Search

A hyperon-nucleon potential for the strangeness $S=-1$ sector ($\Lambda N$, $\Sigma N$) up to third order in the chiral expansion is presented. SU(3) flavor symmetry is imposed for constructing the interaction, however, the explicit SU(3) symmetry breaking by the physical masses of the pseudoscalar mesons and in the leading-order contact terms is taken into account. A novel regularization scheme is employed which has already been successfully used in studies of the nucleon-nucleon interaction within chiral effective field theory up to high orders. An excellent description of the low-energy $\Lambda p$, $\Sigma^- p$ and $\Sigma^+ p$ scattering data is achieved. New data from J-PARC on angular distributions for the $\Sigma N$ channels are analyzed. Results for the hypertriton and $A=4$ hyper-nuclear separation energies are presented. An uncertainty estimate for the chiral expansion is performed for selected hyperon-nucleon observables., Comment: 30 pages, 13 figures

An N¯N potential is introduced which is derived within chiral effective field theory and fitted to up-to-date N¯N phase shifts and inelasticities, provided by a proper phase-shift analysis of available p¯p scattering data. As an application of this interaction neutron-antineutron oscillations in the deuteron are considered. In particular, results for the deuteron lifetime are presented, evaluated in terms of the free-space n−n¯ oscillation time, utilizing that N¯N potential together with an NN interaction likewise derived within chiral effective field theory.

We utilize the experimentally known difference of the $$\varLambda $$ Λ separation energies of the mirror hypernuclei $${^4_\varLambda \mathrm{He}}$$ Λ 4 He and $${^4_\varLambda \mathrm{H}}$$ Λ 4 H to constrain the $$\varLambda $$ Λ -neutron interaction. We include the leading charge-symmetry breaking (CSB) interaction into our hyperon-nucleon interaction derived within chiral effective field theory at next-to-leading order. In particular, we determine the strength of the two arising CSB contact terms by a fit to the differences of the separation energies of these hypernuclei in the $$0^+$$ 0 + and $$1^+$$ 1 + states, respectively. By construction, the resulting interaction describes all low energy hyperon-nucleon scattering data, the hypertriton and the CSB in $${^4_\varLambda \mathrm{He}}$$ Λ 4 He -$${^4_\varLambda \mathrm{H}}$$ Λ 4 H accurately. This allows us to provide first predictions for the $$\varLambda $$ Λ n scattering lengths, based solely on available hypernuclear data.

We investigate the existence of bound $\Xi$ \break states in systems with $A=4-7$ baryons using the Jacobi NCSM approach in combination with chiral NN and $\Xi$N interactions. We find three shallow bound states for the NNN$\Xi$ system (with $(J^\pi,T)=(1^+,0)$, $(0^+,1)$ and $(1^+,1)$) with quite similar binding energies. The $^5_{\Xi}\mathrm{H}(\frac{1}{2}^+,\frac{1}{2})$ and $^7_{\Xi}\mathrm{H}(\frac{1}{2}^+,\frac{3}{2})$ hypernuclei are also clearly bound with respect to the thresholds $^4\mathrm{He} + \Xi$ and $^6\mathrm{He} +\Xi$, respectively. The binding of all these $\Xi$ systems is predominantly due to the attraction of the chiral $\Xi$N potential in the $^{33}S_1$ channel. A perturbative estimation suggests that the decay widths of all the observed states could be rather small., Comment: 12 pages, 2 figures

