Search

We construct the equation of state of hypernuclear matter and study the structure of neutron stars employing a chiral hyperon-nucleon interaction of the J\"{u}lich--Bonn group tuned to femtoscopic $\Lambda p$ data of the ALICE collaboration, and $\Lambda\Lambda$ and $\Xi$N interactions determined from Lattice QCD calculations by the HAL QCD collaboration that reproduce the femtoscopic $\Lambda\Lambda$ and $\Xi^-p$ data. We employ the ab-initio microscopic Brueckner--Hartree--Fock theory extended to the strange baryon sector. A special focus is put on the uncertainties of the hyperon interactions and how they are effectively propagated to the composition, equation of state, and mass-radius relation of neutron stars. To such end, we consider the uncertainty due to the experimental error of the femtoscopic $\Lambda p$ data used to fix the chiral hyperon-nucleon interaction and the theoretical uncertainty, estimated from the residual cut-off dependence of this interaction. We find that the final maximum mass of a neutron star with hyperons is in the range $1.3-1.4$ $M_\odot$, in agreement with previous works. The hyperon puzzle, therefore, remains still an open issue if only two-body hyperon-nucleon and hyperon-hyperon interactions are considered., Comment: 9 pages, 3 figures, 1 table

Near-threshold $p\bar\Lambda$ mass spectra for the reactions $e^+e^- \to K^- p\bar\Lambda$ and $J/\psi \to K^- p\bar\Lambda$ are investigated with an emphasis on the role played by the interaction in the $p\bar\Lambda$ system. As guideline for the $p\bar\Lambda$ interaction a variety of $\Lambda\bar\Lambda$ potential models is considered that have been established in the analysis of data on $p\bar p\to \Lambda\bar\Lambda$ in the past. Arguments why the properties of the $p\bar\Lambda$ and $\Lambda\bar\Lambda$ interactions can be expected to be very similar are provided. It is shown that the near-threshold enhancement in the invariant mass observed for the $e^+e^-$ reaction can be reproduced quantitatively by the assumed $p\bar\Lambda$ final-state interaction in the partial wave suggested by an amplitude analysis of the experiment. The effect of the $p\bar\Lambda$ final-state interaction in other decays is explored, including the recently measured reactions $B^- \to J/\psi\, \bar p \Lambda$ and $B^+ \to J/\psi\, p \bar\Lambda$. It is found that the final-state interaction improves the description of the measured invariant mass near threshold in most cases., Comment: 9 pages, 11 figures

This work provides the first combined analysis of low-energy p$\Lambda$ scattering, considering both cross section and correlation data. The obtained results establish the most stringent constraints to date on the two-body p$\Lambda$ interaction, pointing to a weaker attraction than so far accepted. The best set of scattering lengths for the spin singlet and triplet are found to range from $f_0, f_1 = (2.1, 1.56)$ to $(3.34, 1.18)~$fm. With a chiral NY potential fine-tuned to those scattering parameters, the in-medium properties of the $\Lambda$ are explored and a potential depth of $U_\Lambda= -36.3\pm 1.3 \mathrm{(stat)}^{+2.5}_{-6.2}\mathrm{(syst)}$ MeV is found at nuclear matter saturation density., Comment: The initial upload contained a wrong entry in Table 1. The 'f1' for point iv) was WRONGLY written as 1.54 fm, whereas the CORRECT value is 1.32 fm

The J\"ulich-Bonn group aims at an extensive study of the baryon-baryon ($BB$) interaction involving strange baryons ($\Lambda$, $\Sigma$, $\Xi$) within SU(3) chiral effective field theory. An overview of achievements and new developments over the past few years is provided. The topics covered are: 1) Derivation of the leading charge-symmetry breaking (CSB) interaction for the $\Lambda N$ system and its application in a study of CSB effects in $A$=$4$ $\Lambda$-hypernuclei. 2) Updated results for the $\Xi N$ interaction at NLO and predictions for $\Xi^- p$ correlation functions. 3) Extension of the $\Lambda N$-$\Sigma N$ interaction to next-to-next-to-leading order., Comment: 8 pages, 5 figures, Contribution to proceedings of HYP2022

Studies of the baryon-baryon interaction involving hyperons within chiral effective field theory, so far performed up to next-to-leading order (NLO) in the chiral expansion, have shown that for the strangeness $S=-1$ ($\Lambda N$, $\Sigma N$) and $S=-2$ ($\Lambda \Lambda$, $\Xi N$) sectors a consistent and satisfactory description of the available scattering data and experimental constraints can be achieved based on the assumption of broken SU(3) flavor symmetry. We explore the possible extension of this approach at the NLO level to strangeness $S=-3$ and $S=-4$ baryon-baryon systems where empirical information is rather scarce. Specifically we address the question how measurements of two-body correlation functions in heavy-ion collisions and/or in high-energetic proton-proton collisions can help to constrain the interaction in channels like $\Xi\Lambda$ or $\Xi\Xi$., Comment: 10 pages, 3 figures, contribution to Chiral Dynamics 2021

