Recognition: unknown
Muon g-2: correlation-induced uncertainties in precision data combinations
Pith reviewed 2026-05-08 02:35 UTC · model grok-4.3
The pith
Uncertainties from unknown correlations in e+e- to hadrons data combinations are subdominant but non-negligible for muon g-2 calculations.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
A controlled variation of the correlation structure at the combined-data level produces covariance matrices that, when propagated to a_mu^HVP, show correlation-induced uncertainties are generally smaller than other sources yet large enough to matter and insufficient to reconcile differences among current e+e- to hadrons data sets.
What carries the argument
A systematic framework that varies the assumed correlation structure directly on the combined data to construct representative covariance matrices for the combination.
If this is right
- Future evaluations of the hadronic vacuum polarization must include an explicit correlation-uncertainty component derived this way.
- Remaining differences between data combinations point to other sources such as normalization or energy-scale issues.
- The method supplies a new, reproducible ingredient for the upcoming KNTW data combination used in muon g-2 analyses.
- The same approach can be applied to any precision observable built from correlated input measurements.
Where Pith is reading between the lines
- If the envelope underestimates the true uncertainty, the method could be extended by including more extreme correlation patterns drawn from the original experimental publications.
- Applying the technique to other correlated data sets, such as those entering lattice QCD calculations or electroweak fits, might reveal analogous hidden uncertainties.
- Clarifying these correlation effects narrows the set of possible explanations for any tension between experimental and theoretical values of the muon magnetic moment.
Load-bearing premise
Varying correlations only after the data have already been combined still captures the full range of possible effects from the original measurement correlations.
What would settle it
Performing a full re-combination of the underlying individual measurements while varying their correlations at the raw-data level and checking whether the resulting spread matches the envelope obtained from the combined-level variation.
Figures
read the original abstract
We present a general and systematic framework to quantify uncertainties arising from imperfectly known systematic correlations in data combinations. Formulated at the level of the combined data, the method enables controlled variation of the correlation structure, leading to the construction of covariance matrices directly on the resulting combination and thus providing a robust and systematic estimate of correlation-induced uncertainties. We apply the method to $e^+e^- \to \mathrm{hadrons}$ cross section data, with the resulting covariance matrices propagated to derived observables, including dispersive determinations of the hadronic vacuum polarization (HVP) contribution to the muon anomalous magnetic moment, $a_\mu^\mathrm{HVP}$. We find that uncertainties from systematic correlation assumptions are generally subdominant but non-negligible, and do not fully account for differences between existing $e^+e^- \to \mathrm{hadrons}$ data combinations. The framework is broadly applicable to correlated data combinations in precision measurements and constitutes a new component of the upcoming KNTW data combination for $a_\mu^\mathrm{HVP}$.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript presents a general framework for quantifying uncertainties from imperfectly known systematic correlations in precision data combinations, formulated at the level of the combined data to enable controlled variation of the correlation structure and construction of associated covariance matrices. Applied to e+e− → hadrons cross-section data, the resulting covariances are propagated to derived observables including the hadronic vacuum polarization (HVP) contribution aμ^HVP to the muon anomalous magnetic moment. The authors conclude that correlation-induced uncertainties are generally subdominant but non-negligible and do not fully account for differences between existing e+e− → hadrons data combinations. The framework is presented as a new component of the upcoming KNTW data combination for aμ^HVP.
Significance. If the central claim holds, this work supplies a practical, systematic tool for assessing a previously difficult-to-quantify uncertainty source in high-precision combinations, with immediate relevance to resolving tensions in the muon g−2 anomaly. By demonstrating that correlation assumptions do not explain the spread in existing HVP determinations, the analysis helps narrow the range of possible origins for discrepancies. The method's formulation at the combined-data level is a strength for applicability to existing datasets, and its planned inclusion in the KNTW combination provides a clear route to community adoption.
major comments (2)
- [§2 (Framework)] §2 (Framework): The central methodological claim—that controlled variation of the correlation structure at the level of the combined data produces a 'robust and systematic estimate' of correlation-induced uncertainties—rests on the assumption that the resulting envelope of covariance matrices is representative of those that could arise from plausible variations in the underlying experimental systematics. Because combination procedures are generally non-invertible, post-combination variation can generate matrices that are either unattainable or overly permissive relative to pre-combination constraints. This is load-bearing for the finding that such uncertainties 'do not fully account for differences between existing e+e− → hadrons data combinations', as the envelope must faithfully reflect the range consistent with the raw data.
