abstract

The first hypernucleus was discovered in Warsaw in September 1952 by Marian Danysz and Jerzy Pniewski. It happened during a time of confusion concerning the newly detected heavy unstable particles. The study of hypernuclei was of considerable help in understanding the properties of strange particles. An account is given of the early history of strange particles and hypernuclear physics.

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We review the mechanism of weak decay of hypernuclei, with emphasis on the non-mesonic decay channels. Various theoretical approaches are discussed and the results are compared with the available experimental data.

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In spite of notable progresses achieved at BNL and KEK during last decade, a consistent understanding of nonmesonic weak decay (NMWD) of \({\mit {\mit \Lambda }}\) hypernuclei is yet to be achieved. Until recently, all the experimental data since the days of bubble chamber and emulsion showed the dominance of the neutron induced channel (\(\mit {\mit \Gamma }_n\)) over the proton induced one (\({\mit \Gamma }_p\)) in the NMWD of \({\mit \Lambda }\) hypernuclei, while the theoretical calculation predicted the predominance of the proton induced one. This inconsistency has been known as the famous ‘\(\mit {\mit \Gamma }_n\)/\({\mit \Gamma }_p\) puzzle’ and the central focus in the study of the decay mechanism of the \({\mit \Lambda }\)  hypernuclei and the baryonic weak interaction. However, important progresses have been made recently in both the experimental and theoretical sides. In this paper, the progresses in the experimental data on NMWD will be presented. The direct comparison of the recent proton and neutron spectra showed the \(\mit {\mit \Gamma }_n\)/\({\mit \Gamma }_p\) ratio, \(0.45\sim 0.51\pm 0.15\)(stat.) much less than unity. This ratio agrees well with the recent theoretical calculations. Though this outcome seems to indicate that the famous long standing puzzle has almost been resolved, the decay asymmetry still remains to be understood.

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The FINUDA detector has been installed at the (\(e^+,\) \(e^-\)) collider DA\(\Phi \)NE at Laboratori Nazionali di Frascati (Italy). The commissioning of the detector was started and will be immediately followed by a data taking run with targets of \(^{6}\)Li, \(^{7}\)Li, \(^{12}\)C, \(^{27}\)Al and \(^{51}\)V. Hypernuclei of the same \(A\) as the target nuclei will be copiously produced by means of the strangeness exchange reaction by stopped \(K^{-}\). The aim of the experiment is to measure simultaneously excitation energy spectra with a resolution better than 1 MeV, lifetime of the \({\mit \Lambda }\) in the different Hypernuclei, partial decay widths \({\mit \Gamma } _{\pi }\), \({\mit \Gamma } _{np}\) and \({\mit \Gamma } _{nn}\) for mesonic and non-mesonic decays, in coincidence. Further information could be gained on neutron-rich Hypernuclei and rare two-body decays. Ideas for the continuation of the program, as well as possible extension to an improved machine (DA\(\Phi \)NE2) will be finally discussed.

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Around 1979, two realistic Nijmegen models of the baryon–baryon interaction were available: the elder model D and the improved new model F. Only model F led to the semiempirical value of the \({\mit \Lambda }\) binding in nuclear matter. When the first CERN observation of \({\mit \Sigma }\) hypernuclei was announced, model F was used to calculate \(V_{\mit \Sigma }\), the potential felt by \({\mit \Sigma }\) in nuclear matter. The result, a repulsive \(V_{\mit \Sigma }\), was unreconcilable with the CERN observation, and prompted theoreticians to use model D which led to an attractive \(V_{\mit \Sigma }\). To explain the existence of narrow \({\mit \Sigma }\) hypernuclear states at a relatively high energy, the theoreticians came forward with such ideas as the ‘bound states embedded in continuum’, or \(V_{\mit \Sigma }(r)\) with a repulsive barrier at the hypernuclear surface. A possible inaccuracy in the CERN experiments was not considered. The first empirical indication that \(V_{\mit \Sigma }\) may be repulsive inside the nuclear core came from the analysis of strong interaction shifts and widths of \({\mit \Sigma }^-\) atoms, which could be explained with the help of model F of the baryon–baryon interaction. Final evidence of the repulsiveness of \(V_{\mit \Sigma }\) was supplied by the new \((K^-,\pi )\) experiments performed at Brookhaven with an order of magnitude better statistics than the old CERN experiments. In the Brookhaven experiments the narrow states of \({\mit \Sigma }\) hypernuclei observed at CERN disappeared. The pion spectra measured in these new experiments are consistent with \(V_{\mit \Sigma }\) repulsive inside nuclei and with model F of the baryon–baryon interaction.

