental method and the resulting uncertainties. We will place the new result in the context of a changing HVP landscape, and will review the future plans for the field.
