Strangelets in heavy ion physics

VUU and (R)QMD model of high energy heavy ion collisions

The NICA (Nuclotron-based Ion Collider fAcility) project is under realization at the Joint Institute for Nuclear Research (JINR, Dubna). The main goal of the project is an experimental study of hot and dense strongly interacting matter in heavy ion (up to Au) collisions at center-of-mass energies up to 11 GeV per nucleon. The physics program will be performed at two experiments, BM@N (Baryonic Matter at Nuclotron) at beams extracted from the Nuclotron, and MPD (Multi-Purpose Detector) at the NICA collider. The aim of the BM@N experiment is to study interactions of relativistic heavy ion beams with fixed targets. The scientific program comprises studies of nuclear matter in the intermediate energy range between experiments at the SIS and NICA/FAIR facilities. The BM@N experiment has recorded first experimental data in the carbon, argon and krypton beams of kinetic energy per nucleon ranging from 2.3 to 4.5 GeV per nucleon. The first measurement of short range correlations of nucleons in carbon nucleus was performed in inverse kinematics with the carbon beam and liquid hydrogen target. The MPD detector is under construction to study hot and baryon rich QCD matter in heavy ion collisions at the NICA collider in the energy range $\sqrt{s_{NN}} = 4 \div 11$ GeV. Physics program includes the study of collective phenomena, $\Lambda$ polarization, dilepton, hyperon and hypernuclei production under extreme conditions of highest baryonic density.

Transition to hot quark matter in relativistic heavy-ion collision

Results obtained from the search for the critical point of strongly interacting matter in relativistic heavy-ion collisions at the CERN-SPS (experiments NA49 and NA61/SHINE) and the RHIC beam energy scan program (experiments STAR and PHENIX) are discussed. Although some intriguing signals were found, establishing firm evidence for the critical point remains a challenging enterprise.

The two-particle azimuthal angle correlation (TPAC) and azimuthal charge balance function (ACBF) are used to study the anisotropic expansion in relativistic heavy ion collisions. It is demonstrated by the relativistic quantum molecular dynamics (RQMD) model and a multi-phase transport (AMPT) model that the small-angle correlation in TPAC indeed presents anisotropic expansion, and the large-angle (or back-to-back) correlation is mainly due to global momentum conservations. The AMPT model reproduces the observed TPAC, but the RQMD model fails to reproduce the strong correlations in both small and large azimuthal angles. The width of ACBF from RQMD and AMPT models decreases from peripheral to central collisions, consistent with experimental data, but in contrast to the expectation from thermal model calculations. The ACBF is insensitive to anisotropic expansion. It is a probe for the mechanism of hadronization, similar to the charge balance function in rapidity.

The project NICA (Nuclotron-based Ion Collider fAcility) aims to study hot and baryon rich QCD matter in heavy ion collisions in the energy range [see formula in PDF] = 4 − 11 GeV. The rich heavy-ion physics program will be performed at two experiments, BM@N (Baryonic Matter at Nuclotron) at beams extracted from the Nuclotron, and at MPD (Multi-Purpose Detector) at the NICA collider. This program covers a variety of phenomena in strongly interacting matter of the highest baryonic density, which includes study of collective effects, production of hyperon and hypernuclei, in-medium modification of meson properties, and event-by-event fluctuations.

The project NICA (Nuclotron-based Ion Collider fAcility) is aimed to study hot and dense baryonic matter in heavy ion collisions in the energy range up to √sNN=11 GeV at the Nuclotron extracted beams and at the NICA collider with average luminosity of L = 1027 cm-2s-1 (for 197Au79). This study will be performed with two experiments, BM@N (Baryonic Matter at Nuclotron) and MPD (MultiPurpose Detector) at the NICA collider.

Various models have been developed to address the ordinary hadronic physics that occurs in relativistic heavy-ion collisions. These include string-based fragmentation models such as the LUND model1, and its extensions in FRITIOF2, which assume that excited hadrons behave as a chain of color dipoles that move like one-dimensional relativistic strings. Interactions are introduced via multiple small momentum exchanges between the color dipoles of two overlapping strings. Other nondynamical models are the dual-parton model3, in which the strings are formed by soft gluon exchange between the valence partons of the colliding hadrons. The quark-gluon string model4 (QGSM), also based on the dual parton model, has been developed to study soft parton collisions, and includes rescattering. The strings in the above models are in fact one-dimensional constructions in momentum space, and string evolution is carried out in this space. They are sometimes referred to as the longitudinal phase space models. Any coordinate space quantities that these models may study come from transformations from momentum space one-dimensional string coordinates to configuration space. Relativistic quantum molecular dynamics (RQMD) calculations have also been performed to study relativistic collision phenomena5. This approach combines resonance formation and decay of light hadronic states, and one-dimensional string fragmentation (LUND model) for very heavy resonances. RQMD follows the full space-time evolution of the light hadronic states, and uses one-dimensional momentum space evolution for the heavy states via the LUND string description.

