Status of the Fermilab Muon (g-2) Experiment

B. Lee Roberts

REVIEW

Status of the Fermilab Muon (g-2) Experiment

B. Lee Roberts

High Energy Physics - Experiment · Submitted 17 Jan 2010 · 20 references

Pith's verdict: A clean, honest conference summary of the Fermilab g-2 program; the only genuinely new content is the last-digit shift from the updated muon-proton moment ratio, and the forward-looking 'should clarify' line quietly assumes the hadronic theory error shrinks.

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arXiv ID1001.2898 (version 2)

Pith IDEI3YPSWM, Pith's permanent record of this paper and its review

CitationB. Lee Roberts. "Status of the Fermilab Muon (g-2) Experiment." arXiv:1001.2898 (2010). https://pith.science/paper/EI3YPSWM

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Editor's note

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This is a proceedings writeup of the Fermilab muon g-2 proposal, not a research paper, and it should be read that way. What's actually new is small but real: the E821 value is restated as 116 592 089(63) × 10⁻¹¹, with the last digit moved because CODATA updated λ = μ_μ/μ_p (ref. 7). That shift is 9 × 10⁻¹¹, and the arithmetic checks out. Everything else — the magic-γ technique, the E821 error budget, the P989 beam plan — is a competent restatement of refs. 5, 6, 8, and 16. The value here is as a compact, accurate orientation to the program, and it does that job well. The physics is stated correctly: Eq. (5), the 3.09 GeV/c magic momentum, the 0.46 ppm stat plus 0.28 ppm syst decomposition, the Recycler re-bunching and the 900 m debuncher decay line. The author is also candid where it matters, explicitly noting that a τ-based hadronic determination drops the tension from ~3.2σ to ~2σ. That disclosure is to his credit and shouldn't be scored against him. The soft spot is the abstract's 'should clarify this difference' (abstract:s3) and the matching line in §4. As Eq. (3) stands, the Standard-Model error is 49 × 10⁻¹¹, about 0.42 ppm — three times the projected 0.14 ppm experimental error. So the claim only holds if the hadronic uncertainty falls too, and the paper says that qualitatively ('along with further advances') but never states the target. The only place the assumption surfaces numerically is the Fig. 1 'Fermilab' band at ±34 × 10⁻¹¹, which implies a theory error near 30 × 10⁻¹¹, with the details deferred to ref. 14. That's a fair thing to flag, but it's a forward-looking sentence in a proceedings, not a load-bearing derivation, and the direction of the caveat is already acknowledged. I'd call it minor. Two smaller things: Eq. (3) has a stray bracket, and the running header still reads 'Instruction for typesetting manuscripts' — cosmetic, but a copyedit pass would catch them. Who should read it: anyone who wants a five-minute accurate picture of where the Fermilab program stood in early 2010, or a teaching reference for the magic-γ method. For citation in real work, go to the P989 proposal and the E821 papers directly. Worth a referee's time as a proceedings contribution, yes — but as a summary, not as a result.

Referee report

Significance

The paper is a clear and useful status summary of a proposal that, if funded and executed, would improve the muon anomaly by a factor of four and would sharpen the interpretation of any LHC discovery through the tan(beta)/sign(mu) sensitivity illustrated in Fig. 1. Its strengths are the honest and internally consistent error decomposition (0.46 ppm statistical and 0.28 ppm systematic combining to 0.54 ppm), the correct arithmetic linking Eqs. (2) and (3) to the quoted 255×10^-11 difference and its ~3.2 sigma significance, the explicit disclosure that a tau-based hadronic determination reduces the tension to ~2 sigma, and a concrete, falsifiable precision target (±0.14 ppm) tied to a cited proposal. The paper is also candid about the funding status and the schedule risk. It is a review/status contribution rather than a primary result, and it should be assessed as such.

