Strangeness in Nuclear and Hadronic Systems

The following sections are included:

• SYMPOSIUM ORGANIZATION

• PREFACE

• OPENING ADDRESS

• Conference Photographs

• CONTENTS

We review recent progress in our understanding of the role of strange quarks in the structure of the nucleon. For the contribution to its mass the result is remarkably small, an order of magnitude smaller than commonly assumed. This has profound consequences for the searches for dark matter which are currently underway. There has also been remarkable progress in the understanding of hypernuclei. In particular, there is a very natural explanation at the quark level of why Λ-hypernuclei are bound whereas Σ-hypernuclei are not. The consequences for dense matter, for example in neutron stars, are not yet fully understood but we know they are significant.

Selected topics in Strangeness Nuclear Physics are reviewed: Λ-hypernuclear spectroscopy and structure, multistrangeness, and mesons in nuclei.

A great progress has been made in strangeness nuclear physics in the past decade. Examples are; 1) The "hyperfine" structure of hypernuclei were measured with the Hyperball, and ΛN spin dependent interactions in p-shell hypernuclei were determined. 2) The "complete measurements" of the weak decay of hypernuclei were made and the np ratio puzzle in the non-mesonic decay was solved. 3) The discovery of a clean event of "Lambpha" and determination of its binding energy concluded that the Λ-Λ interaction is weak attractive. However, we still have important questions to be answered in this field, especially in relation with QCD and nuclear physics. For the future strangeness nuclear physics, we have and will have facilities such as JLab, SPring-8, Daphne, J-PARC, FAIR. We discuss experimental challenges in the strangeness nuclear physics and related fields in the next decade.

The following sections are included:

• Introduction

• The Pentaquark Θ⁺ Revisited

• Meson-Baryon Couplings in QCD

• Conclusion and Outlook

• Acknowledgments

• References

A brief overview of strangeness physics with the CLAS detector at JLab is given, mainly covering the domain of nucleon resonances. Several excited states predicted by the symmetric constituent quark model may have significant couplings to the KΛ or KΣ channels. We will discuss data that are relevant in the search for such states in the strangeness channel, and give an outlook on the future prospects of the N* program at JLab with electromagnetic probes.

The present status of kaon photo- and electroproduction on the nucleon is briefly reviewed. Some current important issues in this field are discussed.

The elementary photo-strangeness production process has been intensively studied based on the high-quality data of the charged kaon channel, γ + p → K⁺ + Λ(Σ⁰). However, there had been no reliable data for the neutral kaon channel γ + n → K⁰ + Λ(Σ⁰) and the theoretical investigations suffer seriously from the lack of the data. In order to have reliable data for the neutral kaon photo-production data, substantial effort has been made to measure the γ + n → K⁰ + Λ process in the π⁺π^- decay channel, using a liquid deuterium target and a tagged photon beam (E_γ = 0.8-1.1 GeV) in the threshold region at the Laboratory of Nuclear Science (LNS), Tohoku University. We have taken exploratory data quite successfully with the use of Neutral Kaon Spectrometer (NKS) at LNS-Tohoku in 2003 and 2004. The data is compared to theoretical models and it indicates a hint that the K⁰ differential cross section has a backward peak in the energy region. The second generation of the experiment, NKS2, is designed to extend the NKS experiment by considerably upgrading the original neutral kaon spectrometer, fully replacing the spectrometer magnet, tracking detectors and all the trigger counters. The new spectrometer NKS2 has significantly larger acceptance for neutral kaons compared with NKS, particularly covering forward angles and much better invariant mass resolution. The estimated acceptance of NKS2 is three (ten) times larger for than that of NKS. The spectrometer is newly constructed and installed at the Laboratory of Nuclear Science, Tohoku University in 2005. The deuterium target data was taken with tagged photon beam in 2006-2007. We will report recent results of NKS2 in this paper. Additionally, a status of the upgrade project that gives us larger acceptance and capability of K⁰ + Λ coincidence measurement will be presented.

Data for the reaction was measured at the LEPS detector using a linearly polarizes photon beam produced by laser-backscattering at the SPring-8 facility. The cross sections are in good agreement with predictions from a theoretical model by Oh, Ko and Nakayama. This model, which uses SU(3) flavor symmetry, suggests that the coupling constants for strange-particle production in the baryon decuplet can be predicted with reasonable accuracy using this symmetry.

