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

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    • 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
    • Dates

       
  • Pramana – Journal of Physics | News

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