The spin-dependent components of the fundamental hyperon-nucleon interactions are largely unknown. We show that under reasonable assumptions, a measurement of the $\Sigma^+ p$ correlation function in high-energy proton-proton or heavy-ion collisions combined with cross section data allows to separate the singlet and the triplet $S$-wave contributions., Comment: 6 pages, 3 figures, discussion extended, references updated

The complexity of threshold phenomena is exemplified on a prominent and long-known case - the structure in the $\Lambda p$ cross section (invariant mass spectrum) at the opening of the $\Sigma N$ channel. The mass splitting between the $\Sigma$ baryons together with the angular momentum coupling in the $^3S_1$-$^3D_1$ partial wave imply that, in principle, up to six channels are involved. Utilizing hyperon-nucleon potentials that provide an excellent description of the available low-energy $\Lambda p$ and $\Sigma N$ scattering data, the shape of the resulting $\Lambda p$ cross section is discussed and the poles near the $\Sigma N$ threshold are determined. Evidence for a strangeness $S=-1$ dibaryon is provided, in the form of a deuteron-like (unstable) $\Sigma N$ bound state. Predictions for level shifts and widths of $\Sigma^-p$ atomic states are given., Comment: 10 pages, 4 figures

The Spin Physics Detector, a universal facility for studying the nucleon spin structure and other spin-related phenomena with polarized proton and deuteron beams, is proposed to be placed in one of the two interaction points of the NICA collider that is under construction at the Joint Institute for Nuclear Research (Dubna, Russia). At the heart of the project there is huge experience with polarized beams at JINR. The main objective of the proposed experiment is the comprehensive study of the unpolarized and polarized gluon content of the nucleon. Spin measurements at the Spin Physics Detector at the NICA collider have bright perspectives to make a unique contribution and challenge our understanding of the spin structure of the nucleon. In this document the Conceptual Design of the Spin Physics Detector is presented.

The Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, provides unique possibilities for a new generation of hadron-, nuclear- and atomic physics experiments. The future antiProton ANnihilations at DArmstadt (PANDA or $\overline{\rm P}$ANDA) experiment at FAIR will offer a broad physics programme, covering different aspects of the strong interaction. Understanding the latter in the non-perturbative regime remains one of the greatest challenges in contemporary physics. The antiproton-nucleon interaction studied with PANDA provides crucial tests in this area. Furthermore, the high-intensity, low-energy domain of PANDA allows for searches for physics beyond the Standard Model, e.g. through high precision symmetry tests. This paper takes into account a staged approach for the detector setup and for the delivered luminosity from the accelerator. The available detector setup at the time of the delivery of the first antiproton beams in the HESR storage ring is referred to as the \textit{Phase One} setup. The physics programme that is achievable during Phase One is outlined in this paper., Comment: 35 pages, 15 figures

Song et al. [Phys. Rev. C 102, 065208 (2020)] presented results for the $\Lambda_c N$ interaction based on an extrapolation of lattice simulations by the HAL QCD Collaboration at unphysical quark masses to the physical point via covariant chiral effective field theory. We point out that their predictions for the $^3D_1$ partial wave disagree with available lattice results. We discuss the origin of that disagreement and present a comparison with predictions from conventional (non-relativistic) chiral effective field theory., Comment: 2 pages, 1 figure

A systematic analysis of nucleon-nucleon scattering amplitudes is available up to a laboratory energy of $3$~GeV in case of the $pp$ system and up to $1.2$ GeV for $pn$. At higher energies there is only incomplete experimental information on $pp$ elastic scattering, whereas data for the $pn$ system are very scarce. We apply the spin-dependent Glauber theory to calculate spin observables of $pd$ elastic scattering at $3$-$50$ GeV/c using $pp$ amplitudes available in the literature and parametrized within the Regge formalism. The calculated vector $A_y^p$, $A_y^d$ and tensor $A_{xx}$, $A_{yy}$ analyzing powers and the spin-correlation coefficients $C_{y,y}$, $C_{x,x}$, $C_{yy,y}$, $C_{xx,y}$ can be measured at SPD NICA and, thus, will provide a test of the used $pN$ amplitudes., Comment: 11 pages,4 figures, to proceedings of the conference "NUCLEUS-2020" (11-17 October 2020, St-Petersburg, Russia)

$\Lambda$-deuteron two-particle momentum correlation functions, to be measured in high-energy heavy-ion collisions, are investigated. In particular, the question is addressed whether such correlations can serve as an additional and alternative source of information on the elementary $\Lambda N$ interaction. The study is performed within the Lednicky-Lyuboshits formalism, utilizing an effective range expansion for the two relevant $S$-wave $\Lambda d$ amplitudes with parameters taken from the literature. It is found that in collisions characterized by a large emitting source the $\Lambda d$ correlation function is predominatly sensitive to the quartet state ($^4S_{3/2}$). In contrast, for small source sizes the contribution from the doublet partial wave ($^2S_{1/2}$) could be significant. Though the latter is constrained by the hypertriton binding energy, its present experimental uncertainty impedes an accurate determination of the doublet amplitude and, in turn, complicates conclusions on the quartet state., Comment: 7 pages, 4 figures

