The experiments NA48 and NA62 at CERN

Currently, a new experiment (NA62) is in the phase of design and development. This experiment is aiming at measuring approx. 100 decays of the very rare channel K+ -> π+ν ν .


The experiment NA48 is located at the Super Proton Synchrotron (SPS) accelerator at CERN/Geneva, studying decays of neutral and charged kaons and hyperons, with a particular focus on the measurement of direct violation of the CP symmetry in kaon decays. The study of symmetry violation under Parity transformation P (that mirrors the space coordinates) and Charge conjugation C (exchanging each particle with its antiparticle) is of great interest, giving information about the structure of the weak interaction, possible new physics beyond the Standard Model as well as the origin of the asymmetry between matter and antimatter. Till recently, direct CP violation has been observed only in the system of neutral kaons.

Furthermore, semileptonic kaon decays are well suited for the determination of the Kobayashi-Maskawa matrix element |Vus|, the so-called Cabibbo angle. NA48 has performed several of the world-beating measurements of this parameter. Finally, we study extremely rare kaon decays down to branching ratios of the order 10-9 (1 decay out of 1 billion, looking for a needle in a haystack, so to speak). Apart from a deeper understanding of the weak interaction, it is possible to study various parameters of the Chiral Perturbation Theory (ChPT). The most precise measurements of the pp scattering lengths and, as a consequence, of the leading ChPT parameter <0|qq|0> have been performed by NA48.

NA48 - One detector for three experiments

The first period of data taking by the NA48 experiment was in 1997. Until the end of 2001, KL and KS decays were recorded simultaneously to measure the parameter Re(e'/e) of direct CP violation in the system of neutral kaons. In addition, we measured several rare and very rare KL decays.

In 2002, the beam configuration was changed for the successor experiment NA48/1, stopping the KL beam, but increasing the intensity of KS mesons by a factor of ~200 to study rare KS and  hyperon decays. The experiment holds the world's largest sample of KS and Ξ0 decays.

For 2003 and 2004, the beam line was changed again to study decays of charged kaons in the NA48/2 experiment. The main objective is the search for CP violation in K- and K+ decays, but we focus on the measurement of various rare decays as well. With the final NA48/2 experiment, the data taking was completed.