G-parity-violating amplitudes in the J/ψ → π+π- decay

The decays of the negative G-parity meson G-parity into even numbers of pions violate G-parity. Such decays, as well as other G-parity decays into hadrons, can be parametrized in terms of three main intermediate virtual states: one photon, one photon plus two gluons, and three gluons. Since the electromagnetic interaction does not conserve G-parity, G-parity decays into positive G-parity final states should be dominantly electromagnetic. Nevertheless, the one-photon contribution to J/psi ->pi(+)pi(-), that can be estimated by exploiting the cross section sigma(e(+)e(-)-> pi(+)pi(-)), differs from the observed decay probability for more than 4.5 standard deviations. We present a computation of the gg gamma amplitude based on a phenomenological description of the decay mechanism in terms of dominant intermediate states eta gamma, eta'gamma and f(1)(1285)gamma. The obtained value is of the order of the electromagnetic contribution.