We study the prospects for deducing constraints on the interaction of charmed baryons with nucleons from measurements of two-particle momentum correlation functions for $\Lambda_c p$. The correlation functions are calculated for $\Lambda_c N$ and $\Sigma_c N$ interactions that have been extrapolated from lattice QCD simulations at unphysical masses of $m_\pi=410-570$ MeV to the physical point using chiral effective field theory as guideline. In addition, we consider phenomenological $Y_c N$ models from the literature to explore the sensitivity of the results to the properties of the interaction in detail. We find that a measurement of the $\Lambda_c p$ correlation functions could indeed allow one to discriminate between strongly attractive $\Lambda_c N$ forces, as predicted by some phenomenological models, and a weakly attractive interaction as suggested by the presently available lattice simulations., Comment: 8 pages, 4 figures

The $\Lambda N$ and $\Sigma N$ interactions are considered at next-to-leading order in SU(3) chiral effective field theory. Different options for the low-energy constants that determine the strength of the contact interactions are explored. Two variants are analysed in detail which yield equivalent results for $\Lambda N$ and $\Sigma N$ scattering observables but differ in the strength of the $\Lambda N \to \Sigma N$ transition potential. The influence of this difference on predictions for light hypernuclei and on the properties of the $\Lambda$ and $\Sigma$ hyperons in nuclear matter is investigated and discussed. The effect of the variation in the potential strength of the $\Lambda N$-$\Sigma N$ coupling (also called $\Lambda -\Sigma$ conversion) is found to be moderate for the considered $^3_\Lambda \rm H$ and $^4_\Lambda \rm He$ hypernuclei but sizable in case of the matter properties. Further, the size of three-body forces and their relation to different approaches to hypernuclear interactions is discussed., Comment: 22 pages, 10 figures

The weak decay parameter $\alpha_-$ of the $\Lambda$ is an important quantity for the extraction of polarization observables in various experiments. Moreover, in combination with $\alpha_+$ from $\bar\Lambda$ decay it provides a measure for matter-antimatter asymmetry. The weak decay parameter also affects the decay parameters of the $\Xi$ and $\Omega$ baryons and, in general, any quantity in which the polarization of the $\Lambda$ is relevant. The recently reported value by the BESIII collaboration of $0.750(9)(4)$ is significantly larger than the previous PDG value of $0.642(13)$ that had been accepted and used for over 40 years. In this work we make an independent estimate of $\alpha_-$, using an extensive set of polarization data measured in kaon photoproduction in the baryon resonance region and constraints set by spin algebra. The obtained value is 0.721(6)(5). The result is corroborated by multiple statistical tests as well as a modern phenomenological model, showing that our new value yields the best description of the data in question. Our analysis supports the new BESIII finding that $\alpha_-$ is significantly larger than the previous PDG value. Any experimental quantity relying on the value of $\alpha_-$ should therefore be re-considered., Comment: 6 pages, 1 figure

A qualitative discussion on the range of the potentials as they result from the phenomenological meson-exchange picture and from lattice simulations by the HAL QCD Collaboration is presented. For the former pion- and/or $\eta$-meson exchange are considered together with the scalar-isoscalar component of correlated $\pi\pi /K \bar K$ exchange. It is observed that the intuitive expectation for the behavior of the baryon-baryon potentials for large separations, associated with the exchange of one and/or two pions, does not always match with the potentials extracted from the lattice simulations. Only in cases where pion exchange provides the longest ranged contribution, like in the $\Xi N$ system, a reasonable qualitative agreement between the phenomenological and the lattice QCD potentials is found for baryon-baryon separations of $r \gtrsim 1$ fm. For the $\Omega N$ and $\Omega\Omega$ interactions where isospin conservation rules out one-pion exchange a large mismatch is observed, with the potentials by the HAL QCD Collaboration being much longer ranged and much stronger at large distances as compared to the phenomenological expectation. This casts some doubts on the applicability of using these potentials in few- or many-body systems., Comment: 8 pages, 9 figures

The in-medium properties of a baryon-baryon interaction for the strangeness $S=-2$ sector derived within chiral effective field theory up to next-to-leading order are investigated. The considered $\Xi N$ interaction is in line with available empirical constraints on the $\Lambda\Lambda$ $S$-wave scattering length and on $\Xi N$ elastic and inelastic cross sections. In particular, there are no near-threshold bound states in the $\Xi N$ system. A conventional $G$-matrix calculation for this interaction is performed and reveals that the single-particle potential of the $\Xi$-hyperon in nuclear matter is moderately attractive as suggested by recent experimental evidence for the existence of $\Xi$-hypernuclei., Comment: 9 pages, 3 figures

Two-particle momentum correlation functions as measured in heavy ion collisions or in high-energetic proton-proton collisions are studied. Special emphasis is put on systems like $\Lambda\Lambda$ or $K^-p$ where effects from the coupling to other channels could be relevant. In both cases other channels open at relatively low momenta or are already open at the reaction threshold. To have a solid basis, realistic coupled-channel interactions for $\Lambda\Lambda-\Xi N-\Lambda\Sigma-\Sigma\Sigma$ and $\pi\Lambda-\pi\Sigma-\bar KN$ are utilized in the actual calculations. It is found that the opening of the $\Xi N$ channel leaves a trace in the $\Lambda\Lambda$ correlation function that could be detectable in experiments. Should the proposed $H$-dibaryon be located close to or below the $\Xi N$ it will have a very pronounced effect. The presence of open channels in systems like $\Xi^- p$ or $K^-p$ does influence the correlation functions significantly at low momenta and will certainly complicate any dedicated analysis., Comment: 13 pages, 7 figures; table added, several comments added

