KABES: a novel beam spectrometer for NA48

In order to investigate predictions concerning CP violation in the charged kaon sector, a new beam line providing concurrently K+ and K− has been constructed at CERN for the NA48/2 experiment. Several modifications and upgrades have been made in the apparatus; one of them being the implementation of a beam spectrometer named KABES. This detector is based on the time projection chamber principle; the amplification of the ionization signal is achieved by using Micromegas devices. The performance of KABES is found to be excellent in high-intensity hadron beams. The achieved space resolution of 100 μm provides a measurement of track momentum with a precision better than 1% and the time resolution, better than 1 ns, allows the charged kaons in NA48 to be identified with almost no ambiguity. The measurement of the direction and momentum of the K+ and K− tracks makes possible the precise study of their decay modes, particularly those for which one or more particles escape detection in the NA48 detector.