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COSY–Jülich at the Forschungszentrum Jülich–KFA and LEAR at CERN are proton and antiproton cooler rings, respectively, with similar, supplementary, and opposite features at the same time for studying hadronic strong interaction properties. In this written contribution from the two internal target experiments COSY-11 (which is in preparation and will be installed early 1994) and JETSET (which is in a data taking status at CERN) only an outline of the experiment at COSY–Jülich will be given. The interesting results of the JETSET experiment, where the \(\bar p \to \phi \phi \) reaction has been studied at different incident \(\bar pp\) momenta, are still in a preliminary status and have been presented elsewhere, recently (O. Steinkamp at the HADRON’93 conference and K. Röhrich at the PANIC’93 conference, see the respective proceedings). The main physics case for both experiments is the production of mesons and mesonic states involving strangeness.

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Eta-nucleon interaction and eta-nucleus dynamics are discussed. The possibility of using \(\eta \) to probe unnatural-parity nuclear states and to study spin–isospin correlations between two nucleons are demonstrated.

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The GEM detector system is described. Meson production near threshold in \(p + d\) reactions leading to two- and three-body final states is discussed. Details of the search for bound states in the cases of \(\pi ^-\)’s and \(\eta \)’s are given.

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The development of a thin target for liquid hydrogen isotopes with extremely thin windows is described. Its importance for external cooled beams is discussed.

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The characteristics and the working conditions of the new focal plane drift chambers at the magnetic spectrograph BIG KARL are described. One chamber was tested with an 1 GeV electron beam. The drift time spectrum, the efficiency and the position resolution are discussed. A gas supply system for an argon/ethane gas mixture was used. The composition of the detector was monitored by two proportional counters with a \(^{55}\)Fe X-ray source.

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Recent results on \(\omega \pi ^0\) partial-wave analysis and model-independent measurements of rare \(\omega \to \eta \gamma \) decay branching ratio from the GAMS Collaboration are presented. A partial-wave analysis of the 38 GeV/c data confirms the existence of the \(\rho \)(2200) radial-orbital excitation of the \(\rho \)(770) ground-state observed earlier in the same experiment. A new state, \(\rho _5\)(2350), was also observed in this analysis. Masses, widths, and production cross sections for these states are given. The branching ratio for \(\omega \to \eta \gamma \) decay was also measured and is compared with previous model-dependent measurements and with the predictions of a naive quark model. The measured value rules out the destructive \(\omega \)–\(\rho \) interference, thus resolving ambiguity inherent to the earlier experiments.

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Planned high resolution measurements of pions at very small angles in coincidence with neutrons from the \((p,n)\) reaction on \(^{12}\)C at 800 MeV are discussed. The experiment is scheduled for the Neutron Time-of- flight Facility NTOF at LAMPF. It is based upon the results of recent coincidence measurements for \((p,n)\) reactions in the \(\Delta \) resonance region carried out at KEK by J. Chiba et al. The location of the \(\Delta \) peak in the neutron spectrum was found to be dependent on the coincident particles, in qualitative agreement with a theoretical model which suggests that a significant component of the shift is related to spin-longitudinal \((\sigma \cdot q)\) correlations. In that model, coherent pions, pions which traverse the nucleus as in elastic/inelastic pion scattering, are the signature of the spin-longitudinal eorrelations. Some evidence for coherent pions can be found in the KEK coincidence data. The experiment scheduled for this summer at LAMPF is a measurement of the total energy of the \(n + \pi ^+\) with much higher resolution than the KEK experiment, so that the ground state of \(^{12}\)C can be clearly separated from the low-lying excited states. A later measurement of the neutron polarisatiou in coincidence with the pions is expected to determine whether the spin-longitudinal response is strongly enhanced.