We generalize the Jacobi no-core shell model (J-NCSM) to study double-strangeness hypernuclei. All particle conversions in the strangeness $S=-1,-2$ sectors are explicitly taken into account. In two-body space, such transitions may lead to the coupling between states of identical particles and of non-identical ones. Therefore, a careful consideration is required when determining the combinatorial factors that connect the many-body potential matrix elements and the free-space two-body potentials. Using second quantization, we systematically derive the combinatorial factors in question for $S=0,-1,-2$ sectors. As a first application, we use the J-NCSM to investigate $\Lambda \Lambda$ s-shell hypernuclei based on hyperon-hyperon (YY) potentials derived within chiral effective field theory at leading order (LO) and up to next-to-leading order (NLO). We find that the LO potential overbinds $^{\text{ }\text{ }\text{ } \text{}6}_{\Lambda \Lambda}\text{He}$ while the prediction of the NLO interaction is close to experiment. Both interactions also yield a bound state for $^{\text{ }\text{ }\text{ } \text{}5}_{\Lambda \Lambda}\text{He}$. The $^{\text{}\text{ }\text{ }\text{}4}_{\Lambda \Lambda}\text{H}$ system is predicted to be unbound., Comment: 23 pages, 3 figures

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 $$\overline{\mathrm{P}}$$ 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 Phase One setup. The physics programme that is achievable during Phase One is outlined in this paper.

The complexity of threshold phenomena is exemplified on a prominent and long-known case - the structure in the cross section (invariant mass spectrum) at the opening of the channel. The mass splitting between the baryons together with the angular momentum coupling in the - 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 and scattering data, the shape of the resulting cross section is discussed and the poles near the threshold are determined. Evidence for a strangeness dibaryon is provided, in the form of a (unstable) bound state in the vicinity of the threshold. Predictions for level shifts and widths of atomic states are given.

We extend the recently developed Jacobi no-core shell model to hypernuclei. Based on the coefficients of fractional parentage for ordinary nuclei, we define a basis where the hyperon is the spectator particle. We then formulate transition coefficients to states that single out a hyperon-nucleon pair which allow us to implement a hypernuclear many-baryon Hamiltonian for $p$-shell hypernuclei. As a first application, we use the basis states and the transition coefficients to calculate the ground states of $^{4}_{\Lambda}$He, $^{4}_{\Lambda}$H, $^{5}_{\Lambda}$He, $^{6}_{\Lambda}$He, $^{6}_{\Lambda}$Li, and $^{7}_{\Lambda}$Li and, additionally, the first excited states of $^{4}_{\Lambda}$He, $^{4}_{\Lambda}$H, and $^{7}_{\Lambda}$Li. In order to obtain converged results, we employ the similarity renormalization group (SRG) to soften the nucleon-nucleon and hyperon-nucleon interactions. Although the dependence on this evolution of the Hamiltonian is significant, we show that a strong correlation of the results can be used to identify preferred SRG parameters. This allows for meaningful predictions of hypernuclear binding and excitation energies. The transition coefficients will be made publicly available as HDF5 data files., Comment: 20 pages, 1 table, 12 figures

$\Lambda$-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 structure of single-$\Lambda$ hypernuclei is studied using the chiral hyperon-nucleon potentials derived at leading order (LO) and next-to-leading order (NLO) by the J\"{u}lich--Bonn--Munich group. Results for the separation energies of $\Lambda$ single-particle states for various hypernuclei from $^5_{\Lambda}$He to $^{209}_{\,\,\,\,\,\Lambda}$Pb are presented for the LO interaction and the 2013 (NLO13) and 2019 (NLO19) versions of the NLO potentials. It is found that the results based on the LO potential show a clear tendency for overbinding while those for the NLO13 interaction underbind most of the considered hypernuclei. A qualitatively good agreement with the data is obtained for the NLO19 interaction over a fairly large range of mass number values when considering the uncertainty due to the regulator dependence. A small spin-orbit splitting of the $p$-, $d$-, $f$-, and $g$-wave states is predicted by all interactions, in line with the rather small values observed in pertinent experiments., Comment: 9 pages, 3 figures, 2 tables

