60 research outputs found
Velocity of sound in relativistic heavy-ion collisions
We have studied the rapidity distribution of secondary hadrons produced in
nucleus-nucleus collisions at ultra-relativistic energies within the ambit of
the Landau's hydrodynamical model. A reasonable description of the data can
also be obtained by using the Bjorken's hydrodynamical model if the boost
invariance is restricted to a finite rapidity range. The sensitivity of the
hadronic spectra on the equation of state vis- a -vis the velocity of sound has
been discussed. The correlation between the velocity of sound and the
freeze-out temperature has been indicated. The effects of the non-zero widths
of various mesonic and baryonic degrees of freedom up to the mass value ~ 2.5
GeV is seen to be small.Comment: 9 pages and 11 figures. Major changes. To appear in Physical Review
Studying freeze-out and hadronization in the Landau hydrodynamical model
We study the rapidity spectra in ultra-relativistic heavy ion collisions in
the framework of the Landau hydrodynamical model. We find that thermal smearing
effects improve the agreement with experimental results on pion rapidity
spectra. We describe a simple model of the hadronization and discuss its
consequences regarding the pion multiplicity and the increasing entropy
condition.Comment: 7 pages, 3 figure
Momentum Kick Model Description of the Ridge in (Delta-phi)-(Delta eta) Correlation in pp Collisions at 7 TeV
The near-side ridge structure in the (Delta phi)-(Delta eta) correlation
observed by the CMS Collaboration for pp collisions at 7 TeV at LHC can be
explained by the momentum kick model in which the ridge particles are medium
partons that suffer a collision with the jet and acquire a momentum kick along
the jet direction. Similar to the early medium parton momentum distribution
obtained in previous analysis for nucleus-nucleus collisions at 0.2 TeV, the
early medium parton momentum distribution in pp collisions at 7 TeV exhibits a
rapidity plateau as arising from particle production in a flux tube.Comment: Talk presented at Workshop on High-pT Probes of High-Density QCD at
the LHC, Palaiseau, May 30-June2, 201
Imaging the Space-Time Evolution of High Energy Nucleus-Nucleus Collisions with Bremsstrahlung
The bremsstrahlung produced when heavy nuclei collide is estimated for
central collisions at the Relativistic Heavy Ion Collider. Bremsstrahlung
photons with energies below 100 to 200 MeV are sufficient to discern the gross
features of the space-time evolution of electric charge, if they can be
separated from other sources of photons experimentally. This is illustrated
explicitly by considering two very different models, one Bjorken-like, the
other Landau-like, both of which are constructed to give the same final charge
rapidity distribution.Comment: 9 pages revtex style, 9 embedded PS figure
Bremsstrahlung from a Microscopic Model of Relativistic Heavy Ion Collisions
We compute bremsstrahlung arising from the acceleration of individual charged
baryons and mesons during the time evolution of high-energy Au+Au collisions at
the Relativistic Heavy Ion Collider using a microscopic transport model. We
elucidate the connection between bremsstrahlung and charge stopping by
colliding artificial pure proton on pure neutron nuclei. From the intensity of
low energy bremsstrahlung, the time scale and the degree of stopping could be
accurately extracted without measuring any hadronic observables.Comment: 25 pages using revtex with 9 embedded EPS figures, modified somewhat
the discussion on the method in sect. II B, to appear in Phys. Rev.
Direct photons at low transverse momentum -- a QGP signal in pp collisions at LHC
We investigate photon production in a scenario of quark-gluon plasma
formation in proton-proton scattering at 7 TeV. It is shown that thermal photon
yields increase quadratically with the charged particle multiplicity. This
gives an enhanced weight to high multiplicity events, and leads to an important
photon production even in minimum bias events, where the thermal photons
largely dominate over the prompt ones at transverse momentum values smaller
than 10 GeV/c.Comment: 4 pages, 4 figure
A Co-moving Coordinate System for Relativistic Hydrodynamics
The equations of relativistic hydrodynamics are transformed so that steps
forward in time preserves local simultaneity. In these variables, the
space-time coordinates of neighboring points on the mesh are simultaneous
according to co-moving observers. Aside from the time step varying as a
function of the location on the mesh, the local velocity gradient and the local
density then evolve according to non-relativistic equations of motion. Analytic
solutions are found for two one-dimensional cases with constant speed of sound.
One solution has a Gaussian density profile when mapped into the new
coordinates. That solution is analyzed for the effects of longitudinal
acceleration in relativistic heavy ion collisions at RHIC, especially in
regards to two-particle correlation measurements of the longitudinal size
Detailed description of accelerating, simple solutions of relativistic perfect fluid hydrodynamics
In this paper we describe in full details a new family of recently found
exact solutions of relativistic, perfect fluid dynamics. With an ansatz, which
generalizes the well-known Hwa-Bjorken solution, we obtain a wide class of new
exact, explicit and simple solutions, which have a remarkable advantage as
compared to presently known exact and explicit solutions: they do not lack
acceleration. They can be utilized for the description of the evolution of the
matter created in high energy heavy ion collisions. Because these solutions are
accelerating, they provide a more realistic picture than the well-known
Hwa-Bjorken solution, and give more insight into the dynamics of the matter. We
exploit this by giving an advanced simple estimation of the initial energy
density of the produced matter in high energy collisions, which takes
acceleration effects (i.e. the work done by the pressure and the modified
change of the volume elements) into account. We also give an advanced
estimation of the life-time of the reaction. Our new solutions can also be used
to test numerical hydrodynamical codes reliably. In the end, we also give an
exact, 1+1 dimensional, relativistic hydrodynamical solution, where the initial
pressure and velocity profile is arbitrary, and we show that this general
solution is stable for perturbations.Comment: 34 pages, 8 figures, detailed write-up of
http://arxiv.org/abs/nucl-th/0605070
Fluid Dynamics of Relativistic Quantum Dust
The microscopic transport equations for free fields are solved using the
Schwinger function. Thus, for general initial conditions, the evolution of the
energy-momentum tensor is obtained, incorporating the quantum effects exactly.
The result for relativistic fermions differs from classical hydrodynamics,
which is illustrated for Landau and Bjorken type initial conditions in this
model of exploding primordial matter. Free fermions behave like classical dust
concerning hydrodynamic observables. However, quantum effects which are present
in the initial state are preserved.Comment: 5 pages; LaTe
On an exact hydrodynamic solution for the elliptic flow
Looking for the underlying hydrodynamic mechanisms determining the elliptic
flow we show that for an expanding relativistic perfect fluid the transverse
flow may derive from a solvable hydrodynamic potential, if the entropy is
transversally conserved and the corresponding expansion "quasi-stationary",
that is mainly governed by the temperature cooling. Exact solutions for the
velocity flow coefficients and the temperature dependence of the spatial
and momentum anisotropy are obtained and shown to be in agreement with the
elliptic flow features of heavy-ion collisions.Comment: 10 pages, 4 figure
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