February 8, 2000
The muon magnetic anomaly may contain contributions from physics beyond the standard model. At the Brookhaven National Laboratory (BNL) a precision experiment aims for a measurement of the muon magnetic anomaly $a_{\mu}$ to 0.35 ppm, where conclusions about various theoretical approaches beyond standard theory can be expected. The difference between the spin precession and cyclotron frequencies is measured in a magnetic storage ring with highly homogeneous field. Data taking is in progress and part of all recorded data has been analyzed. Combining all experimental results to date yields preliminarily $a_{\mu}(expt)=1~165~921(5) \cdot 10^{-9}$ (4 ppm) in agreement with standard theory.
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February 8, 2001
A precise measurement of the anomalous g value, a_mu=(g-2)/2, for the positive muon has been made at the Brookhaven Alternating Gradient Synchrotron. The result a_mu^+=11 659 202(14)(6) X 10^{-10} (1.3 ppm) is in good agreement with previous measurements and has an error one third that of the combined previous data. The current theoretical value from the standard model is a_mu(SM)=11 659 159.6(6.7) X 10^{-10} (0.57 ppm) and a_mu(exp)-a_mu(SM)=43(16) X 10^{-10} in which a_mu(e...
November 17, 2002
The muon g-2 experiment at Brookhaven National Laboratory measures the anomalous magnetic moment of the muon, $a_\mu$, very precisely. This measurement tests the Standard Model. The analysis for the data collected in 2000 (a $\mu^+$ run) is completed and the accuracy on $a_\mu$ is improved to 0.7 ppm, including statistical and systematic errors. The data analysis was performed blindly between the precession frequency and the field analysis groups in order to prevent a possibl...
January 20, 2005
Our recent series of measurements at Brookhaven National Laboratory determined the muon anomalous magnetic moment \amu to a precision of 0.5 ppm. The final result--representing the average of five running periods using both positive and negative muons--is $\amu ^\pm = 11 659 208(6) \times 10^{-10}$. It lies 2.7 standard deviations above the standard model expectation, which is based on updates given at this Workshop. Importantly, only the $e^{+}e^{-}$ annihilation and new KLO...
January 10, 2004
The anomalous magnetic moment of the negative muon has been measured to a precision of 0.7 parts per million (ppm) at the Brookhaven Alternating Gradient Synchrotron. This result is based on data collected in 2001, and is over an order of magnitude more precise than the previous measurement of the negative muon. The result a_mu= 11 659 214(8)(3) \times 10^{-10} (0.7 ppm), where the first uncertainty is statistical and the second is sytematic, is consistend with previous measu...
June 28, 2001
The Muon (g-2) Experiment (E821) at Brookhaven National Laboratory (BNL) has measured the anomalous magnetic moment of the positive muon to an unprecedented precision of 1.3 parts per million. The result, a_{\mu^+} = (g-2)/2 = 11 659 202(14)(6) X 10^{-10}, is based on data recorded in 1999 and is in good agreement with previous measurements. Upcoming analysis of data recorded in 2000 and 2001 will substantially reduce the uncertainty on this measurement. Comparison of the new...
April 7, 2021
We present the first results of the Fermilab Muon g-2 Experiment for the positive muon magnetic anomaly $a_\mu \equiv (g_\mu-2)/2$. The anomaly is determined from the precision measurements of two angular frequencies. Intensity variation of high-energy positrons from muon decays directly encodes the difference frequency $\omega_a$ between the spin-precession and cyclotron frequencies for polarized muons in a magnetic storage ring. The storage ring magnetic field is measured u...
January 10, 2003
The muon anomalous magnetic moment measurement, when compared with theory, can be used to test many extensions to the standard model. The most recent measurement made by the Brookhaven E821 Collaboration reduces the uncertainty on the world average of a_mu to 0.7 ppm, comparable in precision to theory. This paper describes the experiment and the current theoretical efforts to establish a correct standard model reference value for the muon anomaly.
November 9, 2001
A summary is given of the present status of the theory and experiment of the anomalous magnetic moment of the muon. A difference between predicted and measured values is an indication of physics beyond the Standard Model. A new experimental number has produced a value which differs from a recent Standard Model prediction by about 1.6 standard deviations. When the new result was first announced, the discrepancy was about 2.6 standard deviations, but theorists have recently fou...
May 15, 2001
The muon (g-2) experiment at BNL has completed four data runs for the positive muon, beginning in 1997 and has just finished its first run for the negative muon. Recently the analysis of a 1.3 ppm result based on the 1999 run was completed and published (a_\mu^+ = 11,659,202(14)(6) x 10^-10). The result shows a tantalizing discrepancy with the Standard Model prediction of 2.6 times the combined experimental and theoretical uncertainty. The muon (g-2) experiment at BNL is ulti...
February 20, 2006
We present the final report from a series of precision measurements of the muon anomalous magnetic moment, a_mu = (g-2)/2. The details of the experimental method, apparatus, data taking, and analysis are summarized. Data obtained at Brookhaven National Laboratory, using nearly equal samples of positive and negative muons, were used to deduce a_mu(Expt) = 11 659 208.0(5.4)(3.3) x 10^-10, where the statistical and systematic uncertainties are given, respectively. The combined u...