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The two-pion contributions to the HVP correction of the muon g-2

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

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Aida X El-Khadra, Shaun Lahert

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 late 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 calculate the hadronic vacuum-polarization (HVP) contribution, which is the largest source of theory error. 

Our Blue Waters project targets one of the largest sources of error in this calculation:  the statistical fluctuations at large Euclidean times.   The  correlation  functions  calculated  in  the Blue  Waters  project  are  needed  to  quantify  the  contributions  from  two-pion  states  which dominate at large Euclidean times, and which will be used to reconstruct the HVP contribution in that region with much smaller errors.  While the ensemble 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.