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Fits of pion–nucleus potentials to large sets of pionic atom data reveal departures of parameter values from the corresponding free \(\pi N\) parameters. These medium effects can be quantitatively reproduced by a chiral-motivated model where the pion decay constant is modified in the medium or by including the empirical on-shell energy dependence of the amplitudes. No consistency is obtained between pionic atoms and the free \(\pi N\) interaction when an extreme off-shell chiral model is used. The role of the size of data sets is briefly discussed.

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Recent experiments on production of \({\mit \Lambda }{\mit \Lambda }\) Hypernuclei have provoked renewed interest in extracting the \({\mit \Lambda }{\mit \Lambda }\) interaction from the few events identified since the inception of this field forty years ago. Few-body calculations relating to this issue are reviewed, particularly with respect to the possibility that \(A=4\) marks the onset of \({\mit \Lambda }{\mit \Lambda }\) binding to nuclei. The Nijmegen soft-core model potentials NSC97 qualitatively agree with the strength of the \({\mit \Lambda }{\mit \Lambda }\) interaction deduced from the newly determined binding energy of \(_{{\mit \Lambda }{\mit \Lambda }}^{6}\)He. Applying the extended NSC97 model to stranger nuclear systems suggests that \(A=6\) marks the onset of \({\mit \Xi }\) binding, with a particle stable \(_{{\mit \Lambda }{\mit \Xi }}^{6}\)He, and that strange hadronic matter is robustly bound.

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5-quark baryon \({\mit \Theta }^{+}\) with \(S=+1\) was discovered in photoproduction from the neutron in \(^{12}\)C at LEPS of SPring-8. A Gaussian significance was \(4.6\sigma \). The mass and width of the \({\mit \Theta }^{+}\) were \(1.54\pm 0.01\) GeV/\(c^{2}\) and smaller than 25 MeV/\(c^{2}\), respectively. Recent results from other experiments confirmed the existence of the \({\mit \Theta }^{+}\). The \({\mit \Theta }^{+}\) can be interpreted as a molecular meson–baryon resonance or alternatively as an exotic five quark state (\(uudd\bar {s}\)). Photon beam asymmetries for the \(p\)(\(\gamma \), \(K^{+}\))\({\mit \Lambda }\) and \(p\)(\(\gamma \), \(K^{+}\))\({\mit \Sigma }^{0}\) reactions were measured at \(E_{\gamma }=1.5\)–2.4 GeV and \(0.6\lt \cos (\theta ^{\rm c.m.}_{K^+})\lt 1.0\) by using linearly polarized photon beam. The measured asymmetries are positive and gradually increase with rising photon energy. There is no theoretical prediction which perfectly reproduces the measurements. Including the new results in the development of theoretical models is crucial for understanding the reaction mechanism and to test the presence of missing resonances.

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Various models of the \(K^-\) nucleus potential have been compared and tested in fits to kaonic atom data. The calculations give basically two vastly different predictions for the depth of the \(K^-\) optical potential at the nuclear density. The study of the \((K^-_{\rm stop}, \pi )\) reaction could help to distinguish between \(K^-\) optical potentials as the \({\mit \Lambda }\)-hypernuclear formation rates are sensitive to the details of the initial-state \(K^-\) wave function.

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Using a germanium detector array, Hyperball, we have measured \(\gamma \) rays from several \({\mit \Lambda }\) hypernuclei. In the previous experiments, spin-dependence of \({\mit \Lambda } N\) effective interaction was investigated. In the latest experiment, we have studied \(^{11}_{\mit \Lambda }\)B in which six \(\gamma \) transitions have been observed. The result of this experiment suggests that the level structure is quite different from a theoretical prediction based on the \({\mit \Lambda } N\) spin-dependent effective interaction parameters determined in the previous experiments.

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Studies of \({\mit \Lambda } {\mit \Lambda } \)-double-hypernuclei and \({\mit \Omega } \)-atoms by means of \(\gamma \)-ray spectroscopy with Ge detectors represent a unique tool to investigate \(YN\) and \(YY\) interaction and to measure the only directly observable quadrupole moment of a hadron. These challenging experiments will be performed by the PANDA collaboration (Proton ANtiproton at DArmstadt) at the High Energy Storage Ring (HESR) of the future GSI facility. For the \({\mit \Lambda } {\mit \Lambda } \)-double-hypernuclear \(\gamma \)-ray spectroscopy, a rate of several hundreds \(\gamma \)-ray events per day is expected.