Isobar models for the electromagnetic production of K⁺ and K⁰ are discussed with emphasis on the K⁰ photoproduction off neutron. Predictions of the models for the K⁰ photoproduction on deuteron are compared with the recent data and some properties of the elementary amplitudes are shown.

Photoproduction of hyperons is a promising channel to achieve a complete amplitude analysis. Many observables have been measured and interpreted. The status is discussed here. Recent data obtained with the Crystal Barrel/TAPS setup at ELSA are shown and future plans for hyperon photoproduction are presented.

A measurement of the H(e, e′K⁺) reaction was performed at Hall A, TJNAF as part of the hypernuclear experiment E94-107. Data was taken at very low Q² (~ 0.07 (GeV/c)²) and W = 2.2 GeV. Kaons were detected along the direction of the momentum transferred by the incident electron (θ_CM = 6°).

These measurements provide data about the Σ⁰/Λ ratio which drops rapidly with Q², the angular dependence of the cross sections as Q² → 0, and the dependence of the cross section with respect to Q², W and θ_CM.

The dependence of the cross section at very forward angles has been poorly known. Available models are inadequate to describe the results.

The measurement of the elementary cross section will constrain models for the elementary reaction which are inadequate to describe these results. It is also a key ingredient in the hypernuclear spectroscopy studies performed at the same kinematics. Details of the calculations and results will be shown.

Recent results concerning the production of K⁺, K^-, ɸ, and Λ particles in the reaction system Ar+KCl at 1.76 AGeV measured by the HADES Collaboration are presented. Transverse momentum distributions have been measured in a large fraction of the phase space. For the first time, at SIS energies, K⁺, K^- and ɸ mesons have been measured independently and the slope parameter for ɸ mesons could be extracted. A large set of statistics has been collected for the produced and Λ in the phase space region around mid-rapidity. The high quality of these data render them very suitable for comparisons with theoretical models.

The differential and total cross sections were measured for the γp → ηp and γd → ηpn reactions at E_γ ≤ 1150 MeV by using an electro-magnetic (EM) calorimeter SCISSORS II at the Laboratory of Nuclear Science (LNS), Tohoku University. The total cross section on the deuteron shows a bump around E_γ = 1 GeV, while no bump is observed in the same energy region of that on the proton. This bump is attributed to be a nucleon resonance excited from the neutron, and it is a candidate of anti-decuplet penta-quark baryons with hidden strangeness.

It was difficult, however, to detect all the γ's coming from η decay since the solid angle of SCISSORS II was only 12.6% in total. Statistics of the detected η produced events is poor and systematic uncertainty of the obtained cross section is not small due to low acceptance. A new EM calorimeter complex called FOREST with a solid angle of about 4π sr has been constructed. The spin and parity of the relevant resonance are expected to be determined by the experiments with FOREST.

Among experiments looking for strangeness in nuclear systems, electron scattering Parity-Violation (PV) type experiments aim mainly at measuring the strange quark contributions to the form factors of the proton. They can be accessed by measuring the asymmetry in longitudinally polarized electron elastic scattering. The PV asymmetry is measured at the 10^-7 level of accuracy, and when combined with the electromagnetic form factors of the nucleon, the strange form factors can be determined. The full separation of form factors according to quark flavour requires measurements at forward angles on hydrogen and at backward angles on hydrogen and deuterium. The experimental setup used for G0 in the two different configurations is described. The status of the analysis and the current results are presented and discussed in relation with other experiments past and planned. A few comments are also made regarding some other aspects of physics accessible in simultaneous measurements: neutral currents in NΔ transitions, parity violation in inclusive π^- production and 2_γ contributions to elastic scattering.

We present the results of photoproduction cross sections of the ground state cascade Ξ^- and the first excited state Ξ*^-(1530) measured with the CLAS detector. The photoproduction of the cascade resonances has been investigated in the reactions γp → K⁺K⁺(X) and γp → K⁺K⁺π^-(X). The differential and total cross sections of the Ξ^- were determined for photon beam energies from 2.75 to 4.75 GeV and are consistent with a production mechanism of Y* → K⁺Ξ^- through a t-channel process. The cross-section of the Ξ*^-(1530) has been determined for photon beam energies from 3.35 to 4.75 GeV. The reaction γp → K⁺K⁺π^-(Ξ⁰) has also been investigated in the search for excited cascade resonances decaying to π^-Ξ⁰. No significant signal of excited cascade states other than the well-known Ξ*^-(1530) is observed.

