Abstract
I discuss the history of the muon (g-2)(g−2) measurements, beginning with the Columbia-Nevis measurement that observed parity violation in muon decay, and also measured the muon gg-factor for the first time, finding g_\mu=2gμ=2. The theoretical (Standard Model) value contains contributions from quantum electrodynamics, the strong interaction through hadronic vacuum polarization and hadronic light-by-light loops, as well as the electroweak contributions from the WW, ZZ and Higgs bosons. The subsequent experiments, first at Nevis and then with increasing precision at CERN, measured the muon anomaly a_\mu = (g_\mu-2)/2aμ=(gμ−2)/2 down to a precision of 7.3 parts per million (ppm). The Brookhaven National Laboratory experiment E821 increased the precision to 0.54 ppm, and observed for the first time the electroweak contributions. Interestingly, the value of a_\muaμ measured at Brookhaven appears to be larger than the Standard Model value by greater than three standard deviations. A new experiment, Fermilab E989, aims to improve on the precision by a factor of four, to clarify whether this result is a harbinger of new physics entering through loops, or from some experimental, statistical or systematic issue.
Highlights
The muon was first observed in cosmic rays by Paul Kunze [1] as a “particle of uncertain nature”1
As the precision on aμ was increased in a series of three experiments at CERN, it became necessary to come up with a new way of focusing the beam, which eliminated the need for magnetic gradients
For the CERN-3, E821 and E989 experimental conditions, the results presented here are the same as those in these references
Summary
The muon was first observed in cosmic rays by Paul Kunze [1] as a “particle of uncertain nature”. The muon was first observed in cosmic rays by Paul Kunze [1] as a “particle of uncertain nature”1 It was definitively identified by Anderson and Neddemeyer [2], and confirmed by Street and Stevenson [3], and by Nishina et al, [4]. There was significant confusion as to the nature of this new particle It interacted too weakly with matter [5] to be the Yukawa particle [6], and it did not spontaneously decay to an electron and a γ ray [7, 8], nor did it convert to an electron in the field of a nucleus [8]. It became possible that the muon might be like a heavy electron, which was a complete mystery
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
