Status Of The Fermilab Muon G 2 Experiment

The New Muon (g-2) Collaboration at Fermilab has proposed to measure the anomalous magnetic moment of the muon, a{sub {mu}}, a factor of four better than was done in E821 at the Brookhaven AGS, which obtained a{sub {mu}} = [116592089(63)] x 10−11 ± 0.54 ppm. The last digit of a{sub {mu}} is changed from the published value owing to a new value of the ratio of the muon-to-proton magnetic moment that has become available. At present there appears to be a difference between the Standard-Model value and the measured value, at the ≈= 3 standard deviation level when electron-positron annihilation data are used to determine the lowest-order hadronic piece of the Standard Model contribution. The improved experiment, along with further advances in the determination of the hadronic contribution, should clarify this difference. Because of its ability to constrain the interpretation of discoveries made at the LHC, the improved measurement will be of significant value, whatever discoveries may come from the LHC.

The measurement of the anomalous magnetic moment of muon provides a precision test of the Standard Model. The Brookhaven muon g-2 experiment (E821) measured the muon magnetic moment anomaly with 0.54 ppm precision, a more than 3 deviation from the Standard Model predictions, spurring speculation about the possibility of new physics. The new g-2 experiment at Fermilab (E989) will reduce the combined statistical and systematic error of the BNL experiment by a factor of 4. An overview of the new experiment is described in this article.

A new measurement of the anomalous magnetic moment of the muon, $a_{\mu} \equiv (g-2)/2$, will be performed at the Fermi National Accelerator Laboratory with data taking beginning in 2017. The most recent measurement, performed at Brookhaven National Laboratory and completed in 2001, shows a 3.5 standard deviation discrepancy with the standard model prediction of $a_\mu$. The new measurement will accumulate 21 times those statistics using upgraded detection and storage ring systems, enabling a measurement of $a_\mu$ to 140 ppb, a factor of 4 improvement in the uncertainty the previous measurement. This improvement in precision, combined with recent and ongoing improvements in the evaluation of the QCD contributions to the $a_\mu$, could provide a 7.5$\sigma$ discrepancy from the standard model if the current difference between experiment and theory is confirmed, a possible indication of new physics.

There is a long standing discrepancy between the Standard Model prediction for the muon g-2 and the value measured by the Brookhaven E821 Experiment. At present the discrepancy stands at about three standard deviations, with a comparable accuracy between experiment and theory. Two new proposals -- at Fermilab and J-PARC -- plan to improve the experimental uncertainty by a factor of 4, and it is expected that there will be a significant reduction in the uncertainty of the Standard Model prediction. I will review the status of the planned experiment at Fermilab, E989, which will analyse 21 times more muons than the BNL experiment and discuss how the systematic uncertainty will be reduced by a factor of 3 such that a precision of 0.14 ppm can be achieved.

This book reviews the present state of knowledge of the anomalous magnetic moment a=(g-2)/2 of the muon. The muon anomalous magnetic moment is one of the most precisely measured quantities in elementary particle physics and provides one of the most stringent tests of relativistic quantum field theory as a fundamental theoretical framework. It allows for an extremely precise check of the standard model of elementary particles and of its limitations.

At what point does theory depart the realm of testable hypothesis and come to resemble something like aesthetic speculation, or even theology? The legendary physicist Wolfgang Pauli had a phrase for such ideas: He would describe them as "not even wrong," meaning that they were so incomplete that they could not even be used to make predictions to compare with observations to see whether they were wrong or not. In Peter Woit's view, superstring theory is just such an idea. In Not Even Wrong , he shows that what many physicists call superstring "theory" is not a theory at all. It makes no predictions, even wrong ones, and this very lack of falsifiability is what has allowed the subject to survive and flourish. Not Even Wrong explains why the mathematical conditions for progress in physics are entirely absent from superstring theory today and shows that judgments about scientific statements, which should be based on the logical consistency of argument and experimental evidence, are instead based on the eminence of those claiming to know the truth. In the face of many books from enthusiasts for string theory, this book presents the other side of the story.

Precision measurements of fundamental quantities have played a key role in pointing the way forward in developing our understanding of the universe. Though the enormously successful Standard Model (SM) describes the breadth of both historical and modern experimental particle physics data, it is necessarily incomplete. The muon $g-2$ experiment executed at Brookhaven concluded in 2001 and measured a discrepancy of more than three standard deviations compared to the Standard Model calculation. Arguably, this remains the strongest hint of physics beyond the SM. A new initiative at Fermilab is under construction to improve the experimental accuracy four-fold. The current status is presented here.

The Muon g-2 Experiment at Fermilab will measure the anomalous magnetic moment of the muon to a precision of 140 parts per billion, which is a factor of four improvement over the previous E821 measurement at Brookhaven. The experiment will also extend the search for the electric dipole moment (EDM) of the muon by approximately two orders of magnitude, with a sensitivity down to 10-21 e.cm. Both of these measurements are made by combining a precise measurement of the 1.45T storage ring magnetic field with an analysis of the modulation of the decay rate of higher-energy positrons (from anti-muons), recorded by 24 calorimeters and 3 straw tracking detectors. Furthermore, the recent progress in the alignment of the electrostatic quadrapole plates and the trolley rails inside the vacuum chambers, and in establishing the uniform storage ring magnetic field will be described.

A new measurement of the anomalous magnetic moment of the muon, a? ≡ (g - 2)/2, will be performed at the Fermi National Accelerator Laboratory. The most recent measurement, performed at Brookhaven National Laboratory and completed in 2001, shows a 3.3-3.6 standard deviation discrepancy with the Standard Model predictions for a?. The new measurement will accumulate 21 times those statistics, measuring a? to 140 ppb and reducing the uncertainty by a factor of 4. The data acquisition system for this experiment must have the ability to record deadtime-free records from 700 ?s muon spills at a raw data rate of 18 GB per second. Data will be collected using 1296 channels of ?TCA-based 800 MSPS, 12 bit waveform digitizers and processed in a layered array of networked commodity processors with 24 GPUs working in parallel to perform a fast recording and processing of detector signals during the spill. The system will be controlled using the MIDAS data acquisition software package. Lastly, the described data acquisition system is currently being constructed, and will be fully operational before the start of the experiment in 2017.

A new experiment at Fermilab will measure the anomalous magnetic moment of the muon with a precision of 140 parts per billion (ppb). This measurement is motivated by the results of the Brookhaven E821 experiment that were first released more than a decade ago, which reached a precision of 540 ppb. As the corresponding Standard Model predictions have been refined, the experimental and theoretical values have persistently differed by about 3 standard deviations. If the Brookhaven result is confirmed at Fermilab with this improved precision, it will constitute definitive evidence for physics beyond the Standard Model. The experiment observes the muon spin precession frequency in flight in a well-calibrated magnetic fi eld; the improvement in precision will require both 20 times as many recorded muon decay events as in E821 and a reduction by a factor of 3 in the systematic uncertainties. This paper describes the current experimental status as well as the plans for the upgraded magnet, detector and storage ring systems that are being prepared for the start of beam data collection in 2017.