We also present the latest results of a search for the Φ^--(1862) exotic pentaquark state in a photoproduction experiment on a deuterium target. A high-statistics sample of π^-Ξ^- events have been collected and analyzed. A preliminary invariant mass spectrum of the π^-Ξ^- system is presented, which is used to set upper limits on the photoproduction of the Φ^-- pentaquark state.

We present and discuss the most recent version of the extended-soft-core (ESC) interactions. The ESC-model describes the nucleon-nucleon (NN), hyperon-nucleon (YN), and hyperon-hyperon (YY), in terms of meson-exchanges using (broken) SU_F(3)-symmetry. In this approach to baryon-baryon (BB) the dynamics is derived from (i) one-boson-exchanges (OBE), (ii) two-meson-exchanges (TME), and (iii) meson-pair-exchanges (MPE), (iv) gluon-exchanges, and (v) quark-core effects. In the OBE-sector, a special feature is the importance of the axial-vector meson potentials, and the inclusion of a zero in the scalar- and axial- meson form-factors. Novelties are the inclusion of (a) odderon-exchange, and (b) special pronounced effects of the appearance of forbidden six-quark configurations. With these ingredients, a rather flexible dynamical framework is constructed. Namely, it appeared feasible to keep the parameters of the model in reasonable accordance with the predictions of the 3P0 quark-pair-creation model (QPC). This is the case for the meson- and meson-pair-baryon coupling constants and the F/(F + D)-ratio's as well. The NN, YN, and YY results for this model are rather promising. In particular, we improved the ΛN spin-orbit interaction greatly by the inclusion of (a) the Brown, Downs, and Iddings anti-symmetric spin-orbit potentials, and (b) new corrections to the MPE-potentials. Also, the special quark-core effects provide ample repulsion in the Σ⁺p(³S₁, T = 3/2)- and ΣN(¹S₀,T = l/2)-channels. The new version of the ESC-model reported here will be referred to as ESC07 henceforth.

In the G-matrix approach, two topics are discussed. One is the spin-dependent components of ΛN interactions. The other is the derivation of Σ-nucleus interactions.

We derive single-hyperon potentials for light nuclei, based on the G-matrix calculations of the quark-model baryon-baryon interactions developed by the Kyoto-Niigata group. The Ξ¹²C(0⁺) and Ξ¹⁶O potentials have non-trivial oscillating behavior, reflecting strong isospin dependence of the ΞN interaction; namely, attractive isospin I = 0 ΞN interaction and weakly repulsive I = 1 interaction. The latter repulsive effect is largely enhanced in the intermediate region of the Ξ-core potential, resulting in very weak attraction at the surface region.

We study pΞ⁰ and pΛ forces by using quenched lattice QCD. The Bethe-Salpeter amplitude is calculated for the lowest scattering state of the systems. The numerical calculation is twofold: (i) For the pΞ⁰, the potentials and scattering lengths are obtained by using 32³ × 32 lattice with β = 5.7, the lattice spacing of a = 0.1416(9) fm, and two kinds of ud quark mass corresponding to m_π ≃ 0.37 GeV and 0.51 GeV. The present results indicate that the pΞ⁰ interactions are both attractive at ¹S₀ and ³S₁ channels, and the interaction in the ³S₁ is more attractive than in the ¹S₀. These attractive forces become stronger as the u, d quark mass decreases, (ii) For the pΛ, the potentials are calculated by using the 32³ × 48 lattice, and two kinds of ud quark mass corresponding to m_π ≃ 0.47 GeV and 0.51 GeV. The present preliminary result shows that the pΛ interactions are both attractive at ¹S₀ and ³S₁ channels.

We determine ΛΛ scattering parameters from a ΛΛ invariant mass spectrum that was obtained by ¹²C(K^-,K⁺ΛΛ) reaction at the KEK Proton Synchrotron. In the framework of Watson's procedure, the obtained scattering length and effective range are most consistent with the values predicted by using the Nijmegen soft core models (NSC97's). However, the predicted values by using the Nijmegen hard-core ND (G-matrix) and the extended soft-core (ESC00) models are out of two standard deviations from the determined scattering parameters.

