Researches On Novel Schemes Of Optoelectrostatic Storage Ring And Precision Measurement Of The Electron Electric Dipole Moment

The development of cold molecules techniques has laid a solid foundation in a wide range of research areas,such as precision measurement of physical constants,high-resolution spectroscopy and cold collisions.Among these,the measurement of the electron?s electric dipole moment?eEDM?,one of the most important experiments that unveil the myths of matter-antimatter distribution in the universe and the charge-parity symmetry violation,has long been the platform that targets in searching the new physics beyond the Standard Model.Comparing with the Large Hadron Collider,the table-size eEDM experiment exhibits giant advantage in the terms of the machine cost and operation feasibility.Although a fruitful achievement has been made towards the eEDM measurement,the non-zero value has still not been obtained,as well as the lack of the eEDM experiment in the domestic research society,due to the great difficulties in the detection techniques and the strict technical specifications.Therefore,the eEDM experiment is not only necessary to verify the models beyond the Standard Model,but plays a significant role in our independent research on the high-precision,high-resolution and high-sensitivity techniques.In order to proceed to the theory and experiment of the eEDM measurement,we discuss the new methods for preparation of the cold molecules and the new schemes for eEDM precision measurement based on cold molecules,aiming to set up a new cold molecular measurement system that is capable of achieving high experimental sensitivity.First of all,we proposed the design of the optoelectrostatic storage ring that is used to decelerate and trap polar molecules,especially those of asymmetric top or heavy polar molecules for eEDM precision measurement.The dynamics of an optoelectrostatic storage ring is theoretically investigated,which is composed of an orbiting red-detuned laser beam and an electrostatic quadrupole ring.A three-dimensional?3D?hybrid potential well for molecules of interest is formed in the focus spot of the red-detuned laser beam.The potentials of the molecules experienced in the combined optical and electrical fields,as well as the behavior of motional molecules under the influence of the hybrid potential well,are then investigated.Later on,the deceleration and trapping processes of the molecules in the hybrid potential well are numerically simulated using Monte-Carlo method and corresponding results are presented.The study in this thesis indicates that this optoelectrostatic storage ring,featuring a 3D potential well of controllable orbiting speeds,can serve as a good platform for the production and manipulation of cold polar molecules.In this thesis,the decelerating distance of the heavy polar molecules in the optoelectrostatic storage ring is estimated to be only about 5 cm,and meanwhile,since the measurement time of the polar molecules for the eEDM measurement in the optoelectrostatic storage ring has been effectively elongated,it therefore turns out to be a good method to obtain lower statistical uncertainty thus making the optoelectrostatic storage ring a good platform for preparing and controlling the cold molecules.Secondly,we investigated the electronic,rovibrational and hyperfine structures of the ²⁰⁸Pb¹⁹F radicals using an effective Hamiltonian approach.Comparing with other eEDM candidates,²⁰⁸Pb¹⁹F radicals exhibit larger internal effective field and lower magnetic g factor as well as its ground states as the eEDM measurement state.These features are all based on the complete understanding of the molecular spectrum of ²⁰⁸Pb¹⁹F radicals,so we theoretically derived the field-free spectrum and the field-dependent Stark spectrum of A??=0??X₁??=0?transition.According to the Stark spectrum,static electric field of strength 8.2 kV/cm is applied to optimize the spectrum that is ideal for eEDM signal collection.Finally,an optical interferometer measurement scheme is introduced for the PbF eEDM measurement.In this scheme,a molecular beam source of PbF molecules enters a region with 8.2 kV/cm E field where linearly polarized light creates the initial coherent state of the molecule.The molecules then enter a resonance region.At the end of the resonance region,molecules are detected using the pseudo-continuous resonant enhanced multiphoton ionization?pc-REMPI?technique.Finally,a level of 10^-30 e·cm/day^1/2 is estimated as the sensitivity of eEDM measurement.This calculated result makes the ²⁰⁸Pb¹⁹F molecule very competitive in the eEDM measurement,when compared with the most recent ThO result of d_e=(4.3±3.1_stat±2.6_syst)×10^-30 e·cm?Nature,562,355?2018??.Because of the complex energy level structure,PbF is not suitable for direct laser cooling.Thus,the statistical sensitivity of the PbF eEDM measurement is limited by the interaction time in the interferometer.In order to optimize the measurement sensitivity and overcome the current experiment limit,the new scheme of the sensitive eEDM measurement with laser-cooled ²⁰²Hg¹⁹F molecules is presented.For²⁰²Hg¹⁹F molecules,the electronic,rovibrational and hyperfine structures are investigated with the effective Hamiltonian approach and the highly diagonal Franck-Condon factors?FCFs?of the main transitions are verified by the Rydberg-Klein-Rees inversion?RKR?method and the Morse approximation.A feasible sideband modulation scheme is proposed according to the calculated hyperfine levels of(3²?_1/2?=0,=1?rotational state.In order to enhance optical cycling,the microwave remixing method is employed to address all the necessary levels.The Zeeman effect and the hyperfine structure magnetic g factors of the(3²?_1/2?=0,=1?state are studied subsequently.Finally,its statistical sensitivity for the eEDM measurement is estimated to be about 6×10^-32 e·cm in the trap,indicating that ²⁰²Hg¹⁹F might be a promising laser-cooled eEDM candidate.Finally,in order to characterize the PbF molecular flux density that is utilized towards the eEDM measurement,we developed the cavity-enhanced laser-induced fluorescence?CELIF?method for the absolute density measurement.Nitrogen dioxide?NO₂?seeded in argon is measured using a pulsed laser beam for the first time.The cavity ring down?CRD?and LIF signal is acquired simultaneously;the CRD signal is used for normalizing the LIF signal and determining the relationship between the measured CELIF signal and the NO₂ number density.The minimum detectable NO₂density,in the 60 s of acquisition time,is measured to be?3.6±0.1?×10⁸ cm^-3 with signal-to-noise ratio of 3.This method can be used for characterizing PbF buffer gas beam in the future,where the information of the absolute density of PbF buffer gas beam is extremely necessary for the calculation of the absorption cross section,the design of the detection system,and the estimation of the statistical uncertainty in the final precision eEDM measurement.