We study the manifestation of the $\Delta^{++}-\Delta^-$ component of the deuteron wave function in the exclusive reaction $\bar p d \to \pi^- \pi^- \Delta^{++}$. Due to the large binding energy the internal motion in the $\Delta-\Delta$ system is relativistic. We take this into account within the light-cone (LC) wave function formalism and, indeed, found large differences between calculations based on the LC and non-relativistic (NR) wave functions. We demonstrate, that the consistent LC treatment of the $\Delta-\Delta$ system plays the key role in the separation of the signal and background. Within the LC approach, the characteristic shape of the momentum distribution of the $\Delta-\Delta$ bound system predicted by the meson-exchange model is well visible on the background of usual annihilations at beam momenta between 10 and 15 GeV/c., Comment: 44 pages, 21 figures, sect. 3 extended, references added, results unchanged, accepted in Phys. Rev. C

The vector and tensor analysing powers in deuteron-proton elastic scattering have been measured in the forward hemisphere at deuteron kinetic energies of 1.2 GeV and 2.27 GeV using the ANKE spectrometer at the COSY storage ring. The results are compared with other experimental data and with predictions made within the framework of Glauber multiple scattering theory., Comment: 11 pages with 8 figures. To be submitted for publication

The reaction $K^-d \to \pi \Sigma n$ is studied within a Faddeev-type approach, with emphasis on the specific kinematics of the E31 experiment at J-PARC, i.e. $K^-$ beam momentum of $p_K = 1$ GeV/c and neutron angle of $\theta_n=0^\circ$. The employed Faddeev approach requires as main input amplitudes for the two-body subsystems $\bar KN \to \bar KN$ and $\bar KN \to \pi\Sigma$. For the latter results from recently published chiral unitary models of the $\bar KN$ interaction are utilized. The $\bar KN \to \bar KN$ amplitude itself, however, is taken from a recent partial-wave analysis. Due to the large incoming momentum of the $K^-$, the $\bar KN$ interaction is probed in a kinematical regime where those chiral potentials are no longer applicable. A comparison of the predicted spectrum for various $\pi \Sigma$ charge channels with preliminary data is made and reveals a remarkable agreement as far as the magnitude and the line shape in general is concerned. Noticeable differences observed in the $\pi\Sigma$ spectrum around the $\bar KN$ threshold, i.e. in the region of the $\Lambda$(1405) resonance, indicate a sensitivity to the details of the employed $\bar KN \to \pi\Sigma$ amplitudes and suggest that pertinent high-precision data could indeed provide substantial constraints on the structure of the $\Lambda$(1405)., Comment: 15 pages, 9 figures

Chiral effective field theory is utilized for extrapolating results on the $\Lambda_c N$ interaction, obtained in lattice QCD at unphysical (large) quark masses, to the physical point. The pion-mass dependence of the components that constitute the $\Lambda_c N$ potential up to next-to-leading order (pion-exchange diagrams and four-baryon contact terms) is fixed by information from lattice QCD simulations. No recourse to SU(3) or SU(4) flavor symmetry is made. It is found that the results of the HAL QCD Collaboration for quark masses corresponding to $m_\pi = 410$--$570$ MeV imply a moderately attractive $\Lambda_c N$ interaction at $m_\pi = 138$ MeV with scattering lengths of $a\approx -1$ fm for the $^1S_0$ as well as the $^3S_1$ partial waves. For such an interaction the existence of a charmed counterpart of the hypertriton is unlikely but four- and/or five-baryons systems with a $\Lambda_c$ baryon could be indeed bound., Comment: 7 pages, 2 figures; table added, several comments added

A formalism for treating the scattering of decuplet baryons in chiral effective field theory is developed. The minimal Lagrangian and potentials in leading-order SU(3) chiral effective field theory for the interactions of octet baryons ($B$) and decuplet baryons ($D$) for the transitions $BB\to BB$, $BB\leftrightarrow DB$, $DB\to DB$, $BB\leftrightarrow DD$, $DB\leftrightarrow DD$, and $DD\to DD$ are provided. As an application of the formalism we compare with results from lattice QCD simulations for $\Omega\Omega$ and $N\Omega$ scattering. Implications of our results pertinent to the quest for dibaryons are discussed., Comment: 26 pages, 6 figures; minor corrections in the text, references added

The validity of SU(4)-flavor symmetry relations of couplings of charmed $D$ mesons to light mesons and baryons is examined with the use of $^3{\rm P}_0$ quark-pair creation model and nonrelativistic quark model wave functions. We focus on the three-meson couplings $\pi\pi\rho$, $KK\rho$ and $DD\rho$ and baryon-baryon-meson couplings $NN\pi$, $N\Lambda K$ and $N\Lambda_c D$. It is found that SU(4)-flavor symmetry is broken at the level of 30% in the $DD\rho$ tree-meson couplings and 20% in the baryon-baryon-meson couplings. Consequences of these findings for DN cross sections and existence of bound states D-mesons in nuclei are discussed., Comment: 5 pages, 3 figures

