arXiv subjects

J. Haidenbauer

Publications and source records attributed to J. Haidenbauer.

At least 163 records · Page 9Linked to original sources

arXiv2001

A meson exchange model for the YN interaction

We present a new model for the hyperon-nucleon (Lambda N, Sigma N) interaction, derived within the meson exchange framework. The model incorporates the standard one boson exchange contributions of the lowest pseudoscalar and vector meson multiplets with coupling constants fixed by SU(6) symmetry relations. In addition - as the main feature of the new model - the exchange of two correlated pions or kaons, both in the scalar-isoscalar (sigma) and vector-isovector (rho) channels, is included.

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arXiv2001

Quark model study of the triton bound stat

The three-nucleon bound state problem is studied employing nucleon-nucleon potentials derived from a basic quark-quark interaction. We analyze the effects of the nonlocalities generated by the quark model. The calculated triton binding energies indicate that quark-model nonlocalities can yield additional binding in the order of few hundred keV.

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arXiv2001

Incoherent Photoproduction of $η$-mesons from the Deuteron near Threshold

Incoherent photoproduction of the $η$-meson on the deuteron is studied for photon energies from threshold to 800 MeV. The dominant contribution, the $γ$N-$η$N amplitude, is described within an isobar model. The final state interaction derived from the CD-Bonn potential is included and found to be important for the description of the production cross section close to threshold. Possible effects from the $ηN$ final state interaction are discussed.

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arXiv2000

Long- and medium-range components of the nuclear force in quark-model based calculations

Quark-model descriptions of the nucleon-nucleon interaction contain two main ingredients, a quark-exchange mechanism for the short-range repulsion and meson-exchanges for the medium- and long-range parts of the interaction. We point out the special role played by higher partial waves, and in particular the 1F3, as a very sensitive probe for the meson-exchange part employed in these interaction models. In particular, we show that the presently available models fail to provide a reasonable description of higher partial waves and indicate the reasons for this shortcoming.

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arXiv2000

The reactions p + n --> d + omega and p + n --> d + phi near threshold

The reactions p+n-->d+omega and p+n-->d+phi are studied within a relativistic meson-exchange model of hadronic interactions. Predictions for the total cross sections and for the angular distributions of the vector mesons are presented. The resulting cross sections near threshold are around 10 - 30 microb for p+n-->d+omega$ and 200 - 250 nb for p+n-->d+phi. A moderate deviation of the cross section ratio sigma_{p+n-->d+phi} / sigma_{p+n-->d+omega} from that of the Okubo-Zweig-Iizuka rule is predicted.

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arXiv2000

Near threshold Lambda and Sigma production in pp collisions

A model calculation for the reactions $pp\to pΛK^+$ and $pp\to NΣK$ near their thresholds is presented. It is argued that the experimentally observed strong suppression of $Σ^0$ production compared to $Λ$ production at the same excess energy could be due to a destructive interference between the $π$ and $K$ exchange contributions in the reaction $pp\to pΣ^0 K^+$. Predictions for $pp\to pΣ^+ K^0$ and $pp\to nΣ^+ K^+$ are given.

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arXiv2000

On the Migdal-Watson approach to FSI effects in meson production in NN collisions

The influence of the nucleon-nucleon final state interaction (FSI) on properties of the meson production amplitude near threshold is discussed. For the nucleon-nucleon interaction a simple Yamaguchi potential as well as realistic potential models are considered. It is shown that FSI effects cannot be factorized from the production amplitude. The absolute magnitude of FSI effects depends on the momentum transfer (or on the mass of the produced meson) and hence is not universal. Only in the case of the production of rather heavy mesons like eta' or phi FSI effects become universal. The Jost function approach to FSI effects is critically examined.

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arXiv2000

A two-pion exchange three-nucleon force based on a realistic pi-N interaction

The contribution of a $ππ$-exchange three-body force to the three-nucleon binding energy is calculated in terms of a $πN$ amplitude. The latter is based on a meson-theoretical model of $πN$ interaction developed by the Jülich group. Similar to a previous study based on simple phenomenological $πN$ potentials a very small effect of the resulting three-body force is found. Possible origins of the two-orders-of-magnitude descrepancy between the present result and the values obtained for the Tucson-Melbourne three-body force are investigated. Evidence is provided that this discrepancy is most likely due to strikingly different off-shell properties of the $πN$ amplitudes underlying the two approaches.

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arXiv2000

The reactions $pp\to pΛK^+$ and $pp\to pΣ^0K^+$ near their thresholds

The reactions $pp\to pΛK^+$ and $pp\to pΣ^0K^+$ are studied near their thresholds. The strangeness production process is described by the $π$- and $K$ exchange mechanisms. Effects from the final state interaction in the hyperon-nucleon system are taken into account rigorously. It is found that the $Λ$ production is dominated by $K$ exchange whereas $K$- as well as $π$ exchange play an important role for the $Σ^0$ case. It is shown that the experimentally observed strong suppression of $Σ^0$ production compared to $Λ$ production at the same excess energy can be explained by a destructive interference between $π$ and $K$ exchange in the reaction $pp\to pΣ^0K^+$. Implications of such an interference on the reaction $pp\to nΣ^+K^+$ are pointed out.

