Observation of the fully reconstructed $D^{0}\overline{D}$$^{0}$ pair with long lifetimes in a high resolution hydrogen bubble chamber and the European Hybrid Spectrometer

In an experiment with a 360 GeV/c $\pi^{-}$ 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 $\pi^{-}p$ to $D^{0}D^{0}+8$ prongs. The fully reconstructed decay modes are $D^{0} \rightarrow K^{-}\pi^{+}\pi^{0}\pi^{0}$ and $D^{0} \rightarrow K^{+}\pi^{+}\pi^{-}\pi^{-}$, with all six charged tracks being detected in the spectrometer and all four photons from the $\pi^{0}$ decays detected in the lead glass gamma detection system. The $D^{0}$ has momentum $119.0 \pm 0.6$ GeV/c, $x_{F}=0.31$, length $4.1 \pm 0.1$ mm and proper lifetime $(2.1 \pm 0.1)\times10^{-13}$s. The $D^{0}$ has momentum $78.5 \pm 0.3$ GeV/c, $x_{F}=0.19$, length $7.5 \pm 0.1$ mm and proper lifetime $(5.9 \pm 0.1)\times 10^{-13}$s.