Dispersive analysis with ρ-ω mixing produces a two-parameter fit describing BESIII data on the J/ψ→π⁰γ* form factor from 0 to 2.8 GeV and extracts a (62 ± 21)° relative phase between strong and electromagnetic modes.
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Two-pion contribution to hadronic vacuum polarization
10 Pith papers cite this work. Polarity classification is still indexing.
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abstract
We present a detailed analysis of $e^+e^-\to\pi^+\pi^-$ data up to $\sqrt{s}=1\,\text{GeV}$ in the framework of dispersion relations. Starting from a family of $\pi\pi$ $P$-wave phase shifts, as derived from a previous Roy-equation analysis of $\pi\pi$ scattering, we write down an extended Omn\`es representation of the pion vector form factor in terms of a few free parameters and study to which extent the modern high-statistics data sets can be described by the resulting fit function that follows from general principles of QCD. We find that statistically acceptable fits do become possible as soon as potential uncertainties in the energy calibration are taken into account, providing a strong cross check on the internal consistency of the data sets, but preferring a mass of the $\omega$ meson significantly lower than the current PDG average. In addition to a complete treatment of statistical and systematic errors propagated from the data, we perform a comprehensive analysis of the systematic errors in the dispersive representation and derive the consequences for the two-pion contribution to hadronic vacuum polarization. In a global fit to both time- and space-like data sets we find $a_\mu^{\pi\pi}|_{\leq 1\,\text{GeV}}=495.0(1.5)(2.1)\times 10^{-10}$ and $a_\mu^{\pi\pi}|_{\leq 0.63\,\text{GeV}}=132.8(0.4)(1.0)\times 10^{-10}$. While the constraints are thus most stringent for low energies, we obtain uncertainty estimates throughout the whole energy range that should prove valuable in corroborating the corresponding contribution to the anomalous magnetic moment of the muon. As side products, we obtain improved constraints on the $\pi\pi$ $P$-wave, valuable input for future global analyses of low-energy $\pi\pi$ scattering, as well as a determination of the pion charge radius, $\langle r_\pi^2 \rangle = 0.429(1)(4)\,\text{fm}^2$.
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representative citing papers
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A general framework quantifies correlation-induced uncertainties in precision data combinations and applies it to e+e- to hadrons cross sections for muon g-2 HVP determinations.
The updated SM prediction for the muon anomalous magnetic moment is 116592033(62)×10^{-11}, showing no tension with the experimental average of 38(63)×10^{-11}.
Lattice QCD on finer grids yields a_μ^LO-HVP = 715.1(3.4)×10^{-10}, producing a standard-model prediction for a_μ that differs from experiment by only 0.5 sigma.
Global analysis constrains fermionic DM to 120-350 GeV and CP-odd scalar to 350-600 GeV in a scotogenic extension, with DESI potentially ruling out inverted neutrino hierarchy and Z invisible width compatible with data at 3 sigma.
The paper provides an overview of theoretical calculations for lepton anomalous magnetic moments arising from quantum corrections in the Standard Model.
Pedagogical review explaining how causality implies analyticity and its use in scattering amplitudes, form factors, and resonance extraction in hadronic physics.
The Standard Model value for the muon anomalous magnetic moment is 116591810(43)×10^{-11}, 3.7σ below the Brookhaven experimental measurement.
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The anomalous magnetic moment of the muon in the Standard Model
The Standard Model value for the muon anomalous magnetic moment is 116591810(43)×10^{-11}, 3.7σ below the Brookhaven experimental measurement.