arXiv subjects

C. Hanhart

Publications and source records attributed to C. Hanhart.

191 records · Page 11Linked to original sources

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

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

On the treatment of $NN$ interaction effects in meson production in $NN$ collisions

We clarify under what circumstances the nucleon--nucleon final state interaction fixes the energy dependence of the total cross--section for the reaction $NN \to NNx$ close to production threshold, where $x$ can be any meson whose interaction with the nucleon is not too strong. We strongly criticize the procedure used recently by several authors to include the final state interaction in the reactions under discussion. In addition, we give a formula that allows one to estimate the effect of the initial state interaction for the production of heavy mesons.

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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

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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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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arXiv1995

Faddeev approach to the octet and decuplet baryons

A relativistic Faddeev model for the baryon octet is extended to treat the baryon decuplet. We find that after determining the model parameters in the mesonic sector the masses of both nucleon and delta deviate by less than 5\% from the experimental data and show only a very weak dependence on the constituent quark mass.

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