A lattice QCD study of the contribution of two-pion states to the hadronic vacuum polarization correction of the muon’s magnetic moment

Aida X El-Khadra, University of Illinois at Urbana-Champaign

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A central goal of high-energy physics is to search for new particles and forces beyond the particle-physics Standard Model. The muon anomalous magnetic moment is sensitive to contributions from new particles and is also one of the most precisely measured quantities in particle physics, with an experimental uncertainty of 0.54 parts-per-million. At present, the measurement disagrees with Standard-Model theory expectations by more than three standard deviations.

The Fermilab Muon g – 2 Experiment, which recently started running, will ultimately reduce the experimental error by a factor of four; first results are expected in early 2019. To identify definitively whether any deviation observed is due to new particles or forces, the theory error must be reduced to a commensurate level. An ongoing project by our collaboration uses numerical lattice quantum chromodynamics to target the hadronic vacuum-polarization contribution, which is the largest source of theory error.

The calculation proposed here complements our ongoing project by calculating additional correlation functions to quantify contributions from two-pion states which become important at large Euclidean times. While the ensemble to be used in this project is relatively small, the large number of propagator inversions needed to compute the additional correlation functions requires a petascale machine such as Blue Waters.