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The race to find the electric dipole moment

The University of Montreal actually has an ivory tower!

Congress HQ: the University of Montreal actually has an ivory tower!

By Hamish Johnston at the 2013 CAP Congress in Montreal

Yesterday I had lunch with Jeff Martin of the University of Winnipeg, who is a member of an international team that aims to measure the electric dipole moment (EDM) of the neutron at TRIUMF in Vancouver.

This might seem like a strange goal – after all, the neutron is famous for being electrically neutral. But the neutron is a composite particle made of charged quarks, so it might just have a permanent EDM.

Measuring an EDM would be a significant step forward in the search for physics beyond the Standard Model (SM) of particle physics. A neutron EDM is just about forbidden by the SM, which allows for a tiny value far beyond the capabilities of current experiments. However, models beyond the SM do allow for much larger values of EDM and therefore making such a measurement would provide a wealth of grist for the theoretical mill.

Martin and colleagues will make their search using ultracold neutrons (UCN) that are produced by spallation using an accelerator at TRIUMF. The hot (or fast) neutrons will be slowed down to a lethargic 30 km/h by passing them through superfluid helium. They will then be sent to a trap, where the team will manipulate the spins of the neutrons using nuclear-magnetic-resonance techniques. Finally, the spin states of the neutrons will be determined. The measurement will be done in a very strong electric field, and then repeated with the field pointing in the opposite direction. An EDM would appear as a slight difference in the distribution of spin states.

Martin told me that the team could achieve a two-orders-of-magnitude improvement over the current state of the art. This just might be good enough to see physics beyond the SM.

However, Martin and colleagues are not the only game in town; there are about half a dozen other experiments looking for an EDM in neutrons and other particles. Earlier this month I wrote a news article about the discovery of pear-shaped nuclei, which offer an alternative route to measuring an EDM.

Let the race begin!

You read more about the UCN programme at TRIUMF here.

If you want to know more about EDM physics, Chad Orzel has written a nice article for us about the search.

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One comment to The race to find the electric dipole moment

  1. M. Asghar

    The most precise expermental work on ghe neutron electric dipole moment(NEDM) has been carried using the ultra cold neutrons(UCN) from the high flux reactor in the Laue-Langevin Institute in Grenoble(France) for more than 40 years with the latest limit of dn < 2.9.10^-26 e.cm. However, the expectation of a much higher UCN flux (than from Grenoble reactor)for a higher precision for NEDM from the spallation sources such as at the Paul scherrer Institute in Switzerland remains largely unfulfilled.

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