Spectroscopic Study Of PbF And Te₂ Molecules Towards The Measurement Of The Electron's Electric Dipole Moment (eEDM)

The Standard Model of particle physics has made significant progress in understanding the interaction mechanisms of elementary particles since the middle of the 20^th century,but it still fails to explain phenomena including the matter–antimatter asymmetry,origins of dark matter and dark energy,and fundamental nature of the gravitational force,all of which have prompted numerous explorations beyond the Standard Model.Because theoretical extensions to the Standard Model(e.g.Supersymmetric models)generally predict that elementary particles might have intrinsic electric dipole moments that can be detected under the current state-of-the-art conditions,precise measurement of their non-zero values can then be proposed for accurate test of new physics and new mechanisms beyond the Standard Model and it is currently regarded as one of the most effective methods for testing CP violations under weak and electromagnetic interactions.In recent years,experimental researches on precision measurement of the electron's Electric Dipole Moment(e EDM)combining atomic and molecular physics as well as precision spectroscopic measurement technology have gradually emerged worldwide.By conducting experiments on these polar heavy-atom diatomic molecules,one can characterize the Standard Model in the low-energy limit and obtain the restriction conditions of the effective field theory,thus constraining the scope of application for extension models.These molecules include but are not limited to Yb F,Th O and Hf F⁺,which have been characterized for their own specific advantages and disadvantages in measuring the e EDM.Here we proposed the e EDM measurement using lead monofluoride(Pb F)molecules,which is featured in the buffer gas cooling technique,internal coherent state preparation using an optical pumping method as well as sensitive spectroscopic measurement of e EDM related signal in a Q_fe(1/2)state-selected transition.Although the proposal has advantages such as long coherent time,immunity to external magnetic field and sensitive spectroscopic approach,there are still two important problems remained to be solved.First,previous spectroscopic studies were all related to supersonic beams of Pb F and unable to obtain good population in low J states and in low velocities,therefore the buffer gas cooling apparatus based on Pb F molecules should be constructed.Second,the laser frequency will definitely drift during the experiment,leading to unstable state preparation and unreliable spectroscopic detection in the Q_fe(1/2)state-selected transition.Based on the above requirements,the first generation of apparatus including the Pb F buffer gas cooling beam source and a laser-induced fluorescence detection system were built to generate a cryogenically cooled Pb F molecular beam and the spectral detection of the B?X₁ transition has been achieved.The energy level structures of A and X₁ states were evaluated using the effective Hamiltonian approach,and the frequency of Q_fe(1/2)sensitive transition was therefore determined.The Doppler-free spectrum of ¹³⁰Te₂ has been studied via the saturated absorption method near the band origin of the Pb F A?X₁ transition while the preliminary frequency stabilization system has been built.Multiple transition bands of ¹³⁰Te₂B₁?X₁₁transition have been assigned while Dunham parameters and diatomic constants of B₁state of ¹³⁰Te₂ have been fitted and analyzed by the linear least square algorithm,which provide frequency reference lines for laser frequency stabilization as well as the spectroscopic detection of the Q_fe(1/2)transition and will be utilized eventually for the preparation of the coherent state for the Pb F ground state and the measurement of the Pb F A?X₁ transition in the near future.The precision measurement of e EDM based on cold Pb F molecules is one of the few experimental projects in China that search for the permanent Electric Dipole Moments of elementary particles.This thesis lays an significant foundation both experimentally and theoretically for the preparation of coherent states in the Pb F A?X₁ transition and the e EDM signal measurement in the Q_fe(1/2)sensitive transition.Our work here fills the blanks of the buffer gas cooling generation of Pb F molecules and the reference spectral lines required for state preparation,frequency stabilization and spectroscopic detection,thus steadily advancing the research progress of e EDM precision measurement using Pb F molecules,and contributing to the understanding of the new physics and new mechanisms beyond the Standard Model such as exploring the CP violations,matter-antimatter asymmetry,and the origin of dark matter and dark energy.