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Main results coming from the extensive study of strangeness signals from heavy ion collisions at the CERN SPS energy range are discussed. A systematics of production rates is given, as a function of strangeness content of the products, and of the incident energy, centrality and the mass of the colliding nuclei. Different interpretations of the results are briefly discussed.

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ANKE is a magnetic spectrometer and detection system at an internal target position of COSY-Jülich optimized for charged kaon detection. Recent results from ANKE on kaon production in \(pp\) and \(pD\) interactions are reported. From the \(pp\) data first absolutely normalized angular and invariant-mass spectra for the reaction \(pp\to dK^+\bar K^0\) have been obtained. A partial-wave decomposition reveals a strong contribution of \(S\)-wave \(K\bar K\)-pairs with low relative energy, suggesting dominance of resonant kaon production via the \(a_0^+\)(980). This indicates that systematic studies of the light scalar resonances \(a_0~/~f_0\)(980) are possible at COSY. Final goal of these measurements — requiring a neutral-particle detector which is not yet available — is to obtain information about the charge-symmetry breaking \(a_0\)–\(f_0\) mixing. From the analysis of the \(pD\) data it is concluded that the \(K^+\)-production cross section on the neutron is significantly larger as compared to the proton. A cross-section ratio of \(\sigma _n~/~\sigma _p\sim 4\) is deduced.

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A review of strange particle production in heavy ion collisions at incident energies from SIS up to collider energies is presented. A statistical model assuming chemical equilibrium and local strangeness conservation (i.e.  strangeness conservation per collision) describes most of the observed features. It is demonstrated that the \(K^-\) production at SIS energies occurs predominantly via strangeness exchange and that this channel is approaching chemical equilibrium. The observed maximum in the \(K^+/\pi ^+\) excitation function is also seen in the ratio of strange to non-strange particle production. The appearance of this maximum around 30 \(A\,\)GeV is due to the energy dependence of the chemical freeze-out parameters temperature \(T\) and baryo-chemical potential \(\mu _B\).

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Particles with large transverse momentum (\(p_{\rm T}\)) produced during the initial phase of a nuclear collision can be used to probe the dense excited matter created during the collision process. The \(p_{\rm T}\) spectra of neutral pions and charged hadrons in Au+Au and \(d+{\rm Au}\) collisions GeV are compared to \(p+p\) spectra at the same \(\sqrt {s_{NN}}\). In central Au+Au collisions a factor of 4–5 suppression of high \(p_{\rm T}\) neutral pion and charged hadron yields is observed compared to expectations from scaled \(p+p\) results. No suppression of high \(p_{\rm T}\) particles is observed in \(d+{\rm Au}\) collisions, suggesting that the observed suppression in central Au+Au collisions is due to the produced dense matter.

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We present recent results of heavy-ion experiments performed by the FOPI collaboration at the SIS accelerator in Darmstadt. The studied observables, such as the isotopic ratios, the flow of nuclear fragments and their rapidity density distributions, provide necessary information to judge about the dynamics of heavy-ion reactions at intermediate energies. Comparison of the measured yields of strange- and anti-strange particles allows to conclude about the production of normally not measured \({\mit \Sigma }^+\) and \({\mit \Sigma }^-\) hyperons.

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In this talk we review the important role played by chiral SU(3) symmetry in hadron physics. Exciting new results on the formation of baryon resonances as implied by chiral coupled-channel dynamics are presented and discussed. The results are the consequence of progress made in formulating a consistent effective field theory for the meson-baryon scattering processes in the resonance region. Strangeness channels are found to play a decisive role in the formation of resonances. As a further application of chiral coupled-channel dynamics the properties of antikaons and hyperon resonances in cold nuclear matter are reviewed.

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HADES is a second generation experiment designed to study dielectron production in proton, pion, and heavy ion induced reactions at the GSI accelerator facility in Darmstadt. The physics programme of HADES is focused on in-medium properties of the light vector mesons. In this contribution we discuss relevance of dielectron spectroscopy to the problem of hadron mass origin. We present status of the HADES experiment, demonstrate its capability to identify rare dielectron signal and show first experimental results obtained from C+C reactions at 2 \(A\)GeV.

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The study of high-energy nucleus–nucleus collisions will be one of the major activities at the future accelerator facility in Darmstadt. The goal of the research program is the exploration of the QCD phase diagram in the region of high baryon densities. Relevant experimental observables and the proposed detector system will be discussed.

