We study the polarization of particles in relativistic heavy-ion collisions at very high energy along the beam direction within a relativistic hydrodynamic framework. We show that this component of ...the polarization decreases much slower with center-of-mass energy compared to the transverse component, even in the ideal longitudinal boost-invariant scenario with nonfluctuating initial state, and that it can be measured by taking advantage of its quadrupole structure in the transverse momentum plane. In the ideal longitudinal boost-invariant scenario, the polarization is proportional to the gradient of temperature at the hadronization and its measurement can provide important information about the cooling rate of the quark-gluon plasma around the critical temperature.
We present a sophisticated treatment of the hydrodynamic evolution of ultrarelativistic heavy ion collisions, based on the following features: initial conditions obtained from a flux tube approach, ...compatible with the string model and the color glass condensate picture; an event-by-event procedure, taking into the account the highly irregular space structure of single events, being experimentally visible via so-called ridge structures in two-particle correlations; the use of an efficient code for solving the hydrodynamic equations in 3+1 dimensions, including the conservation of baryon number, strangeness, and electric charge; the employment of a realistic equation of state, compatible with lattice gauge results; the use of a complete hadron resonance table, making our calculations compatible with the results from statistical models; and a hadronic cascade procedure after hadronization from the thermal matter at an early time.
We present a calculation of the global polarization of
Λ
hyperons in relativistic Au–Au collisions at RHIC Beam Energy Scan range
s
NN
=
7.7
-
200
GeV with a
3
+
1
-dimensional cascade
+
viscous ...hydro model, UrQMD
+
vHLLE. Within this model, the mean polarization of
Λ
in the out-of-plane direction is predicted to decrease rapidly with collision energy from a top value of about 2% at the lowest energy examined. We explore the connection between the polarization signal and thermal vorticity and estimate the feed-down contribution to
Λ
polarization due to the decay of higher mass hyperons.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present a new event generator based on the three-fluid hydrodynamics approach for the early stage of the collision, followed by a particlization at the hydrodynamic decoupling surface to join to a ...microscopic transport model, UrQMD, to account for hadronic final state interactions. We present first results for nuclear collisions of the FAIR/NICA energy scan program (Au+Au collisions, $\sqrt{s_{NN}}=4-11$ GeV). We address the directed flow of protons and pions as well as the proton rapidity distribution for two model EoS, one with a first order phase transition the other with a crossover type softening at high densities. The new simulation program has the unique feature that it can describe a hadron-to-quark matter transition which proceeds in the baryon stopping regime that is not accessible to previous simulation programs designed for higher energies.
Abstract We present a calculation of the global polarization of $$\Lambda $$ Λ hyperons in relativistic Au–Au collisions at RHIC Beam Energy Scan range $$\sqrt{s_\mathrm {NN}}=7.7{-}200$$ s NN = 7.7 ...- 200 GeV with a $$3+1$$ 3 + 1 -dimensional cascade $$\,+\,$$ + viscous hydro model, UrQMD $$\,+\,$$ + vHLLE. Within this model, the mean polarization of $$\Lambda $$ Λ in the out-of-plane direction is predicted to decrease rapidly with collision energy from a top value of about 2% at the lowest energy examined. We explore the connection between the polarization signal and thermal vorticity and estimate the feed-down contribution to $$\Lambda $$ Λ polarization due to the decay of higher mass hyperons.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Light cluster production at NICA Bastian, N. -U.; Batyuk, P.; Blaschke, D. ...
The European physical journal. A, Hadrons and nuclei,
08/2016, Letnik:
52, Številka:
8
Journal Article
Recenzirano
Odprti dostop
.
Light cluster production at the NICA accelerator complex offers unique possibilities to use these states as “rare probes” of in-medium characteristics such as phase space occupation and early flow. ...In order to explain this statement, in this contribution theoretical considerations from the nuclear statistical equilibrium model and from a quantum statistical model of cluster production are supplemented with a discussion of a transport model for light cluster formation and with results from hydrodynamic simulations combined with the coalescence model.
We develop a combined hydro-kinetic approach which incorporates a hydrodynamical expansion of the systems formed in A+A collisions and their dynamical decoupling described by escape probabilities. ...The method corresponds to a generalized relaxation time ({tau}{sub rel}) approximation for the Boltzmann equation applied to inhomogeneous expanding systems; at small {tau}{sub rel} it also allows one to catch the viscous effects in hadronic component-hadron-resonance gas. We demonstrate how the approximation of sudden freeze-out can be obtained within this dynamical picture of continuous emission and find that hypersurfaces, corresponding to a sharp freeze-out limit, are momentum dependent. The pion m{sub T} spectra are computed in the developed hydro-kinetic model, and compared with those obtained from ideal hydrodynamics with the Cooper-Frye isothermal prescription. Our results indicate that there does not exist a universal freeze-out temperature for pions with different momenta, and support an earlier decoupling of higher p{sub T} particles. By performing numerical simulations for various initial conditions and equations of state we identify several characteristic features of the bulk QCD matter evolution preferred in view of the current analysis of heavy ion collisions at RHIC energies.
PDF