Jefferson Lab experiment E91-016 studied kaon electroproduction on hydrogen, deuterium and helium targets at a beam energy of 3.245 GeV and four-momentum transfer, Q², ranging from 0.34 to 0.5 GeV². Among a variety of other topics, part of this study was the investigation of the threshold region for signatures of final-state interaction between the electroproduced Λ-hyperon and spectator neutron. Compared to a purely quasi-free description, an excess yield was observed in the threshold region. This is compared to the predictions from three different hyperon-nucleon potentials. Though the data exhibit some sensitivity to the tested hyperon-nucleon potentials, further studies would require a more dedicated measurement with better resolution in the threshold region.

Λ(1405) is investigated as a resonance in a coupled channel baryon-meson scattering with a 'bound state embedded in the continuum' (BSEC). This BSEC is introduced by hand, as a state not originated from a simple baryon-meson system. We assume it comes from the three-quark state.

There appears a resonance of a large width in the Σπ scattering below the threshold by assuming the baryon meson interaction whose channel dependence is (1) flavor-flavor type like the chiral unitary approach, (2) flavor-flavor type with a lower-momentum cut-off, or (3) the same as that of the quark cluster model. It is necessary to introduce a BSEC for the latter two cases in order to reproduce the peak.

The calculation including a BSEC seems to be preferable to reproduce the scattering length. Our calculation gives the observed value when the BSEC contribution to the resonance is roughly half of that of the channel.

In order to understand the structure of the X(3872), we have studied the effects of the core state coupling to the multi-hadronic states such as , p J/ψ, etc. We have calculated the transition strength S(E) using the Green's function approach with the simple solvable interactions. We have also studied the S(E) in the case of no core state, namely the molecule. Since the calculated shapes of the transition strengths are different from each other, we shall be able to determine the degree of the mixing of the state in the X(3872) from the shape of the energy spectrum.

Theoretical hypernuclear photoproduction spectra are demonstrated by choosing typical medium-heavy nuclear targets such as ²⁸Si, ⁴⁰Ca, and ⁵²Cr. The predictions provide us with interesting opportunities of spectroscopic study beyond p-shell on the dynamical coupling between a hyperon and nuclear core excitations.

Hypernuclear spectroscopy with electron beam at JLab Hall C has been studied since 2000. The first experiment, JLab E89-009, demonstrated the possibility of the (e,e′K⁺) reaction for hypernuclear spectroscopy by achieving an energy resolution of better than 1 MeV (FWHM). The second experiment, JLab E01-011 employed a newly constructed high resolution kaon spectrometer and introduced a vertically tilted electron arm setup to avoid electrons from bremsstrahlung and Moeller scattering. The setup allowed us to have 10 times yield rate and 4 times better signal to accidental ratio with expected energy resolution of 400 keV (FWHM). The third experiment, JLab E05-11B will be performed in 2009 with employing newly constructed high resolution electron spectrometer and a new charge-separation magnet. With the fully customized third generation experimental setup, we can study a variety of targets up to medium-heavy ones such as ⁵²Cr.

The characteristics of the Jefferson LAB electron beam, together with those of the experimental equipments, offer a unique opportunity to study hypernuclear spectroscopy via electromagnetic induced reactions. Experiment 94-107 started a systematic study on lp-shell targets, ¹²C, ⁹Be and ¹⁶O. We present the results from ¹²C, ¹⁶O and very preliminary results from ⁹Be. For ¹²C for the first time measurable strength in the core-excited part of the spectrum between the ground state and the p_Λ state was shown in for the first time. A high-quality ¹⁶_ΛN spectrum was produced for the first time with sub-MeV Energy resolution. A very precise B_Λ value for ¹⁶_ΛN, calibrated against the elementary (e.e′K⁺) reaction on hydrogen, has also been obtained. Final data on ⁹Be will be available soon. The missing energy resolution is the best ever obtained in hypernuclear production experiments.

Detailed structure calculations in , and are performed within the framework of the microscopic of four-body cluster models. We adopted effective ΞN interactions derived from the Nijmegen interaction models, which give rise to substantially attractive Ξ-nucleus potentials in accordance with the experimental indications. and are predicted to have bound states. We propose to observe the bound states in future (K^-, K⁺) experiments using ⁷Li and ¹⁰B targets in addition to the standard ¹²C target. The experimental confirmation of these states will provide information on the spin- and isospin-averaged ΞN interaction.

