CryoEDM is a particle physics experiment aiming to measure the electric dipole moment (EDM) of the neutron to a precision of ~10−28ecm.
The collaboration is remarkably small for a modern particle physics experiment (around 30 people).
A neutron EDM is believed to exist at some level to explain the matter-antimatter asymmetry of the Universe, although to date every measurement has given a value consistent with zero.
Modern EDM experiments work by measuring a shift in the neutron Larmor spin precession frequency
Clearly when the electric field is reversed, this produces a shift in the precession frequency proportional to the EDM.
The precession frequency is measured using the Ramsey separated oscillatory field magnetic resonance method, in which a large number of spin polarized ultra-cold neutrons are stored in an electric and magnetic field.
The signal generator used to apply the pulse is then gated off while the neutron spins precess about the magnetic field axis at the precession frequency; after a period of ~100s, another field pulse is applied to rotate the spins by
Magnetic field fluctuations (a significant source of systematic error) were monitored using atomic mercury magnetometer.
Moving from a room temperature to a cryogenic measurement, means it has been necessary to rebuild the entire apparatus.
The experiment achieved a number of accomplishments: multiple operations of cryostat at 0.6 K (300 L superfluid He volume), superthermal UCN production at expected rate, demonstrated transport to Ramsey Chamber and detectors, development/operation of solid-state UCN detectors in LHe, as well as installation and operation of SQUID magnetometry system.
However, in December 2013 STFC's Science Board decided to perform a “managed withdrawal” from CryoEDM, due to scale of program required to reach a new physics result in a competitive timescale outside of anticipated available resource levels.