Brueckner theory is used to investigate the in-medium properties of a $\Lambda$-hyperon in nuclear and neutron matter, based on hyperon-nucleon interactions derived within SU(3) chiral effective field theory (EFT). It is shown that the resulting $\Lambda$ single-particle potential $U_\Lambda(p_\Lambda =0,\rho)$ becomes strongly repulsive for densities $\rho$ of two-to-three times that of normal nuclear matter. Adding a density-dependent effective $\Lambda N$-interaction constructed from chiral $\Lambda NN$ three-body forces increases the repulsion further. Consequences of these findings for neutron stars are discussed. It is argued that for hyperon-nuclear interactions with properties such as those deduced from the SU(3) EFT potentials, the onset for hyperon formation in the core of neutron stars is expected to be shifted to extremely high baryon density, thus potentially resolving the so-called hyperon puzzle., Comment: 6 pages, two figures; longer discussion about uncertainties added

Cross sections for the charm-production reactions $\bar p p \to \bar \Lambda_c^- \Sigma_c^+$, $\bar \Sigma_c\Sigma_c$, $\bar \Xi_c\Xi_c$, and $\bar \Xi_c'\Xi_c'$ are presented, for energies near their respective thresholds. The results are based on a calculation performed in the meson-exchange framework in close analogy to earlier studies of the J\"ulich group on the strangeness-production reactions $\bar p p \to \bar \Lambda\Sigma$, $\bar \Sigma\Sigma$, $\bar \Xi\Xi$ by connecting the two sectors via SU(4) flavor symmetry. The cross sections are found to be in the order of $0.1 - 1$ $\mu b$ at energies of $100$ MeV above the respective thresholds, for all considered channels. Complementary to meson-exchange, where the charmed baryons are produced by the exchange of $D$ and $D^*$ mesons, a charm-production potential derived in a quark model is employed for assessing uncertainties. The cross sections predicted within that picture turned out to be significantly smaller., Comment: 17 pages, 7 figures

The reaction $e^+e^- \to \bar \Lambda \Lambda$ is investigated for energies close to the threshold. Specific emphasis is put on the role played by the interaction in the final $\bar \Lambda \Lambda$ system which is taken into account rigorously. For that interaction a variety of $\bar \Lambda \Lambda$ potential models is employed that have been constructed for the analysis of the reaction $\bar p p \to \bar \Lambda \Lambda$ in the past. The enhancement of the effective form factor for energies close to the $\bar \Lambda \Lambda$ threshold, seen in pertinent experiments, is reproduced. Predictions for the $\Lambda$ electromagnetic form factors $G_M$ and $G_E$ in the timelike region and for spin-dependent observables such as spin-correlation parameters are presented., Comment: 8 pages, 4 figures

The $\vec{p}p \rightarrow pK^{+}\Lambda$ reaction has been measured with the COSY-TOF detector at a beam momentum of $2.7\,\mathrm{GeV}/c$. The polarized proton beam enables the measurement of the beam analyzing power by the asymmetry of the produced kaon ($A_N^{K}$). This observable allows the $p\Lambda$ spin triplet scattering length to be extracted for the first time model independently from the final-state interaction in the reaction. The obtained value is $a_{t} = (-2.55 ^{+0.72}_{-1.39} {}_{\textrm{stat.}} \pm 0.6_{\textrm{syst.}} \pm 0.3_{\textrm{theo.}})\mathrm{fm}$. This value is compatible with theoretical predictions and results from model-dependent analyses., Comment: Revised version as accepted for publication in PRC

Scattering of protons with transversal polarization $p_y^p$ on deuterons with tensor polarization $P_{xz}$ provides a null-test signal for time-reversal (T) invariance violating but parity (P) conserving effects. We calculate the corresponding null-test observable at beam energies 100-1000 MeV within the spin-dependent Glauber theory considering T-violating P-conserving nucleon-nucleon interactions. The S-wave component of the deuteron wave function as well as the D-wave are taken into account and the latter is found to play an important role for the magnitude and the energy dependence of the observable in question. Specifically, with inclusion of the D wave the maximum of the obtained signal is shifted to higher beam energies, i.e. to 700-800 MeV., Comment: 6 pages, 3 figures

The strangeness $S=-2$ baryon-baryon interaction is studied in chiral effective field theory up to next-to-leading order. The potential at this order consists of contributions from one- and two-pseudoscalar-meson exchange diagrams and from four-baryon contact terms without and with two derivatives. SU(3) flavor symmetry is imposed for constructing the interaction in the $S=-2$ sector. Specifically, the couplings of the pseudoscalar mesons to the baryons are fixed by SU(3) symmetry and, in general, also the contact terms are related via SU(3) symmetry to those determined in a previous study of the $S=-1$ hyperon-nucleon interaction. The explicit SU(3) symmetry breaking due to the physical masses of the pseudoscalar mesons ($\pi$, $K$, $\eta$) is taken into account. It is argued that the $\Xi N$ interaction has to be relatively weak to be in accordance with available experimental constraints. In particular, the published values and upper bounds for the $\Xi^- p$ elastic and inelastic cross sections apparently rule out a somewhat stronger attractive $\Xi N$ force and, specifically, disfavor any near-threshold deuteron-like bound states in that system., Comment: 17 pages, 7 figures

