The reaction ppbar -> Lambda_c-Lambda_cbar close to threshold

Predictions for the charm-production reaction antiproton-proton -> antiLambda_c-Lambda_c for energies near the threshold are presented. The calculations are performed in a meson-exchange framework in close analogy to our earlier study on antiproton-proton -> antiLambda-Lambda by connecting the two processes via SU(4) symmetry. The obtained antiLambda_c-Lambda_c production cross sections are in the order of 1 to 7 \mub, i.e. a factor of around 10 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.Comment: 12 pages, 4 figure

Coupled-channel effects in hadron-hadron correlation functions

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 adde

Strangeness S=-3 and -4 baryon-baryon interactions in chiral EFT

I report on recent progress in the description of baryon-baryon systems within chiral effective field theory. In particular, I discuss results for the strangeness S=-3 to -4 baryon-baryon systems, obtained to leading order.Comment: 4 pages, 2 figures, Contribution to the proceedings of the 12th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU2010), May 31-June 4, 2010, College of William and Mary, Williamsburg, Virgini

Scattering of charmed baryons on nucleons

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 adde

Charm production in antiproton-proton annihilation

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.Comment: 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 201

Production of charmed pseudoscalar mesons in antiproton-proton annihilation

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 adde

Production of charmed baryons in pˉp\bar p p collisions close to their thresholds

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 figure

The ψ\psi(3770) resonance and its production in pˉp→DDˉ\bar pp \to D \bar D

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 figure

Elastic pbar-d scattering and total pbar-d cross sections

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 correcte

Triton photodisintegration with realistic potentials

The photodisintegration of $^{3}$H is treated by means of coupled integral equations using separable versions of the Paris and the Bonn potentials in their kernel. The differential cross section for the inverse reaction is obtained via detailed balance. For the latter process good agreement with the data is found when including final-state interaction, meson exchange currents, higher partial waves in the potential, and electric quadrupole contributions in the electromagnetic interaction.Comment: 5 pages LaTeX and 5 postscript figures included, uses epsfig.sty and espcrc1.sty. Talk given at the XVth International Conference on Few-Body Problems in Physics (22-26 July, 1997, Groningen, The Netherlands). To be published in the conference proceedings in Nucl. Phys.