International Journal of Modern Physics A

Excitation of the nucleon at low Q² and energies up to several GeV reveals clearly measurable structures that indicate the existance of resonances. A major goal of experiments carried out at the accelerator facility ELSA in Bonn/Germany is to explore this resonance structure, which gives valuable input to models describing the QCD structure of the nucleon. Resonance contributions for nuclear reaction channels, such as single pion, two pion and eta production from the experiments can be given using the Bonn-Gatchina partial wave analysis¹. The talk at the conference MESON 2008 in Krakow gave an overview of results from experiments at ELSA and plans for the near future.

The KEK experiment E570 has measured the Balmer-series x-rays of kaonic ⁴He atoms using large-area silicon drift x-ray detectors (SDDs) in order to study the low-energy -nucleus strong interaction. The energy of the 3d → 2p transition was determined to be 6467 ± 3(stat) ± 2(syst) eV. The resulting strong-interaction energy-level shift is in agreement with theoretical calculations, thus eliminating a long-standing discrepancy between theory and experiment. Using a similar setup, the E17 experiment at J-PARC, the first experiment to be carried out in the hadron hall of J-PARC, will measure the 3d → 2p x-rays of kaonic ³He.

With precision X-ray spectroscopy of kaonic hydrogen at the DAΦNE electron-positron collider at Laboratori Nazionali di Frascati the chiral symmetry breaking scenario in the strangeness sector will be investigated by studying the K^-p s-wave interaction at threshold. This is possible by observing the strong interaction induced shift and width of the 1s state in kaonic hydrogen atoms. The results of the first measurement at LNF with DEAR (DAΦNE Exotic Atom Research) will be given and the new SIDDHARTA (Silicon Drift Detector for Hadronic Atom Research with Timing Application) project will be described, which is aiming at a substantial improvement of the preceding DEAR result.

The FINUDA spectrometer is installed at one of the interaction points of the DAΦNE e⁺e^- collider in Frascati(I). By stopping the low energy K^- from the ɸ(1020) decays, FINUDA performed a rich program of studies of K^- induced interactions on a set of nuclear targets. A survey of the results will be given, with emphasis on the study of non-mesonic weak decays of Λ-hypernuclei and on the search for deeply bound kaonic nuclear clusters.

The extracted s-wave scattering amplitude from both the polarized and unpolarized d + d → ⁴He + η reaction at 2385.5 MeV/c allowed to determine the scattering length which fulfills the requirements for bound η. In the p + ²⁷Al → ³He + p + π^- + X reaction studied at recoil free kinematics the η meson is produced almost at rest and so it can be bound with enhanced probability. This state proceeds via N*(1535) resonance and the decay products proton and pion emitted into opposite direction are detected in concidence with ³He produced at zero degree. Under these conditions some hints for bound state can be observed with an upper limit of the cross section of ≈ 0.5 nb.

We consider two ways of the experimental determination of the S-wave ππ scattering lengths: from K → 3π decays and from K_e4 decays. In both cases the unitary cusps, which emerge due to the difference in the charged and neutral pion masses, play a crucial role. We construct a systematic effective field theory framework which can be used to describe decay amplitudes in the cusp region.

The latest results from the NA48/2 collaboration on charged kaon decays will be reviewed in this paper. The high statistics available, collected during 2003 and 2004 runs, allows the study of charged kaon decays up to branching ratios (BR) of ~ 10^-8. The status of the analyses of several radiative decays (K^± → π^±π⁰γ, K^± → π^±γγ, K^± → π^±e⁺e^-γ and K^± → π^±e⁺e^-) will be discussed, including BR measurements and possible ChPT tests.

The isovector–vector and the isovector–axial-vector current are related by a chiral transformation. These currents can be called chiral partners at the fundamental level. In a world where chiral symmetry was not broken, the corresponding current-current correlators would show the same spectral information. In the real world chiral symmetry is spontaneously broken. A prominent peak — the ρ-meson — shows up in the vector spectrum (measured in e⁺e^--collisions and τ-decays). On the other hand, in the axial-vector spectrum a broad bump appears — the a₁-meson (also accessible in τ-decays). It is tempting to call ρ and a₁ chiral partners at the hadronic level. Strong indications are brought forward that these "chiral partners" do not only differ in mass but even in their nature: The ρ-meson appears dominantly as a quark-antiquark state with small modifications from an attractive pion-pion interaction. The a₁-meson, on the other hand, can be understood as a meson-molecule state mainly formed by the attractive interaction between pion and ρ-meson. A key issue here is that the meson-meson interactions are fixed by chiral symmetry breaking. It is demonstrated that one can understand the vector and the axial-vector spectrum very well within this interpretation. It is also shown that the opposite cases, namely ρ as a pion-pion molecule or a₁ as a quark-antiquark state lead to less satisfying results. Finally speculations on possible in-medium changes of hadron properties are presented.