Major objections (1)

[Abstract (s3), Eq. (3), §4] The interpretive claim that the improved experiment 'should clarify this difference' is not quantitatively supported as written. Eq. (3) quotes a Standard-Model uncertainty of 49×10^-11 (about 0.42 ppm), which is roughly three times the projected ±0.14 ppm experimental error and comparable to E821's present total error. The only post-Fermilab combined uncertainty that appears anywhere in the manuscript is the ±34×10^-11 'Fermilab' band in Fig. 1, which implicitly assumes the theory error falls from 49 to about 30×10^-11, with the justification deferred to ref. 14. The authors do acknowledge the qualitative dependence ('along with further advances in the determination of the hadronic contribution'), so this is not an error, but a single explicit sentence stating the assumed post-Fermilab hadronic uncertainty (and hence the projected significance of the comparison) would make the central motivation checkable rather than implicit. Without it, a reader cannot tell whether the 0.14 ppm measurement is intended to be theory-limited or statistics-limited at the time of comparison.

Minor objections (8)

[Eq. (1)] The definition reads 'a = (g − 2)2', in which the division by two has been lost in typesetting; it should be (g − 2)/2. The same equation's magnetic-moment expression should be checked for the same reason.
[Eqs. (2) and (3)] Both displayed equations have typesetting damage: Eq. (2) reads '×10−110.54 ppm' where a multiplication sign and spacing are needed before the ppm figure, and Eq. (3) contains a stray closing bracket in '116 591 834(49)]× 10−11'. These should be corrected in proof.
[§2.1] 'pmagic = 3.09 Gev/c' should read 'GeV/c'. In §3, 'we could achieve a a comparable error for µ−' has a duplicated article, and 'NOV A' should be 'NOvA'.
[Fig. 1 and caption] The parenthetical '(Figure courtesy of D. Stöckinger)' interrupts the caption mid-sentence and should be moved to the end. The caption should also state explicitly that the vertical axis is Delta chi-squared and that the sensitivity band assumes the SPS1a benchmark, since the reach in tan(beta) is scenario-dependent and the figure is used to support a general claim about LHC interpretation.
[§1 and §2, discussion of lambda] It would help the reader to state explicitly that the 9×10^-11 shift from the revised lambda corresponds to about 0.14 of the total E821 error and therefore does not materially affect the quoted discrepancy. As written, the abstract's remark that 'the last digit of a_mu is changed' understates the size of the shift relative to the error bar.
[References 9 and 11] The Standard-Model value in Eq. (3) rests on ref. 9 (arXiv:0908.4300), and the tau-based comparison rests on ref. 11, which is listed as 'submitted to Eur. Phys. J.'. Since both are unpublished at the time of writing, the authors should note their status in the text or add a published cross-check so that the quoted a_mu^SM can be traced to a citable source.
[§2.1, organization] The paragraph beginning 'The experiment consists of repeated fills of the storage ring' introduces data-taking and detector operation rather than the magic-gamma technique, and reads as belonging to §2 or §3. Consider relocating it, or retitling the subsection.
[§3] The plan runs on mu+ first and on mu- only in the Project X era. A sentence noting that the mu+/mu- comparison is itself a valuable systematic cross-check (as it was for E821) would strengthen the case for the later running and connect the schedule to the physics case.

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The paper

The paper claims

A proposed Fermilab experiment aims to measure the muon's anomalous magnetic moment four times more precisely than the Brookhaven result, to test a roughly three-sigma tension with the Standard Model.

The reading

The paper reports the status of a proposal to move the decommissioned Brookhaven muon storage ring to Fermilab and re-run the $(g-2)$ measurement with a fourfold improvement in precision, from $0.54$ ppm to about $0.14$ ppm. The physics case is a persistent gap: the measured anomaly $a_μ = [116592089(63)] × 10^{-11}$ sits above the Standard-Model prediction $a_μ^{SM}[e^+e^-] = [116591834(49)] × 10^{-11}$ by about $3.2$ standard deviations when electron-positron annihilation data fix the hadronic vacuum polarization. A fourfold better measurement, paired with expected improvements in that hadronic piece, would either confirm a genuine deviation from the Standard Model or close it. The author also argues the result matters whatever the LHC finds, because the sign and size of any new-physics contribution to $a_μ$ constrain how discoveries at the LHC should be interpreted.

