General Physics Physics Seminar 7 November 2002


Testing time-reversal symmetry using cold molecules

Rick Bethlem

FOM Instituut voor Plasmafysica 'Rijnhuizen'
Nieuwegein, The Netherlands


At very high precision a molecule is no longer adequately described as a system containing protons, neutrons and electrons only. Rather, it is necessary to include a sea of virtual particles surrounding them, allowed to exist for very short times by the Heisenberg uncertainty principle. Therefore, by performing very sensitive spectroscopic measurements we can learn how these virtual particles interact with the constituents of an atom or a molecule. This ushers molecular physics in an area which has traditionally been reserved to particle physicists.

Of particular interest are interactions which lead to a nonzero electric dipole moment (EDM) of an electron. The dipole moment is a measure for the charge distribution of the particle. An EDM would imply an asymmetry with respect to time reversal (T), commonly referred to as T-violation. According to the Standard Model, the EDM of the electron is too small to be detected by any presently conceivable method. However, it is generally believed that the Standard Model is incomplete, and extensions to the Standard Model predict considerably larger values for the electron dipole moment, comparable to, or larger than, the current experimental upper limit. Increasing the experimental accuracy may therefore make it possible to either exclude these theories or to see evidence for physics beyond the standard model.

One of the most sensitive experiments to date uses the lanthanide monofluoride, YbF, molecule. The sensitivity of this experiment would be greatly improved if a means would be available to cool and trap these molecules. In this talk I will report on our progress in building a Stark-decelerator for YbF.