- [§4 (Application and propagation)] §4 (Application and propagation): The propagation of the constructed covariances to aμ^HVP is presented without an explicit demonstration that the post-combination envelope reproduces the spread obtained by varying correlations at the pre-combination level on the same dataset. Without this validation, it remains unclear whether the reported subdominant-but-non-negligible uncertainties are a faithful representation or an artifact of the post-combination formulation.
minor comments (2)
- [Abstract] The abstract would benefit from a single sentence outlining the key mathematical definition of the controlled variation (e.g., how the correlation matrix is parameterized and varied).
- Notation for the combined covariance matrix and its correlation component should be introduced consistently in the text and figures to avoid ambiguity when the method is applied to other datasets.
Simulated Author's Rebuttal
We thank the referee for their careful reading of the manuscript and for the constructive comments, which help clarify important aspects of the framework's assumptions and validation. We address each major comment below and outline the revisions we will make.
read point-by-point responses
-
Referee: §2 (Framework): The central methodological claim—that controlled variation of the correlation structure at the level of the combined data produces a 'robust and systematic estimate' of correlation-induced uncertainties—rests on the assumption that the resulting envelope of covariance matrices is representative of those that could arise from plausible variations in the underlying experimental systematics. Because combination procedures are generally non-invertible, post-combination variation can generate matrices that are either unattainable or overly permissive relative to pre-combination constraints. This is load-bearing for the finding that such uncertainties 'do not fully account for differences between existing e+e− → hadrons data combinations', as the envelope must faithfully reflect the range consistent with the raw data.
Authors: We thank the referee for highlighting this subtlety in the post-combination formulation. The framework is deliberately constructed at the level of the already-combined data to enable its use with existing combinations, where the full pre-combination experimental details and correlation matrices are frequently unavailable or incompletely specified. The variation is performed by systematically scanning correlation coefficients over physically allowed intervals (typically [0,1] for each systematic component), which generates a conservative envelope. While we acknowledge that non-invertibility implies some matrices in the envelope may not be exactly realizable from any pre-combination configuration, the envelope is constructed to be an upper bound on the possible correlation-induced uncertainty. Even under this conservative bound, the resulting uncertainties remain subdominant and insufficient to explain the spread among existing combinations. We will add an explicit discussion of this conservative character and the rationale for the post-combination approach in the revised §2. revision: partial
-
Referee: §4 (Application and propagation): The propagation of the constructed covariances to aμ^HVP is presented without an explicit demonstration that the post-combination envelope reproduces the spread obtained by varying correlations at the pre-combination level on the same dataset. Without this validation, it remains unclear whether the reported subdominant-but-non-negligible uncertainties are a faithful representation or an artifact of the post-combination formulation.
Authors: We agree that a direct head-to-head comparison on the real dataset would be desirable. In the current manuscript we validate the framework on a set of toy models that replicate the statistical structure, binning, and correlation patterns of the e+e− → hadrons data; in these controlled cases the post-combination envelope reproduces the pre-combination uncertainty range to within a few percent (slightly conservative, as expected). For the actual experimental compilations, a full pre-combination scan is not feasible without access to the complete raw datasets and the precise combination algorithms used by each group—information that is not uniformly available. We will expand §4 to present the toy-model validation results quantitatively and to discuss the practical limitations on direct pre-combination checks for the published data sets, thereby clarifying that the reported uncertainties are not an artifact of the method. revision: partial
Circularity Check
Framework for correlation uncertainties formulated at combined-data level with no reduction to inputs by construction
full rationale
The paper introduces a new general framework to quantify correlation-induced uncertainties by controlled variation of the correlation structure directly on the already-combined data points, then constructs covariance matrices on the combination and propagates them to derived observables such as a_μ^HVP. The central claims—that these uncertainties are subdominant yet non-negligible and do not fully account for differences between existing combinations—follow from applying this variation procedure to the e+e- → hadrons dataset. No derivation step reduces by the paper's own equations to a fitted parameter renamed as a prediction, nor does any load-bearing premise rest solely on self-citation of prior author work. The reference to the upcoming KNTW combination is incidental and not used to justify the method or results. The approach is self-contained against external benchmarks and does not match any enumerated circularity pattern.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Controlled variation of the correlation structure at the level of the combined data produces a representative envelope of covariance matrices.
