Title : Effect of electron correlation on  positronium
formation in positron-helium scattering.
authors :Puspitapallab Chaudhuri$^1$, S. K. Adhikari$^1$, 
B. Talukdar $^2$ and S. Bhattacharya $^2$.
Affiliation : $^1$Instituto de F\'isica Te\'orica, UNESP,
               01405-900, s\~ao Paulo, S\~ao Paulo, Brazil
              $^2$ Department of physics, Visva Bharati University,
               Santiniketan 731235, India     
Summary : A three-parameter correlated wave function for the helium
ground state is used to study the positronium formation from helium.
An exact analytical expression for the first Born scattering amplitude
for Ps-formation and differential and total cross sections are 
calculated. It is demonstrated that the inner electronic correlation
of the target atom plays a crucial role in explaining the discrepency
between theory and experiment.