arXiv subjects

K. Nakayama

Publications and source records attributed to K. Nakayama.

118 records · Page 7Linked to original sources

arXiv2001

Pseudoscalar and vector meson production in NN collisions

Heavy meson production in nucleon-nucleon collisions is discussed within a meson exchange model of hadronic interactions, paying special attention to the basic dynamics that determine the behavior of the cross sections near the threshold energy. The pp-->ppϕreaction is discussed as an example of the production of vector mesons in NN collisions. For the pseudoscalar meson production, results for the ηproduction in both the pp and pn collisions are presented.

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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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arXiv1999

eta' meson production in proton-proton collisions

The pp -> pp eta' reaction is investigated within a relativistic meson-exchange model of hadronic interactions. We explore the role of nucleonic and mesonic, as well as the N* resonance currents, in producing eta' mesons. In order to learn more about the production mechanisms, new measurements in the energy region far from the threshold are required.

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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

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

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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arXiv1996

The influence of negative-energy states on proton-proton bremsstrahlung

We investigate the effect of negative-energy states on proton-proton bremsstrahlung using a manifestly covariant amplitude based on a T-matrix constructed in a spectator model. We show that there is a large cancellation among the zeroth-order, single- and double-scattering diagrams involving negative-energy nucleonic currents. We thus conclude that it is essential to include all these diagrams when studying effects of negative-energy states.

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arXiv1994

Proton-proton bremsstrahlung below and above pion-threshold: the influence of the $Δ$-isobar

The proton-proton bremsstrahlung is investigated within a coupled-channel model with the $Δ$ degree of freedom. The model is consistent with the $NN$ scattering up to 1 GeV and the $γNΔ$ vertex determined in the study of pion photoproduction reactions. It is found that the $Δ$ excitation can significantly improve the agreements with the $pp \rightarrow ppγ$ at $E_{lab}=280$ MeV. Predictions at $E_{lab}=550$ and $800$ MeV are presented for future experimental tests.

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arXiv1993

Projected Linear Response Theory for Charge-Exchange Excitations and Double Beta Decay

The projected random phase approximation (PRPA) for charge-exchange excitations is derived from the time-dependent variational principle. Explicit results for the unperturbed energies (including the self-energy corrections), the PRPA matrices, and the transition matrix elements are presented. The effect of the projection procedure on the two-neutrino $ββ$ decay in $^{76}Ge$ is briefly discussed.

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