Hypernuclear gamma-ray spectroscopy experiments at J-PARC using the next generation Germanium detector array, Hyperball-J is discussed. An overview of the first experiment (E13) is summarized and the present preparation status of the magnetic spectrometer system and Hyperball-J is given. Possible gamma-ray spectroscopy studies of the sd-shell Λ hypernuclei, especially of magnesium isotopes, are presented.

The FINUDA (FIsica NUcleare a DAΦNE) experiment was built in order to study the interactions of stopped K^- on nuclei, with emphasis on Hypernuclear spectroscopy and Hypernuclei decays. Due to the nice performances of the spectrometer, it proved also suited to study, more generally, final states with several particles and able to recostruct secondary vertices, hence greatly enlarging the physical topics that could be addressed.

We study properties of Λ hypernuclei in an extended Skyrme-Hartree-Fock model employing recent modern nucleonic Skyrme forces together with a microscopic lambda-nucleon interaction derived from Braeckner-Hartree-Fock calculations of hypernuclear matter with the Nijmegen soft-core hyperon-nucleon potentials. We show in particular recent results of deformed and neutron-rich hypernuclei close to the dripline.

The pion plays an important role for the structure of nucleus and nuclear matter. We propose a new theoretical framework, named the tensor optimized shell model (TOSM) to calculate the tensor interaction together with the unitary correlation operator method (UCOM) for the short range repulsion. We are able to handle the pion exchange interaction directly in the proposed framework. We compare the calculated results for ⁴He with the rigorous calculation to show the power of TOSM to treat the tensor interaction. We then discuss the important role of pion in hypernuclei due to excitation of Σ baryon from Λ state.

Several aspects about Λ-hypernuclei in the relativistic mean field theory, including the effective Λ-nucleon coupling strengths based on the successful effective nucleon-nucleon interaction PK1, hypernuclear magnetic moment and -hypernuclei, have been presented. The effect of tensor coupling in Λ-hypernuclei and the impurity effect of to nuclear structure have been discussed in detail.

We study the binding of hypernuclei based on the latest version of quark-meson coupling model, and estimate the photoproduction cross sections for the reaction using the bound Λ spinors obtained in the model.

We use the self-consistent mean-field theory to discuss the ground state and decay properties of Λ hypernuclei. We first discuss the deformation of Λ hypernuclei using the relativistic mean-field (RMF) approach. We show that, although most of the hypernuclei have a similar deformation parameter to the core nucleus, the shape of ²⁸Si is drastically altered, from oblately deformed to spherical, if a Λ particle is added to this nucleus. We then discuss the pionic weak decay of neutron-rich Λ hypernuclei using the Skyrme Hartree-Fock + BCS method. We show that, for a given isotope chain, the decay rate increases as a function of mass number, due to the strong neutron-proton interaction.

Fundamental interest on Non Mesonic Weak Decay (NMWD) is that it provides practically the only means to study the elementary ΔS = 1 baryon-baryon weak interaction process, ΛN→NN (Λp → np and Λn → nn), since it is difficult to be realized in the free space. Thanks to the recent developments in experimental and theoretical studies, the relative strength of two channels, the Γ_n/Γ_p ratios whose experimental and theoretical values have showed a long standing discrepancy have been converged to ~0.5 and the discrepancy problem finally has been solved.^1–3 However, despite the progresses, the decay interaction of NMWD is not yet well established and there remain the important issues such as the discrepancy of asymmetry parameter between experimental and theoretical values, confirmation of 3-body NMWD process, and whether the I = 1/2 rule for ΔS = 1 decay would hold or not in NMWD. Especially the recent experimental indication of the 3-body decay process ΛNN →NNN whose contribution was predicted to be significant in the theoretical calculations seems to be strong and showed a surprisingly large contribution in the quenching of singles and coincidence nucleon yields in NMWD. Recent results of the asymmetry parameter α^nm of NMWD showed small values for both s-shell and p-shell and consistent with each other. However, the discrepancy of the theoretical values from those of experimental ones remains to be understood. It now becomes one of the urgent issues in NMWD study to determine the contribution of the 3-body NMWD channel experimentally, in order to understand the discrepancy of the asymmetry papameter, and to test the ΔI = 1/2 rule for NMWD which are the main purposes of J-PARC 50 GeV PS experiment, E18 and E22.

The FINUDA experiment has performed a systematic study of mesonic weak decay of p-shell Λ-hypernuclei. Recent results on the mesonic decay spectra and ratios are illustrated and discussed.

