Flow Of Kaons Research Articles

Kaon flow in Au+Au collisions at 1.23AGeV measured with HADES

We present results on the anisotropic transverse flow of kaons (K+, K0S and K−) in Au+Au collisions at √sNN = 2:42 GeV measured with HADES. It was proposed already in the mid-nineties that kaon flow close to its production threshold might be a good probe for the kaon-nucleon potential and, consequently, or the nuclear equation-of-state. The presented analysis was performed on more than 2 billion events of the 40% most central collisions, which opened the possibility of analyzing the kaon flow differentially as a function of transverse momentum, rapidity, and centrality, even in this low-energy regime. The measurements are compared to microscopic transport model predictions and to other data at similar collision energies. Implications on the properties of compressed nuclear matter will be discussed.

Predictions forsNN=5.02TeV Pb + Pb collisions from a multiphase transport model

We present predictions from the string melting version of a multi-phase transport model on various observables in Pb+Pb collisions at $\sqrt {s_{NN}}=5.02$ TeV. We use the same version of the model as an earlier study that reasonably reproduced dN/dy, $p_{\rm T}$-spectra and elliptic flow of charged pions and kaons at low-$p_{\rm T}$ for central and semi-central heavy ion collisions at 200 GeV and 2.76 TeV. While we compare with the already-available centrality dependence data on charged particle $dN/d\eta$ at mid-pseudorapidity in Pb+Pb collisions at 5.02 TeV, we make predictions on identified particle dN/dy, $p_{\rm T}$-spectra, azimuthal anisotropies $v_n (n=2,3,4)$, and factorization ratios $r_{n}(\eta^{a},\eta^{b}) (n=2,3)$ for longitudinal correlations.

Directed flow in heavy-ion collisions from the PHSD transport approach

Recent STAR data for the directed flow of protons, antiprotons, charged pions and kaons obtained within the beam energy scan (BES) program are analyzed within the Parton- Hadron-String-Dynamics (PHSD/HSD) transport models. Both versions of the kinetic approach are used to clarify the role of partonic degrees of freedom. The PHSD results, simulating a partonic phase and its coexistence with a hadronic one, are roughly consistent with the STAR data. Generally, the semi-qualitative agreement between the measured data and model results supports the idea of a crossover type of quark-hadron transition which softens the nuclear EoS but shows no indication of a first-order phase transition. Furthermore, the directed flow of kaons and antikaons is evaluated in the PHSD approach from √sNN ≈ 5-12 GeV which shows a high sensitivity to the hadronic potentials in the FAIR/NICA energy regime √sNN ≤⃒ 8 GeV.

Directed Flow of Charged Kaons in Au+Au Collisions from the BES Program at RHIC

We report the measurement of the directed flow (v1) for charged kaons in Au+Au collisions at =7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV as a function of rapidity and compare these results for pions, protons and antiprotons. These new kaon results may help to constrain the medium properties and collision dynamics including the in-medium kaon potential and baryon number transport in these collisions.

Parton/hadron dynamics in heavy-ion collisions at FAIR energies

Recent STAR data for the directed flow of protons, antiprotons and charged pions obtained within the beam energy scan program are analyzed within the Parton-Hadron-String-Dynamics (PHSD/HSD) transport models. Both versions of the kinetic approach are used to clarify the role of partonic degrees of freedom. The PHSD results, simulating a partonic phase and its coexistence with a hadronic one, are roughly consistent with the STAR data. Generally, the semi-qualitative agreement between the measured data and model results supports the idea of a crossover type of quark-hadron transition which softens the nuclear EoS but shows no indication of a first-order phase transition. Furthermore, the directed flow of kaons and antikaons is evaluated in the PHSD/HSD approachesfrom √sNN ≈ 3 - 200 GeV which shows a high sensitivity to hadronic potentials in the FAIR/NICA energy regime √sNN ≤ 8 GeV.

Parton/hadron dynamics in heavy-ion collisions at FAIR energies

Recent STAR data for the directed flow of protons, antiprotons and charged pions obtained within the beam energy scan program are analyzed within the Parton-Hadron-String-Dynamics (PHSD/HSD) transport models. Both versions of the kinetic approach are used to clarify the role of partonic degrees of freedom. The PHSD results, simulating a partonic phase and its coexistence with a hadronic one, are roughly consistent with the STAR data. Generally, the semi-qualitative agreement between the measured data and model results supports the idea of a crossover type of quark-hadron transition which softens the nuclear EoS but shows no indication of a first-order phase transition. Furthermore, the directed flow of kaons and antikaons is evaluated in the PHSD/HSD approachesfrom $\sqrt{s_{NN}} \approx$ 3 - 200 GeV which shows a high sensitivity to hadronic potentials in the FAIR/NICA energy regime $\sqrt{s_{NN}} \le$ 8 GeV.