What carries the argument

The magic-$γ$ technique. The spin precession frequency relative to the cyclotron frequency is $ω_a = -(Qe/m)[a_μ B - (a_μ - 1/(γ^2-1)) β × E/c]$, and at $γ = 29.3$ the coefficient of the electric field vanishes, so electrostatic quadrupoles can provide vertical focusing without contaminating the precession measurement. The anomaly then follows from two measured frequencies, $a_μ = R/(λ - R)$ with $R = ω̃_a/ω_p$, where $ω_p$ is the proton Larmor frequency used to map the field and $λ = μ_μ/μ_p$ comes from muonium hyperfine structure. This identity is what converts a field-map plus spin-precession measurement into a fundamental constant, and it is why the revision of $λ$ shifts the quoted $a_μ$.

Extended reading notes

Core claim

This is a status and proposal paper, not a new measurement. Its central claim is that the Fermilab program (P989) can reach equal statistical and systematic errors of $±0.1$ ppm, for a combined $0.14$ ppm on $a_μ$ — a factor of four beyond E821's $±0.54$ ppm. The mechanism is the same magic-momentum technique that E821 validated: store polarized muons at $γ = 29.3$ ($p = 3.09$ GeV/$c$) in a uniform $1.45$ T super-ferric dipole ring of $7.112$ m radius, with electrostatic quadrupoles for vertical focusing so that the electric field cancels from the spin-precession difference frequency $ω_a$. Fermilab's advantage is beam: roughly $10^{12}$ protons per bunch at 10–20 ms intervals, an 18 Hz fill rate versus 4.4 Hz at Brookhaven, a 900 m pion decay line in the antiproton debuncher, a pion flash reduced twentyfold, and a stored-muon-per-proton ratio five to ten times higher. The author also notes that the published E821 value has been revised upward by $9 × 10^{-11}$ because the muon-to-proton magnetic moment ratio $λ$ has a new recommended value.

Load-bearing premise

The size of the claimed discrepancy, and hence much of the motivation, depends on taking the electron-positron-based determination of the hadronic vacuum polarization as the correct one; the paper itself notes that using hadronic tau decays instead cuts the tension from about 3.2 sigma to about 2 sigma.

Editorial extensions

If this is right

A $0.14$ ppm measurement would shrink the experimental error below the uncertainty on the hadronic vacuum polarization contribution, making the comparison with theory limited by the Standard-Model calculation rather than by the experiment.
If the central value stays near E821's, the roughly three-sigma discrepancy becomes a genuine target for LHC interpretation, since the sign of the deviation fixes the sign of the supersymmetry $μ$ parameter.
If the central value moves toward the $e^+e^-$-based Standard-Model prediction, the case for light new physics coupled to muons is substantially weakened.
The same apparatus running on $μ^-$ in a later beam era would test CPT and the sign structure of any new contribution.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

The projected post-Fermilab error bar of $±34 × 10^{-11}$ in the $Δa_μ$ band of Fig. 1 assumes both the experimental improvement and a roughly halved hadronic uncertainty; if the latter does not materialize, the effective reach of the experiment is smaller than the headline number suggests.
Because the $e^+e^-$ and $τ$-decay routes to the leading hadronic term differ by more than the quoted theory error, the discrepancy is as much a statement about which hadronic data set is trusted as about muon physics; a Fermilab measurement sharpens the arbitration.
The dependence of the supersymmetry interpretation on $ an β$ and $ ext{sgn}(μ)$ means the $(g-2)$ result functions as a prior on LHC parameter fits, not merely as an independent check — a role that grows if the LHC sees sleptons or charginos.
Lattice determinations of the hadronic vacuum polarization, which the paper does not invoke, are an independent third route that could resolve the $e^+e^-$ versus $τ$ split before the new experiment reports.

Original abstract

The New Muon $(g-2)$ Collaboration at Fermilab has proposed to measure the anomalous magnetic moment of the muon, $a_\mu$, a factor of four better than was done in E821 at the Brookhaven AGS, which obtained $a_\mu = [116 592 089 (63)] \times 10^{-11}$ $\pm 0.54$ ppm. The last digit of $a_{\mu}$ 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 $\simeq 3$ 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 compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 4,550 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.04 · states limitation 0.31 · human participants 0.03 · controlled comparison 0.20 · randomized assignment 0.01 · states quantitative result 0.86 · compares with prior results 0.87 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; show every role.