Stimulated by recent indications that the binding energy of the hypertriton could be significantly larger than so far assumed, requirements of a more strongly bound $^3_\Lambda {\rm H}$ state for the hyperon-nucleon interaction and consequences for the binding energies of $A=4,5$ and $7$ hypernuclei are investigated. As basis a $YN$ potential derived at next-to-leading order in chiral effective field theory is employed, Faddeev and Yakubovsky equations are solved to obtain the corresponding $3$- and $4$-body binding energies, respectively, and the Jacobi no-core shell model is used for $^5_\Lambda$He and $^7_\Lambda$Li. It is found that the spin-singlet $\Lambda p$ interaction would have to be much more attractive which can be, however, accommodated within the bounds set by the available $\Lambda p$ scattering data. The binding energies of the $^4_\Lambda {\rm He}$ hypernucleus are predicted to be closer to the empirical values than for $YN$ interactions that produce a more weakly bound $^3_\Lambda {\rm H}$. The quality of the description of the separation energy and excitation spectrum for $^7_\Lambda$Li remains essentially unchanged., Comment: 8 pages, 3 figures; version that was published in Phys. Lett. B

The Julich-Bonn-Munich Group has performed extensive studies of baryon-baryon interactions involving strange baryons (\(\varLambda \), \(\varSigma \), \(\varXi \)) within chiral effective field theory (EFT). A selection of the achieved results is presented. In particular, a calculation of the in-medium properties of a hyperon-nucleon interaction derived within chiral EFT and fitted to \(\varLambda N\) and \(\varSigma N\) scattering data is reviewed. Implications on the properties of neutron stars and, specifically, on the so-called hyperon-puzzle are addressed. In addition, results for baryon-baryon scattering in the strangeness \(S=-2\) sector, obtained at next-to-leading order in the chiral expansion, are presented.

Electromagnetic form factors of hyperons ($\Lambda$, $\Sigma$, $\Xi$) in the timelike region, accessible in the reaction $e^+e^- \to \bar YY$, are studied. The focus is on energies close to the reaction thresholds, where the properties of these form factors are significantly influenced by the interaction in the final $\bar YY$ system. This interaction is taken into account in the calculation, utilizing $\bar YY$ potential models that have been constructed by the J\"ulich group for the analysis of data from the reaction $\bar pp \to \bar YY$ in the past. The enhancement of the effective form factor for energies close to the threshold, seen in experiments of $e^+e^- \to \bar \Lambda \Lambda$ and $e^+e^- \to \bar \Sigma^0\Lambda$, is reproduced. With regard to the reactions $e^+e^- \to \bar \Sigma^- \Sigma^+, \ \bar\Sigma^0\Sigma^0, \ \bar\Sigma^+\Sigma^-$ a delicate interplay between the three channels is observed in the results at low energies, caused by the $\bar\Sigma\Sigma$ interaction. Predictions for the electromagnetic form factors $G_M$ and $G_E$ in the timelike region are presented for the $\Lambda$, $\Sigma$, and $\Xi$ hyperons., Comment: 13 pages, 10 figures

Neutron-antineutron ($n-\bar n$) oscillations in the deuteron are considered. Specifically, the deuteron lifetime is calculated in terms of the free-space $n-\bar n$ oscillation time $\tau_{n-\bar n}$ based on $NN$ and $\bar NN$ interactions derived within chiral effective field theory (EFT). This results in $(2.6\pm 0.1) \times 10^{22}\,\tau^2_{n-\bar n}$ s, which is close to the value obtained by Dover and collaborators more than three decades ago, but disagrees with recent EFT calculations that were performed within the perturbative scheme proposed by Kaplan, Savage, and Wise. Possible reasons for the difference are discussed., Comment: 5 pages, 1 figure

Charmed nuclei are investigated utilizing $\Lambda_c N$ 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. Calculations of the energies of $\Lambda_c$ single-particle bound states for various charmed nuclei from $^{\ 5}_{\Lambda_c}$Li to $^{209}_{\Lambda_c}$Bi are performed using a perturbative many-body approach. This approach allows one to determine the finite nuclei $\Lambda_c$ self-energy from which the energies of the different bound states can be obtained. Though the $\Lambda_c N$ interaction inferred from the lattice results is only moderately attractive, it supports the existence of charmed nuclei. Already the lightest nucleus considered is found to be bound. The spin-orbit splitting of the p- and d-wave states turns out to be small, as in the case of single $\Lambda$ hypernuclei. Additional calculations based on the Faddeev-Yakubovsky equations suggest that also $A=4$ systems involving a $\Lambda_c$ baryon are likely to be bound, but exclude a bound $^{\, 3}_{\Lambda_c}$He state., Comment: 13 pages, 5 figures