The rich experimental landscape of exclusive vector meson production at the high energy electron–proton collider HERA is reviewed, with emphasis on the transition from soft to hard diffraction and QCD interpretations.

This paper describes the methods and goals of the spectroscopy programme of COMPASS using hadron beams, and reports on first results from a short pilot run using a 190 GeV/c pion beam, carried out in 2004. A partial wave analysis of the reaction π^-N → π^-π^-π⁺ N' shows significant production of a state with spin-exotic quantum numbers J^PC = 1^-+ at 1.6 GeV/c².

The ABC effect – an intriguing low-mass enhancement in the ππ invariant mass spectrum – is known from inclusive measurements of two-pion production in nuclear fusion reactions. Exclusive measurements have been carried out at CELSIUS/WASA and WASA@COSY for the fusion reactions leading to d, ³He and ⁴He. They all reveal this effect to be a σ channel phenomenon combined with a resonance-like behavior in the total cross section. The latter points to the formation of an isoscalar dibaryonic resonance, which couples to the pn channel as well as to a ΔΔ intermediate state.

One major focus of the physics studied at the COoler SYnchrotron COSY of the Forschungszentrum Jülich is the production of mesons and hyperons in the hadron-hadron scattering with the aim to investigate relevant production processes, interactions of the participating particles as well as symmetries and symmetry breaking. Due to the excellent experimental conditions at COSY also single- and double-polarization measurements can be performed with high reaction rates. This contribution gives an overview about the physics program which is currently under investigation at the three big COSY installations ANKE, COSY-TOF and WASA-at-COSY.

The production of mesons containing strangeness is studied using elementary and heavy-ion probes with the FOPI detector at GSI-SIS. The observed inclusive cross section of neutral kaons points to an in-medium modification in the production. The momentum dependent ratio of cross sections of light and heavy target nuclei turns out to be a sensitive observable for the in-medium potential strength in transport codes. The experiments will continue studying the production of charged kaons with elementary probes including the search for deeply bound antikaon nuclear clusters in proton proton collisions.

We reported the observation of Y(2175) in ϕf₀(980) mass spectrum in J/ψ → ηϕf₀(980) with f₀(980) → π⁺π^-, the partial wave analysis results of J/ψ → γϕϕ, the measurement of , , and the observation of threshold enhancement in , based on 5.8 × 10⁷ J/ψ events collected at BESII. The measurement of ψ(2S) radiative decays with 1.4 × 10⁷ ψ(2S) events as well as the measurement of D decay branching fractions with 33 pb^-1 data collected at and around 3.773 GeV are also presented.

The physics program of the Crystal Ball spectrometer at MAMI-C began in early 2007. Experiments utilize the upgraded electron accelerator that provides high intensity beams of circularly and linearly polarized real photons with maximum energy of 1.5 GeV. The highly segmented nearly 4π acceptance detection system consists of the Crystal Ball, particle identification detector and versatile endcap TAPS. A wide range of physics topics is under study including the production and decay of η, ω, and η' mesons, the investigation of coherent meson photoproduction on nuclei, measurements of polarization and double polarization observables in meson photoproduction on proton and neutron. The current status of the experiment and some preliminary results are reported.

Results obtained in π^- Be interactions at 27, 36.6 and 41 GeV/c are presented. Decay f₁(1285) → π⁺π^-π⁰ is observed; the dominant mechanism of the isospin symmetry violation in this decay is the a₀(980) – f₀(980) mixing. The intensity of this mixing is measured. An upper limit on possible f₁(1285) – a₁(1260) mixing is obtained. Preliminary results of a study of (ωɸ) system are shown. Plans for coming upgrade of the detector are presented.

With the new stage of the MAMI accelerator, the physics program on hadron physics at MAMI will be extended up to an end point energy of 1.5 GeV. A few selected experiments on electro production are presented to show examples on nucleon structure and baryon resonance structure studies. The photo production program at MAMI was described in a separate talk in this conference.

