Updated DIRAC spectrometer at CERN PS for the investigation of ππ and πK atoms

The DIRAC spectrometer installed at CERN PS was redesigned and upgraded in order to study simultaneously Aππ and AπK atoms, namely the bound states of π+π–, and π+K–, π–K+ mesons. The detector system which is able to accept a high intensity beam such as 2 - 6 × 1011 primary protons per second, the electronics and the data-acquisition system adapted to handle very large amount of data actually allowed to identify successfully π, K, p, e and µ and to give the possibility to select π-π and π-K pairs in the off-line analysis. The setup’s capability of giving a high resolution in the reconstruction of the relative momentum in the pair-CMS Q gave the possibility to analyze the distributions of its components, in order to identify the signal from pairs originating from hadronic atoms, and to measure their lifetimes in the ground state and π-π and π-K s-wave scattering lengths. The setup also allowed to study long-lived excited states of π-π atoms