An $\bar N$N potential is reviewed which has been derived within chiral effective field theory by the Jülich-Bonn group. By construction it reproduces $\bar N$N phase shifts and inelasticities, provided by an elaborate phase-shift analysis of available $\bar p$p scattering data. This interaction is then employed in a study of neutron-antineutron oscillations in the deuteron. In particular, the deuteron lifetime is considered, and results for it are presented in terms of the free-space n – $\bar n$ oscillation time, based on that $\bar N$N potential in combination with an NN interaction likewise derived within chiral effective field theory.

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 weak decay parameter ${\ensuremath{\alpha}}_{\ensuremath{-}}$ of the $\mathrm{\ensuremath{\Lambda}}$ is an important quantity for the extraction of polarization observables in various experiments. Moreover, in combination with ${\ensuremath{\alpha}}_{+}$ from $\overline{\mathrm{\ensuremath{\Lambda}}}$ decay it provides a measure for matter-antimatter asymmetry. The weak decay parameter also affects the decay parameters of the $\mathrm{\ensuremath{\Xi}}$ and $\mathrm{\ensuremath{\Omega}}$ baryons and, in general, any quantity in which the polarization of the $\mathrm{\ensuremath{\Lambda}}$ 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 ${\ensuremath{\alpha}}_{\ensuremath{-}}$, 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 ${\ensuremath{\alpha}}_{\ensuremath{-}}$ is significantly larger than the previous PDG value. Any experimental quantity relying on the value of ${\ensuremath{\alpha}}_{\ensuremath{-}}$ should therefore be reconsidered.

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

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

A low-energy spin-physics program is being developed at the COSY storage ring. To support the planned experimental activities, several experimental tools for polarized beams and targets have been developed. The paper presents the physics case and the readiness of the setup for its realization. QC 20190905. QC 20191203Although the hadron physics program has been officially terminated, various experimental activities are underway at the COSY storage ring of Forschungszentrum Jülich. Besides the feasibility studies related to the search for electric dipole moments [2], low-energy spin-physics experiments employing polarized beam and targets appear as an additional focus. This paper is devoted to these studies.

Evidence of non-nucleonic degrees of freedom in nuclei has long been sought. The authors show that the use of relativistic (light-cone) wave functions for the ${\mathrm{\ensuremath{\Delta}}}^{++}$-${\mathrm{\ensuremath{\Delta}}}^{\ensuremath{-}}$ component of the deuteron leads to a shape of the signal for this contribution that is significantly different from the use of nonrelativistic wave functions in the $\overline{p}\phantom{\rule{0}{0ex}}d\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}\phantom{\rule{0}{0ex}}{\ensuremath{\pi}}^{\ensuremath{-}}\phantom{\rule{0}{0ex}}{\mathrm{\ensuremath{\Delta}}}^{++}$ reaction. Comparing with background reactions the results suggest that components as low as 0.3% could be observed.

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

We analyze the origin of the structure observed in the reaction $J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\eta}}^{\ensuremath{'}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ for ${\ensuremath{\eta}}^{\ensuremath{'}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ invariant masses close to the antiproton-proton ($\overline{p}p$) threshold, commonly associated with the $X(1835)$ resonance. Specifically, we explore the effect of a possible contribution from the two-step process $J/\ensuremath{\psi}\ensuremath{\rightarrow}\phantom{\rule{0ex}{0ex}}\ensuremath{\gamma}\overline{N}N\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\eta}}^{\ensuremath{'}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$. The calculation is performed in the distorted-wave Born approximation which allows an appropriate inclusion of the $\overline{N}N$ interaction in the transition amplitude. The $\overline{N}N$ amplitude itself is generated from a corresponding potential recently derived within chiral effective field theory. We are able to describe the invariant-mass dependence of the measured spectra for the reactions $J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}\overline{p}p$ and $J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\eta}}^{\ensuremath{'}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ around the $\overline{p}p$ threshold. The structure seen in the ${\ensuremath{\eta}}^{\ensuremath{'}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ spectrum emerges as a threshold effect due to the opening of the $\overline{p}p$ channel.