The New Muon $(g-2)$ Collaboration at Fermilab has proposed to measure the anomalous magnetic moment of the muon, $a_\mu$, a factor of four better than was done in E821 at the Brookhaven AGS, which obtained $a_\mu = [116 592 089 (63)] \times 10^{-11}$ $\pm 0.54$ ppm. The last digit of $a_{\mu}$ 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 $\simeq 3$ 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.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#	sentence	role	the authors' own work	states the main conclusion	strength
s0	The New Muon $(g-2)$ Collaboration at Fermilab has proposed to measure the anomalous magnetic moment of the muon, $a_\mu$, a factor of four better than was done in E821 at the Brookhaven AGS, which obtained $a_\mu = [116 592 089 (63)] \times 10^{-11}$ $\pm 0.54$ ppm.	contribution 0.64	0.19	0.13	asserted 0.96
s1	The last digit of $a_{\mu}$ 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.	background 0.50	0.25	0.05	asserted 1.00
s2	At present there appears to be a difference between the Standard-Model value and the measured value, at the $\simeq 3$ standard deviation level when electron-positron annihilation data are used to determine the lowest-order hadronic piece of the Standard Model contribution.	background 0.69	0.14	0.28	hedged possibility 0.88
s3	The improved experiment, along with further advances in the determination of the hadronic contribution, should clarify this difference.	future work 0.56	0.10	0.28	hedged possibility 0.65
s4	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.	interpretation 0.93	0.09	0.15	asserted 0.95

What kind of paper the classifier reports this is: position or commentary 0.95 · evidence from literature 0.62.

What was examined, and what was not

sources read

arXiv listing abstract v2

not examined

full text
figures and tables
references and citing sentences
relations to other papers

levels run

P abstract

not run

S sections
T body sentences
C citations
R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures

**Figure 1.** A “blueband” plot showing the LHC and muon (g − 2) sensitivities to tanβ. The (Figure courtesy of D. St¨ockinger) 2 Measuring aµ The measurement of aµ uses the spin precession resulting from the torque experienced by the magnetic moment when placed in a magnetic field. An ensemble of polarized muons is introduced into a magnetic field, where they are stored for the measurement period. Assuming that the muon velocity is transverse to the magnetic field (β~ · B~ = 0), the rate at which the spin turns relative to the momentum vector is given by the difference frequency between the s

**Figure 2.** The time spectrum of decay electrons from the 2001 E821 running period, when µ − were stored. (From Ref. [5] ) The E821 storage ring was constructed as a “super-ferric” magnet [17], meaning that the iron determined the shape of the magnetic field. Thus B0 needed to be well below saturation and was chosen to be 1.45 T. The resulting ring had a central orbit radius of 7.112 m, and 12 detector stations were placed symmetrically around the inner radius of the storage ring. The detector geometry and number were optimized to detect the high-energy decay electrons, which carry the large

Figures reproduced from arXiv:1001.2898 by the authors.

References

Works cited (20)

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[2]

J. Schwinger, Phys. Rev. 73 , 416L (1948), and Phys. Rev. 76 790 (1949). The former paper contains a misprint in the expression for a_e that is corrected in the longer paper

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J.P. Miller, E. de Rafael and B.L. Roberts, hep-ph/0703049, and Rep. Prog. Phys. 70 , (2007) 795-881

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G. Bennett, et al., (Muon (g-2) Collaboration), Phys. Rev. D73 , 072003 (2006), and references therein

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New Muon (g-2) Collaboration, http://lss.fnal.gov/archive/test-proposal/0000/fermilab-proposal-0989.shtml

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M. Davier, A. H\"ocker, B. Malaescu, C.Z. Yuan and Z. Zhang, arXiv:0908.4300 Aug. 2009

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J. Prades, E. de Rafael and A. Vainshtein, in Lepton Dipole Moments , Advanced Series on Directions in High Energy Physics -Vol.20, ed. B. Lee Roberts and William J. Marciano, World Scientific, p. 303, (2010); and arXiv:0901.0306, Jan. 2009

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M. Davier, A. H\"ocker, G. L\'opez Castro, B. Malescu, H.X. Mo, G. Toledo S\'anchez, P. Wang, C.Z. Yuan and Z. Zhang, arXiv:0906.5443, 2009 and submitted to Eur. Phys. J