Theoretical calculations predict the modification of properties of vector mesons, such as a shift in their masses and/or broadening of their widths in dense nuclear matter. These effects can be related to partial restoration of chiral symmetry at high density or temperature. The light vector mesons (ρ, ω, and ϕ) were photo-produced on ²H, C, Ti, Fe, and Pb targets at the Thomas Jefferson National Laboratory using the CEBAF Large Acceptance Spectrometer (CLAS). The data were taken with a beam of tagged photons with energies up to 4 GeV. The properties of the ρ vector meson at normal nuclear densities and zero temperature,were investigated via their rare leptonic decay to e⁺e^-. This decay channel is preferred over hadronic modes in order to eliminate final state interactions in the nuclear matter. A combinatorial background was subtracted from the invariant mass spectra using a well-established event-mixing technique. The ρ meson mass spectrum was extracted after the ω and ϕ signals were removed in a nearly model-independent way. The rho meson mass distributions were extracted for each of the targets. Comparisons were made between the ρ mass spectra from the heavy targets (A > 2) with the mass spectrum extracted from the deuterium target. With respect to the ρ-meson mass, we obtain a small shift compatible with zero. Also, we measure widths consistent with standard nuclear many-body effects such as collisional broadening and Fermi motion.

In this experiment, due to the long lifetimes and momenta greater than 0.8 GeV, the ω and ϕ mesons have a high probability of decaying outside the nucleus in their vacuum state. However, their in-medium widths can be accessed through their absorption inside the nucleus. Preliminary results on the ratios of the nuclear transparencies of the ω and ϕ mesons as a function of the number of target nucleons A, have been obtained and indicate a substantial widening in the medium.

The HADES experiment, installed at GSI, Darmstadt, measures di-electron production in A + A, p/π + N and p/π + A collisions. Here, the π⁰ and η Dalitz decays have been reconstruced in the exclusive p + p reaction at 2.2 GeV to form a reference cocktail for long-lived di-electron sources. In the C+C reaction at 1 and 2 GeV/u, these long-lived sources have been subtracted from the measured inclusive e⁺e^- yield to exhibit the signal from the early phase of the collision. The results suggest that resonances play an important role in dense nuclear matter.

The CLAS Collaboration is operating the CLAS detector at theThomas Jefferson National Laboratory (JLab) in USA. The unique combination of the detector large acceptance and high intensity of the continuous electron beam of CEBAF has opened the way to a comprehensive study of the hadrons structure in a kinematic domain between nuclear and particle physics. Meson spectroscopy plays a central role in the physics program of the Collaboration. Many exclusive channels have been studied with virtual and real photon beams in a wide kinematic domain providing key information about the hadron structure as well as the reactions dynamic. In this contribution, the rich physics program covered by present and future experiments will be reviewed.

The Belle experiment at the KEKB asymmetric-energy e⁺e^- collider provides an excellent environment not only for B physics, but also for studies in charm and charmonium spectroscopy. The paper gives a summary of recent Belle achievements in this field.

We report on the most recent progress in charm and charmonium spectroscopy. Many new states have been discovered in the high statistics data sets from B-factories and CLEO experiment. Some of these particles are candidates for being exotic non states. We will concentrate on results obtained at the BABAR experiment which are based on up to ≈ 470 fb^-1 of e⁺e^- collisions at the ϒ(4S) resonance at the PEP-II linear accelerator at SLAC.

We present the current status of the study at the Tevatron, of the exclusive processes: and , produced via two photon interactions; , and from Double Pomeron Exchange (DPE); and, , and ; from photon-pomeron fusion (photoproduction). In closing we briefly discuss the plans for, and benefits of, studying exclusive physics at the LHC.

The DAΦNE collider has been recently upgraded in order to implement a new collision scheme based on large Piwinski angle and cancellation of the synchro-betatron resonances by means of electromagnetic sextupoles (Crab-Waist compensation). The novel approach has proved to be effective in improving beam-beam interaction and collider luminosity. The results and the measurements taken during commissioning as well as the perspectives for the SIDDHARTA run are presented and discussed.

The PANDA (AntiProton Annihilations at Darmstadt) experiment will investigate and collisions in the anti-proton beam momentum range p_beam = 1–15 GeV/c, corresponding to a center-of-mass energy of , at the future FAIR (Facility for Anti-Proton and Ion Research) accelerator complex at GSI, Darmstadt, Germany.

The Beijing Electron Collider has been upgraded (BEPCII) to a two-ring collider with a design luminosity of 1 × 10³³cm^-2s^-1 at a center-of-mass energy of 3.78 GeV. It will operate between 2 and 4.6 GeV in the center of mass. With this luminosity, the BESIII detector will be able to collect, for example, 10 billion J/ψ events in one year of running. This will be a unique facility in the world opening many physics opportunities. BEPCII and BESIII are both currently being commissioned, first events have been obtained, and data taking will take place in fall 2008.