The reaction ${K}^{\ensuremath{-}}d\ensuremath{\rightarrow}\ensuremath{\pi}\mathrm{\ensuremath{\Sigma}}n$ is studied within a Faddeev-type approach, with emphasis on the specific kinematics of the E31 experiment at J-PARC, i.e., ${K}^{\ensuremath{-}}$ beam momentum of ${p}_{K}=1$ GeV/$c$ and neutron angle of ${\ensuremath{\theta}}_{n}={0}^{\ensuremath{\circ}}$. The employed Faddeev approach requires as main input amplitudes for the two-body subsystems $\overline{K}N\ensuremath{\rightarrow}\overline{K}N$ and $\overline{K}N\ensuremath{\rightarrow}\ensuremath{\pi}\mathrm{\ensuremath{\Sigma}}$. For the latter, results from recently published chiral unitary models of the $\overline{K}N$ interaction are utilized. The $\overline{K}N\ensuremath{\rightarrow}\overline{K}N$ amplitude itself, however, is taken from a recent partial-wave analysis. Because of the large incoming momentum of the ${K}^{\ensuremath{-}}$, the $\overline{K}N$ interaction is probed in a kinematical regime where those chiral potentials are no longer applicable. A comparison of the predicted spectrum for various $\ensuremath{\pi}\mathrm{\ensuremath{\Sigma}}$ 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 $\ensuremath{\pi}\mathrm{\ensuremath{\Sigma}}$ spectrum around the $\overline{K}N$ threshold, i.e. in the region of the $\mathrm{\ensuremath{\Lambda}}$(1405) resonance, indicate a sensitivity to the details of the employed $\overline{K}N\ensuremath{\rightarrow}\ensuremath{\pi}\mathrm{\ensuremath{\Sigma}}$ amplitudes and suggest that pertinent high-precision data could indeed provide substantial constraints on the structure of the $\mathrm{\ensuremath{\Lambda}}$(1405).

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

A study of the antinucleon-nucleon interaction within chiral effective theory is presented. This novel approach suggested by Weinberg for investigating nucleon-nucleon interaction can be adapted straightforwardly to the antinucleon-system. The antinucleon-nucleon potential is derived up to next-to-next-to-next-order in the chiral expansion. The low-energy constants associated with arising contact interactions are fixed by a fit to phase shifts and inelasticities provided by a recently published phase-shift analysis of antiproton-proton scattering data. Theachieved description of the antinucleon-nucleon amplitudes is excellent and of a qualitycomparable to the one found in case of the nucleon-nucleon interaction at the same order.

Apart from the $pd$ reaction also the scattering of antiprotons with transversal polarization $p_y^p$ on deuterons with tensor polarization $P_{xz}$ provides a null-test signal for time-reversal-invariance violating but parity conserving effects. Assuming that the time-reversal-invariance violating $\bar NN$ interaction contains the same operator structure as the $NN$ interaction, we discuss the energy dependence of the null-test signal in $\bar pd$ scattering on the basis of a calculation within the spin-dependent Glauber theory at beam energies of 50-300 MeV., 6 pages, one figure; prepared for the proceedings of the International Conference on Exotic Atoms and related topics - EXA2017 (September 11-15, Wien, Austria)

The set of coupled Faddeev equations for the K¯NN–πΣN system is derived and the reaction K−d → πΣn, for which measurements are currently performed at J-PARC, is analyzed based on it. The present results in which the transition to the πΣN system is treated perturbatively show a peak in the Λ(1405) resonance region, but no clear enhancement above the K¯N threshold as suggested by the preliminary data of the J-PARC experiment. We point out that the observed enhancement originates from the quasi-free scattering between the incident K− and one of the nucleons in the deuteron, and we argue for the necessity of including full πΣN three-body processes in a realistic calculation.

