A new measurement of the branching ratio of K(S) → γ γ

AbstractThe decay rate of K S → γγ has been measured with the NA48 detector at theCERN SPS. A total of 149 K S → γγ events have been observed. The branchingratio is determined to be (2.58 ±0.36(stat) ±0.22(sys)) ×10 −6 . 1 Present address: EP Division, CERN, 1211 Gen`eve 23, Switzerland. 2 Funded by the U.K. Particle Physics and Astronomy Research Council. 3 On leave from Sezione INFN di Firenze, I-50125 Firenze, Italy. 4 On leave from Osterreichische Akademie der Wissenschaften, Institut f¨¨ ur Hoch-energiephysik, A-1050 Wien, Austria. 5 On leave from Joint Institute for Nuclear Research, Dubna,141980, Russian Fed-eration. 6 Dipartimento di Fisica dell’Universit`a di Modena e Reggio Emilia, I-41100, Mod-ena, Italy. 7 Instito di Fisica dell’Universit`a di Urbino, I-61029 Urbino, Italy. 8 Funded by the German Federal Minister for Research and Technology (BMBF)under contract 7MZ18P(4)-TP2. 9 Funded by Institut National de Physique des Particules et de Physique Nucl´eaire(IN2P3), France.