$\overline{p} p \to 2 \pi^{+} 2 \pi^{-}$ annihilation at two different target densities

The OBELIX spectrometer (installed at the low energy antiproton ring of CERN) has taken data on the NN annihilation in liquid hydrogen and in gaseous hydrogen at 3bar. The results of the spin-parity analysis on the pp annihilation into four charged pions at this two target densities are here briefly described. (18 refs).