Recent results from the ongoing study of the baryon–baryon interaction within chiral effective field theory (EFT) by the Jülich–Bonn–Munich Group are reported. Specifically, a calculation of the in-medium properties of a hyperon–nucleon (YN) interaction derived within chiral EFT and fitted to ΛN and ΣN scattering data is reviewed. Furthermore, the relevance of three-body forces for hypernuclei is addressed and potentials for the leading order three-baryon interactions are discussed, which involve contact terms and irreducible one- and two-meson exchange diagrams. Finally, first results for baryon–baryon scattering in the strangeness S = −2 sector, obtained in chiral EFT up to NLO, are presented.

The $\stackrel{P\vec}{p}p\ensuremath{\rightarrow}p{K}^{+}\mathrm{\ensuremath{\Lambda}}$ reaction has been measured with the COSY-TOF detector at a beam momentum of $2.7\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}/c$. 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 $p\mathrm{\ensuremath{\Lambda}}$ 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 ${a}_{t}=(\ensuremath{-}2.{55}_{\ensuremath{-}1.39}^{+0.72}{}_{\mathrm{stat}.}\ifmmode\pm\else\textpm\fi{}0.{6}_{\mathrm{syst}.}\ifmmode\pm\else\textpm\fi{}0.{3}_{\mathrm{theo}.})\mathrm{fm}$. This value is compatible with theoretical predictions and results from model-dependent analyses.

Results for the antinucleon-nucleon ($\bar NN$) interaction obtained at next-to-next-to-next-to-leading order in chiral effective field theory (EFT) are reported. A new local regularization scheme is used for the pion-exchange contributions that has been recently suggested and applied in a pertinent study of the $NN$ force within chiral EFT. Furthermore, an alternative strategy for estimating the uncertainty is utilized that no longer depends on a variation of the cutoffs. The low-energy constants associated with the arising contact terms are fixed by a fit to the phase shifts and inelasticities provided by a phase-shift analysis of $\bar pp$ scattering data. An excellent description of the $\bar NN$ amplitudes is achieved at the highest order considered. Moreover, because of the quantitative reproduction of partial waves up to $J=3$, there is also a nice agreement on the level of $\bar pp$ observables. Specifically, total and integrated elastic and charge-exchange cross sections agree well with the results from the partial-wave analysis up to laboratory energies of $300$ MeV, while differential cross sections and analyzing powers are described quantitatively up to $200$-$250$ MeV. The low-energy structure of the $\bar NN$ amplitudes is also considered and compared to data from antiprotonic hydrogen., 33 pages, 15 figures

Cross sections for the charm-production reactions $\overline{p}p\ensuremath{\rightarrow}{\overline{\mathrm{\ensuremath{\Lambda}}}}_{c}^{\ensuremath{-}}{\mathrm{\ensuremath{\Sigma}}}_{c}^{+}$, ${\overline{\mathrm{\ensuremath{\Sigma}}}}_{c}{\mathrm{\ensuremath{\Sigma}}}_{c}$, ${\overline{\mathrm{\ensuremath{\Xi}}}}_{c}{\mathrm{\ensuremath{\Xi}}}_{c}$, and ${\overline{\mathrm{\ensuremath{\Xi}}}}_{c}^{\ensuremath{'}}{\mathrm{\ensuremath{\Xi}}}_{c}^{\ensuremath{'}}$ 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 $\overline{p}p\ensuremath{\rightarrow}\overline{\mathrm{\ensuremath{\Lambda}}}\mathrm{\ensuremath{\Sigma}}$, $\overline{\mathrm{\ensuremath{\Sigma}}}\mathrm{\ensuremath{\Sigma}}$, $\overline{\mathrm{\ensuremath{\Xi}}}\mathrm{\ensuremath{\Xi}}$ by connecting the two sectors via SU(4) flavor symmetry. The cross sections are found to be in the order of $0.1\char21{}1\text{ }\text{ }\ensuremath{\mu}\mathrm{b}$ 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 turn out to be significantly smaller.

