814 research outputs found
Is the Polarized Antiquark Sea in the Nucleon Flavor Symmetric?
We show that the model which naturally explains the
asymmetry in the nucleon and is in quantitative agreement with the Gottfried
sum rule data, also predicts that in the proton and . At the input scale, these results can be derived even analytically. Thus
the violation of the flavor symmetry is more serious in the polarized case than
in the unpolarized case. In contrast, many recent analyses of the polarized
data have made a simplifying assumption that all the three 's
have the same sign and magnitude. We point out the need to redo these analyses,
allowing for the alternate scenario as described above. We present predictions
of the model for the asymmetry in polarized scattering, which can be
tested at RHIC; these are quite different from those available in the
literature.Comment: Talk given at the International Conference on Quark-Nuclear Physics
(QNP2000), 21-25 Feb. 2000, CSSM, University of Adelaide, Australia. v2: refs
added, discussion enlarged, conclusions unchanged. A short version has
appeared in NP(A) proceedings. This (long) version is to appear in PR(C).
Tables of polarized and unpolarized PDFs can be obtained by writing to the
Autho
Relativistic heavy-ion collisions
The field of relativistic heavy-ion collisions is introduced to the
high-energy physics students with no prior knowledge in this area. The emphasis
is on the two most important observables, namely the azimuthal collective flow
and jet quenching, and on the role fluid dynamics plays in the interpretation
of the data. Other important observables described briefly are constituent
quark number scaling, ratios of particle abundances, strangeness enhancement,
and sequential melting of heavy quarkonia. Comparison is made of some of the
basic heavy-ion results obtained at LHC with those obtained at RHIC. Initial
findings at LHC which seem to be in apparent conflict with the accumulated RHIC
data are highlighted.Comment: Updated version of the lectures given at the First
Asia-Europe-Pacific School of High-Energy Physics, Fukuoka, Japan, 14-27
October 2012. Published as a CERN Yellow Report (CERN-2014-001) and KEK
report (KEK-Proceedings-2013-8), K. Kawagoe and M. Mulders (eds.), 2014, p.
219. Total 21 page
Aspects of causal viscous hydrodynamics
We investigate the phenomenology of freely expanding fluids, with different
material properties, evolving through the Israel-Stewart (IS) causal viscous
hydrodynamics, and compare our results with those obtained in the relativistic
Eckart-Landau-Navier-Stokes (ELNS) acausal viscous hydrodynamics. Through the
analysis of scaling invariants we give a definition of thermalization time
which can be self-consistently determined in viscous hydrodynamics. Next we
construct the solutions for one-dimensional boost-invariant flows. Expansion of
viscous fluids is slower than that of one-dimensional ideal fluids, resulting
in entropy production. At late times, these flows are reasonably well
approximated by solutions obtained in ELNS hydrodynamics. Estimates of initial
energy densities from observed final values are strongly dependent on the
dynamics one chooses. For the same material, and the same final state, IS
hydrodynamics gives the smallest initial energy density. We also study
fluctuations about these one-dimensional boost-invariant backgrounds; they are
damped in ELNS hydrodynamics but can become sound waves in IS hydrodynamics.
The difference is obvious in power spectra due to clear signals of
wave-interference in IS hydrodynamics, which is completely absent in ELNS
dynamics.Comment: 27 pages, 17 figures, references added, minor changes, version to
appear in Phys. Rev. (C
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