NA31 experiment

CP-violation was first theoretically developed for the Standard Model by Kobayashi and Maskawa in 1973 when they introduced a third generation of quark (bottom and top) and thus extended the Cabibbo matrix to the 3x3 CKM matrix, parameterizing the couplings between quark-mass eigenstates and the charge weak gauge bosons.

Determined from the relative decay rates of short- and long-lived neutral kaons into two neutral and charged pions, respectively, the so-called ε'/ε ratio which expresses the relative strength of direct CP-violation[2] was known to be small but expected to be different from zero in the Standard Model.

The measurement of this small deviation from zero was the aim of NA31 in order to prove the existence of direct CP-violation in kaon decays under weak interaction.

The detector was compounded by wire chambers combined with calorimetry in order to determine K0 parameters (e.g. energy, decay vertex).

A great precision on these parameters is required to define well the phase space for all the decay modes which are to be compared.