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Charge exchange reactions to the \(\Delta \)-resonance region reveal a systematic downward energy shift of the \(\Delta \) peak position in nuclei as compared to the proton target. Part of this shift is caused by a coherent medium effect on the spin-longitudinal response function. The coherent effect is produced by the attractive \(\pi \) exchange interaction between \(\Delta \)-hole states in the medium. This shift is consistent with pion total cross section data. No shift is observed in the spin-transverse channel. In order to obtain more evidence for the coherent mode, exclusive cross section data of the \(^{12}\)C(\(^3\)He,\(t \pi ^+\))\(^{12}\)C(g.s.) reaction are analyzed. We observe a strong energy shift in the coherent pion production cross section. The coherent pions have a peak energy of \(E_{\pi } = 250\) MeV and a strongly forward peaked angular distribution, i.e. most of the pions can be detected in the direction of the momentum transfer \(\vec {q}\). In addition it is shown that the quasi-free decay is suppressed in the energy domain where the decay nucleon has a small energy. At SATURNE a \(\pi ^+\) — coincidence spectrum was isolated where pions only inside a certain energy domain were taken into account. The features mentioned above prove that this spectrum consists to a great extent of coherent pions.

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Differential cross sections for \(\omega \) production at 180\(^{\circ }\) in the c.m. system were measured from threshold up to a c.m. momentum of 625 MeV/\(c\). The cross sections observed at low c.m. momenta are not yet understood theoretically. Data are compared to the prediction of an empirical model by C. Wilkin [1], which provides a first step towards understanding near threshold w production.

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The Time of Flight Spectrometer offers the possibility to measure charged particles with a \(4\pi \) acceptance. By measuring the two protons of the reaction \(pp \to pp\eta (\eta ^{\prime })\) or the \(^3\)He of the reaction \(pd \to ^3\)He, \(\eta (\eta ^{\prime })\) the \(\eta (\eta ^{\prime })\) can be detected in the missing mass distribution. These measurements will cover momenta and scattering angles which have not been measured up to now.

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The resonance-like excitation function that is observed in (\(\pi ^+,\pi ^-)\)-reactions near 50 MeV in all investigated nuclei, has not been explained by conventional reaction mechanisms. We demonstrate that the world data base is reproduced with few parameters assuming a narrow resonance in the \(\pi NN\)-subsystem with mass 2065 MeV, \(J^P = 0^-\) and isospin even.

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To complement planned experiments in which deeply bound pionic atom states are to be produced, the reaction \((\pi ^-, \pi ^0)\) was examined close to threshold. Branching ratios for that reaction on CH\(_2\), \(^{27}\)Al, \(^{31}\)P, \(^{32}\)S, \(^{45}\)Sc, and \(^{115}\)In were determined experimentally. The results were compared with previous experimental work and with a calculation based on the Panofsky ratio. The results can be understood in terms of the shell structure of the target nuclei.

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The \(\Delta \)(1232) resonance dominates pion-nucleon scattering at energies below 300 MeV, the region in which pion-nucleus scattering has been well studied using spectrometers at the meson factories. Above this energy region few pion-nucleus scattering data exist. Recently, spectrometers at Brookhaven, LAMPF, KEK, and DUBNA have been used to obtain initial data for pion-nucleus scattering in this energy region. In this talk, we review some data that have been obtained using the LAS spectrometer at LAMPF.

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Gross properties of the interaction of pions, K\(^+\) and K\(^-\) with nuclei are reviewed. The pion-nucleus interaction below 200 MeV is related to the mean free path of pions in nuclei and the difference between the region below and above 50 MeV is emphasized. At zero energy the ‘missing’ \(s\)-wave repulsion in pionic atoms is still an open problem. Kaonic atoms have been analysed with a density dependent interaction that connects smoothly at low densities to the repulsive interaction expected for free nucleons. Total cross sections for K\(^+\) nucleus interaction have been analysed with various prescriptions and improved fits have been obtained when an explicit \(p\)-wave term is included and the \(s\)-wave term is enhanced in the nuclear medium.

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A large variety of experimental data on pion-nucleus interactions in the bombarding energy range of 0–3000 MeV, on nucleon-induced plan production, and on cumulative nucleon production, when a two-step process of pion production followed by absorption on nucleon pairs within a target is taken into account, are analyzed with the Cascade-Exciton Model of nuclear reactions. Comparison is made with other up-to-date models of these processes. The contributions of different pion absorption mechanisms and the relative role of different particle production mechanisms in these reactions are discussed.

