arXiv subjects

J. Haidenbauer

Publications and source records attributed to J. Haidenbauer.

170 records · Page 10Linked to original sources

arXiv1998

Meson-Exchange Model for the YN Interaction

We report on progress in the development of a microscopic model for the hyperon-nucleon interaction within the meson-exchange framework, which incorporates both one-meson as well as correlated two-meson exchange contributions. The main new feature of the model is the exchange of two correlated pions or kaons, both in the scalar-isoscalar and the vector-isovector channels. In the scalar channel it provides the main part of the intermediate-range interaction between two baryons, thereby eliminating the need for the fictitious sigma meson, which has been an unavoidable element of effective one-boson-exchange descriptions.

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arXiv1998

The reactions $pp\to ppπ^0$ and $pp\to dπ^+$ at threshold: The role of the isoscalar $πN$ scattering amplitude

We examine the role of the elementary isoscalar pion--nucleon scattering amplitude in the description of the processes $pp \to ppπ^0$ and $pp\to dπ^+$ at threshold. We argue that the presently used tree level dimension two approximation used in chiral perturbation theory is insufficient as input by direct comparison with the $π$N scattering data. We also show that a successful semi--phenomenological boson--exchange model does better in the description of these data. The influence of the violation of crossing symmetry in the meson--exchange model has to be studied in more detail. We stress that further investigations of the process $pp\to dπ^+$ can pave the way to a deeper understanding of the pion dominated part of the transition operator.

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arXiv1998

$η^{\prime}$ production in proton-proton scattering close to threshold}

The $pp \to pp η^{\prime}$ (958) reaction has been measured at COSY using the internal beam and the COSY-11 facility. The total cross sections at the four different excess energies \mbox{$ Q = ~1.5 ~MeV, ~1.7 ~MeV, ~2.9 ~MeV,$ and $ ~4.1 MeV$} have been evaluated to be \mbox{$ σ= 2.5 \pm 0.5~nb$, $~~~ 2.9 \pm 1.1~nb$, $~~~ 12.7 \pm 3.2~nb$, ~ and $~~~ 25.2 \pm 3.6 ~nb $}, respectively. In this region of excess energy the $η^{\prime}$ (958) cross sections are much lower compared to those of the $π^0$ and $η$ production.

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arXiv1998

Total Cross Section of the Reaction pp \to pK^+ΛClose to Threshold

The energy dependence of the total cross section for the pp \to pK^+Λreaction was measured in the threshold region covering the excess energy range up to 7MeV. Existing model calculations describe the slope of the measured cross sections well, but are too low by a factor of two to three in rate. The data were used for a precise determination of the beam momentum of the COSY-synchrotron.

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arXiv1998

Production of $ω$-mesons in proton-proton collisions

The production of $ω$-mesons in proton-proton collisions for proton incident energies up to 2.2 GeV is investigated within a meson-exchange model of hadronic interactions. We find a large cancellation between the dominant $πρω$ meson-exchange current and nucleonic current contributions. A comparison with preliminary data from SATURNE calls for the inclusion of off-shell form factors at the $NNω$ and $πρω$ production vertices. Due to the present lack of knowledge of these form factors, together with the destructive interference mentioned above, the relative magnitude of the nucleonic and meson-exchange current contributions cannot be determined from existing total cross section data. However, it is shown that the angular distribution of the produced $ω$-mesons provides an unique and clear signature of the magnitude of these currents, thus allowing one to disentangle these two basic reaction mechanisms.

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arXiv1997

The quark-meson coupling model for Lambda, Sigma and Xi hypernuclei

The quark-meson coupling (QMC) model, which has been successfully used to describe the properties of both infinite nuclear matter and finite nuclei, is applied to a systematic study of $Λ, Σ$ and $Ξ$ hypernuclei. Assumptions made in the present study are, (i) the (self-consistent) exchanged scalar, and vector, mesons couple only to the u and d quarks, and (ii) an SU(6) valence quark model for the bound nucleons and hyperon. The model automatically leads to a very weak spin-orbit interaction for the $Λ$ in a hypernucleus. Effects of the Pauli blocking at the quark level, particularly in the open, coupled, $ΣN - ΛN$ channel (strong conversion), is also taken into account in a phenomenological way.

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arXiv1996

Threshold meson production in nucleon-nucleon collisions

A brief overview on recent model calculations for near threshold pion production in nucleon-nucleon collisions is given. Results from our own investigations of the reactions $pp \rightarrow ppπ^0$ and $pn \rightarrow dπ^0$ are presented. Direct production, heavy meson exchange and pion rescattering are taken into account. For the latter a T-matrix obtained from a microscopic model of the $πN$ interaction is employed. We obtain a significant contribution from rescattering, but not enough to describe the data for $pp \to ppπ^0$. The missing production rate can be provided by heavy meson exchanges. For the first time the effect of off--shell rescattering is investigated for the reaction $pn \rightarrow dπ^0$. Isoscalar rescattering in combination with isovector rescattering is able to describe the s-wave production data. We confirm that heavy meson exchanges are negligible in this reaction.

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arXiv1995

The reaction $pp \to ppπ^0$ near threshold

We perform a momentum-space calculation of the reaction $pp \rightarrow ppπ^0$ near threshold. Direct production and pion rescattering are taken into account. For the latter a T-matrix obtained from a microscopic model of the $πN$ interaction is employed. The effects of some approximations commonly used in studies of $ pp \rightarrow ppπ^0$ \ are discussed. We find that those approximations overestimate the cross section and also modify its energy dependence. We obtain a significant contribution from rescattering, but not nearly enough to describe the data.

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