The FINUDA experiment has performed a systematic study of the NonMesonic Weak Decay (NMWD) of Λ hypernuclei analizing all the data collected from 2003 up to 2007. The results of a measurement of the spectra of protons coming from the NMWD of , , , , , , and are the subject of this paper.

The axial vector a₁-meson exchange is introduced in the nonmesonic weak decay model. The a₁-exchange is found to give remarkable modifications of the parity-conserving decay potentials in ^1,3S → ^1,3S and ³S₁ → ³D₁ channels at short range. Calculated asymmetry parameters α_Λ for s- and p-shell hypernuclei in the 'π + 2π/ρ + 2π/σ + ω + K + ρπ/a₁ + σπ/a₁'-exchange model are obtained to be positive and small, which are consistent with the available data.

Recent progress on the precision laser spectroscopy of antiprotonic helium atoms, as well as on the x-ray spectroscopy of kaonic helium atoms are presented. These two may appear to be unrelated topics (except for the fact that both being exotic helium atoms), but in fact a past study of kaonic helium system led to the serendipitous discovery of antiprotonic helium. Some historical background connecting these two exotic helium atoms, as well as future prospects are discussed.

We report on recent relativistic mean-field calculations of multi- nuclei^1,2 which were performed fully and self-consistently across the periodic table. The separation energy as well as the nuclear and -meson densities were found to saturate with the number of antikaons in the nuclear medium. Saturation appears robust against a wide range of variations, including the nuclear model used and the type of boson fields mediating the strong interactions. In addition, we have explored properties of kaonic hypernuclei — strange systems made of nucleons, hyperons and K^- mesons. We observed saturation also in these objects. Since the separation energy does not exceed 200 MeV, multi- nuclei lie energetically well above multi-hyperonic nuclei and it is unlikely that kaon condensation could occur in strong-interaction self-bound hadronic matter.

Novel data from the absorption reaction in light nuclei are presented. The data were collected by the FINUDA spectrometer running at the DAΦNE ɸ-facility, Laboratori Nazionali di Frascati (LNF), Italy.

Several experiments engaging kaon beams have been carried out to study the existence of deeply bound kaonic state. We proposed an alternative method, which exploits a p + p reaction at 3.5 GeV incoming energy to search for the most elementary of the kaonic states: ppK^-. This experiment is planned with the FOPI spectrometer at GSI and a silicon-based trigger system has been developed to increase the detection capability of the existing system for the reaction of interest. Several tests have been performed under realistic beam conditions to test the feasibility of the measurement and the proof of principle of the trigger system. The positive results of such measurements are shown in this contribution together with the expected rates extracted from simulations.

We study the consequence of chiral SU(3) symmetry in the kaon-nucleon phenomenology, by deriving the effective single-channel potential. It turns out that the π∑ interaction is strongly attractive and plays an important role for the structure of the Λ(1405) resonance. We discuss the implication of effective potential for the few-body kaonic nuclei.

The prototype of a nuclear cluster, K^-pp, has been investigated using effective potentials based on chiral SU(3) dynamics. Variational calculation shows a bound state solution with shallow binding energy B(K^-pp) = 20 ± 3 MeV and broad mesonic decay width . The pair in the K^-pp system exhibits a similar structure as the Λ(1405). We have also estimated the dispersive correction, p-wave interaction, and two-nucleon absorption width.

At the Institut für Kernphysik in Mainz, Germany, the microtron MAMI has been upgraded to 1.5 GeV electron beam energy and can now be used to study strange hadronic systems. The magnetic spectrometer KAOS from GSI was dismantled and re-installed in the spectrometer facility operated by the A1 collaboration. The spectrometer's primary purpose is to study strangeness electro-production. Its compact design and its capability to detect negative and positive charged particles simultaneously under forward scattering angles complements the existing spectrometers.

In 2008, an important milestone has been reached by the successful measurement of kaon production off a liquid hydrogen target. The identification of Λ and ∑⁰ hyperons in the missing mass spectra has demonstrated the capability of the extended facility to perform strangeness electro-production spectroscopy.

To operate KAOS as a double-arm spectrometer under zero degree scattering angle major modifications are needed. A new vacuum chamber was constructed and installed, a new coordinate detector with many thousands of channels was built and tested, a new trigger system for the high rate environment was developed, and a magnetic chicane for the primary electron beam is under construction.

