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Register a new userHyperon dynamics and production of multi-strangeness hypernuclei in heavy-ion collisions at 3A GeV
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Within the microscopic transport, systematic investigation of the many facets of hyperons and hypernuclei up to strangeness $S = -2$ are carried out for $^{197}$Au + $^{197}$Au and $^{40}$Ca + $^{40}$Ca at the incident energy of $3A$ GeV. The spatial, temporal and density distributions of hyperon production, absorption and freeze-out are thoroughly investigated. The rapidity and kinetic energy spectra of $Xi$ hyperons and double $Lambda$ hypernuclei are analyzed. It is revealed that the chemical balance of hyperon production is established in baryon-baryon channels while the opposite is found in baryon-meson channels. It turns out that the rapidity spectra of $^{4,5}_{LambdaLambda}$X are single-peak and more than two orders of magnitude lower than that of $^{3}_{Lambda}$H. Formation of double $Lambda$ hypernuclei through $Xi$ hypernuclei as intermediate states is also discussed in kinematics.
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The dynamics of exotic hypernuclei in heavy-ion collisions has been investigated thoroughly with a microscopic transport model. All possible channels on hyperon ($Lambda$, $Sigma$ and $Xi$) production near threshold energies are implemented in the transport model. The light complex fragments (Z$leq$2) are constructed with the Wigner-function method. The classical phase-space coalescence is used for recognizing heavy nuclear and hyperfragments and the statistical model is taken for describing the decay process. The nuclear fragmentation reactions of the available experimental data from the ALADIN collaboration are well reproduced by the combined approach. It is found that the in-medium potentials of strange particles influence the strangeness production and fragment formation. The hyperfragments are mainly created in the projectile or target-like rapidity region and the yields are reduced about the 3-order magnitude in comparison to the nuclear fragments. The hypernuclear dynamics of HypHI data is well described with the model. The possible experiments for producing the neutron-rich hyperfragments at the high-intensity heavy-ion accelerator facility (HIAF) are discussed.
Within the framework of quantum molecular dynamics transport model, the isospin and in-medium effects on the hyperon production in the reaction of $^{197}$Au + $^{197}$Au are investigated thoroughly. A repulsive hyperon-nucleon potential from the chiral effective field theory is implemented into the model, which is related to the hyperon momentum and baryon density. The correction on threshold energy of the elementary hyperon cross section is taken into account. It is found that the $Sigma$ yields are suppressed in the domain of midrapidity and kinetic energy spectra with the potential. The hyperons are emitted in the reaction plane because of the strangeness exchange reaction and reabsorption process in nuclear medium. The $Sigma^{-}/Sigma^{+}$ ratio depends on the stiffness of nuclear symmetry energy, in particular in the high-energy region (above 500 MeV).
The stopping behaviour of baryons in massive heavy ion collisions (at SPS, RHIC and LHC) is investigated within different microscopic models. At SPS-energies the predictions range from full stopping to virtually total transparency. Experimental data are indicating strong stopping. The initial baryo-chemical potentials and temperatures at collider energies and their impact on the formation probability of strange baryon clusters and strangelets are discussed.
A study of the horn in the particle ratio $K^+/pi^+$ for central heavy-ion collisions as a function of the collision energy $sqrt{s}$ is presented. We analyse two different interpretations: the onset of deconfinement and the transition from a baryon- to a meson-dominated hadron gas. We use a realistic equation of state (EOS), which includes both hadron and quark degrees-of-freedom. The Taub-adiabate procedure is followed to determine the system at the early stage. Our results do not support an explanation of the horn as due to the onset of deconfinement. Using only hadronic EOS we reproduced the energy dependence of the $K^+/pi^+$ and $Lambda/pi^-$ ratios employing an experimental parametrisation of the freeze-out curve. We observe a transition between a baryon- and a meson-dominated regime; however, the reproduction of the $K^+/pi^+$ and $Lambda/pi^-$ ratios as a function of $sqrt{s}$ is not completely satisfying. We finally propose a new idea for the interpretation of the data, the roll-over scheme, in which the scalar meson field $sigma$ has not reached the thermal equilibrium at freeze-out. The rool-over scheme for the equilibration of the $sigma$-field is based on the inflation mechanism. The non-equilibrium evolution of the scalar field influences the particle production, e.g. $K^+/pi^+$, however, the fixing of the free parameters in this model is still an open issue.
We study the production of (hyper-)nuclei and di-baryons in most central heavy Ion collisions at energies of $E_{lab}=1-160 A$ GeV. In particular we are interested in clusters produced from the hot and dense fireball. The formation rate of strange and non-strange clusters is estimated by assuming thermal production from the intermediate phase of the UrQMD-hydro hybrid model and alternatively by the coalescence mechanism from a hadronic cascade model. Both model types are compared in detail. For most energies we find that both approaches agree in their predictions for the yields of the clusters. Only for very low beam energies, and for di-baryons including $Xi$s, we observe considerable differences. We also study the production of anti-matter clusters up to top RHIC energies and show that the observation of anti-$^4He$ and even anti-$^4_{Lambda}He$ is feasible. We have found a considerable qualitative difference in the energy dependence of the strangeness population factor $R_H$ when comparing the thermal production with the coalescence results.
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