Reference graph
Works this paper leans on
-
[1]
Discussion ofd ρaπ+π− µ Although all uncertainties on derived quantities have been determined at the level of the underlying spectra, a discussion at the level of the integrated observable aπ+π− µ is warranted. Fig. 11 shows the change ina π+π− µ for separate global and local decorrelations ofσ KNT19 ππ . FIG. 11. Contribution of the KNT19π +π− channel to...
-
[2]
BaBar–KLOE
Comparison with DHMZ19 At the time of KNT19 (and, therefore, WP20), the most precise and thus dominant datasets in theπ +π− channel were BaBar [111, 112] and KLOE [113–116]. These datasets exhibit a tension where the BaBar/KLOE σππ data were (before the CMD-3 measurements) gener- ally the highest/lowest lying data in the centralρreso- nance region, with B...
2020
-
[3]
S. J. Brodsky and E. De Rafael, Phys. Rev.168, 1620 (1968)
1968
-
[4]
B. E. Lautrup and E. De Rafael, Phys. Rev.174, 1835 (1968)
1968
- [5]
-
[6]
Jegerlehner,The Anomalous Magnetic Moment of the Muon, Vol
F. Jegerlehner,The Anomalous Magnetic Moment of the Muon, Vol. 274 (Springer, Cham, 2017)
2017
-
[7]
Jegerlehner, EPJ Web Conf.118, 01016 (2016), arXiv:1511.04473 [hep-ph]
F. Jegerlehner, EPJ Web Conf.118, 01016 (2016), arXiv:1511.04473 [hep-ph]
-
[8]
Jegerlehner, EPJ Web Conf.166, 00022 (2018), arXiv:1705.00263 [hep-ph]
F. Jegerlehner, EPJ Web Conf.166, 00022 (2018), arXiv:1705.00263 [hep-ph]
-
[9]
Jegerlehner, EPJ Web Conf.218, 01003 (2019), arXiv:1711.06089 [hep-ph]
F. Jegerlehner, EPJ Web Conf.218, 01003 (2019), arXiv:1711.06089 [hep-ph]
-
[10]
Jegerlehner, EPJ Web Conf.199, 01010 (2019), arXiv:1809.07413 [hep-ph]
F. Jegerlehner, EPJ Web Conf.199, 01010 (2019), arXiv:1809.07413 [hep-ph]
-
[11]
S. Eidelman and F. Jegerlehner, Z. Phys. C67, 585 (1995), arXiv:hep-ph/9502298
-
[12]
M. Benayoun, P. David, L. DelBuono, O. Leitner, and H. B. O’Connell, Eur. Phys. J. C55, 199 (2008), arXiv:0711.4482 [hep-ph]
-
[13]
M. Benayoun, P. David, L. DelBuono, and F. Jegerlehner, Eur. Phys. J. C72, 1848 (2012), arXiv:1106.1315 [hep-ph]
-
[14]
M. Benayoun, P. David, L. DelBuono, and F. Jegerlehner, Eur. Phys. J. C73, 2453 (2013), arXiv:1210.7184 [hep-ph]
-
[15]
M. Benayoun, P. David, L. DelBuono, and F. Jegerlehner, Eur. Phys. J. C75, 613 (2015), arXiv:1507.02943 [hep-ph]
-
[16]
M. Benayoun, L. Delbuono, and F. Jegerlehner, Eur. Phys. J. C80, 81 (2020), [Erratum: Eur.Phys.J.C 80, 244 (2020)], arXiv:1903.11034 [hep-ph]
-
[17]
Reevaluation of the Hadronic Contributions to the Muon g-2 and to alpha(MZ)
M. Davier, A. Hoecker, B. Malaescu, and Z. Zhang, Eur. Phys. J. C71, 1515 (2011), [Erratum: Eur.Phys.J.C 72, 1874 (2012)], arXiv:1010.4180 [hep-ph]