Dynamically exact calculations of a quasi-bound state in the $\bar{K}\bar{K}N$ three-body system are performed using Faddeev-type AGS equations. As input two phenomenological and one chirally motivated $\bar{K}N$ potentials are used, which describe the experimental information on the $\bar{K}N$ system equally well and produce either a one- or two-pole structure of the $\Lambda(1405)$ resonance. For the $\bar{K}\bar{K}$ interaction separable potentials are employed that are fitted to phase shifts obtained from two theoretical models. The first one is a phenomenological $\bar{K}\bar{K}$ potential based on meson exchange, which is derived by SU(3) symmetry arguments from the J\"ulich $\pi \pi - \bar{K} K$ coupled-channels model. The other interaction is a variant of the first one, which is adjusted to the $KK$ s-wave scattering length recently determined in lattice QCD simulations. The position and width of the $\bar{K}\bar{K}N$ quasi-bound state is evaluated in two ways: (i) by a direct pole search in the complex energy plane and (ii) using an "inverse determinant" method, where one needs to calculate the determinant of the AGS system of equations only for real energies. A quasi-bound state is found with binding energy $B_{\bar{K}\bar{K}N} = 12 - 26$ MeV and width $\Gamma_{\bar{K}\bar{K}N} = 61 - 102$ MeV, which could correspond to the experimentally observed $\Xi(1950)$ state., Comment: 18 pages, 2 figures, 2 tables

Brueckner theory is used to investigate the properties of hyperons in nuclear matter. The hyperon-nucleon interaction is taken from chiral effective field theory at next-to-leading order with SU(3) symmetric low-energy constants. Furthermore, the underlying nucleon-nucleon interaction is also derived within chiral effective field theory. We present the single-particle potentials of Lambda and Sigma hyperons in symmetric and asymmetric nuclear matter computed with the continuous choice for intermediate spectra. The results are in good agreement with the empirical information. In particular, our calculation gives a repulsive Sigma-nuclear potential and a weak Lambda-nuclear spin-orbit force., Comment: 13 pages, 10 figures, 5 tables; v2: published version, minor changes

The production of a $D\bar D$ meson-pair in antiproton-proton ($\bar p p$) annihilation close to the production threshold is investigated, with special emphasis on the role played by the $\psi$(3770) resonance. The study is performed in a meson-baryon model where the elementary charm production process is described by baryon exchange. Effects of the interactions in the initial and final states are taken into account rigorously, where the latter involves also those due to the $\psi$(3770). The predictions for the $D\bar D$ production cross section are in the range of 30 -- 250 nb, the contribution from the $\psi$(3770) resonance itself amounts to roughly 20 -- 80 nb., Comment: 6 pages, 6 figures

The $\eta N$ final state is isospin-selective and thus provides access to the spectrum of excited nucleons without being affected by excited $\Delta$ states. To this end, the world database on eta photoproduction off the proton up to a center-of-mass energy of $E\sim 2.3$ GeV is analyzed, including data on differential cross sections, and single and double polarization observables. The resonance spectrum and its properties are determined in a combined analysis of eta and pion photoproduction off the proton together with the reactions $\pi N\to \pi N$, $\eta N$, $K\Lambda$ and $K\Sigma$. For the analysis, the so-called J\"ulich coupled-channel framework is used, incorporating unitarity, analyticity, and effective three-body channels. Parameters tied to photoproduction and hadronic interactions are varied simultaneously. The influence of recent MAMI $T$ and $F$ asymmetry data on the eta photoproduction amplitude is discussed in detail., Comment: 21 pages, 10 figures. Updated to the published version

Mechanisms of the charge exchange reaction $dp\to \{pp\}_{\!s} N\pi$, where $\{pp\}_{\!s}$ is a two-proton system at low excitation energy, are studied at beam energies 1 -- 2 GeV and for invariant masses $M_X$ of the final $N\pi $ system that correspond to the formation of the $\Delta(1232)$ isobar. The direct mechanism, where the initial proton is excited into the $\Delta(1232)$, dominates and explains the existing data on the unpolarized differential cross section and spherical tensor analyzing power $T_{22}$ for $M_X> 1.2$ GeV/$c^2$. However, this model fails to describe $T_{20}., Comment: 6 pages, 3 figures; talk given at Baldin ISHEPP XXII

A systematic analysis of the near-threshold enhancement in the $\bar pp$ invariant mass spectrum seen in the decay reactions $J/\psi \to x \bar pp$ and $\psi (3686) \to x \bar pp$ $(x = \gamma,\, \omega,\, \rho,\, \pi,\, \eta)$ is presented. The enhancement is assumed to be due to the $\bar NN$ final-state interaction (FSI) and the pertinent FSI effects are evaluated in an approach that is based on the distorted-wave Born approximation. For the $\bar NN$ interaction a recent potential derived within chiral effective field theory and fitted to results of a partial-wave analysis of $\bar pp$ scattering data is considered and, in addition, an older phenomenological model constructed by the J\"ulich group. It is shown that the near-threshold spectrum observed in various decay reactions can be reproduced simultaneously and consistently by our treatment of the $\bar pp$ FSI. It turns out that the interaction in the isospin-1 $^1S_0$ channel required for the description of the $J/\psi \to \gamma \bar pp$ decay predicts a $\bar NN$ bound state., Comment: 13 pages, 12 figures

