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The European High Performance Computing Joint Undertaking (EuroHPC JU)

Smeared R-ratio and HVP contributions to g๐œ‡โˆ’ 2 with leading isospin-breaking effects

1,270,600
Awarded Resources (in node hours)
Leonardo Booster
System Partition
1 May 2024 - 30 April 2025
Allocation Period

The project proposes a high-statistics computation of lattice correlation functions starting from isospin-symmetric QCD and including the leading isospin-breaking effects, with the twofold aim of increasing the accuracy and evaluating the leading isospin-breaking corrections for key observables such as the energy-smeared R-ratio of e+e- into hadrons and the hadronic vacuum polarization (HVP) contributions to the muon anomalous magnetic moment, gรฐยล“โ€กรขห†โ€™ 2.

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, we shall obtain a robust precise determination of these observables in QCD+QED with u, d, s and c quarks. By evaluating correlators of two weak currents we also plan an accurate study of inclusive hadronic tau-meson decays.

Producing first principles Standard Model (SM) predictions for the R-ratio with few hundred MeV energy resolution and for the gรฐยล“โ€กรขห†โ€™ 2 HVP window-like and possibly full contributions will play a crucial role in assessing the (dis)agreement between SM predictions and experimental data concerning both e+e- into hadrons and gรฐยล“โ€กรขห†โ€™ 2.

This is a key contribution of Lattice Field Theory to Particle Physics at the precision frontier.