Observation of a fully reconstructed D0D0 pair with long proper lifetimes in a high resolution hydrogen bubble chamber and the European hybrid spectrometer

Abstract In an experiment with 360 GeV/ c π − beam at the CERN SPS using the high resolution hydrogen bubble chamber LEBC and the European Hybrid Spectrometer, an event has been observed of the type π − p → D 0 D 0 + 8 prongs. The fully reconstructed decay modes are D 0 → K − π + π 0 π 0 and D 0 → K + π + π − π − , with all six charged tracks being detected in the spectrometer and all four photons from the π 0 decays detected in the lead glass gamma detection system. The D 0 has momentum 119.0 ± 0.6 GeV/ c , x F = 0.31, length 4.1 ± 0.1 mm and proper lifetime (2.1 ± 0.1) × 10 −13 s. The D 0 has momentum 78.5 ± 0.3 GeV/ c , x F = 0.19, length 7.5 ± 0.1 mm and proper lifetime (5.9 ± 0.1) × 10 −13 s.