arXiv subjects
Publications and source records attributed to A. Sibirtsev.
We calculate the total cross section for $πN \to J/ΨN$ based on $ρ$-meson exchange. On the basis of this calculation we predict a maximal reaction rate arising from the OZI-violating $J/Ψ{\leftrightarrow}ρπ$ vertex in tree-level. Our estimate for the maximum reaction rate is still one order of magnitude smaller than the existing predictions which were based on the other OZI-violating mechanisms.
We address the question what information, other than the Final State Interaction parameters, one can extract from data on near-threshold meson production.
Within the one-pion exchange model we calculate the near-threshold $η^{\prime}$ production from $pp$ collisions including the final state interaction between the protons. Since the description of the data is quite well we conclude that $η, ρ$ or $ ω$ exchange currents either play no role or cancel each other to a large extent in this reaction.
We calculate the momentum dependence of the $ρ$-meson selfenergy based on the dispersion relation for the $ρN$ scattering amplitude $f(ω$) at low nuclear density. The imaginary part of $f(ω)$ is determined from the optical theorem, while the total $ρN$ cross section is obtained within the VDM at high energy and within the resonance model at low energy. Our numerical results indicate a sizeable broadening of the $ρ$-meson width in the medium especially for low relative momenta $p$ while the real part of the $ρ$ selfenergy is found to change its sign and becomes repulsive already at momenta above 100 MeV/c. Extrapolating to nuclear saturation density $ρ_0$ we find a dropping of the $ρ$-mass for $p \approx$ 0 in line with the QCD sumrule analysis of Hatsuda while at high energy an increase of the $ρ$-mass in line with the prediction by Eletsky and Joffe is obtained. However, when including a broadening of the baryonic resonances in the medium, the $ρ$-meson mass shift at $p \approx$ 0 becomes slightly repulsive whereas the width increases substantially.
We calculate the momentum-dependent potentials for $K^+$ and $K^-$ mesons in a dispersion approach at nuclear density $ρ_0$ using the information from the vacuum $K^+ N$ and $K^- N$ scattering amplitudes, however, leaving out the resonance contributions for the in-medium analysis. Whereas the $K^+$ potential is found to be repulsive ($\approx$ + 30 MeV) and to show only a moderate momentum dependence, the $K^-$ selfenergy at normal nuclear matter density turns out to be $\approx$ - 200 MeV at zero momentum in line with kaon atomic data, however, decreases rapidly in magnitude for higher momenta. The antikaon production in p + A reactions is calculated within a coupled transport approach and compared to the data at KEK including different assumptions for the antikaon potentials. Furthermore, detailed predictions are made for $p + ^{12}C$ and $p + ^{207}Pb$ reactions at 2.5 GeV in order to determine the momentum dependent antikaon potential experimentally.
We analyse the $pp \to p ΛK$ cross section recently measured at COSY arguing that the enhancement of the production cross section at energies close to the reaction threshold should be due to the $Λp$ final state interaction. We find that the experimental $Λp$ elastic scattering data as well as the predictions from the Jülich-Bonn model are in reasonable agreement with the new results on $K^+$-meson production. We propose to study directly the final state interaction by measurements of the cross section as a function of the hyperon momentum in the $Λp$ cm system.
The cross sections of the reaction $pp \to N K Y$ for $K^+$ or $K^0$ mesons and $Λ$ or $Σ$ hyperons are calculated within the boson exchange model including pion and kaon exchange diagrams. We analyze the dependence of the results on the accuracy of the input $πN$ amplitude. By fixing the $πNN $ coupling constant and the cut-off parameter $Λ_π$ at the $πNN$ vertex we calculate the contribution from the kaon exchange diagram and obtain the ratio of the $KN Λ$ and $KN Σ$ coupling constants by a fit to the experimental data. This ratio is in a good agreement with the SU(6) prediction. Our calculated total cross sections for the different reaction channels are fitted by simple expressions and compared with other parameterizations used in the literature. Furthermore, the gross features of the production cross section close to threshold are discussed.
We analyse the $p p \to p ΛK^+$ total cross section data which were recently measured by the COSY-11 collaboration at an energy 2~MeV above the reaction threshold. Our analysis suggests that the measurement of the invariant mass spectrum for the $ΛK^+$ at energies around 100 MeV above the threshold can provide a new constraint on the theoretical calculations for this reaction. In particular, the measurement can give a clue as to whether the reaction is dominated by resonance excitation or not. Thus, it should contribute to further understanding of the strangeness production mechanism. We show the invariant mass spectra for the $ΛK^+$ system in these optimal kinematic conditions calculated by several approaches, and demonstrate that our suggestion is experimentally feasible.
We analyze the production of $ρ$-mesons in $p + A$ reactions including both the production by proton-nucleon as well as pion-nucleon collisions within a coupled channel transport approach. The final state interactions of the $ρ$-meson with nucleons are evaluated from a resonance model which allows to extract elastic and inelastic cross sections. We include the latter final state interactions, the $ρ$-meson decay into two pions as well as the final pion-nucleon interactions within the transport approach. We find the invariant mass distribution of pion pairs to be sensitive to the $ρ$-meson properties in the nuclear medium. However, due to the strong final state interactions of pions only light targets like $^{12}C$ might be suited to extract a $ρ$-signal from the uncorrelated two pion background which carries information about the in-medium properties of the $ρ$-meson.
