Harvard Physicists featured in Science
Collaborators John Doyle, Professor of Physics, and Gerald Gabrielse, George Vasmer Leverett Professor of Physics, with Professor David DeMille from Yale, recently had their research featured on the cover of the academic journal, Science. The article, Order of Magnitude Smaller Limit on the Electric Dipole Moment of the Electron, significantly constrains theories that go beyond the Standard Model (SM), often called New Physics. The SM is our current understanding of fundamental particles in the Universe, but is known to be incomplete.
The EDM is an asymmetric charge distribution along the magnetic axis of the electron. It can be thought of as a slight bulge of the otherwise spherical electron, a shape that violates a basic time symmetry of Nature (called “T-violation”). Using cold thorium monoxide molecules, they found an upper limit for the dipole of |de| < 8.7 X 10−29 e·cm with 90% confidence, an order of magnitude improvement in sensitivity relative to the previous best limit. This result shows that the electron is round to a fantastically high degree, 12 times more so than demonstrated in previous measurements. This new result constrains T-violating physics at the TeV energy scale, constraining CP violation up to energy scales similar to, or higher than, those explored directly at the Large Hadron Collider.
The experiment took place in the LISE and Jefferson laboratories (connected by many optical fibers) and was performed by what Doyle and Gabrielse call “an extraordinary group of graduate students, postdocs, technical staff and undergraduates”. Unlike most particle physics experiments, this experiment fits into a couple of rooms, rather than large caverns.
The new result significantly impacts possible Supersymmetry (SUSY) theories, a favored class of New Physics models, because it “greatly constrains SUSY parameters while leaving some variants of Supersymmetry alive for future tests,” stated Doyle. This work also implies that it is more and more improbable that the LHC will detect supersymmetric particles, even after the update of its energy.
One might speculate that this could be bad news for the possibility of finding evidence of physics beyond Standard Model. “We know that the incomplete Standard Model cannot be the final word. Our measurement has now eliminated some important and otherwise plausible ways that supersymmetric particles could have addressed the incompleteness. The quest to figure out what is really going on is still exciting, important and more intriguing,” said Gabrielse.
For now, they believe their findings are consistent with the Standard Model, whose Higgs Boson was recently discovered, and they hope to increase the accuracy of their measurement over the next five years. If discovered, the EDM could support New Physics theories that explain key physics questions, including the dominance of matter in the Universe and the question of Dark Matter.