The NA48 liquid-krypton calorimeter

The NA48 experiment at CERN was primarily designed to measure the value of $\Re(\epsilon '/\epsilon)$, the parameter of direct CP- violation, from two-pion decays in simultaneous $K_{L}^{0}$ and $K_{S}^{0}$ beams produced at two different targets. Data for this measurement were taken from 1997 to 2001. The value obtained from the data taken in 1997-1999 is $\Re(\epsilon '/\epsilon) = (15.3 \pm 2.6) \times 10^{-4}$. The remaining data are being analyzed at present. In 2002 and the following years, rare-decay and CP-violation studies will be made in a high-intensity $K_{S}^{0}$ beam and in simultaneous beams of charged kaons, using basically the same apparatus. Photons from neutral-pion decays are detected by a liquid-krypton calorimeter. For the $\Re(\epsilon '/\epsilon)$ measurement it is very important to suppress the huge background from $K_{L}^{0} \to 3\pi^{0}$ decays, which requires very good spatial, energy and time resolution.