Muon g−2 and Δα connection
Massimo Passera
Padua University
Mardi 23/03/2021, 16:00

After a review of the discrepancy between the Standard Model theory and experimental measurement of the muon magnetic moment anomaly, a_μ=(g_μ-2)/2, I will discuss its connection to precision electroweak (EW) predictions via their common dependence on hadronic vacuum polarization effects. The same data for the total e+e-→hadrons cross section, σ_had(s), are used as input into dispersion relations to estimate the hadronic vacuum polarization contributions, a_μ^{had,VP}, as well as the five-flavor hadronic contribution to the running QED coupling at the Z-pole, Δα_had(5)(M_Z), which enters natural relations and global EW fits. The EW fit prediction of Δα_had(5)(M_Z)=0.02722(41) agrees well with Δα_had(5)(M_Z)=0.02761(11) obtained from the dispersion relation approach, but exhibits a smaller central value suggestive of a larger discrepancy Δa_μ = a_μ^exp - a_μ^SM than currently expected. Postulating that the Δa_μ difference may be due to unforeseen missing σ_had(s) contributions, implications for M_W, sin2θ_eff_lep and M_H obtained from global EW fits are investigated. Shifts in σ_had(s) needed to bridge Δa_μ are found to be excluded above sqrt(s)≳0.7  GeV at the 95% C.L. Moreover, prospects for Δa_μ originating below that energy are deemed improbable given the required increases in the hadronic cross section.

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