Two-pion contribution to hadronic vacuum polarization

Colangelo, Gilberto; Hoferichter, Martin; Stoffer, Peter (2019). Two-pion contribution to hadronic vacuum polarization. Journal of High Energy Physics, 2019(2) Springer 10.1007/JHEP02(2019)006

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We present a detailed analysis of e⁺e⁻ → π⁺π⁻ data up to √s = 1GeV in the framework of dispersion relations. Starting from a family of ππ P -wave phase shifts, as derived from a previous Roy-equation analysis of ππ scattering, we write down an extended Omnès 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 ω 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 aππμ |≤1 GeV = 495.0(1.5)(2.1) × 10⁻¹⁰ and aππμ| ≤ 0.63 GeV= 132.8(0.4)(1.0) × 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 ππ P-wave, valuable input for future global analyses of low-energy ππ scattering, as well as a determination of the pion charge radius, ⟨r²π ⟩ = 0.429(1)(4) fm².

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Theoretical Physics

UniBE Contributor:

Colangelo, Gilberto; Hoferichter, Martin and Stoffer, Peter

Subjects:

500 Science > 530 Physics

ISSN:

1029-8479

Publisher:

Springer

Language:

English

Submitter:

Esther Fiechter

Date Deposited:

14 May 2019 13:34

Last Modified:

14 May 2019 13:34

Publisher DOI:

10.1007/JHEP02(2019)006

ArXiv ID:

1810.00007

BORIS DOI:

10.7892/boris.127978

URI:

https://boris.unibe.ch/id/eprint/127978

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