Using new data on pion production in p+p interactions from the NA49 experiment, it is demonstrated that the detailed features of double differential pion cross sections are well reproduced over most of the phase space from the decay of a representative sample of known mesonic and baryonic resonances.

Thirteen resonances reaching up to spin four tensor-mesons and including the newly measured N* states up to the N*(1680) have been used. The p_T integrated Feynman x_F distributions in the high-x_F region 0.4 < x_F < 0.9 are quantitatively reproduced as well as the p_T distributions up to 2 GeV/c and beyond at all x_F.

In both these phase space regions direct effects of parton dynamics such as valence quark fragmentation or parton scattering are generally evoked in order to provide a basis of understanding. The saturation of the measured yields by resonance decay casts a doubt on these assumptions.

The mechanism by which a resonance may be attracted to a sharp threshold is described with several examples. It involves a threshold cusp interfering constructively with either or both (i) a resonance produced via confinement, (ii) attractive t- and u-channel exchanges. More generally, it is suggested that resonances are eigenstates generated by mixing between confined states and long-range meson and baryon exchanges.

We present a set of once subtracted dispersion relations which implement crossing symmetry conditions for the ππ scattering amplitudes below 1 GeV. We compare and discuss the results obtained for the once and twice subtracted dispersion relations, known as Roy's equations, for three ππ partial JI waves, S0, P and S2. We also show that once subtracted dispersion relations provide a stringent test of crossing and analyticity for ππ partial wave amplitudes, remarkably precise in the 400 to 1.1 GeV region, where the resulting uncertainties are significantly smaller than those coming from standard Roy's equations, given the same input.

This is a summary of the MESON2008 workshop in Kraków. The original powerpoint summary with all the figures can be found on the conference webpage and in the proceedings of the original talks in this volume. These Proceedings of the summary will therefore not contain the original figures which can be looked up at the two locations mentioned.

The positive parity scalar and axial-vector charmed strange mesons are generated by coupled-channel dynamics through the s-wave scattering of Goldstone bosons off the pseudoscalar and vector D(D_s)-meson ground states. The attraction leading to the specific masses of these states reflects the chiral symmetry breaking scale which characterizes the Weinberg-Tomozawa interaction in the chiral Lagrangian. Chiral corrections to order are calculated and found to be small. The and mesons decay either strongly into the isospin-violating π⁰D_s and channels or electromagnetically. We show that the π⁰-η and (K⁰D⁺-K⁺D⁰) mixings act constructively to generate strong widths of the order of 140 keV. The one-loop contribution to the radiative decay amplitudes of scalar and axial-vector states is calculated using the electromagnetic Lagrangian to chiral order . We show the importance of taking into account processes involving light vector mesons explicitly in the dynamics of electromagnetic decays to obtain a satisfactory description of the available data.

I discuss exclusive production of the χ_c(0⁺) and f₀(1500) mesons in pp and collisions at high and intermediate energies. QCD diffractive mechanisms as well as some non-diffractive mechanisms are included. Different unintegrated gluon distribution functions (UGDF) are used. Some differential distributions are shown and discussed.

In this representation, some recent results from BESII J/ψ decays have been represented, including the analysis of which is helpful to understand the threshold enhancement structure founded in is from pure final states interference(FSI) or not and the analysis of the enhancement based on it some discussion will be hold if the structure is same one as the baryon excited states N* found in .

We report on recent measurements of branching fractions and CP violation observables of selected charmless hadronic B decays obtained from data collected with the BABAR detector at the PEP-II asymmetric-energy collider, operating at the ϒ(4S) resonance.

We report on our recent calculations of and multi– nuclei. Calculations were performed fully self-consistently across the periodic table using the relativistic mean-field approach. We aimed at detailed analysis of dynamical processes and various thresholds that determine the K^- absorption width. Further, we studied the behavior of the nuclear medium under the influence of increasing strangeness in order to search for condensation precursor phenomena. Last, we explored possibly self-bound strange hadronic configurations consisting of neutrons and mesons and studied their properties.

We have measured a proton energy from the stopped K^- reaction on ⁴He to search for strange tribaryon states at KEK 12 GeV PS. No statistically significant signal was observed in the missing mass spectrum obtained by the inclusive ⁴He(stopped K^-, p) measurement. Upper limits of the formation branching ratio at the 95 % C.L. were derived for neutral tribaryon states with strangeness -1 to be (0.4 ~ 6) × 10^-4, (0.2 ~ 6) × 10^-3 and (0.06 ~ 5) × 10^-2/(stopped K^-) for assumed natural widths of 0, 20 and 40 MeV/c², respectively.