The existence of baryon-baryon bound states in the strangeness sector is examined in the framework of SU(3) chiral effective field theory. Specifically, the role of SU(3) symmetry breaking contact terms that arise at next-to-leading order in the employed Weinberg power counting scheme is explored. We focus on the 1S0 partial wave and on baryon-baryon channels with maximal isospin since in this case there are only two independent SU(3) symmetry breaking contact terms. At the same time, those are the channels where most of the bound states have been predicted in the past. Utilizing $pp$ phase shifts and $\Sigma^+ p$ cross section data allows us to pin down one of the SU(3) symmetry breaking contact terms and a clear indication for the decrease of attraction when going from the NN system to strangeness S=-2 is found, which rules out a bound state for $\Sigma\Sigma$ with isospin I=2. Assuming that the trend observed for S=0 to S=-2 is not reversed when going to $\Xi\Sigma$ and $\Xi\Xi$ makes also bound states in those systems rather unlikely., Comment: 10 pages, 4 figures

The in-medium properties of a hyperon-nucleon potential, derived within chiral effective field theory and fitted to Lambda-N and Sigma-N scattering data, are investigated. Results for the single-particle potentials of the Lambda and Sigma hyperons in nuclear matter are reported, based on a conventional first-order Brueckner calculation. The Sigma-nucleus potential is found to be repulsive, in agreement with phenomenological information. A weak Lambda-nucleus spin-orbit interaction can be achieved by an appropriate adjustment of a low-energy constant corresponding to an antisymmetric Lambda-N -- Sigma-N spin-orbit interaction that arises at next-to-leading order in the effective field theory approach., Comment: 12 pages, 2 figures; several references added, several typos corrected

The reactions ppbar -> e+e- and e+e- -> ppbar are analyzed in the near-threshold region. Specific emphasis is put on the role played by the interaction in the initial- or final antinucleon-nucleon state which is taken into account rigorously. For that purpose a recently published NNbar potential derived within chiral effective field theory and fitted to results of a new partial-wave analysis of ppbar scattering data is employed. Our results provide strong support for the conjecture that the pronounced energy dependence of the e+e- <-> ppbar cross section, seen in pertinent experiments, is primarily due to the ppbar interaction. Predictions for the proton electromagnetic form factors G_E and G_M in the timelike region, close to the NNbar threshold, and for spin-dependent observables are presented. The steep rise of the effective form factor for energies close to the ppbar threshold is explained solely in terms of the ppbar interaction. The corresponding experimental information is quantitatively described by our calculation., Comment: 14 pages, 11 figures

We study the production of charmed mesons (D, D_s) in antiproton-proton annihilation close to the reaction thresholds. The elementary charm production process is described by baryon exchange and in the constituent quark model, respectively. Effects of the interactions in the initial and final states are taken into account rigorously. The calculations are performed in close analogy to our earlier study on pbarp to KbarK by connecting the processes via SU(4) flavor symmetry. Our predictions for the DDbar production cross section are in the order of 10^{-2} -- 10^{-1} mu b. They turned out to be comparable to those obtained in other studies. The cross section for a D_sD_s pair is found to be of the same order of magnitude despite the fact that its production in pbarp scattering requires a two-step process., Comment: 15 pages, 13 figures, some typos corrected, some comments added

The reactions $\gamma p\to\pi^0 p$ and $\gamma p\to\pi^+ n$ are analyzed in a semi-phenomenological approach up to $E\sim2.3$ GeV. Fits to differential cross section and single and double polarization observables are performed. A good overall reproduction of the available photoproduction data is achieved. The J\"ulich2012 dynamical coupled-channel model -which describes elastic $\pi N$ scattering and the world data base of the reactions $\pi N\to\eta N$, $K\Lambda$, and $K\Sigma$ at the same time - is employed as the hadronic interaction in the final state. The framework guarantees analyticity and, thus, allows for a reliable extraction of resonance parameters in terms of poles and residues. In particular, the photocouplings at the pole can be extracted and are presented., Comment: 37 pages, 31 figures. Angles of the photocouplings at the pole adapted to the convention of Phys. Rev. C 87, 068201 (2013)

We update our recent analysis of pbar-d scattering, performed within the Glauber theory including the single- and double pbar-N scattering mechanisms. Specifically, now we consider also Nbar-N amplitudes from a new partial-wave analysis of pbar-p scattering data. Predictions for differential cross sections and the spin observables A_y^d, A_y^pbar, A_xx, A_yy are presented for antiproton beam energies between 50 and 300 MeV. Total polarized cross sections are calculated utilizing the optical theorem. The efficiency of the polarization buildup for antiprotons in a storage ring is investigated., Comment: 4 pages, 5 figures; several typos corrected

The possibility to determine the pLambda scattering length from the final-state interaction in the reaction pp->pKLambda is investigated experimentally. From a transversely polarized measurement, the K analyzing power (A_N) which, in principle, allows one to extract the spin triplet scattering length is studied. An unexpected energy dependence of the forward/backward symmetric part of A_N is found. The influence of N*-resonances on the pLambda invariant mass spectrum is investigated by exploiting the large acceptance for the process pp->pKLambda->pKppi and is found to be the main source of uncertainty for determining the pLambda scattering length.