work page Pith review arXiv 2011
-
[18]
K. Hagiwara, A. D. Martin, D. Nomura, and T. Teub- ner, Phys. Rev. D69, 093003 (2004), arXiv:hep- ph/0312250
-
[19]
K. Hagiwara, A. D. Martin, D. Nomura, and T. Teubner, Phys. Lett. B649, 173 (2007), arXiv:hep- ph/0611102
-
[20]
K. Hagiwara, R. Liao, A. D. Martin, D. Nomura, and T. Teubner, J. Phys. G38, 085003 (2011), arXiv:1105.3149 [hep-ph]
-
[21]
M. Davier, A. Hoecker, B. Malaescu, and Z. Zhang, Eur. Phys. J.C77, 827 (2017), arXiv:1706.09436 [hep- ph]
work page Pith review arXiv 2017
-
[22]
A. Kurz, T. Liu, P. Marquard, and M. Steinhauser, Phys. Lett.B734, 144 (2014), arXiv:1403.6400 [hep-ph]
work page Pith review arXiv 2014
- [23]
-
[24]
The muon $g-2$ and $\alpha(M_Z^2)$: a new data-based analysis
A. Keshavarzi, D. Nomura, and T. Teubner, Phys. Rev. D97, 114025 (2018), arXiv:1802.02995 [hep-ph]
work page Pith review arXiv 2018
-
[25]
Two-pion contribution to hadronic vacuum polarization
G. Colangelo, M. Hoferichter, and P. Stoffer, JHEP02, 006 (2019), arXiv:1810.00007 [hep-ph]
work page Pith review arXiv 2019
-
[26]
M. Hoferichter, B.-L. Hoid, and B. Kubis, JHEP08, 137 (2019), arXiv:1907.01556 [hep-ph]
-
[27]
A. Keshavarzi, D. Nomura, and T. Teubner, Phys. Rev. D101, 014029 (2020), arXiv:1911.00367 [hep-ph]
-
[28]
K. Melnikov and A. Vainshtein, Phys. Rev.D70, 113006 (2004), arXiv:hep-ph/0312226 [hep-ph]
-
[29]
Pseudoscalar-pole contribution to the $(g_{\mu}-2)$: a rational approach
P. Masjuan and P. S´ anchez-Puertas, Phys. Rev.D95, 054026 (2017), arXiv:1701.05829 [hep-ph]
work page Pith review arXiv 2017
-
[30]
Dispersion relation for hadronic light-by-light scattering: two-pion contributions
G. Colangelo, M. Hoferichter, M. Procura, and P. Stof- fer, JHEP04, 161 (2017), arXiv:1702.07347 [hep-ph]
work page Pith review arXiv 2017
-
[31]
Dispersion relation for hadronic light-by-light scattering: pion pole
M. Hoferichter, B.-L. Hoid, B. Kubis, S. Leupold, and S. P. Schneider, JHEP10, 141 (2018), arXiv:1808.04823 [hep-ph]
work page Pith review arXiv 2018
-
[32]
A. Keshavarzi, D. Nomura, T. Teubner, and A. Wright, Phys. Rev. D111, L011901 (2025), arXiv:2409.02827 [hep-ph]
-
[33]
The anomalous magnetic moment of the muon in the Standard Model: an update
R. Alibertiet al., Phys. Rept.1143, 1 (2025), arXiv:2505.21476 [hep-ph]
work page internal anchor Pith review arXiv 2025
-
[34]
L. Di Luzio, A. Keshavarzi, A. Masiero, and P. Paradisi, Phys. Rev. Lett.134, 011902 (2025), arXiv:2408.01123 [hep-ph]
-
[36]
Electromagnetic and strong isospin-breaking corrections to the muon $g - 2$ from Lattice QCD+QED
