A new measurement of the K-+/- -> pi(+/-)gamma gamma decay at the NA48/2 experiment

The NA48/2 experiment at CERN collected two data samples with minimum bias trigger conditions in 2003 and 2004. A measurement of the rate and dynamic properties of the rare decay K-+/- -> pi(+/-)gamma gamma from these data sets based on 149 decay candidates with an estimated background of 15.5 +/- 0.7 events is reported. The model-independent branching ratio in the kinematic range z = (m(gamma gamma)/m(K))(2) > 0.2 is measured to be B-MI(z > 0.2) = (0.877 +/- 0.089) x 10(-6), and the branching ratio in the full kinematic range assuming a particular Chiral Perturbation Theory description to be B(K-pi gamma gamma) = (0.910 +/- 0.075) x 10(-6). (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/)

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