A new measurement of the K ± → π ± γ γ decay at the NA 48 / 2 experiment The NA 48 / 2 Collaboration

Article history: Received 29 November 2013 Received in revised form 8 January 2014 Accepted 13 January 2014 Available online 23 January 2014 Editor: W.-D. Schlatter 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 ± → π±γ γ 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 = (mγ γ /mK )2 > 0.2 is measured to be BMI(z > 0.2) = (0.877±0.089)×10−6, and the branching ratio in the full kinematic range assuming a particular Chiral Perturbation Theory description to be B(Kπγ γ ) = (0.910 ± 0.075) × 10−6. © 2014 The Authors. Published by Elsevier B.V. Funded by SCOAP . 3 Open access under CC BY license. * Corresponding author. E-mail address: eg@hep.ph.bham.ac.uk (E. Goudzovski). 1 Present address: School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT, UK. 2 Supported by a Royal Society University Research Fellowship. 3 Funded by the UK Particle Physics and Astronomy Research Council. 4 Present address: Università degli Studi del Piemonte Orientale, I-13100 Vercelli, Italy. 5 Deceased. 6 Present address: Istituto di Cosmogeofisica del CNR di Torino, I-10133 Torino, Italy. 7 Present address: Dipartimento di Fisica e Scienze della Terra dell’Università e Sezione dell’INFN di Ferrara, I-44100 Ferrara, Italy. 8 Present address: Department of Physics, Imperial College, London, SW7 2BW, UK. 9 Present address: CERN, CH-1211 Genève 23, Switzerland. 10 Present address: Ruprecht-Karls-Universität Heidelberg, D-69120 Heidelberg, Germany. 11 Present address: Laboratori Nazionali di Frascati, I-00044 Frascati, Italy. 12 Present address: Faculty of Physics, University of Sofia “St. Kl. Ohridski”, 1164 Sofia, Bulgaria, funded by the Bulgarian National Science Fund under contract DID02-22. The NA48/2 Collaboration / Physics Letters B 730 (2014) 141–148 143