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Dominik St\"ockinger, in Lepton Dipole Moments , Advanced Series on Directions in High Energy Physics -Vol.20, ed. B. Lee Roberts and William J. Marciano, World Scientific, p. 393, (2010); and J. Phys. G 34 , R45 (2007)

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Andrzej Czarnecki and William J. Marciano, in Lepton Dipole Moments , Advanced Series on Directions in High Energy Physics -Vol.20, ed. B. Lee Roberts and William J. Marciano, World Scientific, p. 11, (2010); and Phys. Rev. D 64 , 013014 (2001)

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Forward citations

Cited by 13 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

Hadronic contribution to the muon anomalous magnetic moment to next-to-next-to-leading order
hep-ph 2014-03 accept novelty 7.0 of 10

The three-loop hadronic vacuum-polarization correction to the muon anomalous magnetic moment is 1.24 ± 0.01 × 10^-10, large enough to belong in the g-2 theory budget.
Explaining electron and muon $g-2$ anomaly in SUSY without lepton-flavor mixings
hep-ph 2019-06 conditional novelty 6.0 of 10

Large threshold corrections to the lepton Yukawa couplings can flip the sign of the SUSY electron g-2 and, combined with flavor-dependent slepton masses, explain both the electron and muon anomalies without lepton fla...
Summary of the ATLAS experiment's sensitivity to supersymmetry after LHC Run 1 - interpreted in the phenomenological MSSM
hep-ex 2015-08 accept novelty 6.0 of 10

Across 310,327 pMSSM points, ATLAS Run 1 excludes about 41% and leaves viable low-fine-tuning spectra whose light top squarks should be reachable at Run 2.
Muon $g-2$ Anomaly in Anomaly Mediation
hep-ph 2021-04 conditional novelty 5.0 of 10

Anomaly mediation with a sizable Higgsino threshold correction can explain the muon g-2 at 1 sigma, implying gluino masses below 2-4 TeV, bino below 2 TeV, and wino below 1-2 TeV.
Gauged $L^{}_{\mu}{-}L^{}_{\tau}$ at a muon collider
hep-ph 2021-01 conditional novelty 5.0 of 10

A 3 TeV, 1 ab^-1 muon collider would exclude gauged L_mu-L_tau mediators up to about 100 TeV and reach couplings near 4e-3 at 1 TeV, covering the g-2 and B-anomaly regions above 100 GeV.

Show 8 more citing papers

Muon $g-2$ at multi-TeV muon collider
hep-ph 2020-12 conditional novelty 5.0 of 10

A multi-TeV muon collider can test heavy new physics explanations of the muon g-2 anomaly, either by producing new particles or by measuring the Higgs-plus-photon cross section predicted by the g-2 operator.
Self-interacting dark matter and muon $g-2$ in a gauged U$(1)_{L_{\mu} - L_{\tau}}$ model
hep-ph 2018-05 conditional novelty 5.0 of 10

A gauged U(1) extension with a vector-like fermion dark matter and a light scalar mediator can simultaneously fit the muon g-2 anomaly and produce the velocity-dependent dark matter self-scattering needed on galactic ...
Flavor-specific scalar mediators
hep-ph 2017-12 conditional novelty 5.0 of 10

A single-flavor scalar mediator can be natural and flavor-safe at masses well below the electroweak scale, provided its coupling is aligned with one fermion mass eigenstate and is weak enough.
Lepton Portal Dark Matter
hep-ph 2014-02 conditional novelty 5.0 of 10

Dark matter coupled only to charged leptons via a charged mediator is constrained by LUX, AMS-02 and 8 TeV LHC data, and a 14 TeV LHC run with 100 inverse femtobarns would probe nucleon cross sections near 2e-46 cm^2 ...
The electroweak contributions to (g-2)_\mu\ after the Higgs boson mass measurement
hep-ph 2013-06 accept novelty 5.0 of 10

With the measured Higgs mass of 125.6 GeV, the Standard Model electroweak contribution to the muon anomalous magnetic moment is (153.6 +/- 1.0) x 10^-11, backed by new exact analytic formulas for the Higgs-dependent t...
Singlet extensions and W boson mass in the light of the CDF II result
hep-ph 2022-04 conditional novelty 4.0 of 10