The production of η mesons at an excess energy of 72 MeV has been studied in the reaction pp → pp(η)γγ. It is shown that a simple model with Pp final states included reproduces observed differential distributions better than the same model restricted to Ss, Sd and Ds final states. The strong influence of the Pp states could be taken as an indication of ρ dominance within an one boson exchange model for the excitation of N*(1535).

The two-pion production in pp-collisions has been investigated in exclusive measurements from threshold up to T_p = 1.36 GeV. Total and differential cross sections have been obtained for the channels pnπ⁺π⁰, ppπ⁺π^-, ppπ⁰π⁰ and also nnπ⁺π⁺. For intermediate incident energies T_p > 1 GeV, i.e. in the region, which is beyond the Roper excitation but at the onset of ΔΔ excitation the total ppπ⁰π⁰ cross section falls behind theoretical predictions by as much as an order of magnitude near 1.2 GeV, whereas the nnπ⁺π⁺ cross section is a factor of five larger than predicted. A model-unconstrained isospin decompostion of the cross section points to a significant contribution of an isospin 3/2 resonance other than the Δ(1232). As a possible candidate the Δ(1600) is discussed.

The reaction pp → ppω was studied at COSY-TOF for excess energies of ϵ = 93 MeV, 129 MeV, 178 MeV. The continuous change of the angular distribution of the ω meson in the overall CMS away from isotropy shows the increasing contribution of higher partial waves to the production process. This finding is supported by the orientation of the ω-spin (measured via the ω decay plane). For one excess energy ϵ = 129 MeV the analyzing power A_y has been found to be compatible with zero. These results will facilitate a quantitative partial wave analysis of this reaction.

A comparison of the close–to–threshold total cross section for the η' production in pp → ppη' and pn → pnη' reactions constitutes a tool to investigate the η' meson structure and the reaction mechanism in the channels of isospin I = 0 and I = 1 and may provide insight into the flavour-singlet (perhaps also into gluonium) content of the η' meson.

In this contribution we present preliminary results of measurement of the quasi-free production of the η' meson in the proton-neutron collisions conducted using the COSY-11 facility.

The Anti-Proton ANnihilation at DArmstadt (PANDA) experiment proposed at the Facility for Antiproton and Ion Research (FAIR) in Darmstadt (Germany) will perform a high-precision spectroscopy of charmonium and exotic hadrons, such as hybrids, glueballs and hypernuclei. A highly intense beam of anti-protons provided by High Energy Storage Ring (HESR) with an unprecedented resolution will scan a mass range of 2 to 5.5 GeV/c².

In preparation for experiments with PANDA, careful and large-scale simulation studies need to be performed in the coming years to determine analysis strategies, to provide feedback for the design, construction and performance optimisation of individual detector components and to design methods for the calibration and interpretation of the experimental results. Results of a simulation for the ElectroMagnetic Calorimeter (EMC), built from lead tungstate (PWO) crystals and placed inside the Target Spectrometer (TS), are presented. The simulations were carried out using the PandaRoot framework, which is based on ROOT and being developed by the PANDA collaboration.

The PANDA detector will allow to investigate the charmonium region in annihilation processes at a energy range for which production cross sections of charmonium states are unknown, in particular for those above the threshold. Cross sections for these states are expected to be rather small, so that it has to be verified that PANDA can cope with small rates. Therefore, several reaction channels have been identified as "benchmark channels" and the PANDA performance has been investigated in Monte Carlo studies. The focus of the charmed benchmark channels is to show the physics performance of the planned apparatus and to investigate the feasibility of separating the physics signal from a huge hadronic background.

PANDA is a future antiproton experiment designed to study fundamental questions of hadron and nuclear physics. It will work as a fixed-target facility, hence – due to the Lorentz boost – the distribution of reaction products will be strongly forward-peaked, in particular for the near-threshold measurements. Thus, the Forward Spectrometer, covering the most forward angles (θ_lab < 10°) is one of the key components of PANDA.

In this contribution, current design of the Forward Spectrometer is presented. Spectrometer components, including dipole magnet, tracking detectors, electromagnetic and hadron calorimeter, muon counters, RICH detector and TOF system are discussed. Results of simulations are shown along with tests of the prototype detectors performed in a high-rate environment.

