Kaon Production Cross Sections Research Articles

Medium effects in proton-inducedK0production at 3.5 GeV

We present the analysis of the inclusive $K^{0}$ production in p+p and p+Nb collisions measured with the HADES detector at a beam kinetic energy of 3.5 GeV. Data are compared to the GiBUU transport model. The data suggest the presence of a repulsive momentum-dependent kaon potential as predicted by the Chiral Perturbation Theory (ChPT). For the kaon at rest and at normal nuclear density, the ChPT potential amounts to $\approx 35$ MeV. A detailed tuning of the kaon production cross sections implemented in the model has been carried out to reproduce the experimental data measured in p+p collisions. The uncertainties in the parameters of the model were examined with respect to the sensitivity of the experimental results from p+Nb collisions to the in-medium kaon potential.

Precision Measurement of Charged Pion and Kaon Differential Cross Sections ine+e−Annihilation ats=10.52 GeV

Measurements of inclusive differential cross sections for charged pion and kaon production in e+ e- annihilation have been carried out at a center-of-mass energy of sqrt[s]=10.52 GeV. The measurements were performed with the Belle detector at the KEKB e+ e- collider using a data sample containing 113×10(6) e+ e- → qq events, where q={u,d,s,c}. We present charge-integrated differential cross sections dσ(h±)/dz for h±={π±,K±} as a function of the relative hadron energy z=2E(h)/sqrt[s] from 0.2 to 0.98. The combined statistical and systematic uncertainties for π± (K±) are 4% (4%) at z∼0.6 and 15% (24%) at z∼0.9. The cross sections are the first measurements of the z dependence of pion and kaon production for z>0.7 as well as the first precision cross section measurements at a center-of-mass energy far below the Z0 resonance used by the experiments at LEP and SLC.

THE INTERACTION OF ρ AND K+ MESONS WITH MATTER

We review in this contribution the information we can obtain from heavy-ion experiments about the interaction of mesons with matter. We demonstrate that the vector mesons seen in experiments come predominantly from low densities. Kaons offer a better opportunity but most of the presently available experimental observables do not allow to analyze separately the three essential unknown quantities: the kaon production cross-section in the medium, the K+N potential interaction at finite densities and temperatures and the kaon (elastic or charge exchange) rescattering cross-section in the medium. We propose a measurement which almost exclusively tests the K+N potential.

Strangeness production from πN collisions in nuclear matter

Kaon production in pion-nucleon collisions in nuclear matter is studied in the resonance model. To evaluate the in-medium modification of the reaction amplitude as a function of the baryonic density we introduce relativistic, mean-field potentials for the initial, final and intermediate mesonic and baryonic states. These vector and scalar potentials were calculated using the quark-meson coupling (QMC) model. The in-medium kaon production cross sections in pion-nucleon interactions for reaction channels with $\Lambda$ and $\Sigma$ hyperons in the final state were calculated at the baryonic densities appropriate to relativistic heavy ion collisions. Contrary to earlier work which has not allowed for the change of the cross section in medium, we find that the data for kaon production are consistent with a repulsive $K^+$-nucleus potential.

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

K+production in baryon-baryon and heavy-ion collisions

Kaon production cross sections in nucleon-nucleon, nucleon-$\ensuremath{\Delta}$, and $\ensuremath{\Delta}$-$\ensuremath{\Delta}$ interactions are studied in a boson exchange model. For the latter two interactions, the exchanged pion can be on-mass shell; only contributions due to a virtual pion are included via the Peierls method by taking into account the finite $\ensuremath{\Delta}$ width. With these cross sections and also those for pion-baryon interactions, subthreshold kaon production from heavy-ion collisions is studied in the relativistic transport model.

Kaons in dense matter, kaon production in heavy-ion collisions, and kaon condensation in neutron stars

The recent past witnesses the growing interdependence between the physics of hadrons, the physics of relativistic heavy-ion collisions, and the physics of compact objects in astrophysics. A notable example is the kaon which plays special roles in all the three fields. In this paper, we first review the various theoretical investigations of kaon properties in nuclear medium, focusing on possible uncertainties in each model. We then present a detailed transport model study of kaon production in heavy-ion collisions at SIS energies. We shall discuss especially the elementary kaon and antikaon production cross sections in hadron-hadron interactions, that represent one of the most serious uncertainties in the transport model study of particle production in heavy-ion collisions. The main purpose of such a study is to constrain kaon in-medium properties from the heavy-ion data. This can provide useful guidances for the development of theoretical models of the kaon in medium. In the last part of the paper, we apply the kaon in-medium properties extracted from heavy-ion data to the study of neutron star properties. Based on a conventional equation of state of nuclear matter that can be considered as one of the best constrained by available experimental data on finite nuclei, we find that the maximum mass of neutron stars is about 2 M ⊙, which is reduced to about 1.5 M ⊙ once kaon condensation as constrained by heavy-ion data is introduced.