Studies of extremely dense matter in heavy-ion collisions at J-PARC

Thermalized matter created in noncentral relativistic heavy-ion collisions is expected to be tilted in the reaction plane with respect to the beam axis. The most notable consequence of this forward-backward symmetry breaking is the observation of rapidity-odd directed flow for charged particles. On the other hand, the production points for heavy quarks are forward-backward symmetric and shifted in the transverse plane with respect to the fireball. The drag on heavy quarks from the asymmetrically distributed thermalized matter generates substantial directed flow for heavy flavor mesons. We predict a very large rapidity-odd directed flow of D mesons in noncentral Au-Au collisions at sqrt[s_{NN}]=200 GeV, several times larger than for charged particles. A possible experimental observation of a large directed flow for heavy flavor mesons would represent an almost direct probe of the three-dimensional distribution of matter in heavy-ion collisions.

We present a mechanism for the separation of strangeness from antistrangeness in the deconfinement transition. For a net strangeness of zero in the total system, the population of s quarks is greatly enriched in the quark-gluon plasma, while the s\ifmmode\bar\else\textasciimacron\fi{} quarks drift into the hadronic phase. This separation could result in ``strangelet'' formation, i.e., metastable blobs of strange-quark matter, which could serve as a unique signature for quark-gluon plasma formation in heavy-ion collisions.

After an introduction and an overview on other models we explain in detail the so called “Quantum” Molecular Dynamics (QMD), which is a successful model to describe heavy ion collisions at intermediate energies in a many-body approach. The results obtained using the QMD prove the success of this model. One has hope to extract some informations on the nuclear Equation of State (EOS) with the help of particles created in the hot and dense region of a heavy ion collision. Therefore, we show how one can calculate particle production within the QMD and present some results which are in good agreement with experimental data. In order to study the effects of the nuclear medium one has to work with so called realistic forces, which can be dealt in the framework of the Bruckner Theory. We show how one can use these forces determined by the Bruckner G-matrix in the QMD and present some results, which show that the nuclear medium effects the heavy ion reaction. It is also explained how one can extract thermal properties of heavy ion collisions from QMD-calculations. One gets reasonable values for the temperature in the central region of a heavy ion collision using this procedure. In the last section we explain the formalism of the relativistic generalization of the QMD, the RQMD (Relativistic QMD).KeywordsQuantum Molecular DynamicsFermi SphereRealistic ForceQuantum Molecular Dynamics ModelDifferential Production Cross SectionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Shock-like freeze-out in relativistic hydrodynamics

We present a systematic study of the kaon to pion multiplicity ratios ${(K}^{+}/{\ensuremath{\pi}}^{+}$ and ${K}^{\ensuremath{-}}/{\ensuremath{\pi}}^{\ensuremath{-}})$ in heavy-ion collisions from AGS to RHIC energy using the relativistic quantum molecular dynamics (RQMD) model. The model describes reasonably well the available experimental data on ${K}^{+}/{\ensuremath{\pi}}^{+}$ and ${K}^{\ensuremath{-}}/{\ensuremath{\pi}}^{\ensuremath{-}}.$ Within the model, we find that the strong increase of the ratios with the number of participants is mainly due to hadronic rescattering of produced mesons with ingoing baryons and their resonances. The enhancement of $K/\ensuremath{\pi}$ in heavy-ion collisions with respect to elementary $p+p$ interactions is larger at AGS than SPS energy, and decreases smoothly with bombarding energy. The total multiplicity ratios at RHIC energy are predicted by RQMD to be ${K}^{+}/{\ensuremath{\pi}}^{+}=0.19$ and ${K}^{\ensuremath{-}}/{\ensuremath{\pi}}^{\ensuremath{-}}=0.15.$

The formation of high-density nuclear matter which may be expected to be attained in high-energy heavy-ion collisions and the subsequent disintegration of dense matter are investigated by means of the hydrodynamics. Head-on collisions of identical nuclei are considered in the nonrelativistic approximation. The compressed density cannot exceed 4 times of the normal one so long as the freedom of only nucleons is considered, and can become higher than 4 times when other freedoms such as the productions of mesons and also nucleon isobars are additionally taken into account. The angular distributions for ejected particles predominate both forwards and backwards at low collision energies, corresponding to the formation of nuclear density less than 2 times of the normal density and become isotropic at the point of 2 times of the normal one. As the collision energy increases further, lateral ejection is intensified gradually.