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We argue that results on deep inelastic \(e\)–\(A\) scattering show partial deconfinement of nucleons inside the nuclear matter enhancing therefore the role played by the partonic degrees of freedom. In particular, we show that magnitude of the nuclear Fermi motion is sensitive to the residual interactions between partons, influencing both the nucleon structure function and the value of nucleon mass in the nuclear medium.

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Results of the intermittency analysis of experimental data obtained with the FOPI detector and the analysis of events simulated by the IQMD model for Au + Au collisions at 600A and 800A MeV are presented. The method of horizontal normalized scaled factorial moments was used. The intermittency analysis for charge-, rapidity- and azimuthal angle observables has shown that results of IQMD simulations with hard equation of state, momentum dependent interactions and standard nucleon–nucleon interaction cross section reproduce experimental data better than simulations with other sets of parameters.

abstract

Correlations of particles produced in heavy ion collisions are sensitive to the space-time structure of the emitting system because of strong and Coulomb Final State Interactions. Moreover, non-identical particle correlations are a unique tool to probe the system collective expansion. The STAR experiment at RHIC allows to measure correlations of non-identical particles with close velocities. We have performed such an analysis from data obtained by the STAR detector for Au+Au collisions at 130 GeV and 200 GeV. The first results indicate that the average space-time emission points of pions, kaons and protons are different. The origin of such differences can be related to the time shift in the emission of different particle species or/and to the strong transverse radial flow. This result provides a new independent evidence that the system created at RHIC undergoes a strong collective transverse expansion.

abstract

Ar+Ni collisions at 77 MeV/\(u\) were studied in the experiment E286 performed at GANIL. An important advantage of this experiment was an application of the neutron detector DEMON for registration of both neutral and charged particles. This feature allows to compare characteristics of neutrons and protons detected by the same detector and gives a possibility to determine the influence of the Coulomb field on the proton emission. Estimation of a charge of the emitting source was performed by comparing energy spectra of neutrons and protons detected under identical experimental conditions. The experimental results were compared with the prediction of the SIMON model [D. Durand, Nucl. Phys. A541, 266 (1992)] and Landau–Vlasov model [Z. Basrak, Ph. Eudes, P. Abgrall, F. Haddad, F. Sébille, Nucl. Phys. A624, 472 (1997)].

abstract

Presented are results from LEP and SLC accelerators concerning precision tests of the electroweak interactions. Discussed are line shape measurements, asymmetries at the \(Z^0\) pole, measurements of the \(W\) mass and results of the global fit to the electroweak data. The results on the Standard Model Higgs are presented as well.

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Nuclear physics plays an essential role in the dynamics of a type II supernova (a collapsing star). Recent advances in nuclear many-body theory allow now to reliably calculate the stellar weak-interaction processes involving nuclei. The most important process is the electron capture on finite nuclei with mass numbers \(A\gt 55\). It is found that the respective capture rates, derived from modern many-body models, differ noticeably from previous, more phenomenological estimates. This leads to significant changes in the stellar trajectory during the supernova explosion, as has been found in state-of-the-art supernova simulations.

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In the inner crust of a neutron star, due to the high density and pressure, nuclei which are still present, are immersed in a neutron superfluid. One then expects that the dynamical properties of nuclei are significantly affected. In order to estimate the magnitude of the effect associated with the presence of a superfluid medium, we formulate the hydrodynamical approach to the nuclear dynamics in the inner crust of neutron stars. We calculate the renormalized nuclear mass and the strength of the medium-induced interaction between nuclei. We argue that these effects noticeably modify the properties of the Coulomb crystal in the inner crust.

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Matter effects on neutrino oscillations in both, a supernova and the Earth, change the observed supernova neutrino spectra. We calculate the expected number of supernova neutrino interactions for ICARUS, SK and SNO detectors as a function of the distance which they traveled in the Earth. Calculations are performed for supernova type II at 10 kpc from the Earth, using standard supernova neutrino fluxes described by thermal Fermi–Dirac distributions and the PREM I Earth matter density profile.

