CryoEDM

CryoEDM is a particle physics experiment aiming to measure the electric dipole moment (EDM) of the neutron to a precision of ~10−28ecm. The name is an abbreviation of cryogenic neutron EDM experiment. The previous name nEDM is also sometimes used, but should be avoided where there may be ambiguity. The project follows the Sussex/RAL/ILL nEDM experiment, which set the current best upper limit of 2.9×10−26ecm. To reach the improved sensitivity, cryoEDM uses a new source of ultracold neutrons (UCN), which works by scattering cold neutrons in superfluid helium. CryoEDM is a particle physics experiment aiming to measure the electric dipole moment (EDM) of the neutron to a precision of ~10−28ecm. The name is an abbreviation of cryogenic neutron EDM experiment. The previous name nEDM is also sometimes used, but should be avoided where there may be ambiguity. The project follows the Sussex/RAL/ILL nEDM experiment, which set the current best upper limit of 2.9×10−26ecm. To reach the improved sensitivity, cryoEDM uses a new source of ultracold neutrons (UCN), which works by scattering cold neutrons in superfluid helium. The experiment is located at the Institut Laue–Langevin in Grenoble. The collaboration includes the nEDM team from Sussex University and RAL, as well as new collaborators from Oxford, and Kure, Japan. The collaboration is remarkably small for a modern particle physics experiment (around 30 people). In 2008 the experiment was ranked as an alpha 5 (top priority) project by STFC, together with the much larger CERN experiments: ATLAS and CMS. For more information see Neutron electric dipole moment Although electrically neutral overall, the neutron is made up of charged quarks. An imbalance of charge on one side would cause a non-zero EDM. This would be a violation of parity (P) and time reversal (T) symmetries. 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. Limits on the neutron EDM are a significant constraint on many particle physics theories. The Standard Model of Particle Physics predicts a value 10−31 – 10−32 ecm, while supersymmetric theories predict values in the range 10−25 – 10−28ecm. Modern EDM experiments work by measuring a shift in the neutron Larmor spin precession frequency ν {displaystyle u } , when the applied electric field E is reversed. This is given by h ν = 2 d E ± 2 μ B {displaystyle h u =2dEpm 2mu B} where d is the EDM, μ {displaystyle mu } is the magnetic dipole moment, B is the magnetic field, and h is the Planck constant, (the ± {displaystyle pm } depends on whether the fields are parallel or antiparallel). Clearly when the electric field is reversed, this produces a shift in the precession frequency proportional to the EDM. As the neutron magnetic dipole moment is non-zero it is necessary to shield or correct for magnetic field fluctuations to avoid a false positive signal.