A density-dependent effective potential for the baryon-baryon interaction in the presence of the (hyper)nuclear medium is constructed, based on the leading (irreducible) three-baryon forces derived within SU(3) chiral effective field theory. We evaluate the contributions from three classes: contact terms, one-pion exchange and two-pion exchange. In the strangeness-zero sector we recover the known result for the in-medium nucleon-nucleon interaction. Explicit expressions for the Lambda-nucleon in-medium potential in (asymmetric) nuclear matter are presented. Our results are suitable for implementation into calculations of (hyper)nuclear matter. In order to estimate the low-energy constants of the leading three-baryon forces we introduce the decuplet baryons as explicit degrees of freedom and construct the relevant terms in the minimal non-relativistic Lagrangian. With these, the constants are estimated through decuplet saturation. Utilizing this approximation we provide numerical results for the effect of the three-body force in symmetric nuclear matter and pure neutron matter on the Lambda-nucleon interaction. A moderate repulsion that increases with density is found in comparison to the free Lambda-nucleon interaction., Comment: 25 pages, 15 figures, 4 tables

Antiproton-deuteron scattering is analyzed within the Glauber theory, accounting for the full spin dependence of the underlying \({\bar{N}N}\) amplitudes. The latter are taken from the Julich \({\bar{N}N}\) models and from a recently published new partial-wave analysis of \({\bar{p}p}\) scattering data. Predictions for differential cross sections and the spin observables \({A_y^d}\), \({A_y^{\bar{p}}}\), Axx, Ayy are presented for antiproton beam energies up to about 300 MeV. The efficiency of the polarization buildup for antiprotons in a storage ring is investigated.

Results from an ongoing study of the hyperon-nucleon system within chiral effective field theory are reported. The investigation is based on the scheme proposed by Weinberg which has been applied rather successfully to the nucleon-nucleon interaction in the past. First results for the hyperon-nucleon interaction at next-to-leading order are presented and discussed.

The Λp interaction close to the ΣN threshold is considered. Specifically, the pronounced structure seen in production reactions like K − d → π − Λ p and p p → K + Λ p around the ΣN threshold is analyzed. Modern interaction models of the coupled Λ N – Σ 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 ± 0.3 MeV for the peak position coincides practically with the threshold energy of the Σ + n channel. This supports the interpretation of the structure as a genuine cusp, signaling an inelastic virtual state in the S 1 3 – 3 D 1 partial wave of the ΣN 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 ΣN threshold. However, its concrete position varies significantly from data set to data set and, thus, a theoretical interpretation is difficult.

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

Dense compact objects like neutron stars or black holes have always been one of Gerry Brown's favorite research topics. This is closely related to the effects of strangeness in nuclear physics. Here, we review the chiral Effective Field Theory approach to interactions involving nucleons and hyperons, the possible existence of strange dibaryons, the fate of hyperons in nuclear matter and the present status of three-body forces involving hyperons and nucleons., Comment: 20 pages, chapter for the memorial book "Gerry Brown 90"

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

We study the production of charmed mesons (D) and baryons (Lambda_c) in antiproton-proton (app) annihilation close to their respective production thresholds. The elementary charm production process is described by either baryon/meson exchange or by quark/gluon dynamics. 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 app -> antiLambda-Lambda and app -> antiK-K by connecting the processes via SU(4) flavor symmetry. Our predictions for the antiLambda_c-Lambda_c production cross section are in the order of 1 to 7 mb, i.e. a factor of around 10-70 smaller than the corresponding cross sections for antiLambda-Lambda However, they are 100 to 1000 times larger than predictions of other model calculations in the literature. On the other hand, the resulting cross sections for antiD-D production are found to be in the order of 10^{-2} -- 10^{-1} microbarn and they turned out to be comparable to those obtained in other studies., 5 pages, 2 figures, Contribution to the proceedings of the 21st European Conference on Few-Body Problems in Physics, Salamanca, Spain, 30 August - 3 September 2010