We discuss the usefulness of the double charge-exchange reactions (DCX) for the production of the neutron-rich Λ-hypernuclei. We believe the (π^-,K⁺) reaction is one of the most promising DCX reactions, and propose to produce the neutron-rich Λ-hypernuclei, and , at the J-PARC 50 GeV PS by the reaction (J-PARC E10 experiment). The design of the experiment is presented.

Combined with high precision on two body decay pions and the unique features of hypernuclear electro-production mechanism, a new experiment aims to effectively access the hypernuclear continuum which offers insight on a wide range of light hypernuclei with variety of possible (Z, A) combinations via production of hyper-fragments. Precise binding energies of various hypernuclear species allow us to address on most of the leading puzzles and inconsistencies and may lead to new important discoveries and findings.

Hypernuclear physics is currently attracting renewed attention. Thanks to the use of stored beams, copious production of double Λ hypernuclei is expected at the experiment which will enable high precision γ-spectroscopy of such nuclei for the first time. In the present work we have studied the population of particle stable, excited states in double hypernuclei after the capture of a Ξ^- within a statistical decay model. In order to check the feasibility of producing and performing γ-spectroscopy of double hypernuclei at , an event generator based on these calculations has been implemented in the simulation framework PANDAROOT.

A schematic Monte Carlo simulation is used to examine the potential of exclusive hyperon-antihyperon pair production close to threshold in antiproton nucleus interactions to extract information on the interaction of antihyperons in nuclei. It is demonstrated that for pairs produced at antiproton momenta of 1.66 GeV/c the asymmetry is sufficiently sensitive even if the density as well as the momentum dependencies of the potentials are considered. Data taken earlier by the PS185 Collaboration prove that these measurements are feasible.

The HypHI experiment for precise hypernuclear spectroscopy with induced reactions of stable heavy ion beams and rare isotope beams is currently under preparation at GSI. The main goal of the HypHI project is to study neutron and proton rich hypernuclei and to measure directly hypernuclear magnetic moments at GSI and FAIR. In the first HypHI experiment (Phase 0) planned in 2009, the feasibility of precise hypernuclear spectroscopy with heavy ion beams will be demonstrated by observing π^- decay channels of , and with ⁶Li projectiles at 2 A GeV impinging on a ¹²C target. An overview of the HypHI project and the details of the Phase 0 experiment will be discussed.

J-PARC Hadron Experimental Facility is designed to carry out a variety of particle and nuclear physics experiments with intense secondary particles generated by 750 kW proton beams. The first construction stage including the experimental hall, the primary beam line, and one secondary beam line (K1.8BR) has been completed at the end of December 2008. In order to handle the high intensity primary beam safely, we have developed many special devices working under severe radiation environment. The present article reports the current status of the Hadron Experimental Facility in detail.

These observations provide a personal perspective regarding the physics presented during this Sendai International Symposium on Strangeness in Nuclear and Hadronic Systems. No attempt has been made to summarize the oral presentations in the sense of a traditional summary talk. Many presentations covered physics from others than that of the speaker. Hopefully, the ideas discussed will outlive the rapporteurs who so ably brought them to life at SENDAI08.

We are planning to measure the neutron rich hypernuclei with the double charge exchange (DCX) reaction. The production cross section of hypernuclei is small with this reaction. Therefore, the high-intensity beam and new chambers which can operate in such beam conditions are necessary. We are developing chambers using GEM. The gain of our chamber is about 7000. There exists dependence of gain on pressure.

We have performed the experiment of K⁰ photoproduction near the threshold region (E_γ = 0.8 - 1.1 GeV) with the liquid deuterium target at the Laboratory of Nuclear Science, Tohoku University (LNS-Tohoku). In this report, a preliminary result for the differential cross section is presented.

The QCD sum rule method is applied to the Θ⁺ pentaquark with quantum numbers . It is found that the sum rule gives positive evidence for the state, while we cannot extract any evidence for the state.

A new cryogenic target production system for a 4π EM Calorimeter, FOREST, has been installed in the GeV-γ experimental hall at the Laboratory of Nuclear Science. The temperature is achieved at 4.5 K in the target cell. It can maintain a solid or liquid H₂/D₂ target. The target system enables us to make up solid or liquid hydrogen in 2 hours.