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We report on a meson exchange model of the pion-nucleon interaction which has recently been developed by our group. Our model accounts for the \(\pi N\) phase shifts in the whole elastic region of the interaction, the low energy parameters and — by an extrapolation of the model to the Cheng–Dashen point — also the \(\pi N\) \(\Sigma \) term. Starting from a recent model of medium modifications of the \(\pi \pi \) scattering amplitude we also investigate medium modifications of correlated \(2\pi \)-exchange in the \(\pi N\) interaction. These modifications give rise to a considerable source of repulsion in the isoscalar \(S\)-wave pion optical potential and thus tend to resolve a longstanding puzzle.

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A brief review and discussion is made of a few topics concerning the pion nucleus interaction at low energies and above the delta region. A many body description of the pion nuclear optical potential at low energies is presented by means of which one obtains a fair reproduction of the data of pionic atoms, including the former “anomalous atoms”, and of the scattering data at low energies in all different reaction channels: elastic, quasielastic and absorption. A connection between the second order optical potential and the “absorption contribution” to the double charge exchange process is made and results are shown for this latter reaction. Of particular interest is the application made of pionic atom data to extract information on neutron distributions in nuclei. At high energies we show some small but systematic discrepancies between theory and experiment which call for some explanation. On the other hand the former and large discrepancies between theory and experiment in single and double charge exchange find a natural explanation by means of the core polarization which renormalizes the isovector \(\pi N\) scattering amplitude.

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Studies of the \(^{12}\)C\((p,\pi )\) and \(^{12}\)C\((p,2\pi )\) reactions on the Indiana Cooler Ring using recoil ion detection will be described. This method allows to simultaneously measure the cross sections for pion production in the different isospin channels with the same target and detection system. The use of very thin internal targets in a storage ring environment greatly reduces the energy resolution limits set by the energy loss of the recoiling ions in the target.

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In contrast to \((p,\pi )\) reactions on nuclear targets which seem to be difficult to interpret, recent pion production experiments with systems with two or three nucleons, very close to threshold, have led to important new insights. In these studies the use of a storage ring with an internal target has been instrumental. Recent research with the Indiana Cooler is illustrated by two specific examples. In the reaction \(pd \to pd\pi ^0\), possible medium modifications of pion production have been studied, while in \(pp \to pp\pi ^0\) we have found experimental evidence for the enhancement of the axial current in nuclear systems.

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We present data on the decay of the \(\Delta \) resonance excited in \(^1\)H, \(^2\)H, \(^4\)He, \(^{12}\)C and \(^{208}\)Pb by the (\(^3\)He,\(t\)) reaction at 2 GeV bombarding energy. The quasi-free decay of the \(\Delta \) resonance and the absorption process on a \((p,n)\) pair are clearly observed. We also find evidence for coherent pion production.

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A microscopical many-body calculation of the self-energy of a positive kaon interacting with a nucleus is carried out for kinetic energies \(T_K\) up to 500 MeV. On top of the well known contribution of the impulse approximation, we have considered the kaon coupling to the pions in the nucleus. Previous approximations for the pionic cloud contribution, specially on the imaginary part, are shown to be inadequate. We also find and evaluate new contributions to the imaginary part from the pionic cloud which were not previously considered. The results for the total and differential cross sections are satisfactory after these new contributions are included, but uncertainties remain in the real part.

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The experiments described in this contribution address the excitation of the nucleon in the second resonance region. The results of total cross section measurements with a tagged photon beam at energies close to the \(\eta \)-production threshold are reported.

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At the CELSIUS cooler storage ring in Uppsala, a detector facility for the study of meson production in light ion collisions has recently come into operation. Neutral mesons, i.e. \(\pi ^0\) and \(\eta \), are detected through their decay into two photons. Charged particles and nuclei recoiling in the forward direction are observed in coincidence with the produced mesons. In this paper, the current status of the detector performance is presented together with the experimental program on meson production.

