Processes (gamma)(gamma) (yields) (pi)(sup 0)(pi)(sup 0) and (eta) (yields) (pi)(sup 0)(gamma)(gamma) at O (p(sup 6)) in the NJL model

摘要

We discuss the processes (gamma)(gamma) (yields) (pi)(sup 0)(pi)(sup 0) and (eta) (yields) (pi)(sup 0)(gamma)(gamma) at O (p(sup 6)) in the momentum expansion. The calculation involves tree-level, one-loop and two-loop diagrams of a chiral effective Lagrangian which is obtained by a bosonization of the NJL model. The importance of integrating out meson resonances (reduction) is pointed out. Our final results for the total cross section of (gamma)(gamma) (yields) (pi)(sup 0)(pi)(sup 0) are in good agreement with the experimental data of the Crystal Ball Collaboration. For the width of the (eta) (yields) (pi)(sup 0)(gamma)(gamma) decay we obtain the value 0.11 eV which has to be compared with the experimental value of (0.84 (+-) 0.18) eV. Alternatively, taking empirical parameters from a vector-meson-dominance model the prediction for the decay width is 0.35 eV. We present a prediction for the differential decay probability as a function of m(sub (gamma)(gamma))(sup 2)/m(sub (eta))(sup 2). 28 refs., 2 figs., 2 tabs. (Atomindex citation 27:009346)