Muon g-2 Theory: the Hadronic Part

By F. Jegerlehner. 2017

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I present a status report of the hadronic vacuum polarization effects for the muon $g-2$, to be considered as an update of [1]. The update concerns recent new inclusive $R$ measurements from KEDR in the energy range 1.84 to 3.72 GeV. For the leading order contributions I find $a_\mu^{\mathrm{had}(1)}=(688.07\pm 4.14)[688.77\pm3.38]\times 10^{-10}$ based on $e^+e^-$data [incl. $\tau$ data], $a_\mu^{\mathrm{had}(2)}= (-9.93\pm 0.07) \times 10^{-10}$ (NLO) and $a_\mu^{\mathrm{had}(3)}= (1.22\pm 0.01) \times 10^{-10}$ (NNLO). Collecting recent progress in the hadronic light-by-light scattering I adopt $\pi^0,\eta,\eta'$ [$95 \pm 12$] + axial--vector [$8 \pm ~3$] + scalar [$-6\pm ~1$] + $\pi,K$ loops [$-20\pm 5$] + quark loops [$22\pm ~4$] + tensor [$1\pm ~0$] + NLO [$3\pm ~2$] which yields $ a^{(6)}_\mu(\mathrm{lbl},\mathrm{had})=(103 \pm 29) \times 10^{-11}.$ With these updates I find $a_\mu^{\rm exp}-a_\mu^{\rm the}=(31.3\pm 7.7)\times 10^{-10}$ a 4.1 $\sigma$ deviation. Recent lattice QCD results and future prospects to improve hadronic contributions are discussed.

Subfields: Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/6b5c2f15591bf0d838f16a69f9113a34d2b536b6