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Two-pion-exchange contributions to the pp\to ppπ^0 reaction  [PDF]
Y. Kim,T. Sato,F. Myhrer,K. Kubodera
Physics , 2007, DOI: 10.1016/j.physletb.2007.10.023
Abstract: Our previous study of the near-threshold pp\to pp\pi^0 reaction based on a hybrid nuclear effective field theory is further elaborated by examining the momentum dependence of the relevant transition operators. We show that the two-pion exchange diagrams give much larger contributions than the one-pion exchange diagram, even though the former is of higher order in the Weinberg counting scheme. The relation between our results and an alternative counting scheme, the momentum counting scheme, is also discussed.
Two-pion-exchange and other higher-order contributions to the $pp\to pp\pi^0$ reaction
Kim, Y.;Sato, T.;Myhrer, F.;Kubodera, K.
High Energy Physics - Phenomenology , 2008, DOI: 10.1103/PhysRevC.80.015206
Abstract: Much effort has been invested on effective-field-theoretical studies of the near-threshold NN \to NN\pi reactions and, in order to deal with the rather large three-momentum transfers involved, the momentum counting scheme was proposed as an alternative to the usual Weinberg counting scheme. To examine the practical utility of the momentum counting scheme, we study here the contributions of higher-order terms to the pp\to pp\pi^0 reaction. We discuss the consequences of the different treatments of the nucleon propagators in these two counting schemes. We also investigate certain higher chiral-order pion-rescattering terms and the five-point counter-term, which turn out to give important contributions.
Two-pion-exchange and other higher-order contributions to the $pp\to ppπ^0$ reaction  [PDF]
Y. Kim,T. Sato,F. Myhrer,K. Kubodera
Physics , 2008, DOI: 10.1103/PhysRevC.80.015206
Abstract: Much effort has been invested on effective-field-theoretical studies of the near-threshold NN \to NN\pi reactions and, in order to deal with the rather large three-momentum transfers involved, the momentum counting scheme was proposed as an alternative to the usual Weinberg counting scheme. To examine the practical utility of the momentum counting scheme, we study here the contributions of higher-order terms to the pp\to pp\pi^0 reaction. We discuss the consequences of the different treatments of the nucleon propagators in these two counting schemes. We also investigate certain higher chiral-order pion-rescattering terms and the five-point counter-term, which turn out to give important contributions.
Large two-pion-exchange contributions to the $pp\to ppπ^0$ reaction  [PDF]
F. Myhrer
Physics , 2006,
Abstract: The large two-pion exchange amplitudes are calculated in HB$\chi$PT and their net contribution to the reaction cross section is large.
Meson Exchange and Pion Rescattering Contributions to the Cross Section for $pp\to ppπ^0$  [PDF]
U. van Kolck,G. A. Miller,D. O. Riska
Physics , 1996, DOI: 10.1016/S0370-2693(96)01225-7
Abstract: Short range meson-exchange mechanisms such as $\rho\to\omega\pi^0$ contribute significantly to the amplitude for $pp\rightarrow pp\pi^0$ near threshold in addition to pion rescattering. The uncertainty of the latter contribution, which depends on poorly determined parameters, is estimated. Allowing for this uncertainty and taking the short range meson-exchange contributions into account makes it possible to reproduce the measured cross section.
Two-pion-exchange effects in the $pp\to ppπ^0$ reaction  [PDF]
F. Myhrer
Physics , 2007,
Abstract: We study the pp \to pp\pi^0 reaction near threshold based on heavy-baryon chiral perturbation theory. We show that the two-pion-exchange diagrams give much larger contribution than the one-pion-exchange diagram which is of lower chiral order in Weinberg's counting scheme. We also discuss the relation of our results to the momentum counting scheme.
Role of heavy-meson exchange in pion production near threshold  [PDF]
C. J. Horowitz,H. O. Meyer,D. Griegel
Physics , 1993, DOI: 10.1103/PhysRevC.49.1337
Abstract: Recent calculations of $s$-wave pion production have severely underestimated the accurately known $pp\rightarrow pp\pi^0$\ total cross section near threshold. In these calculations, only the single-nucleon axial-charge operator is considered. We have calculated, in addition to the one-body term, the two-body contributions to this reaction that arise from the exchange of mesons. We find that the inclusion of the scalar $\sigma$-meson exchange current (and lesser contributions from other mesons) increases the cross section by about a factor of five, and leads to excellent agreement with the data. The results are neither very sensitive to changes in the distorting potential that generates the $NN$ wave function, nor to different choices for the meson-nucleon form factors. We argue that $pp\rightarrow pp\pi^0$\ data provide direct experimental evidence for meson-exchange contributions to the axial current.
The role of the $\Lambda(1405)$ in the $pp\to p K^+\Lambda(1405)$ reaction
Geng, L. S.;Oset, E.
High Energy Physics - Phenomenology , 2007, DOI: 10.1140/epja/i2008-10518-5
Abstract: We report a theoretical study of the $pp\to p K^+\Lambda(1405)$ reaction, which was recently investigated at COSY-J\"{u}lich by using a 3.65 GeV/c circulating proton beam incident on an internal hydrogen target. The reaction is driven by single kaon exchange, single pion exchange, and single rho exchange terms which have very different shapes due to the two pole structure of the $\Lambda(1405)$ and the presence of background terms. The shape for the sum of the three contributions, as well as the total cross section, are consistent with present data within experimental and theoretical uncertainties, using reasonable form factors for the meson-baryon vertices.
Hidden dibaryons in one- and two-pion production in NN collisions  [PDF]
M. N. Platonova,V. I. Kukulin
Physics , 2014,
Abstract: Processes of one- and two-pion production in NN collisions in connection with excitation of intermediate dibaryon resonances are considered. In particular, relative contributions of the conventional meson-exchange and dibaryon excitation mechanisms in the reaction pp --> d{\pi}$^+$ are investigated in detail. It is shown that inclusion of the intermediate isovector dibaryon resonances allows to essentially improve the description of experimental data for this reaction, provided the soft short-range cut-off parameters in the {\pi}NN and {\pi}N{\Delta} vertices are used. Manifestation and importance of intermediate isoscalar and isovector dibaryons in the two-pion production processes are also demonstrated. The possibility of investigating the isovector dibaryon resonances in reactions pp --> d{\pi}{\pi} and pp --> pp{\pi}{\pi} is discussed. An explanation of the observed strong differences between two-pion production cross sections in pn and pp collisions based in part on the analysis of dibaryon structure is suggested.
Production of $a_0$-mesons in pp and pn reactions  [PDF]
E. L. Bratkovskaya,V. Yu. Grishina,L. A. Kondratyuk,M. Buescher,W. Cassing
Physics , 2001, DOI: 10.1088/0954-3899/28/9/307
Abstract: We investigate the cross section for the reaction $NN \to NNa_0$ near threshold and at medium energies. An effective Lagrangian approach with one-pion exchange is applied to analyze different contributions to the cross section for different isospin channels. The Reggeon exchange mechanism is also considered. The results are used to calculate the contribution of the $a_0$ meson to the cross sections and invariant $K \bar K$ mass distributions of the reactions $pp\to pn K^+\bar K^0$ and $pp\to pp K^+K^-$. It is found that the experimental observation of $a_0^+$ mesons in the reaction $pp\to pn K^+\bar K^0$ is much more promising than the observation of $a_0^0$ mesons in the reaction $pp\to pp K^+K^-$.
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