Results for the Lambda N and Sigma N interactions obtained at next-to-leading order in chiral effective field theory are reported. At the order considered there are contributions from one- and two-pseudoscalar-meson exchange diagrams and from four-baryon contact terms without and with two derivatives. SU(3) flavor symmetry is imposed for constructing the hyperon-nucleon interaction while the explicit SU(3) symmetry breaking by the physical masses of the pseudoscalar mesons (pi, K, eta) is taken into account. An excellent description of the hyperon-nucleon system can be achieved at next-to-leading order. It is on the same level of quality as the one obtained by the most advanced phenomenological hyperon-nucleon interaction models., Comment: 29 pages, 14 figures, uses elsarticle.cls and elsart3p.cls

The $\Lambda p$ interaction close to the $\Sigma N$ threshold is considered. Specifically, the pronounced structure seen in production reactions like $K^-d \to \pi^- \Lambda p$ and $pp\to K^+ \Lambda p$ around the $\Sigma N$ threshold is analyzed. Modern interaction models of the coupled $\Lambda N - \Sigma N$ systems generate such a structure either due to the presence of a (deuteron-like) unstable bound state or of an inelastic virtual state. % A determination of the position of the prominent peak as observed in various experiments for the two aforementioned reactions leads to values that agree quite well with each other. Furthermore, the deduced mean value of $2128.7\pm 0.3$ MeV for the peak position coincides practically with the threshold energy of the $\Sigma^+ n$ channel. This supports the interpretation of the structure as a genuine cusp, signaling an inelastic virtual state in the $^3S_1-^3D_1$ partial wave of the $\Sigma N$ isospin 1/2 channel. % There is also evidence for a second peak (or shoulder) in the data sets considered which appears at roughly 10-15 MeV above the $\Sigma N$ threshold. However, its concrete position varies significantly from data set to data set and, thus, a theoretical interpretation is difficult., Comment: accepted for publication Nucl. Phys. A

Results from an ongoing study of baryon-baryon systems with strangeness S=-1 and -2 within chiral effective field theory are reported. The investigations are based on the scheme proposed by Weinberg which has been applied rather successfully to the nucleon-nucleon interaction in the past. Results for the hyperon-nucleon and hyperon-hyperon interactions obtained to leading order are reviewed. Specifically, the issue of extrapolating the binding energy of the H-dibaryon, extracted from recent lattice QCD simulations, to the physical point is addressed. Furthermore, first results for the hyperon-nucleon interaction at next-to-leading order are presented and discussed., Comment: 8 pages, 4 figures, proceedings HYP2012

Elastic scattering of antiprotons on deuteron and 3He targets is studied within the Glauber-Sitenko theory. In case of pbar-d scattering, the single- and double pbar-N scattering mechanisms and the full spin dependence of the elementary pbar-N scattering amplitudes are taken into account on the basis of an appropriately modified formalism developed for p-d scattering. Differential cross sections and analyzing powers are calculated for antiproton beam energies between 50 and 300 MeV, using the Nbar-N model of the Juelich group as input. Results for total polarized cross sections are obtained via the optical theorem. The efficiency of the polarization buildup for antiprotons in a storage ring is discussed., Comment: 6 pages, 4 figures, proceedings SPIN-Praha-2012

Elastic pbar-d scattering is studied within the Glauber theory based on the single- and double pbar-N scattering mechanisms. The full spin dependence of the elementary pbar-N scattering amplitudes is taken into account and both the S- and D-wave components of the deuteron are considered. The treatment of the spin dependence is done in a (properly modified) formalism developed recently by Platonova and Kukulin for the pd -> pd scattering process. Predictions for differential cross sections and the spin observables A_y^d, A_y^pbar, A_xx, A_yy are presented for antiproton beam energies between 50 and 300 MeV, using amplitudes generated from the Nbar-N interaction model developed by the Juelich group. Total polarized cross sections are calculated utilizing the optical theorem. The efficiency of the polarization buildup for antiprotons in a storage ring is investigated., Comment: 14 pages, 15 figures; some comments added, figure added, signs of some spin-dependent cross sections corrected

Elastic piN scattering and the world data of the family of reactions pi^- p --> eta n, K^0 Lambda$, K^0 Sigma^0, K^+ Sigma^-, and pi^+ p --> K^+ Sigma^+ are described simultaneously in an analytic, unitary, coupled-channel approach. SU(3) flavor symmetry is used to relate both the t- and the u- channel exchanges that drive the meson-baryon interaction in the different channels. Angular distributions, polarizations, and spin-rotation parameters are compared with available experimental data. Partial-wave amplitudes are determined and the resonance content is extracted from the analytic continuation, including resonance positions and branching ratios, and possible sources of uncertainties are discussed. The results provide the final-state interactions for the ongoing analysis of photo- and electroproduction data., Comment: 53 pages, 48 figures; results updated to published version