In singlet extensions of the Standard Model the W boson mass shift is at most a few MeV, and at most about 5 MeV with invisible decays, too small to explain the CDF II anomaly.
Kaon-box contribution to the anomalous magnetic moment of the muon
hep-ph 2019-10 accept novelty 4.0 of 10

The charged kaon box contributes about -0.48 x 10^-11 to the muon's anomalous magnetic moment, roughly 3 percent of the pion box, confirming that box diagrams beyond the pion are negligible.
(g-2)_mu and alpha(M_Z^2) re-evaluated using new precise data
hep-ph 2011-05 conditional novelty 4.0 of 10

With new KLOE and BaBar hadronic cross sections folded into a global fit, the Standard Model gives muon g-2 = (11659182.8 +/- 4.9)e-10, leaving a 3.3 sigma discrepancy with experiment.

How the literature uses it

88 arXiv papers cite this in 101 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers whose main result relates to this one's

Found among the papers closest to this one by title and main claim. Pith's classifier compared each pair's main results and a second model family confirmed the relation; checked against two further families, shown conflicts agreed 118 times in 120 and shown same results 218 times in 239. The quoted sentence is the other paper's main claim.

States the same result 2 papers

After the reevaluation of the leading-order hadronic term based on the new \ep data, the theoretical prediction is more than three standard deviations lower than the experimental value.

Standard Model Predictions for the Muon $(g-2)/2$ · 0.88
Including the latest experimental data on e+e- annihilation into hadronsfrom CMD2 and SND for the \pi+\pi- channel and BaBar for multihadron final states, the updated Standard Model prediction disagrees with the measurement dominated by BNL by 3.3 standard deviations, with the theoretical precision exceeding the experimental one.

Muon g-2: a mini review · 0.86

Papers citing it · 49 sentences without a confident label

Uses its data or values 40 papers

After taking into account the small shift in CODATA's published ratio of the muon-to-proton magnetic moment [ref] , the experimental value for $a_μ$ reads [ref] [equation] This leads to the difference [equation] which corresponds to $3.3 σ$ discrepancy.

(g-2)_mu and alpha(M_Z^2) re-evaluated using new precise data · Standard Model Prediction of $g-2$ · 0.94
The muon anomalous magnetic moment $a_μ$ has been measured by the E821 experiment (Muon g-2 Collaboration) at BNL with an impressive accuracy of 0.72 ppm [ref] yielding the present world average a_μ^exp = (11 , 659 , 208.9 ±6.3) ×10^-10

Standard Model Prediction of the Muon Anomalous Magnetic Moment · Introduction · 1.00
Currently, the experimental values for $a_e$ [ref] , $a_μ$ [ref] and $a_τ$ [ref] are given by

Phenomenological constraints on minimally coupled exotic lepton triplets · Contribution to lepton anomalous magnetic moment · 1.00

Cites it as background 11 papers

It can be measured experimentally very precisely [ref] and can likewise be computed precisely in the standard model, see e.g. the review [ref] .

Four-Flavour Leading-Order Hadronic Contribution To The Muon Anomalous Magnetic Moment · Introduction · 0.88
It will be verified by the forthcoming experiments Muon $g-2$ [ref] at Fermilab (USA) and J-PARC $g-2$ [ref] at KEK (Japan).

Off-mass-shell muon anomalous magnetic moment · Introduction · 0.86
On the experimental side there are upcoming new experiments which either use the same method as in the E821 experiment at BNL [ref] but reduce the uncertainties by about a factor four, or even use a completely different technique which would eliminate doubts on possible systematic effects (for details see, e.g., Ref. [ref] ).

Electron contribution to $(g-2)_\mu$ at four loops · Introduction · 0.91

Discussion

Disagree with the review, or know something it missed? Leave a comment, highlight any passage above to comment on it, or challenge this review formally.

[1] [1]

P. Kusch and H.M Foley, Phys. Rev. 73 , 250 (1948)

View on Pith 1948

[2] [2]

J. Schwinger, Phys. Rev. 73 , 416L (1948), and Phys. Rev. 76 790 (1949). The former paper contains a misprint in the expression for a_e that is corrected in the longer paper

View on Pith 1948

[3] [3]

J.P. Miller, E. de Rafael and B.L. Roberts, hep-ph/0703049, and Rep. Prog. Phys. 70 , (2007) 795-881

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