Giles Barr

Abstract:

We present the first observation of the decay KS → π⁺π^-e⁺e^- based upon the data collected in 1998 by the NA48 experiment at CERN. We have identified a clean sample of 56 events with negligible background contamination. Using KL → π⁺π^-πD/⁰ decays as normalization sample, the branching ratio is measured to be BR(KS → π⁺π^-e⁺e^-) = [4,5 ± 0.7 (stat) ± 0.4(syst)] × 10^-5. This result is in good agreement with the theoretical expectations from the mechanism of inner bremsstrahlung. © 2000 Elsevier Science B.V.

Abstract:

The decay rate of K(S) → γγ has been measured with the NA48 detector at the CERN SPS. A total of 149 K(S) → γγ events have been observed. The branching ratio is determined to be (2.58 ± 0.36(stat) ± 0.22(sys)) x 10-6. (C) 2000 Elsevier Science B.V.

Abstract:

The NA48 experiment at the CERN SPS accelerator is making a measurement of the direct CP violation parameter epsilon'/epsilon by comparing the four rates of decay of K-S and K-L into 2(pi)(0) and pi(+)pi(-). To reconstruct the decays into 2 pi(0) the information from the almost 13500 channels of a quasi-homogeneous liquid krypton electromagnetic calorimeter is used. The readout electronics of the calorimeter has been designed to provide a dynamic range from a few MeV to about 50 GeV energy deposition per cell, and to sustain a high rate of incident particles. The system is made by cold charge preamplifiers (working at 120 degrees K), low-noise fast shapers followed by digitizer electronics at 40 MHz sampling rate that employs a gain switching technique to expand the dynamic range, where the gain can be selected for each sample individually (i.e. every 25 ns). To reduce the amount of data collected the system contains a zero suppression circuit based on halo expansion.