Wednesday, January 14, 2015

SUSY Constrained By Electric Dipole Moment Of The Electron

A preprint released in November of 2013 and published in 2014 set a new limit on the electron dipole moment of the electron. It stated its raw data conclusion and explained that:
This corresponds to an upper limit of |de| < 8.7×10−29 e cm with 90 percent confidence, an order of magnitude improvement in sensitivity compared to the previous best limits.
The best fit value is -2.1×10−29 e cm, which is consistent with zero within less than one standard deviation of the best fit value.

A factor of ten improvement on this limitations is expected in the near future.

UPDATE: Previously blogged here without analysis of how it pertains to SUSY exclusions in the main post, although the comments note that "Jester, with numerous caveats, explains that "the simplest explanation of the current data is that there are no superpartners up to at least ~10 TeV.""

The electron EDM constraint is more strict than the anomalous magnetic moment of the muon constraint which limits various superpartners to masses in the low to middle single digit TeV range (with the exception of chiral scalars).

Direct superpartner and additional Higgs boson searches also place less strict limitations on SUSY theories.


I previously noted at Wash Park Prophet in February of 2011 that:
The standard model predicts that the electron's electric dipole moment is less than 10^–38 in units of electron charge times centimeters. That's equivalent to separating an electron and a similar charged particle by a distance of 10^–38 centimeters. . . But extensions of the standard model predict the electric dipole moment to be bigger, between 10^–25 and 10^–30. In 2002, [scientists] published the most stringent limit yet: 1.6 × 10–27.
Experiments in progress costing about $10 million, a bargain in the fundamental physics world, should determine if the electron's electric dipole moment is more than 10^-29 by one of a few possible methods in the next few years.

The minimal supersymmetric standard model, or MSSM, is a standard model extension that holds that every elementary particle has a “superpartner.” One of the simplest versions has been ruled out by the current limit.

An electric dipole moment for an electron of less than 10^-30 would rule out most versions of supersymmetry, and hence, most versions of string theory.
While we haven't quite reached the promised land of 10−30 e cm, the limitation published in 2014 greatly constrains SUSY parameter space.

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