Precise measurements of the $K_{S} \to \gamma\gamma$ and $K_{L} \to \gamma\gamma$ decay rates

Affiliations: CERN Imprint: 10 Oct 2002 Pages: 10 p Subjects: Particle Physics - Experimental Results Accelerator: CERN SPS Experiment: NA48 (CERN Expt. Grey Book) ; Divisional affiliation: EP See record at SLAC Abstract: The K_S -> gammagamma decay rate has been measured with the NA48 detector using a high intensity short neutral beam from the CERN SPS. The measured branching ratio BR(K_S) -> gammagamma = (2.78 +- 0.06_{stat} +- 0.04_{syst}) x 10^{-6}, obtained from 7461 +- 172 K_S -> gammagamma events, is significantly higher than the O(p^4) prediction of Chiral Perturbation Theory. Using a K-L beam the ratio Gamma(K_L-gammagamma / Gamma(K_L -> pi^0pi^0pi^0 = (2.81 +- 0.01_{stat} +- 0.02_{syst}) x 10^{-3} has been measured.