Smeared R-ratio and HVP contributions to g𝜇− 2 at small lattice spacing

This project proposes computations aimed at improving the control of lattice artifacts in high-statistics simulations of lattice correlation functions carried out in isospin-symmetric QCD and including the leading isospin-breaking effects. The overall project, of which this proposal is a continuation, has the goal of studying key observables such as the energy-smeared 𝑅-ratio of e-e+ -› hadrons and the hadronic vacuum polarization (HVP) contributions to the muon anomalous magnetic moment, g𝜇−2. 

Accurate determination of these observables, as well as of inclusive hadronic τ-meson decay rates giving info on CKM matrix elements, will be obtained in QCD+QED with u, d, s and c quarks by exploiting gauge ensembles at the physical point, with spatial sizes up to 𝐿≃7.5 fm and lattice spacings down to a≲0.05 fm, generated by the ETM Collaboration. 

Producing first principles Standard Model (SM) predictions for the 𝑅-ratio with ∼250 MeV energy resolution and for the g𝜇−2 HVP full and window-like contributions will play a crucial role in assessing the (dis)agreement between SM predictions and experimental data concerning both e-e+ -› hadrons and g𝜇−2. This is a key contribution of Lattice Field Theory to Particle Physics at the precision frontier.