The Role of Mesons in Muon g-2

Abstract

The muon anomaly a µ = (g µ − 2)/2 showing a persisting 3 to 4 σ deviation between the SM prediction and the experiment is one of the most promising signals for physics beyond the SM. As is well known, the hadronic uncertainties are limiting the accuracy of the Standard Model prediction. Therefore a big effort is going on to improve the evaluations of hadronic effects in order to keep up with the 4fold improved precision expected from the new Fermilab measurement in the near future. A novel complementary type experiment planned at J-PARC in Japan, operating with ultra cold muons, is expected to be able to achieve the same accuracy but with completely different systematics. So exciting times in searching for New Physics are under way. I discuss the role of meson physics in calculations of the hadronic part of the muon g-2. The improvement is expected to substantiate the present deviation ∆a New Physics µ

Three-pion contribution to hadronic vacuum polarization

“…In this context, the issue of hadronic modeling is most severe in the hadronic light-by-light (HLbL) contribution, for which a data-driven dispersive approach has only been recently developed [11][12][13][14][15][16][17][18]. 1 In contrast, the leading hadronic contribution, hadronic vacuum polarization (HVP), is, in principle, fully determined by the cross section for e + e − → hadrons [22,23], and indeed a combination of the analysis of exclusive channels, inclusive data, and perturbative-QCD constraints are used for current estimates of the HVP contribution [24][25][26][27]. 2 However, only the compilations from [24,25] are exclusively based on the direct integration of the data, while [26,27] do involve some model assumptions, in particular for the ω and φ contributions.…”

“…1 In contrast, the leading hadronic contribution, hadronic vacuum polarization (HVP), is, in principle, fully determined by the cross section for e + e − → hadrons [22,23], and indeed a combination of the analysis of exclusive channels, inclusive data, and perturbative-QCD constraints are used for current estimates of the HVP contribution [24][25][26][27]. 2 However, only the compilations from [24,25] are exclusively based on the direct integration of the data, while [26,27] do involve some model assumptions, in particular for the ω and φ contributions. In general, tensions among data sets are typically taken into account by a local error inflation.…”