The Calculation Of Electron/positronium Scattering By Light Nucleus Atom Basing On Explicitly Correlated Gaussians

The great process of physics have been made in last century originated from the de-velopment of ultracold physics.Bose-Einstein condensate(BEC)had been first created in laboratory.Same as BEC,positron physics has been much promoted by ultracold technology.The scattering process and annihilation in positron physics give rise to the interest of antimatter BEC.The positronium(formed by positron and electron)is one of most possible candidate of antimatter BEC.However the short lifetime and the high temperature of positronium beam limit the application of advanced cooling techniques for positronium.The formation and observation of a positronium BEC has been very challenging.Thus the ab initio calcultion of positron and positronium physics would be helpful for the exploration of positronium BEC.The specific contents are as follows,1.The projection method combined with Explicitly correlated Gaussian has been developed for molecule systerm in the first chapter.This developed projection method has been used to the calculation of doubly excited states of the positronium molecule(Ps2)first.The energy of the 0+(A1)state is-0.12550 a.u.,which is related to the Ps(2S)+Ps(2S)threshold,while the 0+(E)state has an energy of-0.099298 a.u.,which is related to the Ps(2S)+Ps(3S)threshold.Moreover,the resonance positions and reso-nance widths of the two states are calculated using the CR method with the OPP basis sets.These resonance state shed light on the scattering and spectrum experiment be-tween two excited state positronium.2.The exploration of exctied positronium scattering by exctied positronium are given in the second chapter.We intend to calculte the scattering length of two excited positronium(o-Ps(2S)).The stabilization idea combined with the projection method is introduced to determine the scattering length of two excited state positronium.We could confirm the scattering length of Ps(2S)-Ps(2S)is positive.The quantum defect theory is used to estimate the scattering length of Ps(2S)-Ps(2S),which also gives a positive scattering length.The positive scattering length means the Ps(2S)could form a stable BEC.3.The low-energy phase shifts,scattering lengths,and elastic cross-sections of sp-e-He*and sp-Ps-He*scattering are calculated using the advanced CVM combined with the ECG basis.These processes are present as a comparison.The pickoff annihilation rate is zero in spin-polarized Ps-He*scattering.The zero pickoff annihilation rate could enable the utilization of sp-Ps-He*scattering in future experiments.The Ramsauer-Townsend minimum is observed in spin-polarized electron-helium(23S)scattering due to the large polarization of metastable helium.4.The three-body recombination rates and scattering cross section of 4He-4He-T are calculated by using the R-matrix propagation method in the hyperspherical coordi-nate frame in the last chapter.These scattering parameter could be used in future ex-periment.The hyperspherical coordinate is very suited to three body calculation.The hyperspherical coordinate combined with Explicitly correlated Gaussian can be used in four body calculation,this could be helpful in future excited state positronium scatter-ing.