Antiprotonic X-rays from the helium isotopes have been observed at pressures of 36, 72, 375 and 600 mbar. The antiproton beam from LEAR with momenta of 309 and 202 MeV/c has been stopped at these pressures using the cyclotron trap. The X-rays were detected with Si(Li) and intrinsic Ge semiconductor detectors. Absolute Xray yields were determined and the strong-interaction 2p shifts and the 2p and 3 d broadenings measured to be Ezp=(-17_+4)eV, F2p=(25_+9)eV and Fad=(2.14 _+0.18)meV for /~3He and ezp=(-18+_2)eV, F2. =(45_+5) eV and Fad =(2.36 +0.10) meV for/54He.

New measurements of the pionic double charge exchange on SaFe exhibit a pronounced energy dependence of this reaction at low energies in accordance with similar observations on other nuclei. We show that this peculiar energy dependence finds its natural explanation by a resonance in the 7rNN subsystem with JP = 0-,T = 0 and a mass of 2.065 GeV. PACS: 14.20 P, 24.30, 25.80 The substructure of the nucleon should lead to nontrivial, i.e. non-nucleonic resonances in the B = 2 system. Although such dibaryon resonances have been predicted [1,2] since long, no unambiguous evidence for their existence has been found up to now, despite a vast number of dedicated experiments. In this short note we present first evidence for the existence of a low-lying isoscalar 0-dibaryon resonance embedded in the nuclear medium. Due to its quantum numbers this resonance does not couple to the nucleon-nucleon (NN) channel, where most of the searches have been done, but nearly exclusively to the 7rNN-channel [1,2]. Therefore an ideal reaction to look for resonances in this channel is the pionic double charge exchange (DCX) reaction (Tr+, ~r -) or (Tr-, ~r +) on nuclei [3]. Also, since charge conservation ensures that the reaction takes place on at least two nucleons, the DCX is basically a 2-step process with correspondingly very small cross sections, which, however, are extraordinarily sensitive to small NN distances [4][5][6]. The largest DCX cross sections are expected for transitions to double isobaric analog states (DIAT), since in this case there is maximum overlap between initial and final states. On the other hand ground state transitions (GST) on N = Z nuclei are strongly suppressed [4] in a conventional purely nucleonic mechanism.Experimentally the situation is quite different, in particular for GSTs on nuclei having N = Z in initial or final states. Fig. 1 shows the energy dependence of the forward angle cross sections of the DCX measurements on 12C This work has been funded by the German Federal Minister for Research and Technology (BMFT) under the contract numbers 06 TU 656 and 06 KA 266 and by the DFG (Mu 704/3, Graduiertenkolteg)[7] and 56Fe [8,9]. For the latter reaction, both GST leading to the doubly closed shell nucleus 56Ni and DIAT are presented; the data for 35 and 61 MeV are from this work, for details see ref. [8]. The data on 12C exhibit a broad structure near the energy of the A, and then again a strong increase in cross section towards T,~ = 50 MeV. For the GST on 56Fe the energy dependence is markedly different. The cross section in the A region is lower by an order of magnitude relative to the 12C results, whereas at low energies the cross section exhibits a clear resonancelike energy dependence, reaching at T,~ ~ 50 MeV a cross section a~ large as in case of 12C. The behaviour in the A region is well understood as a consequence of strong pion absorption and successive double A mechanism [10]. The

The ionization of antiprotonic noble-gas atoms due to formation and Auger deexcitation was investigated. The experiment was performed at low target pressures (p & 50 hPa) in order to prevent electron refilling from neighboring atoms. For this reason, the cyclotron trap was used. This device is designed to stop as many particles as possible in a small stop volume at even low gas pressure.The degree of ionization was determined in antiprotonic neon, argon, and krypton by means of measuring yields of circular radiative transitions at relatively high principal quantum numbers. X rays were observed between 1.6 and 21.0 keV using a Si(Li) detector. Complete ionization was found in all three cases.

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X-rays of Balmer and Lyman transitions in antiprotonic hydrogen and of Balmer transitions in antiprotonic deuterium were observed at pressures below 300 hPa using Si(Li) semiconductor detectors. The measurement was performed at the LEAR-facility at a beam momentum of 202 MeV/c. In order to stop antiprotons in a low pressure gaseous target with high efficiency, a novel technique, the cyclotron trap has been used. Absolute yields were determined and compared with cascade calculations. A distinct difference in the cascade of antiprotonic hydrogen and deuterium is found. The parameters of strong interaction in antiprotonic hydrogen are determined to be 81~ = -(620 + 100)eV, Fls= (1130 _+ 170) eV and F2p = (32-t-10) meV.