784 research outputs found
Gravitational radiation from elastic particle scattering in models with extra dimensions
In this paper we derive a formula for the energy loss due to elastic N to N
particle scattering in models with extra dimensions that are compactified on a
radius R. In contrast to a previous derivation we also calculate additional
terms that are suppressed by factors of frequency over compactification radius.
In the limit of a large compactification radius R those terms vanish and the
standard result for the non compactified case is recovered.Comment: 17 page
Event-by-event fluctuations of the charged particle ratio from non-equilibrium transport theory
The event by event fluctuations of the ratio of positively to negatively
charged hadrons are predicted within the UrQMD model. Corrections for finite
acceptance and finite net charge are derived. These corrections are relevant to
compare experimental data and transport model results to previous predictions.
The calculated fluctuations at RHIC and SPS energies are shown to be compatible
with a hadron gas. Thus, deviating by a factor of 3 from the predictions for a
thermalized quark-gluon plasma.Comment: This paper clarifies the previous predictions of Jeon and Koch
(hep-ph/0003168) and addresses issues raised in hep-ph/0006023. 2 Figures,
10pp, uses RevTe
Determination of the structure of the in collisions
Currently, the structure of the meson is unknown. Different
competing models of the exotic state exist, including the
possibilities that this state is either a mesonic molecule with dominating composition, a tetraquark, or a -gluon hybrid state. It is expected that the state is rather
strongly coupled to the channel and, therefore, can be produced in
and collisions at PANDA. We propose to test the
hypothetical molecular structure of by studying the or stripping reactions on a nuclear residue.Comment: 19 pages, 8 figures; version accepted in PL
Evidence for flow in pPb collisions at 5 TeV from v2 mass splitting
We show that a fluid dynamical scenario describes quantitatively the observed
mass splitting of the elliptical flow coefficients v2 for pions, kaons, and
protons. This provides a strong argument in favor of the existence of a fluid
dynamical expansion in pPb collisions at 5TeV
Hadronic and electromagnetic probes of hot and dense matter in a Boltzmann+Hydrodynamics model of relativistic nuclear collisions
We present recent results on bulk observables and electromagnetic probes
obtained using a hybrid approach based on the Ultrarelativistic Quantum
Molecular Dynamics transport model with an intermediate hydrodynamic stage for
the description of heavy-ion collisions at AGS, SPS and RHIC energies. After
briefly reviewing the main results for particle multiplicities, elliptic flow,
transverse momentum and rapidity spectra, we focus on photon and dilepton
emission from hot and dense hadronic matter.Comment: To appear in the proceedings of WISH 2010: International Workshop on
Interplay between Soft and Hard interactions in particle production at
ultrarelativistic energies, Catania, Italy, 8-10 September 201
Collisional processes of on-shell and off-shell heavy quarks in vacuum and in the Quark-Gluon-Plasma
We study the heavy quark scattering on partons of the quark gluon plasma
(QGP) being especially interested in the collisional (elastic) scattering
processes of heavy quarks on quarks and gluons. We calculate the different
cross sections for perturbative partons (massless on-shell particles in the
vacuum) and for dynamical quasi-particles (off-shell particles in the QGP
medium as described by the dynamical quasi-particles model "DQPM") using the
leading order Born diagrams. Our results show clearly the effect of a finite
parton mass and width on the perturbative elastic cross sections which depend on temperature , energy density ,
the invariant energy and the scattering angle . Our detailed
comparisons demonstrate that the finite width of the quasi-particles in the
DQPM - which encodes the multiple partonic scattering - has little influence on
the cross section for as well as
scattering except close to thresholds. Thus when studying the dynamics of
energetic heavy quarks in a QGP medium the spectral width of the
degrees-of-freedom may be discarded. We have, furthermore, compared the cross
sections from the DQPM with corresponding results from hard-thermal-loop (HTL)
approaches. The HTL inspired models - essentially fixing the regulators by
elementary vacuum cross sections and decay amplitudes instead of properties of
the QGP at finite temperature - provide quite different results especially
w.r.t. the temperature dependence of the and cross sections (in all
settings). Accordingly, the transport properties of heavy quarks will be very
different as a function of temperature when compared to DQPM results.Comment: 28 pages, 32 figure
Correspondence between HBT radii and the emission zone in non-central heavy ion collisions
In non-central collisions between ultra-relativistic heavy ions, the
freeze-out distribution is anisotropic, and its major longitudinal axis may be
tilted away from the beam direction. The shape and orientation of this
distribution are particularly interesting, as they provide a snapshot of the
evolving source and reflect the space-time aspect of anisotropic flow.
Experimentally, this information is extracted by measuring pion HBT radii as a
function of angle with respect to the reaction plane. Existing formulae
relating the oscillations of the radii and the freezeout anisotropy are in
principle only valid for Gaussian sources with no collective flow. With a
realistic transport model of the collision, which generates flow and
non-Gaussian sources, we find that these formulae approximately reflect the
anisotropy of the freezeout distribution.Comment: 9 pages, 8 figure
Acceptance Dependence of Fluctuation in Particle Multiplicity
The effect of limiting the acceptance in rapidity on event-by-event
multiplicity fluctuations in nucleus-nucleus collisions has been investigated.
Our analysis shows that the multiplicity fluctuations decrease when the
rapidity acceptance is decreased. We explain this trend by assuming that the
probability distribution of the particles in the smaller acceptance window
follows binomial distribution. Following a simple statistical analysis we
conclude that the event-by-event multiplicity fluctuations for full acceptance
are likely to be larger than those observed in the experiments, since the
experiments usually have detectors with limited acceptance. We discuss the
application of our model to simulated data generated using VENUS, a widely used
event generator in heavy-ion collisions. We also discuss the results from our
calculations in presence of dynamical fluctuations and possible observation of
these in the actual data.Comment: To appear in Int. J. Mod. Phys.
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