81 research outputs found
Evidence for creation of strong electromagnetic fields in relativistic heavy-ion collisions
It is proposed to identify a strong electric field created during
relativistic collisions of asymmetric nuclei via observation of pseudorapidity
and transverse momentum distributions of hadrons with the same mass but
opposite charges. The detailed calculation results for the directed flow within
the Parton-Hadron String Dynamics model are given for Cu-Au interactions at the
NICA collision energies of and GeV. The separation effect
is observable at 9 GeV as clearly as at 200 GeVComment: 3 pages, 8 figure
The Chiral Magnetic Effect: Beam-energy and system-size dependence
We consider the energy dependence of the local and
violation in Au+Au and Cu+Cu collisions over a large energy range within a
simple phenomenological model. It is expected that at LHC the chiral magnetic
effect will be about 20 times weaker than at RHIC. At lower energy range this
effect should vanish sharply at energy somewhere above the top SPS one. To
elucidate CME background effects a transport model including magnetic field
evolution is put forward.Comment: 11 pages, 4 figure
Rise of azimuthal anisotropies as a signature of the Quark-Gluon-Plasma in relativistic heavy-ion collisions
The azimuthal anisotropies of the collective transverse flow of hadrons are
investigated in a large range of heavy-ion collision energy within the
Parton-Hadron-String Dynamics (PHSD) microscopic transport approach which
incorporates explicit partonic degrees of freedom in terms of strongly
interacting quasiparticles (quarks and gluons) in line with an
equation-of-state from lattice QCD as well as dynamical hadronization and
hadronic dynamics in the final reaction phase. The experimentally observed
increase of the elliptic flow with bombarding energy is successfully
described in terms of the PHSD approach in contrast to a variety of other
kinetic models based on hadronic interactions. The analysis of higher-order
harmonics and shows a similar tendency of growing deviations
between partonic and purely hadronic models with increasing bombarding energy.
This signals that the excitation functions of azimuthal anisotropies provide a
sensitive probe for the underling degrees of freedom excited in heavy-ion
collisions.Comment: 4 pages, 3 figures, title change
Helicity and vorticity in heavy-ion collisions at NICA energies
Heavy-ion collisions at center-of-mass nucleon collision energies 4.5--11.5
GeV are analyzed within the PHSD transport model. Spectator nucleons are
separated, and the transfer of the initial angular momentum of colliding nuclei
to the fireball formed by participants is studied. The maximal angular momentum
is carried by the fireball in gold-gold collisions with the impact parameter
about 5 fm corresponding to centrality class 10--20\%. The obtained participant
distributions were fluidized and the energy and baryon number densities,
temperature, and velocity fields are obtained in the Landau frame. It is shown
that the velocity field has dominantly Hubble-like transversal and longitudinal
expansion with the vortical motion being only a small correction on top of it.
The vorticity field is calculated and illustrated in detail. The formation of
two oppositely-rotating vortex rings moving in opposite directions along the
axis is demonstrated. Other characteristics of the vortical motion such as
the Lamb vector field and the kinematic vorticity number are considered. The
magnitude of the latter one is found to be smaller than that for the Poiseuille
flow and close to the pure shear deformation corresponding to just a flattening
of fluid cells. The field of hydrodynamic helicity, which is responsible for
the axial vortex effect, is calculated. The separation of positive and negative
helicities localized upper and lower semi-planes with respect to the reaction
plane is shown. It is proved that the areas with various helicity signs can be
probed by the selection of hyperons with positive and negative
projections of their momenta orthogonal to the reaction plane.Comment: 22 pages, 23 figures. Figure labels are corrected, references adde
Event-by-event background in estimates of the chiral magnetic effect
In terms of the parton-hadron-string-dynamics (PHSD) approach - including the
retarded electromagnetic field - we investigate the role of fluctuations of the
correlation function in the azimuthal angle of charged hadrons that is
expected to be a sensitive signal of local strong parity violation. For the
early time we consider fluctuations in the position of charged spectators
resulting in electromagnetic field fluctuations as well as in the position of
participant baryons defining the event plane. For partonic and hadronic phases
in intermediate stages of the interaction we study the possible formation of
excited matter in electric charge dipole and quadrupole form as generated by
fluctuations. The role of the transverse momentum and local charge conservation
laws in the observed azimuthal asymmetry is investigated, too. All these
above-mentioned effects are incorporated in our analysis based on
event-by-event PHSD calculations. Furthermore, the azimuthal angular
correlations from Au+Au collisions observed in the recent STAR measurements
within the RHIC Beam-Energy-Scan (BES) program are studied. It is shown that
the STAR correlation data at the collision energies of = 7.7
and 11.5 GeV can be reasonably reproduced within the PHSD. At higher energies
the model fails to describe the correlation data resulting in an
overestimation of the partonic scalar field involved. We conclude that an
additional transverse anisotropy fluctuating source is needed which with a
comparable strength acts on both in- and out-of-plane components.Comment: 20 pages, 19 figures, to be published in Phys. Rev.
- …