2021 Impact factor 4.991
Particles and Fields

Eur. Phys. J. C 20, 371-388
DOI: 10.1007/s100520100652

$K\rightarrow \pi\pi e^+e^-$ decays and chiral low-energy constants

H. Pichl1, 2

1  INFN, Laboratori Nazionali di Frascati, P.O. Box 13, 00044 Frascati, Italy
2  Institut für Theoretische Physik, Universität Wien, Boltzmanngasse 5, 1090 Wien, Austria

(Received: 27 February 2001 / Published online: 11 May 2001 -© Springer-Verlag / Società Italiana di Fisica 2001)

The branching ratios of the measured decay $K_{\mathrm {L}}\rightarrow \pi^+\pi^-e^+e^-$ and of the still unmeasured decay $K^+\rightarrow\pi^+\pi^0e^+e^-$ are calculated to next-to-leading order in chiral perturbation theory (CHPT). Recent experimental results are used to determine two possible values of the combination (Nr16-N17) of weak low-energy couplings (LECs) from the $\cal{O}(p^4)$ chiral Lagrangian. The values obtained are compared to the predictions of theoretical approaches to weak counter term couplings to distinguish between the two values. Using the favoured value of the combination (Nr16-N17) and taking into account additional assump tions suggested by the considered models, one obtains the branching ratio of the se cond decay as a function of the unknown combination (Nr14+2Nr15) of weak low-energy couplings. Finally, using values of the individual LECs derived from a particular model, one predicts the branching ratio of the K+ decay.

© Società Italiana di Fisica, Springer-Verlag 2001