11,152 research outputs found
Beam-Energy and System-Size Dependence of Dynamical Net Charge Fluctuations
We present measurements of net charge fluctuations in collisions at
19.6, 62.4, 130, and 200 GeV, collisions at
62.4, 200 GeV, and collisions at 200
GeV using the net charge dynamical fluctuations measure . The
dynamical fluctuations are non-zero at all energies and exhibit a rather modest
dependence on beam energy. We find that at a given energy and collision system,
net charge dynamical fluctuations violate scaling, but display
approximate scaling. We observe strong dependence of dynamical
fluctuations on the azimuthal angular range and pseudorapidity widths.Comment: 4 pages, 4 figures, presented at the 19th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008", Jaipur,
India, February 4-10, 200
The Exchange Gate in Solid State Spin Quantum Computation: The Applicability of the Heisenberg Model
Solid state quantum computing proposals rely on adiabatic operations of the
exchange gate among localized spins in nanostructures. We study corrections to
the Heisenberg interaction between lateral semiconductor quantum dots in an
external magnetic field. Using exact diagonalization we obtain the regime of
validity of the adiabatic approximation. We also find qualitative corrections
to the Heisenberg model at high magnetic fields and in looped arrays of spins.
Looped geometries of localized spins generate flux dependent, multi-spin terms
which go beyond the basic Heisenberg model.Comment: 13 pages, 8 figure
Radiative and Collisional Jet Energy Loss in a Quark-Gluon Plasma
We calculate radiative and collisional energy loss of hard partons traversing
the quark-gluon plasma created at RHIC and compare the respective size of these
contributions. We employ the AMY formalism for radiative energy loss and
include additionally energy loss by elastic collisions. Our treatment of both
processes is complete at leading order in the coupling, and accounts for the
probabilistic nature of jet energy loss. We find that a solution of the
Fokker-Planck equation for the probability density distributions of partons is
necessary for a complete calculation of the nuclear modification factor
for pion production in heavy ion collisions. It is found that the
magnitude of is sensitive to the inclusion of both collisional and
radiative energy loss, while the average energy is less affected by the
addition of collisional contributions. We present a calculation of for
at RHIC, combining our energy loss formalism with a relativistic
(3+1)-dimensional hydrodynamic description of the thermalized medium.Comment: 4 pages, 4 figures, contributed to Quark Matter 2008, Jaipur, Indi
Quark Number Fluctuations in a Chiral Model at Finite Baryon Chemical Potential
We discuss the net quark and isovector fluctuations as well as off-diagonal
quark flavor susceptibilities along the chiral phase transition line in the
Nambu--Jona-Lasinio (NJL) model. The model is formulated at non-zero quark and
isospin chemical potentials with non-vanishing vector couplings in the
iso-scalar and iso-vector channels. We study the influence of the quark
chemical potential on the quark flavour susceptibilities in detail and the
dependence of the results on model parameters as well as on the quark mass. The
NJL model findings are compared with recent lattice results obtained in
two--flavor QCD at finite chemical potential. On a qualitative level, the NJL
model provides a consistent description of the dependence of quark number
fluctuations on temperature and baryon chemical potential. The phase diagram
and the position of the tricritical point in the NJL model are also discussed
for different parameter sets.Comment: 33 pages, 11 figures; final version accepted for publication in Phys.
Rev.
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