D. Giusti, V. Lubicz, G. Martinelli, F. Sanfilippo, and S. Simula, Phys. Rev. D99, 114502 (2019), arXiv:1901.10462 [hep-lat]
work page Pith review arXiv 2019
-
[37]
Bors ´anyiet al., Nature593, 51 (2021), arXiv:2002.12347 [hep-lat]
S. Borsanyiet al., Nature593, 51 (2021), arXiv:2002.12347 [hep-lat]
-
[38]
C. Lehner and A. S. Meyer, Phys. Rev. D101, 074515 (2020), arXiv:2003.04177 [hep-lat]
- [39]
- [40]
-
[41]
M. C` eet al., Phys. Rev. D106, 114502 (2022), arXiv:2206.06582 [hep-lat]
-
[42]
C. Alexandrouet al.(Extended Twisted Mass), Phys. Rev. D107, 074506 (2023), arXiv:2206.15084 [hep-lat]
-
[43]
T. Blumet al.(RBC, UKQCD), Phys. Rev. D108, 054507 (2023), arXiv:2301.08696 [hep-lat]
-
[44]
S. Kuberski, M. C` e, G. von Hippel, H. B. Meyer, K. Ot- tnad, A. Risch, and H. Wittig, JHEP03, 172 (2024), arXiv:2401.11895 [hep-lat]
-
[45]
Hybrid calculation of hadronic vacuum polarization in muon g-2 to 0.48\%
A. Boccalettiet al., (2024), arXiv:2407.10913 [hep-lat]
work page internal anchor Pith review Pith/arXiv arXiv 2024
-
[46]
S. Spiegel and C. Lehner, Phys. Rev. D111, 114517 (2025), arXiv:2410.17053 [hep-lat]. 15
-
[47]
T. Blumet al.(RBC, UKQCD), Phys. Rev. Lett.134, 201901 (2025), arXiv:2410.20590 [hep-lat]
-
[48]
D. Djukanovic, G. von Hippel, S. Kuberski, H. B. Meyer, N. Miller, K. Ottnad, J. Parrino, A. Risch, and H. Wit- tig, JHEP04, 098 (2025), arXiv:2411.07969 [hep-lat]
-
[49]
C. Alexandrouet al.(Extended Twisted Mass), Phys. Rev. D111, 054502 (2025), arXiv:2411.08852 [hep-lat]
-
[50]
Bazavovet al.(Fermilab Lattice, HPQCD, MILC), Phys
A. Bazavovet al.(MILC, Fermilab Lattice, HPQCD), Phys. Rev. D111, 094508 (2025), arXiv:2411.09656 [hep-lat]
-
[51]
Bazavovet al.(Fermilab Lattice, HPQCD, MILC), Phys
A. Bazavovet al.(Fermilab Lattice, HPQCD,, MILC), Phys. Rev. Lett.135, 011901 (2025), arXiv:2412.18491 [hep-lat]
-
[52]
T. Blum, P. A. Boyle, V. G¨ ulpers, T. Izubuchi, L. Jin, C. Jung, A. J¨ uttner, C. Lehner, A. Portelli, and J. T. Tsang (RBC, UKQCD), Phys. Rev. Lett.121, 022003 (2018), arXiv:1801.07224 [hep-lat]
work page Pith review arXiv 2018
- [53]
-
[54]
J. L¨ udtke, M. Procura, and P. Stoffer, JHEP04, 130 (2025), arXiv:2410.11946 [hep-ph]
-
[55]
Remarks on higher-order hadronic corrections to the muon g-2
G. Colangelo, M. Hoferichter, A. Nyffeler, M. Passera, and P. Stoffer, Phys. Lett.B735, 90 (2014), arXiv:1403.7512 [hep-ph]
work page Pith review arXiv 2014
-
[56]
Complete Tenth-Order QED Contribution to the Muon g-2
T. Aoyama, M. Hayakawa, T. Kinoshita, and M. Nio, Phys. Rev. Lett.109, 111808 (2012), arXiv:1205.5370 [hep-ph]
work page Pith review arXiv 2012
-
[57]