We report on a detailed investigation of exclusive J/ψ production in proton–proton and proton–antiproton collisions. Predictions for Tevatron and LHC energies are included.

This note addresses the issue of checking Bell's inequalities in elementary particle physics. A new expression for the Bell's inequality is proposed in terms of experimentally measurable angular observables. As an example, the degree of violation of the Bell's inequality in the decays , , and is studied.

Diffractive dissociation reactions at COMPASS provide clean access to mesons with masses below ≈ 2.5 GeV/c². This paper presents a partial wave analysis of about 420 000 π^-Pb → π^-π^-π⁺Pb events at 190 GeV/c beam momentum and with four-momentum transfer t' ∈ [0.1,1] GeV²/c². The well-known a₁(1260), a₂(1320) and π₂(1670) mesons are resolved with high quality. Also the less established states π(1800) and a₄(2040) are seen. In addition, a resonance in the spin-exotic J^PC = 1^-+ wave is observed. A mass-dependent fit results in a mass and width of and , respectively, which is consistent with the disputed hybrid candidate π₁(1600).

Large samples of K^± → 3π and K^± → π⁺π^-e^±ν (K_e4) decays have been collected by the NA48/2 experiment at CERN SPS.

At the π⁺π^- threshold, the π⁰π⁰ invariant mass spectrum of the decay K^± → π^±π⁰π⁰ xhibits a Wigner cusp, from which the S-wave ππ scattering lengths are extracted with high precision.

The same scattering lengths are also independently determined from the accurate measurement of the form factors in the K_e4 decay K^± → π⁺π^-e^±ν.

The quark viscosity in the quark gluon plasma is evaluated in Hard Thermal Loop (HTL) approximation. The different contributions to the viscosity arising from the various components of the quark spectral function are discussed.

We present a preliminary analysis of the photon beam asymmetry observable (Σ) from the photoproduction reaction channel γn → π^-p. This new data was obtained using the near-4π CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Laboratory, USA, employing a linearly polarised photon beam with an energy range 1.1 - 2.3 GeV. The measurement will provide new data to address the poorly established neutron excitation spectrum and will greatly expand the sparse world data-set both in energy and angle.

We discuss production of nonphotonic electrons in proton-proton scattering at RHIC. The distributions in rapidity and transverse momentum of charm and bottom quarks/antiquarks are calculated in the k_t-factorization approach. The hadronization of heavy quarks is done by means of Peterson and Braaten et al. fragmentation functions. The semileptonic decay functions are found by fitting recent semileptonic data obtained by the CLEO and BABAR collaborations.

The VIP (Violation of the Pauli Exclusion Principle) experiment is investigating one of the basic principles of modern physics, searching for anomalous X-rays emitted by copper atoms in a conductor: any detection of these anomalous X-rays would mark a Pauli forbidden transition. VIP is currently taking data at the Gran Sasso underground laboratories, and its scientific goal is to improve by three-four orders of magnitude the previous limit on the probability of Pauli violating transitions, bringing it into the 10^-29÷-30 region. The new experimental results, together with future plans, are presented.

Using chiral effective field theory (EFT) with explicit Δ degrees of freedom we calculated nuclear forces up to next-to-next-to-leading order (NNLO). We found much better convergence of the chiral expansion in all peripheral partial waves. We also observe strong cancellations between charge-symmetry-breaking (CSB) contributions due to nucleon- and Δ-mass splittings in the two-pion-exchange potentials. The CSB potentials appear to be weaker in the Δ-full theory.

A large set of high precision cross sections, vector A_x, A_y and tensor A_xx, A_xy, A_yy analyzing powers for the breakup reaction were measured at 130 MeV beam energy with the detection system covering a large part of the phase space. Results are compared with rigorous theoretical calculations employing various models of the three-nucleon system dynamics. The cross section data allowed to establish evidence for three-nucleon force contributions and to confirm predictions of sizable effect of the Coulomb force in the breakup reaction. Analyzing power data are generally quite well described by theoretical predictions even with pure NN interactions. However, in some regions discrepancies has been observed for tensor analyzing powers, only rarely cured by inclusion of the three nucleon force. This indicates incompletness of the present-day treatment of the spin part of three nucleon system dynamics.

The possibility to select reliably the diproton final state with small excitation energy with the ANKE spectrometer at COSY-Juelich provides a new tool to study hadron interactions at intermediate energies. In this case the final proton pairs are found presumably in the ¹S₀ state which simplifies significantly the theoretical analysis. This approach has been successfully applied to the reactions pd → {pp}_sn at high and low momentum transfer kinematics, as well as to the pp → {pp}_sπ⁰ and pp → {pp}_sγ processes.

