• Collision between two ortho-positronium (Ps) atoms: A four-body Coulomb problem

• # Fulltext

https://www.ias.ac.in/article/fulltext/pram/086/05/1077-1090

• # Keywords

Positronium; elastic collision; exact exchange; CM frame; scattering length; quenching cross-section; non-adiabatic effects.

• # Abstract

The elastic collision between two ortho-positronium (e.g. $S = 1$) atoms is studied using an {\it ab-initio} static exchange model (SEM) in the centre of mass (CM) frame by considering the system as a four-body Coulomb problem where all the Coulomb interaction terms in the direct and exchange channels are treated exactly. A coupled channel methodology in momentum space is used to solve Lippman–Schwinger equation following the integral approach. A new SEM code is developed in which the Born–Oppenheimer (BO) scattering amplitude acts as input to derive the SEM amplitude adapting the partial wave analysis. The $s$-, $p$- and $d$-wave elastic phase shifts and the corresponding partial cross-sections for the spin alignment $S = 0$, i.e., singlet (+) and $S = 2$, i.e., triplet (−) states are studied. An augmented Born approximation is used to includethe contribution of higher partial waves more accurately to determine the total/integrated elastic cross-section $(\sigma)$, the quenching cross-section (σq) and ortho-to-para conversion ratio $(\sigma/\sigma q)$. The effective range theory is used to determine the scattering lengths and effective ranges in the s-wave elastic scattering. The theory includes the non-adiabatic short-range effects due to exchange.

• # Author Affiliations

RAY HASI1 2 3

1. Study Centre, S-1/407/6, B.P. Township, Kolkata 700 094, India
2. Department of Physics, New Alipore College, Kolkata 700 053, India
3. Science Department, National Institute of TTT and Research, Kolkata 700 106, India

• # Pramana – Journal of Physics

Volume 96, 2022
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019