90 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
Exact (1+1)-dimensional flows of a perfect fluid
We present a general solution of relativistic (1+1)-dimensional hydrodynamics
for a perfect fluid flowing along the longitudinal direction as a function of
time, uniformly in transverse space. The Khalatnikov potential is expressed as
a linear combination of two generating functions with polynomial coefficients
of 2 variables. The polynomials, whose algebraic equations are solved, define
an infinite-dimensional basis of solutions. The kinematics of the
(1+1)-dimensional flow are reconstructed from the potential.Comment: 14 pages, 1 figur
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
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
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
Coulomb distortion of pi+/pi- as a tool to determine the fireball radius in central high energy heavy ion collisions
We compute the Coulomb distortion produced by an expanding and highly charged
fireball on the spectra of low transverse momenta and mid rapidity pions
produced in central high energy heavy ion collisions. We compare to data on
Au+Au at 11.6A GeV from E866 at the BNL AGS and of Pb+Pb at 158A GeV from NA44
at the CERN SPS. We match the fireball expanison velocity with the average
transverse momentum of protons and find a best fit to the charged pion ratio
when the fireball radius is about 10 fm at freeze-out. This value is common to
both AGS and SPS data.Comment: 4 pages includes 2 figures, uses espcrc1 and epsfig. To appear in
proceedings of QM99, Torino Italy, May 199
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
Hotter, Denser, Faster, Smaller...and Nearly-Perfect: What's the matter at RHIC?
The experimental and theoretical status of the ``near perfect fluid'' at RHIC
is discussed. While the hydrodynamic paradigm for understanding collisions at
RHIC is well-established, there remain many important open questions to address
in order to understand its relevance and scope. It is also a crucial issue to
understand how the early equilibration is achieved, requiring insight into the
active degrees of freedom at early times.Comment: 10 Pages, 13 Figures, submitted to the proceedings of the Second
Meeting of the APS Topical Group on Hadronic Physics, Nashville, TN, October
22-24, 200
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