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The nuclear method to discover Majorana neutrinos is the neutrinoless double \( \beta \) decay. An interesting alternative is offered by the inverse process, neutrinoless radiative double electron capture, accompanied by a photon emission. Two different mechanisms seem plausible: the magnetic type radiation by an initial electron and the resonant electric type radiation by the final atom. The physical background for these processes is calculated.

abstract

K2K long-baseline experiment is the first attempt to test atmospheric neutrino oscillation results under controlled beam conditions. It was found that the whole collected data sample disfavor no oscillation hypothesis at 4\(\sigma \) level. The full oscillation analysis of \(\nu _{\mu } \to \nu _x\) and \(\nu _{\mu } \to \nu _e\) transformations was performed using data set collected from June 1999 to July 2001. As a result we derive allowed region at 90\(\%\) CL of \(\Delta m^2 = 1.5 - 3.9 \times 10^{-3}~{\rm eV}^2\) for \(\sin ^22\theta _{\mu \tau }=1\) consistent with atmospheric neutrino results. For \(\nu _e\) appearance search, an one observed event remains consistent with \(2.4 \pm 0.6\) background expectation. This allowed to obtain upper limit at 90\(\%\) CL of \(\sin ^22\theta _{\mu e } \lt 0.15\) for the best-fit \(\Delta m^2\) from \(\nu _{\mu }\) disappearance analysis of \(2.8 \times 10^{-3}~{\rm eV}^2\).

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Through the advent of post-accelerated beams with REX-ISOLDE at CERN, probing nuclear properties using transfer reactions and Coulomb excitation of exotic nuclear species is now possible. REX ISOLDE currently provides beams of energy 2.2 MeV/\(u\) (soon be upgraded to 3.1 MeV/\(u\)) into the gamma-ray MINIBALL array, and other instrumentation, at the secondary target position. Examples of research topics currently addressed using REX are presented. Scheduled energy up-grades will increase the physics potential even further. The goal for the next five years will be to accelerate ions up to 5 MeV/\(A\) and higher energies. Increase of primary beam intensity will also be achieved in a phased approach, with a significant enhancement provided by the proposed Superconducting Proton Linac as the primary accelerator.

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We shall discuss most recent advances in the description of weakly bound and unbound nuclear states using either a real ensemble representing (quasi-) bound single-particle states and scattering states (Shell Model Embedded in the Continuum) or a complex Berggren ensemble representing bound single-particle states, single-particle resonances, and non-resonant continuum states (the so-called Gamow Shell Model).

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A very accurate knowledge of the fission barrier shapes is necessary to predict the spontaneous fission life times of nuclei. Using the Strutinsky macroscopic–microscopic method we have performed calculations of the potential energy for even–even transuranic nuclei. The shell and pairing corrections are evaluated using the single-particle energies of the relativistic Woods–Saxon potential [1]. The microscopic corrections are added to the macroscopic energy obtained with the Lublin Strasburg Drop (LSD) model [2] to obtain the total potential energy in the multidimensional space of deformation parameters.

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The unified description of nuclear structure and nuclear reaction aspects allows to calculate, in a consistent manner, the spectroscopic values of the nucleus that is treated as an open quantum system. The \(E_k, ~{\mit \Gamma }_k\) follow from the energy dependent eigenvalues \(\tilde E_k - i/2\) \(\tilde {\mit \Gamma }_k\) of the effective Hamiltonian \({\cal H}\) describing the nucleus embedded in the continuum of decay channels. The coupling matrix elements \(\tilde \gamma _{kc}\) between the resonance states \(k\) and the decay channels \(c\) are calculated by means of the eigenfunctions of \({\cal H}\). They are complex and energy dependent. The \(S\) matrix contains the \(\tilde E_k, ~\tilde {\mit \Gamma }_k\) and \(\tilde \gamma _{kc}\). The \(R\) matrix can therefore be generalized in a natural manner by replacing the standard spectroscopic parameters \(E_k^R, ~{\mit \Gamma }_k^R\) and \(\gamma _{kc}^R\) by the energy dependent functions \(\tilde E_k, ~\tilde {\mit \Gamma }_k\) and \(\tilde \gamma _{kc}\). This new version of \(R\) matrix allows the extraction of spectroscopic information also from nuclear reactions near decay thresholds and in the regime of high level density where narrow resonances appear together with broad ones. Surface effects play a role similar as in the standard theory.

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We develop the realistic continuum shell model which includes the coupling between many-particle (quasi-)bound states and the continuum of one- and two-particle scattering states. This microscopic approach is applied to the description of the two-proton radioactivity from the excited state \(1^-_2\) in \(^{18}\)Ne.

abstract

The matrix elements of the zero-range \(\delta \)-force and the finite range Gogny-type pairing force are compared. The strengths of the \(\delta \)-interaction for rare-earth nuclei are adjusted. Pairing gaps resulting from different pairing interactions are compared to experimental ones.

abstract

A set of parameters of the relativistic-mean-field theory (RMFT) is obtained by adjusting the macroscopic part of the RMFT binding energies of 142 spherical even-even nuclei to the phenomenological Lublin–Strasbourg–Drop (LSD) model.