Positronium formation in helium with electron correlation effect

Effects of electron correlation on positronium formation in positron-helium collisions have been studied using first-order Born and first-order distorted-wave approximations. Two correlated bound-state wavefunctions are proposed to calculate total capture cross sections at incident positron energies from the threshold at 17.8 eV up to 2000 eV. A huge collection of cross section data is compiled using these correlated and several other no-correlation wavefunctions. Present results, as expected, indicate that the electron correlation has a profound effect on the positronium formation. The correlated wavefunction which satisfies a better cusp condition of value 0.46 seems to predict realistic cross sections at all incident energies. (author)