Search for the dark photon in pi(0) decays

A sample of 1.69 x 10(7) fully reconstructed pi(0) -> gamma e(+)e(-) decay candidates collected by the NA48/2 experiment at CERN in 2003-2004 is analyzed to search for the dark photon (A') production in the pi(0) -> gamma A' decay followed by the prompt A' -> e(+)e(-) decay. No signal is observed, and an exclusion region in the plane of the dark photon mass m(A') and mixing parameter epsilon(2) is established. The obtained upper limits on epsilon(2) are more stringent than the previous limits in the mass range 9 MeV/c(2) pi(+/-)A' decay is also evaluated. (C) 2015 The Authors. Published by Elsevier B.V

Study of the K-+/- -> pi(+/-)gamma gamma decay by the NA62 experiment

A study of the dynamics of the rare decay K-+/- -> pi(+/-)gamma gamma has been performed on a sample of 232 decay candidates, with an estimated background of 17.4 +/- 1.1 events, collected by the NA62 experiment at CERN in 2007. The results are combined with those from a measurement conducted by the NA48/2 Collaboration at CERN. The combined model-independent branching ratio in the kinematic range z = (m gamma gamma/m(K))(2) > 0.2 is B-MI(z > 0.2) = (0.965 +/- 0.063) x 10(-6), and the combined branching ratio in the full kinematic range assuming a Chiral Perturbation Theory description is B(K-pi gamma gamma) = (1.003 +/- 0.056) x 10(-6). A detailed comparison of the results with the previous measurements is performed. (C) 2014 The Authors. Published by Elsevier B.V