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Title: Improved shot noise limit of the YbF EDM experiment
Author: Rabey, Isabel
ISNI:       0000 0004 6348 3118
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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The electron is predicted to have a small electric dipole moment (EDM). This fundamental property characterises the distortion of the electron's almost perfectly spherical charge distribution. The size of this distortion (de) is intimately connected to the breaking of time reversal symmetry (T) in nature. The Standard Model of particle physics, which contains a small amount of T-asymmetry, predicts a tiny, non-zero value of the electron EDM, |de| ≃ 10^-38 However, many extensions to the Standard Model, which naturally include additional T-violating effects, also predict much larger values of de that should be detectable using current experimental techniques. Measurements of the electron's EDM constrains these theories, making these experiments a powerful tool in the search for physics beyond the Standard Model. The most precise measurements of the electron EDM have been made using paramagnetic atoms and moleules. This thesis describes the progress made towards a new measurement of the electron EDM using the polar, paramagnetic molecule, YbF. A new state preparation technique is described that optically pumps most of the population from the first and second rotationally excited states into a single hyper fine component of the ground state. This increases the number of molecules entering the experiment by a factor of 6. A new state-selective detection scheme is also described, where multiple laser frequencies are used so that each molecule scatters many photons. This has increased detection efficiency by a factor of 20. In order to reduce magnetic noise in the experiment, new electric field plates have been introduced into the interaction region which have reduced the magnetic Johnson noise by a factor of 100. Together, these improvements increase statistical sensitivity by a factor of 11.4 over the last EDM measurement made using YbF. With an enhanced sensitivity of (5x10^-27/sqrt(Nb)), we can expect to measure the electron's EDM more precisely than ever before, constraining T-violating physics at a higher energy scale.
Supervisor: Sauer, Ben ; Tarbutt, Mike Sponsor: Engineering and Physical Sciences Research Council ; Science and Technology Facilities Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral