The performance of the NA48 detector

The NA48 experiment at the SPS accelerator at CERN aims at measuring the parameter of direct CP-violation, $\epsilon′/\epsilon$ with an accuracy of $2 \times 10^{−4}$. Neutral kaons are produced at two targets located at different distances from the detector, thus creating a “$K_{long}$” and a “$K_{short}$” beam. The experiment measures the decays of kaons from these two beams into two neutral or two charged pions. The detection of photons from neutral-pion decay is achieved by means of a liquid-krypton calorimeter. In order to suppress the huge background from $K_{L}^{0} \to 3\pi^{0}$ decays, very good spatial, energy and time resolution are mandatory. The charged mode $(K^{0}_{L,S} \to \pi^{+}\pi^{−}$ decays) is measured with a spectrometer consisting of four drift chambers and a magnet. Decays from the two beams are distinguished by tagging the protons impinging on the second target by means of a scintillator array. Excellent time resolution and high efficiency are indispensable. Moreover, both the detector and the associated electronics operate in a high-radiation environment. This has given rise to specific problems, and the solutions adopted by NA48 are presented.