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The numerical values for the pion refractive index, pion phase velocity and pionic Cherenkov thresholds in heavy nuclei are presented. The \(\pi ^+\)-differential cross sections for the coherent pions emitted as nuclear mesonic Cherenkov radiation are calculated. Three pionic Cherenkov bands: \(CB1 (\omega =190\div \) 320 MeV), \(CB2 (\omega =900\div \) 960 MeV) and \(CB3=80\div \)1000 GeV) are predicted.

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A short review of recent measurements with antiprotonic atoms is given. It concentrates on results related to mesonic interactions: spin dependence of \(N \bar N\) forces and measurements of neutron haloes in heavy nuclei. The latter involve nuclear interactions of mesons produced in antiproton annihilation.

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The problems of particle interferometry arising from the finite size of the particle sources, various types of the sources, resonances, final state interactions, rescattering and absorption effects are discussed.

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The determination of the pseudoscalar mixing angle from \(\eta \) and \(\eta ^{\prime }\) production in proton–proton collisions and the extraction of the \(\pi \pi \) and \(\pi \eta \) phase shifts at low energies are central topics of the experimental program at COSY. These mesons are produced abundantly in \(\bar pp\) annihilation at rest. The kinematical differences of the two production modes are pointed out. The extraction of the pseudoscalar mixing angle from branching ratios for \(\bar pp\) annihilation requires dynamical corrections due to the fact that the \(\eta \) and \(\eta ^{\prime }\) have different masses. It is argued that the test of dynamical corrections is important for our understanding of \(NN\) and \(N \bar N\) interactions.

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The annihilation of stopped antiprotons at the nuclear surface produced 2–8 pions. Some of them enter the nucleus and can heat it up to nearly 1 GeV excitation energy. We measured with a new double-arm fission fragment spectrometer the masses and kinetic energies of both fragments and their folding angle. The number of particles emitted before and after scission was deduced. Absolute fission rates are determined for some targets. Particle spectra and the distribution of residual nuclei were measured. The neutron-to-proton density ratio in the periphery of nuclei was determined with a new neutron halo effect during the antiproton annihilation. Detailed intranuclear cascade calculations reproduce most of the experimental results.

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Mesonic models predict violation of SU(2) symmetry in the nucleon sea which seems to be necessary to explain the violation of the Gottfried Sum Rule. Careful analysis of the Drell–Yan processes in \(p\)-\(p\) and \(p\)-\(n\) collisions should provide complementary data to the Gottfried Sum Rule on the \(\overline d / \overline u\) asymmetry. Large one-loop corrections in semileptonic hyperon decays can be compensated by a tiny shift in the values of D and F. The meson cloud is an important ingredient in understanding the spin structure of the nucleon.

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We analysed the experimental data on strange particle production in antiproton nucleus annihilations. Following the standard conventional annihilation picture we account for the dominant reaction channels in order to calculate the cross sections observed. The experimental data on single strangeness production are reproduced by the calculations and account for the annihilation on a single nucleon followed by subsequent rescattering proceeding in the hadron phase. The contribution of the discussed process underestimates the experimental results on double strangeness production by an order of magnitude. One of the possible explanation for this discrepancy may be related with the B > 0 annihilation.

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The symmetries in some interesting \(\eta \) meson and charge symmetry breaking processes are under observation. The relevant and crucial few body reactions are presented, with the particular attention put to determining the down-up quark mass difference. The short presentation of the state of the art of world knowledge is summarized.

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The future 15 GeV 100% duty-cycle electron accelerator for hadronic Physics is presented. For a given set of Physics requirements, a three-pass recirculating linear accelerator has been chosen within an European collaboration. This document will explain the choice of the scenario and give a general overview of the machine.

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Progress in meson–nucleus interactions is sketched, including meson production, absorption, and scattering. Extensions to eta meson interactions are becoming very important as extensions to the large body of pi meson data, and several new experiments with positive \(K\) mesons have been completed. \(\pi \) meson reactions themselves have been extended to higher energies, to more complete coverage of the reaction products, and in production, to energies strikingly near threshold.