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Department of Physics and Astronomy
University of Mississippi


Event Information:

  • Tue

    Colloquium: Search for the Neutron Electric Dipole Moment and "what next?"

    4:00 pmLewis Hall 101

    Prajwal Mohan Murthy
    Department of Physics
    University of Chicago

    Search for the Neutron Electric Dipole Moment and "what next?"

    Baryon asymmetry of the universe, i.e. the fact that much of the observed universe is made of matter as opposed to equal amounts of matter and anti-matter, demands violation of Charge-Parity (CP) symmetry. Yet, the amount of CP violation from the Standard Model of particle physics is insufficient to explain the baryon asymmetry of the universe. Observation of a non-zero permanent electric dipole moment (EDM) coupled to the spin of any sub-atomic particle, such as the neutron, is an indication of CP violation. Therefore, measuring the neutron EDM, is a key technique of getting a handle on the amount of CP violation. The neutron EDM from the standard model sources is so small that no experiment has thus far achieved the sensitivity required. Nonetheless, searches for the neutron EDM is an important method by which to test and constrain physics beyond the standard model. The neutron EDM has been measured since the 1940s and the sensitivity of the experiments has improved by over 8 orders of magnitude.

    The most recent series of efforts were conducted at the Paul Scherrer Institute (PSI). This was a room temperature experiment employing the Ramsey technique of separated oscillating fields. These measurements used a 21 l storage chamber, in which ultracold neutrons were stored, and surrounded by 4 layers of mu-metal. Prior to 2006, the series of measurements at the Institut Laue-Langevin (ILL) culminated in the measurement of dn < 3 × 10-26 (90% C.L) [Phys. Rev. D 92, 092003 (2015)] over 5 years of data taking. The ILL apparatus was upgraded significantly with addition of: (i) 16 Cs-133 magnetometers to further characterize the magnetic field environment in the storage chamber, (ii) a new neutron detector system which could simultaneously count both the spin states of the neutron, and (iii) optimized coating inside the storage chamber to maximize the neutron density. The upgraded apparatus was moved to the Paul Scherrer Institute and independently achieved a measurement of dn < 1.8 × 10-26 (90% C.L) [Phys. Rev. Lett. 124, 081803 (2020)] in just 2 years of data taking. The PSI nEDM experiment has also been a source of rich physics program beyond the measurement of the nEDM. It has investigated neutron oscillation, provided input into neutron lifetime measurements, searched for axions, and tested Lorentz Invariance.

    While the search for CPV EDM was first attempted in neutrons, searching for atomic EDM may be a more lucrative avenue, since multiple sources contribute to an atomic EDM, viz. nucleon EDM, nuclear Schiff moment, CP violating interactions between the electrons and the nuclei, and the nuclear MQM also contributes to the atomic EDM. Nuclear Schiff moment and nuclear MQM are significantly enhanced in quadrupole and octupole deformed nuclei. We will also discuss viable candidate isotopes which have maximally enhanced sensitivity to EDMs.


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    Meeting ID: 919 282 27187