The European hybrid spectrometer

Abstract The final version of the European hybrid spectrometer (EHS) is described. EHS was used in the NA27 experiment to study charm particles produced in 360 GeV c π − p and 400 GeV c pp interactions. A rapid cycling, high resolution bubble chamber (LEBC) produced bubbles of 17 μm diameter which were measured with a precision of 2.5 μm. Short-lived charm particles are observed with an efficiency up to 90% (D ± ). The spectrometer accepts 70% of all particles produced, including approximately 100% of those in the forward hemisphere and the momenta of charged particles are measured to better than 1% over the whole momentum range. The charged particle identification detectors give information on 84% of the spectrometer tracks, half of which obtain unique identification. Two lead glass detectors measure the energy of electromagnetic showers such that the π 0 mass distribution has a fwhm of 20 MeV c 2 . Hadronic showers are measured with two iron/scintillator calorimeters. The mass resolutions are 3.0, 0.9 and 11 MeV c 2 for K 0 , Λ 0 and D − charged particles respectively. The D 0 mass is measured to be (1865.1 ± 1.8 ± 0.8) MeV c 2 .