Measurement of the Positive Muon Anomalous Magnetic Moment to 0.7 ppm

TL;DR

A higher precision measurement of the anomalous g value, a(mu)=(g-2)/2, for the positive muon has been made at the Brookhaven Alternating Gradient Synchrotron, based on data collected in the year 2000.

Abstract

A higher precision measurement of the anomalous g value, a_mu = (g-2)/2, for the positive muon has been made at the Brookhaven Alternating Gradient Synchrotron, based on data collected in the year 2000. The result a_{mu^+} = 11 659 204(7)(5) times 10^{-10} (0.7 ppm) is in good agreement with previous measurements and has an error about one half that of the combined previous data. The present world average experimental value is a_mu(exp) = 11 659 203(8) times 10^{-10} (0.7 ppm).

Figures (4)

• Figure 1: A 2-dimensional multipole expansion of the field averaged over azimuth from one out of 22 trolley measurements. Half ppm contours with respect to a central azimuthal average field $B_0 = 1.451\,274\,\mathrm{T}$ are shown. The multipole amplitudes relative to $B_0$, are given at the beam aperture, which has a radius of 4.5 cm and is indicated by the circle.
• Figure 2: Coherent betatron oscillations (CBO) in the $g-2$ time spectra. The Fourier spectrum was obtained from residuals from a fit based on muon decay and spin precession (Eq. \ref{['eq:spectrum']}) alone. The horizontal modulation was at $\omega_\mathrm{cbo,h}/(2\pi)$ = 466 kHz in the year 2000, so that the interference frequency $\omega_\mathrm{cbo,h}-\omega_a$ is numerically close to $\omega_a$, as indicated. The frequency $\omega_a$ is determined from fits that take CBO into account.
• Figure 3: a) The frequency $\omega_a/(2\pi)$ determined from fits to the individual calorimeter time spectra. Data from calorimeters 2 and 20 were discarded, as in the analysis of our 1999 data. b) The fitted frequency $\omega_a/(2\pi)$ versus positron energy. These results come from the analysis described first in the text.
• Figure 4: Recent measurements of $a_\mu$, together with the standard model prediction using the evaluation in Ref. Davier:1998si of $a_\mu(\mathrm{had,1})$ from $e^+e^-$ and $\tau$ decay data.