Elementary Kaon Production Research Articles

Observation of K+d correlations from pA collisions

Results of a first experiment on (K+p) and (K+d) correlations from proton-carbon (pC) and proton-deuteron (pd) interactions at beam energies above and much below the threshold for elementary kaon production in nucleon-nucleon reactions ( TNN = 1580 MeV) are discussed. These data, obtained with the ANKE spectrometer at COSY-Julich, provide first direct evidence for K+ production via the two-step mechanism and an indication for a cluster mechanism. It is shown that both processes contribute significantly in pC collisions at 1200 MeV, while they are strongly suppressed at 2300 MeV and also in pd-interactions at 1344 MeV. It is emphasized that the underlying kinematics can be exploited to distinguish between these reaction mechanisms.

Erratum: Resonance model study of kaon production in baryon-baryon reactions for heavy-ion collisions [Phys. Rev. C59, 369 (1999)

The energy dependence of the total kaon production cross sections in baryon baryon ($N$ and $\Delta$) collisions are studied in the resonance model, which is a relativistic, tree-level treatment. This study is the first attempt to complete a systematic, consistent investigation of the elementary kaon production reactions for both the pion baryon and baryon baryon reactions. Our model suggests that the magnitudes of the isospin-averaged total cross sections for the $N N \to N Y K$ and $\Delta N \to N Y K$ ($Y = \Lambda$ or $\Sigma$) reactions are almost equal at energies up to about 200 MeV above threshold. However, the magnitudes for the $\Delta N$ reactions become about 6 times larger than those for the $N N$ reactions at energies about 1 GeV above threshold. Furthermore, the magnitudes of the isospin-averaged total cross sections for the $N N \to \Delta Y K$ reactions turn out to be comparable to those for the $N N \to N Y K$ reactions at $N N$ invariant collision energies about 3.1 GeV, and about 5 to 10 times larger at $N N$ invariant collision energies about 3.5 GeV. The microscopic cross sections are parametrized in all isospin channels necessary for the transport model studies of kaon production in heavy ion collisions. These cross sections are then applied in the relativistic transport model to study the sensitivity to the underlying elementary kaon production cross sections.

Resonance model study of kaon production in baryon-baryon reactions for heavy-ion collisions

The energy dependence of the total kaon production cross sections in baryon-baryon (N and {Delta}) collisions are studied in the resonance model, which is a relativistic tree-level treatment. This study is the first attempt to complete a systematic consistent investigation of the elementary kaon production reactions for both the pion-baryon and baryon-baryon reactions. Our model suggests that the magnitudes of the isospin-averaged total cross sections for the NN{r_arrow}NYK and {Delta}N{r_arrow}NYK (Y={Lambda} or {Sigma}) reactions are almost equal at energies up to about 200 MeV above threshold. However, the magnitudes for the {Delta}N reactions become about 6 times larger than those for the NN reactions at energies about 1 GeV above threshold. Furthermore, the magnitudes of the isospin-averaged total cross sections for the NN{r_arrow}{Delta}YK reactions turn out to be comparable to those for the NN{r_arrow}NYK reactions at NN invariant collision energies about 3.1 GeV, and about 5 to 10 times larger at NN invariant collision energies about 3.5 GeV. The microscopic cross sections are parametrized in all isospin channels necessary for the transport model studies of kaon production in heavy-ion collisions. These cross sections are then applied in the relativistic transport model to study the sensitivity to the underlying elementary kaonmore » production cross sections. {copyright} {ital 1999} {ital The American Physical Society}« less

Electromagnetic production of the hypertriton

Kaon photoproduction on 3He, γ + 3 He → K + + Λ 3 H , is studied in the framework of the impulse approximation. Realistic 3He wave functions obtained as solutions of Faddeev equations with the Reid soft-core potential are used along with different Λ 3H wave functions. Results are compared for several elementary operator models, which can successfully describe the elementary kaon production off the proton up to a photon lab energy of k = 2.2 GeV. It is found that the corresponding cross sections are small, of the order of several nanobarns. It is also shown that the influence of Fermi motion is important, while the effect of different off-shell assumptions on the cross section is not too significant.

Resonance model study of strangeness production in pp collisions

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 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 BB ( 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.

Kaon production at subthreshold energies

We present a comprehensive investigation of subthreshold and threshold kaon production in the framework of the QMD model. The calculation shows that the kaon yield depends strongly on the nuclear equation of state (EOS) and subthreshold kaon experiments may therefore offer the up to now best possibility to determine this yet unknown property of nuclear matter. Whereas static equations of state are in quite good agreement with the data the more realistic momentum dependent EOS's underpredict the data by about a factor of three. Most kaons are produced in a two step process with an intermediate Δ, a process which is absent in NN collisions. Therefore the kaon yield is much higher than expected from the extrapolation of pp data. We discuss in detail the influence of the elementary kaon production cross section, the contribution of different production channels and the properties of the nuclear environment at the place where the kaon is produced. The decrease of the number of produced kaons per participant with decreasing participant number, which is also observed experimentally, has two sources: The nonmaxwellian momentum distribution for small participant numbers as well as a reduction of the ΔΔ channel. This finding is supported by the observed decrease of high momentum pions. We compare our results with other calculations and discuss in detail the theoretical and experimental uncertainties. They include the yet only vaguely known elementary kaon production cross section at the threshold, the lack of a quantum-mechanical treatment of the two step production process as well as the behaviour of the kaon (and therefore also of the kaon production threshold) in the nuclear environment.

KAON PRODUCTION IN RELATIVISTIC HEAVY-ION COLLISIONS: THE ROLE OF THE ELEMENTARY CROSS SECTION

We investigate kaon production in relativistic heavy-ion reactions by use of a multiple collision approach. We clarify the crucial importance of the elementary kaon production cross section and show that with an appropriate parametrization suggested by phase space considerations, the data for 2.1 GeV/nucleon, Ne+NaF, can be reproduced without the need of kaon rescattering.

Subthreshold kaon production and compression effects

With regard to the use of subthreshold kaons from relativistic heavy-ion collisions as a tool to gain information on the nuclear matter equation of state, we investigate the role of the elementary kaon production cross section. The uncertainties introduced because of the poor knowledge of the latter near threshold are largely eliminated by considering kaon yield ratios.