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.

Λ-hyperon production via the pp → pK+Λ reaction 2 MeV above threshold

The pp → pK + Λ reaction was measured at COSY with a proton beam momentum of 2.345 GeV/c, i.e. with an excess energy of 2 MeV above threshold. The total cross section was determined to be 8.2 ± 1.8 nb. The present data point close to the production threshold indicates, that existing phenomenological parametrizations of the total kaon production cross section are insufficient.

Kaon production cross sections from baryon-baryon interactions

In a one-pion plus one-kaon exchange model, we calculate the kaon production cross sections in nucleon-nucleon, nucleon-delta and delta-delta interactions. We find that this model describes reasonably well the experimental data on kaon production in the proton-proton interaction. Near the kaon production threshold, the cross section obtained from this model is smaller than that from the linear parametrization of Randrup and Ko. For kaon production cross sections from the nucleon-delta and delta-delta interactions, the cross sections are singular in free space, so we calculate them in a nuclear medium by including the (complex) pion self-energy. The results are compared with the scaling ansatz of Randrup and Ko. The theoretical cross sections are then used in a transport model to study kaon production from Au+Au collisions at 1 GeV/nucleon.

Parameterization of spectral distributions for pion and kaon production in proton-proton collisions.

Accurate semi-empirical parameterizations of the energy-differential cross sections for charged pion and kaon production from proton-proton collisions are presented at energies relevant to cosmic rays. The parameterizations depend on the outgoing meson momentum and also the proton energy, and are able to be reduced to very simple analytical formulas suitable for cosmic-ray transport.

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 from hot and dense matter formed in heavy-ion collisions.

In heavy-ion collisions, kaons can be produced from baryon-baryon, meson-baryon, and meson-meson interactions. Simple meson-exchange models are introduced to study kaon production from these processes in the free space. These models are then extended to determine kaon production in hot, dense nuclear matter by taking into account the decreasing hadron masses as a result of the restoration of chiral symmetry and the condensation of kaons. We find that the cross sections for kaon production from all three processes are enhanced. In particular, the effect of decreasing hadron masses on kaon production from the meson-meson annihilation is most significant. In the hydrochemical model for heavy-ion collisions, we demonstrate that the observed enhancement of kaon yield in high-energy heavy-ion collisions can be explained if the medium effect is included.

K/ pi ratios in relativistic nuclear collisions: A signature for the quark-gluon plasma?

Collisions of Si(14.5{ital A} GeV)+Au are investigated in the relativistic-quantum-molecular-dynamics approach. The calculated pseudorapidity distributions for central collisions compare well with recent experimental data, indicating a large degree of nuclear stopping and thermalization. Nevertheless, nonequilibrium effects play an important role in such complex multihadron reactions: They lead to a strong enhancement of the total kaon production cross sections, in good agreement with the experimental data, without requiring the formation of a deconfined quark-gluon plasma.

Medium effect on kaon production from heavy-ion collisions

Both the nucleon-nucleon inelastic and the kaon-production cross sections in dense nuclear matter are evaluated in the one-pion exchange model. The medium effect is included by using the dressed pion propagator determined in the delta-hole model. Compared with the cross sections in free space, it is found that the nucleon-nucleon inelastic cross section is substantially enhanced at high nuclear-matter densities while the kaon-production cross section is only moderately increased. In the normal Vlasov-Uehling-Uhlenbeck model for heavy-ion collisions the total kaon yield is seen to be sensitive to the nuclear equation of state.

On the pion and kaon production in nucleus-nucleus collisions near the absolute threshold

A simple phase-space model of particle production in nucleus-nucleus collisions near the absolute threshold is developed. The model parameters are determined by comparison with pion production experimental data, and then the model is used to estimate the kaon production cross section.

SUBTHRESHOLD KAON- AND PION PRODUCTION IN HEAVY ION COLLISIONS: SIMILARITIFS AND DIFFERENCES

Particle inclusive yields from heavy ion reactions are described by a closed form expression which is not limited to a particular type of particle as long as this is produced in individual baryon-baryon encounters with a small probability. This criterion is satisfied for subthreshold pion and kaon production on which we concentrate. Even though the elementary pion and kaon production cross sections can both be described well by three-particle phase space considerations, the final inclusive production rates differ qualitatively from one another. The reasons for this are discussed.

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.

Comparison of π ±, K ± and p, [formula omitted] production in the central rapidity region in hadron-hadron collisions and in e +e − annihilation

We compare the p T dependence of pion, kaon and proton production cross sections in the central rapidity region in e +e − annihilation events and in proton-proton collisions at ISR energies. We find similarities both in the p T dependence of cross sections and in the particle composition as a function of p T , in agreement with the hypothesis of a universal mechanism of particle production.