Refine
Document Type
- Preprint (47) (remove)
Language
- English (47)
Has Fulltext
- yes (47)
Is part of the Bibliography
- no (47)
Keywords
- Kollisionen schwerer Ionen (11)
- heavy ion collisions (10)
- UrQMD (5)
- QGP (3)
- Quark Gluon Plasma (3)
- Quark-Gluon-Plasma (3)
- Ultrarelativistic Quantum Molecular Dynamics (3)
- Molekulare Dynamik (2)
- UrQMD Modell (2)
- ultrarelativistisch (2)
- Absorption (1)
- Bremsstrahlung (1)
- Charmonium Produktion (1)
- Charmonium production (1)
- Deuteron (1)
- Dielectron (1)
- Dielektron (1)
- Drell-Yan (1)
- Drell-Yan production (1)
- Drell-Yan-Prozess (1)
- Dynamik (1)
- Energie (1)
- Freiheitsgrad (1)
- Hadron (1)
- High Energy Physics - Phenomenology (1)
- IQMD Modell (1)
- IQMD model (1)
- J/ϕ (1)
- Kollision (1)
- Korrelation (1)
- Massenspektrum (1)
- Meson (1)
- Monte-Carlo model for relativistic heavy ion collisions (1)
- Nuclear Theory (1)
- OMD (1)
- QGP signals (1)
- QMD (1)
- Quanten-Molekular-Dynamic (1)
- Quanten-Molekular-Dynamik (1)
- Quantendynamik (1)
- Quantum Molecular Dynamics (1)
- Relativistisch (1)
- SPS (1)
- Statistical model (1)
- URQMD (1)
- Ultra-relativistic Quantum Molecular Dynamics model (1)
- Ultrarelativisitic Quantum Molecular Dynamics model (1)
- Ultrarelativisitisches (1)
- Ultrarelativistic Quantum Molecular Model (1)
- Ultrarelativistisches Quant Molekulares Modell (1)
- UrQMD model (1)
- absorption (1)
- bremsstrahlung (1)
- collision (1)
- degrees of freedom (1)
- deuteron (1)
- dileptons (1)
- energy (1)
- equation of state (1)
- flow (1)
- hadron hadron Kollision (1)
- hadron hadron collision (1)
- hadronic (1)
- hadronic freeze-out (1)
- heavy ion colliders (1)
- heavy-ion collisions (1)
- heiße und dichte Kernmaterie (1)
- high energie (1)
- hohe Energie (1)
- hot and dense nuclear matter (1)
- mass spectra (1)
- microscopic transport theory (1)
- mikroskopische Transporttheorie (1)
- particle ratios (1)
- quark-gluon plasma (1)
- quark-gluon-plasma (1)
- relativistic (1)
- relativistic heavy ion collision (1)
- relativistische schwere Ion Kollision (1)
- schwere Ion Kollision (1)
- schwere Ionen Kollision (1)
- space-momentum correlation (1)
- strangeness (1)
- thermalization (1)
- ultra-relativistic heavy ion collision (1)
- ultrarelativistic heavy-ion collision (1)
- ultrarelativistische (1)
- ultrarelativistische Kollision des schweren Ionen (1)
Institute
Signatures of quark gluon plasma formation in high-energy heavy ion collisions : a critical review
(1998)
Ultra-relativistic heavy ion collisions offer the unique opportunity to probe highly excited dense nuclear matter under controlled laboratory conditions. The compelling driving force for such studies is the expectation that an entirely new form of matter may be created from such reactions. That form of matter, called the Quark Gluon Plasma (QGP), is the QCD analogue of the plasma phase of ordinary atomic matter. However, unlike such ordinary plasmas, the deconfined quanta of a QGP are not directly observable because of the fundamental confining property of the physical QCD vacuum. What is observable are hadronic and leptonic residues of the transient QGP state. There is a large variety of such individual probes.
The centrality dependence of (multi-)strange hadron abundances is studied for Pb(158 AGeV)Pb reactions and compared to p(158 GeV)Pb collisions. The microscopic transport model UrQMD is used for this analysis. The predicted Lambda/pi-, Xi-/pi- and Omega-/pi- ratios are enhanced due to rescattering in central Pb-Pb collisions as compared to peripheral Pb-Pb or p-Pb collisions. A reduction of the constituent quark masses to the current quark masses m_s \sim 230 MeV, m_q \sim 10 MeV, as motivated by chiral symmetry restoration, enhances the hyperon yields to the experimentally observed high values. Similar results are obtained by an ad hoc overall increase of the color electric field strength (effective string tension of kappa=3 GeV/fm). The enhancement depends strongly on the kinematical cuts. The maximum enhancement is predicted around midrapidity. For Lambda's, strangeness suppression is predicted at projectile/target rapidity. For Omega's, the predicted enhancement can be as large as one order of magnitude. Comparisons of Pb-Pb data to proton induced asymmetric (p-A) collisions are hampered due to the predicted strong asymmetry in the various rapidity distributions of the different (strange) particle species. In p-Pb collisions, strangeness is locally (in rapidity) not conserved. The present comparison to the data of the WA97 and NA49 collaborations clearly supports the suggestion that conventional (free) hadronic scenarios are unable to describe the observed high (anti-)hyperon yields in central collisions. The doubling of the strangeness to nonstrange suppression factor, gamma_s \approx 0.65, might be interpreted as a signal of a phase of nearly massless particles.
The disappearance of flow
(1995)
We investigate the disappearance of collective flow in the reaction plane in heavy-ion collisions within a microscopic model (QMD). A systematic study of the impact parameter dependence is performed for the system Ca+Ca. The balance energy strongly increases with impact parameter. Momentum dependent interactions reduce the balance energies for intermediate impact parameters b ~ 4.5 fm. Dynamical negative flow is not visible in the laboratory frame but does exist in the contact frame for the heavy system Au+Au. For semi-peripheral collisions of Ca+Ca with b ~ 6.5 fm a new two-component flow is discussed. Azimuthal distributions exhibit strong collectiv flow signals, even at the balance energy.
The equilibration of hot and dense nuclear matter produced in the central region in central Au+Au collisions at square root s = 200A GeV is studied within the microscopic transport model UrQMD. The pressure here becomes isotropic at t approx 5 fm/c. Within the next 15 fm/c the expansion of the matter proceeds almost isentropically with the entropy per baryon ratio S/A approx 150. During this period the equation of state in the (P, epsilon)-plane has a very simple form, P = 0.15 epsilon. Comparison with the statistical model (SM) of an ideal hadron gas reveals that the time of approx 20 fm/c may be too short to attain the fully equilibrated state. Particularly, the fractions of resonances are overpopulated in contrast to the SM values. The creation of such a long-lived resonance-rich state slows down the relaxation to chemical equilibrium and can be detected experimentally.
Dilepton spectra are calculated within the microscopic transport model UrQMD and compared to data from the CERES experiment. The invariant mass spectra in the region between 300 MeV and 600 MeV depend strongly on the mass dependence of the rho meson decay width which is not sufficiently determined by the Vector Meson Dominance model. A consistent explanation of both the recent Pb+Au data and the proton induced data can be given without additional medium effects.