The hadronic vacuum polarization contribution to $(g_{\hat{I}}¼-2)$: Lattice QCD+QED calculations

Abstract

The anomalous magnetic moment of the muon $a_{\hat{I}}¼$ is one of the most accurate quantities in Particle Physics. The long-standing discrepancy of about $3.7$ standard deviations between the experimental value and the prediction of the Standard Model could represent an intriguing indication of New Physics. The experiments at Fermilab (E989) and at J-PARC (E34) aim at reducing significantly the experimental uncertainty, thus making the theoretical one due to hadronic corrections the main limitation of this stringent test of the Standard Model. In this contribution we present the results of a first-principles lattice calculation of the hadronic vacuum polarization (HVP) contribution to $a_{\hat{I}}¼$, including electromagnetic and $SU(2)$-breaking corrections. Our determination, $a_{\hat{I}}{¼}^{\mathrm{HVP}}=682.0(18.7)\cdot 10^{-10}$, turns out to be in agreement with recent theoretical determinations based on the dispersive analyses of the experimental cross section data for the annihilation process $e^{+}{e}^{-}\to hadrons$. Furthermore, we provide for the first time a lattice estimate for the missing part of $a_{\hat{I}}{¼}^{\mathrm{HVP}}$ not covered in the MUonE experiment, ${\left[a_{\hat{I}}{¼}^{\mathrm{HVP}}\right]}_{>}=91.6(2.0)\cdot 10^{-10}$.

Invited plenary talk at IFAE 2019, Napoli (Italy), 08-10 April 2019. v2: extended version, 5 pages, 1 figure