Search for states using the knock-out reaction at 600 MeV/c

The knock-out reaction has been used to search for narrow states. The experiment was performed using the 600 MeV/c antiproton beam at LEAR and the high-resolution and large-acceptance magnetic spectrometer SPES II. The A-dependence of the annihilation-induced proton spectra has been studied on ²H, ⁶Li, ¹²C, ⁶³Cu, ²⁰⁸Pb and ²⁰⁹Bi. The quasi-free elastic scattering observed in the lighter targets, and the comparison with the free scattering, also observed in this experiment, determine an effective proton number N_eff for 1s- and 1p-shell protons. No evidence for narrow bound or resonant states could be found. Upper limits for their production are one order of magnitude lower than certain theoretical predictions, but consistent with the properties of the interaction, as established from recent elastic and inelastic scattering as well as from studies of antiprotonic atoms.