Hadronic Light-­by-­Light Scattering Contribution to the Muon Anomalous Magnetic Moment from Lattice QCD with Chiral Fermions

PI Name: 
Thomas Blum
PI Email: 
thomas.blum@uconn.edu
Institution: 
University of Connecticut
Allocation Program: 
ALCC
Allocation Hours at ALCF: 
180 Million
Year: 
2016
Research Domain: 
Physics

A  primary  goal  of  physics  is  to  describe  everything  in  the  universe  through  its  most  fundamental  forces  and  particles.  The  current  culmination  of  this  goal  is  The  Standard Model, which successfully describes electromagnetism, the weak force, the strong force and the  particles  they  act  on.  The  Standard  Model  is  so  successful  that  it  has  remained  fundamentally  unchanged  for  the  past  50  years.  Beyond  Standard  Model  physics  is  an exciting  area  of  research  aiming  to  look  for  experiments  that  violate  the  Standard  Model  and  require  a  new  theory  for  the  universe.  Recently,  experiments  on  the  muon,  a fundamental particle in the Standard Model, suggest the true value of its magnetic moment may  be  in  disagreement  with  what  is  predicted  by  the  Standard  Model.  However,  the  detected difference between theory and experiment is within the error tolerances of both the theory and experiment. Does the muon magnetic moment agree with predictions of the Standard Model, or is it evidence of a break in one of physics most important theories?  To answer this question, a new experiment is underway that will measure the muon magnetic moment to a very high degree of accuracy. To compare the result to theory, computations must  be  made  to  determine  the  prediction  of  the  Standard  Model  to  the  same  level  of  accuracy.  The  goal  of  this  project  is  to  compute  the  hadronic  contributions  to  the  muon anomalous magnetic moment from first principles using lattice quantum chromodynamics (QCD),  the  fundamental  theory  in  the  Standard  Model  of  the  strong  nuclear  force  that  describes the interactions of quarks and gluons. The hadronic contributions represent the largest of the theory uncertainties, and their accurate determination is crucial to compare the Standard Model with the precise experimental measurement at Fermilab to potentially discover new physics.