The J-PARC E15 experiment is an experimental search for the simplest kaonic nuclear states using the in-flight ³He(K^-,n) reactions. In this paper, the experimental feature and the current status are briefly presented.

We are now preparing for the third generation (e, e′K⁺) Λ hypernuclear spectroscopic experiment at Hall C, Jefferson Lab (USA). The goal of the experiment is the precise spectroscopy of hypernuclei in wide mass region. We have constructed a new high resolution electron spectrometer "HES" dedicated to (e, e′K⁺) hypernuclear study. We can expect the total energy resolution of the experiment is about 350 keV(FWHM).

We report on a HADES measurement of the strange hadrons K^±, and Λ in the reaction Ar(1.76 A·GeV)+KCl and present an estimate of the remaining fraction of strangeness, corresponding mainly to the Σ^0,± hyperons.

The 3rd generation hypernuclear spectroscopic study via the (e, e′K⁺) reaction at JLab Hall C is planned with new scattered electron spectrometer (HES) and a splitter magnet, which makes it possible to measure medium-heavy mass region hypernuclei with excellent energy resolution of ~ 350 keV, better S/N ratio and higher statistics than 2nd generation experiment. We developed several detectors for the next experiment and all detectors are under commissioning at JLab. The beamtime is scheduled during Summer to Autumn in the year 2009.

The second generation hypernuclear spectroscopy was successfully performed in Jefferson Laboratory (JLab) Hall C in the summer of 2005. A systematic error depends on analysis procedure was estimated by detailed simulation.

A Λ particle in free space decays uniquely into π meson and a nucleon through the weak interaction. In the nuclear medium, the pionic decay mode is suppressed by the Pauli exclusion principle, because the released nucleon momentum is much smaller than the Fermi momentum (k_F ~ 270MeV/c). In addition to this decay mode, another decay mode, Λ + N → N + N (i.e., non-mesonic decay), becomes possible in the nuclear medium, and is dominant except for light hypernuclei …

Ξ-hypernucleus gives us a wealth of information about the Ξ-N interaction, while its existence is not confirmed. We will perform a Ξ-hypernuclear spectroscopy experiment at J-PARC (E05 experiment) which aims to produce via the ¹²C(K^-,K⁺) reaction.

The photo-production of ɸ mesons from CH₂, C and Cu targets at backward angles has been measured in the photon-energy range from 1.5 to 2.4 GeV. We describe the experiment and the preliminary results.

As the first hypernuclear γ-ray spectroscopy experiment at the J-PARC K1.8 beam line (J-PARC E13), we will study several light hypernuclei via the high precision γ-ray spectroscopy technique.

A large solid angle electro-magnetic calorimeter system, FOREST, has been constructed at LNB-Sendai to study the π⁰ and η photo-production reactions. FOREST consists of three electro-magnetic calorimeters: pure CsI crystals, Lead/SciFi blocks and Lead Glass Cherenkov counters. It covers about 90% of the total solid angle.

We will perform an experimental search for Θ⁺ pentaquark via the π^-p → K^-X reaction at the J-PARC K1.8 beamline using high-resolution spectrometers for both incident and scattered particles. This experiment is a natural expansion of KEK-E522.

This article explains a systematic study of double strangeness system at J-PARC, which is called J-PARC E07.

We investigate the structure of the neutron-rich hypernucleus by using a shell-model calculation with a Λ-Σ coupling effect. The calculated Σ-mixing probability and energy shift in are found to be about 0.34 % and 0.28 MeV which are coherently enhanced by the Λ-Σ coupling configurations.

It has been well known that many open-shell nuclei are deformed in the ground state. In this study, we investigate the deformation property of Λ hypernuclei using the relativistic mean field (RMF) method, as a choice of effective NN and NΛ interactions. We will demonstrate below that the shape of ¹²C and ²⁸Si nuclei is drastically changed when a Λ particle is added to them …

For the hypernuelear gamma-ray spectroscopy experiment at J-PARC, the new germanium detector array Hyperball-J is under construction. New Ge detectors with a mechanical cooler are developed for Hyperball-J.

The optical feature of the Jefferson Lab HKS spectrometer system with on-target magnetic field and the need to obtain high energy resolution make it necessary to develop new spectrometer calibration procedure. This paper provides a summary of the high precision optical and kinematics calibration procedure we have developed.

The following sections are included:

• Photo Session

• Scientific Program

• List of Participants