Strangeness production in heavy ion collisions -Constraining the KN – potential in medium

We review the strangeness production in heavy ion collisions at energies around the NN production threshold and discuss recent measurements of the FOPI collaboration on charged kaon flow over a wide impact parameter range. The data are compared to comprehensive state-of-the-art transport models. The dense nuclear matter environment produced in those collisions may provide unique opportunities to form strange few body systems. The FOPI detector is especially suited to reconstruct such states by their charged particle decays. Apart from strongly decaying states special emphasis will be put on the search for long living weakly decaying states, i.e. Hyper-Nuclei. Light hyper nuclei are reconstructed by their two body decay channels and the production of Hyper-Tritons is studied with respect to Λ and t(3He).

Strangeness production in heavy-ion collisions around 2A GeV in FOPI

Recent FOPI data on strangeness production in central Al+Al and Ni+Ni collisions at 1.9A GeV are presented, including yields of K0, Λ, strange resonances Σ*±(1385) and K*0(892), and results of searches for kaonic bound states in the Λp-channel. An emphasis is put on the findings on directed flow of charged kaons as well as comparison of ratios of integrated yields to the statistical model calculations.

The identification of rare charged kaons in heavy-ion collisions at relativistic energies by time-of-flight with the HADES spectrometer

Detailed performance simulations of the HADES RPC time-of-flight wall have been undertaken. The most delicate situation is the identification of K − mesons close to the mid-rapidity region. While momentum resolution does not appear to be an issue, the small non-Gaussian tails in the time response are a clear problem. It will be argued that the use of redundant information supplied by time coincidence between the two layers (possible in the HADES design) can drastically improve the situation. The uniformity of acceptance for the two layer coincidence will be discussed. A possible distortion to the reconstructed kaon flow due to the wall occupancy, which is not isotropic with respect to the reaction plane because of the flow pattern of the much more abundant protons, pions and deuterons, has also been studied.

Kaon production at subthreshold energies: what do we learn about the nuclear medium?

The IQMD model is used to compare spectra and elliptic flow of kaons produced at subthreshold energies with data taken at the SIS accelerator at GSI. We find that temperatures of the spectra are dominated by the rescattering of the kaons. The study of elliptic flow observables indicates the influence of rescattering as well as of the optical potential of the kaons with increasing dominance of the optical potential at lower incident energies.

Kaon production and propagation at intermediate relativistic energies

We systematically study ${K}^{+}$ observables in nucleus-nucleus collisions at 1--2A GeV within the Boltzmann-Uehling-Uhlenbeck (BUU) transport model. We compare our calculations with the KaoS data on the kaon multiplicities and spectra. In addition, the kaon collective flow is computed and compared with the FOPI and KaoS data. We show that the elliptic kaon flow measured recently by the KaoS Collaboration is best described by using the Brown-Rho parametrization of the kaon potential, ${U}_{K}({\ensuremath{\rho}}_{0})\ensuremath{\simeq}30\phantom{\rule{0.3em}{0ex}}\text{MeV}$.

Effect of resonance decays on hadron elliptic flows

Within the quark coalescence model, we study effects of resonance decays, and of the quark momentum distribution in hadrons, on the elliptic flows of stable hadrons. We find that, with the exception of rho-meson decays, the resonance decays could have a significant effect on pion elliptic flow. However, most secondary pions stem from the rho-meson decays, resulting in a reduced effect of resonance decays on their flow. Proton and kaon flows as well as the lambda flow are, however, not much affected by resonance decays. The distribution of quark momentum in hadrons also influences their elliptic flows, leading to a better agreement with experimental flow data when compared with the naive quark coalescence model, which only allows quarks with equal momentum to form a hadron.

Covariant kaon dynamics and kaon flow in heavy ion collisions

The influence of the chiral mean field on the $K^+$ transverse flow in heavy ion collisions at SIS energy is investigated within covariant kaon dynamics. For the kaon mesons inside the nuclear medium a quasi-particle picture including scalar and vector fields is adopted and compared to the standard treatment with a static potential. It is confirmed that a Lorentz force from spatial component of the vector field provides an important contribution to the in-medium kaon dynamics and strongly counterbalances the influence of the vector potential on the $K^+$ in-plane flow. The FOPI data can be reasonably described using in-medium kaon potentials based on effective chiral models. The information on the in-medium $K^+$ potential extracted from kaon flow is consistent with the knowledge from other sources.

Transition to meson-dominated matter at RHIC. Consequences for kaon flow

Anisotropic flow of kaons and antikaons is studied in heavy-ion collisions at CERN SPS and BNL RHIC energies within the microscopic quark–gluon string model. In the midrapidity range the directed flow of kaons v1 differs considerably from that of antikaons at SPS energy (Elab=160 AGeV), while at RHIC energy (s=130 AGeV) the excitation functions of both, kaon and antikaon, flows coincide within the statistical error bars. The change is attributed to formation of dense meson-dominated matter at RHIC, where the differences in interaction cross sections of kaons and antikaons become unimportant. The time evolution of the kaon anisotropic flow is also investigated. The elliptic flow of these hadrons is found to develop at midrapidity at times 3⩽t⩽10 fm/c, which is much larger than the nuclear passing time tpass=0.12 fm/c. As a function of transverse momentum the elliptic flow increases almost linearly with rising pt. It stops to rise at pt⩾1.5 GeV/c reaching the saturation value v2K(pt)≈10%.