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arXiv2000

Polarization phenomena in the reaction NN to NNpi near threshold

First calculations for spin-dependent observables of the reactions $pp \to ppπ^0$, $pp \to pnπ^+$ and $pp \to dπ^+$ near threshold are presented, employing the Jülich model for pion production. The influence of resonant (via the excitation of the $Δ(1232)$) and non-resonant p-wave pion production mechanisms on these observables is examined. For the reactions $pp \to pnπ^+$ and $pp \to dπ^+$ nice agreement of our predictions with the presently available data on spin correlation coefficents is observed whereas for $pp \to ppπ^0$ the description of the data is less satisfying.

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arXiv2000

Energy Dependence of the Near-Threshold Total Cross-Section for the pp --> pp eta' Reaction

Total cross sections for the pp --> pp eta' reaction have been measured in the excess energy range from Q = 1.53 MeV to Q = 23.64 MeV. The experiment has been performed at the internal installation COSY-11 using a stochastically cooled proton beam of the COoler SYnchrotron COSY and a hydrogen cluster target. The determined energy dependence of the total cross section weakens the hypothesis of the S-wave repulsive interaction between the eta' meson and the proton. New data agree well with predictions based on the phase-space distribution modified by the proton-proton final-state-interaction (FSI) only.

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arXiv1999

Eta and eta-prime meson production in the reaction pn -> dM near threshold

The two-step model with pi-, rho- and omega- exchanges taken into account is applied to investigate the reactions pn -> d eta and pn -> d eta-prime. The existing experimental data on the reaction pn -> d eta are analysed and predictions for the cross section of the reaction pn -> d eta-prime are presented. It is found that pi- as well as rho exchange yield significant contributions in both reactions. The effect of the final state interaction is also studied.

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arXiv1999

$ϕ$-meson production in proton-proton collisions

The production of $ϕ$-mesons in proton-proton collisions is investigated within a relativistic meson-exchange model of hadronic interactions. The experimental prerequisites for extracting the $NNϕ$ coupling strength from this reaction are discussed. In the absence of a sufficient set of data, which would enable an accurate determination of the $NNϕ$ coupling strength, we perform a combined analysis, based on some reasonable assumptions, of the existing data for both $ω$- and $ϕ$-meson production. We find that the recent data from the DISTO collaboration on the angular distribution of the $ϕ$ meson indicate that the $NNϕ$ coupling constant is small. The analysis yields values for $g_{NNϕ}$ that are compatible with the OZI rule.

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arXiv1998

Comparison of Lambda and Sigma(0) Threshold Production in Proton-Proton Collisions

Threshold measurements of the associated strangeness production reactions pp --> p K(+) Lambda and pp --> p K(+) Sigma(0) are presented. Although slight differences in the shapes of the excitation functions are observed, the most remarkable feature of the data is that at the same excess energy the total cross section for the Sigma(0) production appears to be about a factor of 28 smaller than the one for the Lambda particle. It is concluded that strong Sigma(0)-p final state interactions, and in particular the Sigma-N --> Lambda-p conversion reaction, are the likely cause of the depletion for the yield in the Sigma signal. This hypothesis is in line with other experimental evidence in the literature.

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arXiv1998

Comparison of triton bound state properties using different separable representations of realistic potentials

The quality of two different separable expansion methods ({\sl W} matrix and Ernst-Shakin-Thaler) is investigated. We compare the triton binding energies and components of the triton wave functions obtained in this way with the results of a direct two-dimensional treatment. The Paris, Bonn {\sl A} and Bonn {\sl B} potentials are employed as underlying two-body interactions, their total angular momenta being incorporated up to $j \leq 2$. It is found that the most accurate results based on the Ernst-Shakin-Thaler method agree within 1.5% or better with the two-dimensional calculations, whereas the results for the {\sl W}-matrix representation are less accurate.

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arXiv1998

The Reaction $pp \to ppϕ$ and the Validity of the OZI Rule

The reaction $pp \to pp ϕ$ is investigated within a relativistic meson-exchange model of hadronic interactions. The possibility of extracting the $NNϕ$ coupling constant from a study of this process is explored. A combined analysis of $ω-$ and $ϕ$-meson production in proton-proton collisions utilizing recent data on these reactions is carried out and yields values for $g_{NNϕ}$ that are compatible with the OZI rule.

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arXiv1998

Role of the $Δ$ isobar in the reaction $NN \to NNπ$ near threshold

A model calculation for pion production in nucleon-nucleon collisions is presented. Direct production, pion rescattering and contributions from pair diagrams are taken into account. The amplitudes for the elementary processes are based on well established microscopic models of nucleon-nucleon and pion-nucleon scattering. The $Δ(1232)$ is included explicitly and is found to play an important role even at energies close to production threshold. A good overall agreement with existing data from the pion production threshold up to the Delta resonance region is achieved.

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arXiv1998

Two-Loop Chiral Perturbation Theory and the Pion-Pion Phase Shifts

We want to test the predictive power of Chiral Perturbation Theory (ChPT). In this work, we use the ChPT pion-pion scattering amplitude, including two loop contributions, and we obtain S- and P-wave low-energy phase shifts. We show that, by varying just one free parameter, the resulting S- and P-wave phase shifts are in reasonable agreement with the experimental data.

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