Within the Glauber formalism and a BUU transport model we analyze the $η$-photoproduction data from nuclei and evaluate the in-medium $ηN$ cross section. Our results indicate that the $ηN$ cross section is almost independent of the $η$ energy up to 200 MeV.
We reanalyse the production of $p\bar{p}$ pairs in proton-nucleus and nucleus-nucleus collisions employing novel elementary cross sections for baryon-baryon and pion-baryon production channels based on a boson-exchange model. In contrast to previous transport studies performed in the literature the secondary pion induced channel is found to be most important in both p+A and A+A collisions at subthreshold energies. A detailed comparison with the experimental data available indicates that sizeable attractive $\bar{p}$ potentials in the order of - 100 to - 150 MeV at normal nuclear matter density are needed to reproduce the size and shape of the experimental spectra.
We study the production of $Λ$ hyperons in $p + A$ reactions on the basis of a BUU transport approach from 1.1 to 1.9 GeV and evaluate the properties of the hypernuclei produced in particular with respect to their momentum distribution in the laboratory frame. Due to elastic $ΛN$ scattering large cross sections for the production of heavy hypernuclei in the order of 100 - 400 $μb$ are predicted for p + U at 1.5 - 1.9 GeV laboratory energy. Whereas the $K^+ Y$ production channels are expected to be only slightly modified in the nuclear medium, the antikaon production should be enhanced substantially due to large attractive $K^-$ selfenergies in dense matter. We predict an enhancement of the inclusive $K^-$ yield in p + $^{208}$Pb collisions of a factor of $\approx$ 10 at 2 GeV laboratory energy.
The antikaon production cross section from nucleon-nucleon reactions near threshold is studied in a meson exchange model. We include both pion and kaon exchange, but neglect the interference between the amplitudes. In case of pion exchange the antikaon production cross section can be expressed in terms of the antikaon production cross section from a pion-nucleon interaction, which we take from the experimental data if available. Otherwise, a $K^*$-resonance exchange model is introduced to relate the different reaction cross sections. In case of kaon exchange the antikaon production cross section is related to the elastic $KN$ and $\bar KN$ cross sections, which are again taken from experimental measurements. We find that the one-meson exchange model gives a satisfactory fit to the available data for the $NN\to NNK\bar K$ cross section at high energies. We compare our predictions for the cross section near threshold with an earlier empirical parameterization and that from phase space models.
Results for the energy dependence of the elementary kaon production cross sections in proton-proton collisions are reported. Calculations are performed within an extended version of the resonance model which was used for the previous studies of elementary kaon production in pion-nucleon and pion-$Δ$ collisions. Although the model treatment is within the {\it empirical} tree level (observed widths for the resonances are used), it is fully relativistic, and includes all relevant baryon resonances up to 2 GeV. One of the purposes of this study is to provide the results for the simulation codes of subthreshold kaon production in heavy ion collisions. This is the first, consistent study of the elementary kaon production reactions including both $πB$ and $B B$ ($B=N, Δ$) collisions on the same footing. Comparisons are made between the calculated results and the existing semi-empirical parametrizations which are widely used for the simulation codes, as well as the experimental data.
We analyse the production and propagation of kaons and antikaons in Ni + Ni reactions from 0.8--1.85 GeV/u within a coupled channel transport approach including the channels $BB \to K^+YN, πB\to K^+Y, BB \to NN K \bar{K}, πB\to N K\bar{K}, K^+B\to K^+B, \bar{K} B\to \bar{K}B, Y N\to \bar{K} NN, ππ\to K \bar{K}$ as well as $πY\to \bar{K}N$ and $\bar{K} N\to πY$ for the antikaon absorption. Whereas the experimental $K^+$ spectra can be reproduced without introducing any selfenergies for the mesons in Ni + Ni collisions from 0.8 to 1.8 GeV/u, the $K^-$ yield is underestimated by a factor of 5--7 at 1.66 and 1.85 GeV/u. However, introducing density dependent antikaon masses as proposed by Kaplan and Nelson, the antikaon spectra can be reasonably well described.
We study the production of $K^+, ρ, ω$ and $ϕ$ mesons in $p + ^{12}C$ reactions on the basis of empirical spectral functions. The high momentum, high removal energy part of the spectral function is found to be negligible in all cases close to the absolute threshold. Furthermore, the two-step process ($pN \rightarrow πN N; πN \rightarrow N + K^+, ρ, ω, ϕ$) dominates the cross section at threshold energies in line with earlier calculations based on the folding model.
We study the $Δ$-excitation in $\overline{p}d$ annihilation at rest. The invariant spectra of the $π^+p$ and $π^-p$ systems selecting the protons with momenta above 400 MeV/c are analyzed. The calculations reproduces reasonably the experimental data.
The $Δ$-excitation in $\overline{p}d$ annihilation at rest was studied. The annihilation amplitude from the statistical model and the $πN$ amplitude from the resonance model were adopted in our calculations. We analyze the invariant mass of the $π^+p$ and $π^-p$ systems selecting the protons with momenta above 400 MeV/c and with respect to the different final reaction channels. Our model reproduces reasonably the experimental data.