Transverse Flow of Kaons in Heavy-Ion Collisions

The transverse flow of positively charged kaons from heavy-ioncollisions at intermediate energy is investigated within theframework of the quantum molecular dynamics model. The calculatedresults show that the experimental data are only consistent with thoseincluding the kaon mean-field potential from the chiral Lagrangian.This indicates that the transverse flow pattern of kaons is a usefulprobe of the kaon potential in a nuclear medium.

Anisotropic flow of strange particles in heavy-ion collisions at RHIC energies

Anisotropic flow of Ks, K̄s and Λs is studied in heavy-ion collisions at SPS and RHIC energies within the microscopic quark–gluon string model. At SPS energy the directed flow of kaons differs considerably at midrapidity from that of antikaons, while at RHIC energy kaon and antikaon flows coincide. The change is attributed to the formation of dense meson-dominated matter at RHIC, where the differences in interaction cross-sections of hadrons become unimportant. The directed flows of strange particles, v1K,K̄,Λ (y), have universal negative slope at |y| ⩽ 2 at RHIC. The elliptic flow of strange hadrons is developed at midrapidity at times 3 ⩽ t ⩽ 10 fm/c. It increases almost linearly with rising pt and stops rising at pt ⩾ 1.5 GeV/c reaching the same saturation value v2K,Λ(pt) ≈ 10% in accord with experimental results.

STUDIES OF SUPERDENSE HADRONIC MATTER IN A RELATIVISTIC TRANSPORT MODEL

Transport models have been very useful in studying the properties of the hot, dense matter that is created in relativistic heavy-ion collisions. We review here a Relativistic Transport (ART) Model and its applications in heavy ion collisions at beam energies below about 10 AGeV available from the Alternating Gradient Synchrotron at Brookhaven National Laboratory. The model allows one to study not only the reaction dynamics leading to the formation of superdense hadronic matter, but also to explore the effects due to the nuclear equation of state and the deformation/orientation of the colliding nuclei on the size and lifetime of the superdense matter. We also discuss the dependence of the central baryon and energy densities, the degree of thermalization, and the collective radial flow velocity of the superdense matter on the beam energy. We further review how the properties of the superdense hadronic matter can be determined from studying the collective flow of nucleons, pions and kaons in these collisions. We finally discuss the mechanisms for kaon production in relativistic heavy-ion collisions and review the progress in extracting the kaon in-medium properties from these collisions.

Antiflow of kaons in relativistic heavy ion collisions

We compare relativistic transport model calculations to recent data on the sideward flow of neutral strange ${K}_{s}^{0}$ mesons for Au+Au collisions at $6A\mathrm{GeV}.$ A soft nuclear equation of state is found to describe very well the positive proton flow data measured in the same experiment. In the absence of the kaon potential, the ${K}^{0}$ flow pattern is similar to that of protons. The kaon flow becomes negative if a repulsive kaon potential determined from the impulse approximation is introduced. However, this potential underestimates the data which exhibit larger antiflow. An excellent agreement with the data is obtained when a relativistic scalar-vector kaon potential, that has stronger density dependence, is used. We further find that the transverse momentum dependence of directed and elliptic flow is quite sensitive to the kaon potential in dense matter.

Global observables and secondary interactions in central Au+Au reactions ats=200AGeV

The Ultra-relativistic Quantum Molecular Dynamics model (UrQMD) is used to study global observables in central reactions of Au+Au at $\sqrt{s}=200$ AGeV (RHIC). Strong stopping governed by massive particle production is predicted if secondary interactions are taken into account. The underlying string dynamics and the early hadronic decoupling implies only small transverse expansion rates. However, rescattering with mesons is found to act as a source of pressure leading to additional flow of baryons and kaons, while cooling down pions.

Kaon differential flow in relativistic heavy-ion collisions

Using a relativistic transport model, we study the azimuthal momentum asymmetry of kaons with fixed transverse momentum, i.e., the differential flow, in heavy-ion collisions at beam momentum of 6 GeV/c per nucleon, available from the Alternating Gradient Synchrotron (AGS) at the Brookhaven National Laboratory (BNL). We find that in the absence of kaon potential the kaon differential flow is positive and increases with transverse momentum as that of nucleons. The repulsive kaon potential as predicted by theoretical models, however, reduces the kaon differetnial flow, changing it to negative for kaons with low momenta. Cancellation between the negative differential flow at low mementa and the positive one at high momenta is then responsible for the experimentally observed nearly vanishing in-plane transverse flow of kaons in heavy ion experiments.