Researchers at Imperial College London have measured the electric field surrounding an electron, and determined that it is almost perfectly spherical. The team placed an upper limit of one part in 1018 on the deviation from a perfect sphere. Their result is consistent with zero asymmetry.
The measurement was made using dipolar molecules of ytterbium fluoride which are placed in a magnetic field. The rate of spin is measured as the fields are varied. A variation in the rate of spin would indicate a slightly oval-shaped electron. The full findings were reported in Nature (doi:10.1038/nature10104)
The standard model predicts an electron which is very slightly egg-shaped: to one part in 1028. Supersymmetry predicts a slightly larger deviation: between one part in 1014 and one part in 1019. A factor of ten improvement in the accuracy of the measurement could either confirm or disprove supersymmetry.
"We cannot rule out supersymmetry but we're certainly putting pressure on the theory," says John Hudson from the Imperial team.
The search for supersymmetry, a theory which has been proposed as a solution to the heirachy problem, is closing in, but with still no evidence that it exists. With the LHC still reporting no sign of supersymmetry, could this elegant theory be nearing the end of the road?