The data on the vector A_y and tensor A_yy, A_xx, A_xz analyzing powers for the and reactions at E_d = 200 and 270 MeV are presented. The data demonstrate large values of analyzing powers and their strong variation versus the scattering angle. The observed negative sign of the tensor analyzing powers for these reactions at small angles clearly demonstrate the sensitivity to the D/S ratio of the ³H and ³He wave functions, respectively. The calculations performed within one-nucleon exchange model with the use of the standard three-nucleon bound state wave functions fail to reproduce the data on the tensor analyzing powers.

Analyzing powers measurement A_y, A_yy and A_xx for the d - p elastic scattering were performed at the Internal Target Station of Nuclotron at JINR at E_d = 880 and 2000 MeV. These data are necessary to obtain the information on the 3NF structure and the relativistic effects. They are also important for development of the efficient deuteron beam polarimetry at high energies.

The results of the analyzing powers at E_d = 880 MeV covered the angular range from 60 to 140° in the c.m.s. are compared with several theoretical calculations.

The preliminary data on the analyzing powers measurement A_y, A_yy at E_d = 2000 MeV are discussed.

Spallation is one of possible scenarios of proton - nucleus reaction considered nowadays. Pions are the most abundantly produced mesons during the reactions. Boltzmann-Uehling-Uhlenbeck (BUU) model was used to describe pion spectra, results will be presented.

In order to study the role of pions and clustering phenomena in nuclei, two experiments have been performed using the AGOR accelerator facility. In collisions of two nuclei a pion and a fused nucleus were produced. The examined reactions were ⁴He(³He, π⁰)⁷Be and ⁶Li(⁴He, π⁰)¹⁰B at beam energies about 10 MeV above the coherent pion production threshold (256 MeV and 236.4 MeV, respectively). Since the available energy is well below the pion production threshold in an elementary nucleon-nucleon process, a highly coherent mechanism is needed. We identified the reaction by measuring the fused system in the magnetic spectrometer and the produced neutral pions in the Plastic Ball detection system with large acceptance. Our experimental setup provided the exclusive cross sections by identifying all products in overdetermined kinematics. Here we present the preliminary results of the analysis for the second reaction. Angular distribution of neutral pions will be discussed.

We discuss some properties of the central π^--meson carbon reactions at 40 GeV/c. While these results were obtained many years ago they have not been explained completely. We attempt to interpret following: results regime change on the behavior of some characteristics of the events as a function of the centrality; anomaly peak on the angular distributions of the slow protons emitted in these reactions; charge asymmetry on the π^--mesons production in the back hemisphere in lcs.

Understanding of the results could help to explain the new ones coming from the modern central experiments at high and ultrarelativistic energies.

New formulae for the resonant scattering and the production amplitudes near an inelastic threshold are derived. It is shown that the Flatté formula, frequently used in experimental analyses, is not sufficiently accurate. Its application to data analysis can lead to a substantial distortion of the effective mass spectra and of the resonance pole positions.

A unitary parameterization, satisfying a generalized Watson theorem for the production amplitudes, is proposed. It can be easily applied to study production processes, multichannel meson-meson interactions and the resonance properties, including among others the scalar resonances a₀(980) and f₀(980).

A dynamical coupled channels formalism is used to investigate the η–meson production mechanism on the proton induced by pions, in the total center-of-mass energy region from threshold up to 2 GeV. We show how and why studying exclusively total cross section data might turn out to be misleading in pinning down the reaction mechanism.

The amplitude for photoproduction γp → ϒp is calculated in a pQCD k_⊥-factorization approach. The total cross section for diffractive ϒs is compared to recent HERA data. The amplitude is used to predict the cross section for exclusive proces in hadronic reactions at Tevatron energies. We also included absorption effects.

The ABC effect, a low-mass enhancement in the invariant ππ mass, is observed in double-pionic fusion reactions leading to a bound nuclear system in the final state. From previous measurements there have been indications that this phenomenon is resctricted to the σ channel of the ππ system. With exclusive measurements of the pp → dπ⁺π⁰ reaction at T_p = 1.1 GeV we demonstrate that, indeed, the ABC effect does not occur in the vector-isovector ππ channel (ρ channel) despite the fact that the ΔΔ excitation is oberved to be the dominant reaction process. We also show that this reaction is well described by a t-channel ΔΔ excitation with the subsequent decay into the vector-isovector ππ channel given by the ρ channel operator.