A. Czarnecki, W. J. Marciano, and A. Vainshtein, Phys. Rev.D67, 073006 (2003), [Erratum: Phys. Rev.D73, 119901 (2006)], arXiv:hep-ph/0212229 [hep-ph]
-
[58]
The electroweak contributions to (g-2)_\mu\ after the Higgs boson mass measurement
C. Gnendiger, D. St¨ ockinger, and H. St¨ ockinger-Kim, Phys. Rev.D88, 053005 (2013), arXiv:1306.5546 [hep- ph]
work page Pith review arXiv 2013
-
[59]
J. Bijnens, N. Hermansson-Truedsson, and A. Rodr´ ıguez-S´ anchez, Phys. Lett.B798, 134994 (2019), arXiv:1908.03331 [hep-ph]
- [60]
-
[61]
S. Volkov, Phys. Rev. D100, 096004 (2019), arXiv:1909.08015 [hep-ph]
-
[62]
S. Volkov, Phys. Rev. D110, 036001 (2024), arXiv:2404.00649 [hep-ph]
- [63]
-
[64]
R. H. Parker, C. Yu, W. Zhong, B. Estey, and H. M¨ uller, Science360, 191 (2018), arXiv:1812.04130 [physics.atom-ph]
work page Pith review arXiv 2018
-
[65]
Morel, Z
L. Morel, Z. Yao, P. Clad´ e, and S. Guellati-Kh´ elifa, Nature588, 61 (2020)
2020
- [66]
-
[67]
M. Hoferichter, J. L¨ udtke, L. Naterop, M. Procura, and P. Stoffer, Phys. Rev. Lett.134, 201801 (2025), arXiv:2503.04883 [hep-ph]
-
[68]
Dispersion relation for hadronic light-by-light scattering: theoretical foundations
G. Colangelo, M. Hoferichter, M. Procura, and P. Stof- fer, JHEP09, 074 (2015), arXiv:1506.01386 [hep-ph]
work page Pith review arXiv 2015
-
[69]
G. Eichmann, C. S. Fischer, E. Weil, and R. Williams, Phys. Lett. B797, 134855 (2019), [Erratum: Phys.Lett.B 799, 135029 (2019)], arXiv:1903.10844 [hep-ph]
-
[70]
J. Leutgeb and A. Rebhan, Phys. Rev. D101, 114015 (2020), arXiv:1912.01596 [hep-ph]
-
[71]
L. Cappiello, O. Cat` a, G. D’Ambrosio, D. Grey- nat, and A. Iyer, Phys. Rev. D102, 016009 (2020), arXiv:1912.02779 [hep-ph]
-
[72]
P. Masjuan, P. Roig, and P. Sanchez-Puertas, J. Phys. G49, 015002 (2022), arXiv:2005.11761 [hep-ph]
-
[73]
J. Bijnens, N. Hermansson-Truedsson, L. Laub, and A. Rodr´ ıguez-S´ anchez, JHEP10, 203 (2020), arXiv:2008.13487 [hep-ph]
-
[74]
J. Bijnens, N. Hermansson-Truedsson, L. Laub, and A. Rodr´ ıguez-S´ anchez, JHEP04, 240 (2021), arXiv:2101.09169 [hep-ph]
-
[75]
I. Danilkin, M. Hoferichter, and P. Stoffer, Phys. Lett. B820, 136502 (2021), arXiv:2105.01666 [hep-ph]
- [76]
-
[77]
J. Leutgeb, J. Mager, and A. Rebhan, Phys. Rev. D 107, 054021 (2023), arXiv:2211.16562 [hep-ph]
-
[78]
M. Hoferichter, B. Kubis, and M. Zanke, JHEP08, 209 (2023), arXiv:2307.14413 [hep-ph]
-
[79]
M. Hoferichter, P. Stoffer, and M. Zillinger, JHEP04, 092 (2024), arXiv:2402.14060 [hep-ph]
- [80]
-
[81]
O. Deineka, I. Danilkin, and M. Vanderhaeghen, Phys. Rev. D111, 034009 (2025), arXiv:2410.12894 [hep-ph]
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.