Muon g − 2 Hadronic Vacuum Polarization from Lattice QCD

PI Name: 
John Laiho
PI Email:
Syracuse University
Allocation Program: 
Allocation Hours at ALCF: 
66 Million
Research Domain: 

The Standard Model of particle physics has been enormously successful in describing the sub-­‐  atomic  world  of  particle  physics.  A  persistent  exception  to  this  success  is  the  disagreement  between  the  Standard  Model  prediction  and  measurements  of  the  muon’s anomalous magnetic moment. The muon is a fundamental particle, similar to the electron, and  the  “anomalous”  part  of  the  magnetic  moment  stems  from  quantum  mechanical  interactions between the muon and elementary particles of all kinds. If the disagreement holds up, it would signal the presence of new, otherwise unobserved physical phenomena. The  disagreement  between  theory  and  experiment  is  not  yet  definitive,  so  a  new  experiment, aiming to reduce the measurement uncertainties fourfold, is being mounted at Fermilab. To receive a full return on this investment, the weakest parts of the theory have to  be  commensurately  improved.  This  allocation  supports  using  lattice  QCD,  which  is  acknowledged to be the only theoretical tool up to the task, to carry out the first ab initio calculations  of  the  hadronic  contributions  to  the  anomalous  magnetic  moment.  Uncertainties  in  these  calculations  (obtained  in  less  sophisticated  ways)  are  the  main theoretical obstacle to establishing new physics in the muon’s magnetic moment. This work will either underpin a major discovery or, should theory and experiment end up in accord, be a powerful constraint on new models of particle physics.