The data for near-threshold cross section for the reaction pp → ppɸ published by the DISTO and ANKE Collaboration are analyzed in order to evaluate the OZI ratio at low energies by taking into account corrections from the kinematics and the final-state interaction. Combining these new data with the few measurements available at higher energies the limit for the OZI rule violation is evaluated and the possible contribution from a five-quark baryonic resonance coupled to the ɸp system is estimated.

We discuss a possible interpretation of the scalar mesons f₀(980) and a₀(980) as hadronic molecules - bound states of K and mesons. Using a phenomenological Lagrangian approach we calculate strong as well as the electromagnetic decay properties of both scalars. The covariant and gauge invariant model, which also allows for finite size effects of the hadronic molecule, delivers results in good agreement with experimental data.

New isospin mixing potential directly reproducing 1s level shift of kaonic hydrogen atom and other experimental data was constructed. Two forms of the potential reproducing one- and two-pole structure of Λ(1405) resonance were used. Accurate K^-p scattering length was calculated using the obtained potentials.

We have measured excitation function for dp → pppπ^- reaction near the η production threshold. We observe an enhancement of the counting rate above the threshold which can originate from the production of the η meson in the reaction dp → ³He η and its subsequent absorption on neutron in the ³He nucleus leading to creation of the pπ^- pair.

We report here on recent advances that shed light on the topic of scalar meson sector, which is controversial up to date. We study the scattering and spectroscopy of the strongly interacting mesons in coupled channels with quantum numbers J^PC = 0⁺⁺ and I = 0 and I = 1/2, up to a center of mass energy . Our framework is based on Unitary Chiral Perturbation Theory, but extended now to include many more channels. The resonant content of our fits is discussed, with the appearence of σ, f₀(980), f₀(1310), f₀(1500), f₀(1710) and f₀(1790) for I = 0 and the κ and the for I = 1/2.

In the analysis a status and parameters of the scalar, vector, and tensor mesonic resonances are obtained and compared with other results. Possible classification of the resonance states in terms of the SU(3) multiplets is discussed.

We review how the use of recent precise data on kaon decays together with forward dispersion relations (FDR) and Roy's equations allow us to determine the sigma resonance pole position very precisely, by using only experimental input. In addition, we present preliminary results for a modified set of Roy-like equations with only one subtraction, that show a remarkable improvement in the precision around the σ region. We also improve the matching between the parametrizations at low and intermediate energy of the S0 wave, and show that the effect of this on the sigma pole position is negligible.

The AMADEUS experiment will perform the first complete experimental study of the case of the so-called Deeply Bound Kaonic Nuclear States or simply Kaonic Clusters. Such a study has deep consequences in a still open sector of the strangeness hadronic/nuclear physics: how the hadron masses and hadron interactions change in the nuclear medium with consequences on the structure of cold dense hadronic matter. AMADEUS will perform exclusive - full acceptance - measurements, all particles in the formation and decay processes will be detected.

The dielectron yield in pp and dp reactions at a beam kinetic energy of 1.25 GeV/u has been measured using the HADES spectrometer at GSI. In proton-proton reactions the most abundant source above the π⁰ Dalitz region is expected to be Δ Dalitz decay. The obsearved large difference in dielectron production in pp and dp systems suggests that dielectron production in the dp system is dominated by a np process. In order to separate Δ Dalitz decays and np bremsstrahlung we compare the dielectron yield observed in pp with the one of dp reactions measured at the same beam energy.

The HADES collaboration studied dielectron production in C+C, p+p, and d+p reactions, with the main goal to investigate properties of vectors mesons through their dielectron decay. Production of e⁺e^- pairs in Ar+KCl collisions at a beam energy of 1.756 A GeV was measured recently by the collaboration and preliminary results of the experimental data analysis will be reported. Pair spectra will be compared with a prediction of a thermal model based on the Monte Carlo event generator Pluto.

The photoproduction of K⁺ mesons is an important challenge to recent QCD based chiral perturbation theories in the strange quark sector and is an important constraint on the nucleon excitation spectrum. We present preliminary data from a new high precision measurement using the Crystal Ball detector. The measurement pioneers a new technique for tagging strangeness using detailed cluster analysis in segmented calorimeters which has potential wider application at present and future hadron physics facilities.

It is presented the generalized multiconfiguration model to decay of the multipole giant resonances (MGR), which is based on the shell models (with limited basis) and microscopic model of pre-equilibrium decay with statistical account for complex configurations 2p2h, 3p3h etc. The model is applied to analysis of reaction (μ^-n) on the nucleus ⁴⁰Ca.