W. Clark Griffith
UW Physics

The measurement of a finite permanent electric dipole moment (EDM) on any atom or particle would reveal a new source of CP violation outside of the Standard Model.   At present, the tightest bound on any EDM comes from our vapor cell measurement with Hg 199 atoms, which set an upper limit of |d| < 2.1 x 10<SUP>-28</SUP> e cm.  This level of sensitivity is well within the range of predictions from many theoretical extensions of the Standard Model, such as Supersymmetry, which in its most basic form predicts a Hg EDM about 100 times larger than our upper bound.  The current version of the experiment uses a stack of four vapor cells in a common magnetic field, and oppositely directed electric fields in the two middle cells.  The nuclear spin precession frequency is measured in the four cells, and an EDM would reveal itself as an electric field correlated frequency difference between the middle cell frequencies.  The outer two cells at zero electric fields are used as magnetometers to help cancel magnetic field noise and check for systematic effects.