752 research outputs found
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
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 Freeze-Out in A+A Collisions meets the Lattice QCD Parton-Hadron Transition Line
We analyze hadrochemical freeze-out in central Pb+Pb collisions at CERN SPS
and LHC energies. Employing the UrQMD hybrid transport model we study the
effects of the final hadron/resonance expansion phase on the hadron
multiplicities established at hadronization. The bulk meson yields freeze out
directly at hadronization whereas the baryon-antibaryon sector is subject to
significant alterations, due to annihilation and regeneration processes. We
quantify the latter changes by survival factors for each species which are
applied to modify the statistical model predictions for the data. The modified
SM analysis recovers the hadronization points, which coincide with the recent
lattice QCD predictions of the parton-hadron transition line at finite
baryochemical potential.Comment: Proceedings of the 8th International Workshop on Critical Point and
Onset of Deconfinement, March 11 to 15, 2013 Napa, California, US
UrQMD calculations of two-pion HBT correlations in p+p and Pb+Pb collisions at LHC energies
Two-pion Hanbury-Brown-Twiss (HBT) correlations for p+p and central Pb+Pb
collisions at the Large-Hadron-Collider (LHC) energies are investigated with
the ultra-relativistic quantum molecular dynamics model combined with a
correlation afterburner. The transverse momentum dependence of the
Pratt-Bertsch HBT radii , , and is extracted from
a three-dimensional Gaussian fit to the correlator in the longitudinal
co-moving system. In the p+p case, the dependence of correlations on the
charged particle multiplicity and formation time is explored and the data
allows to constrain the formation time in the string fragmentation to fm/c. In the Pb+Pb case, it is found that is overpredicted
by nearly 50%. The LHC results are also compared to data from the STAR
experiment at RHIC. For both energies we find that the calculated
ratio is always larger than data, indicating that the
emission in the model is less explosive than observed in the data.Comment: 9 pages, 4 figures, 1 table. Talk given by Qingfeng Li at the 11th
International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio,
Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in
Journal of Physics: Conference Series (JPCS
Jets, Bulk Matter, and their Interaction in Heavy Ion Collisions at Several TeV
We discuss a theoretical scheme that accounts for bulk matter, jets, and the
interaction between the two. The aim is a complete description of particle
production at all transverse momentum () scales. In this picture, the
hard initial scatterings result in mainly longitudinal flux tubes, with
transversely moving pieces carrying the of the partons from hard
scatterings. These flux tubes constitute eventually both bulk matter (which
thermalizes and flows) and jets. We introduce a criterion based on parton
energy loss to decide whether a given string segment contributes to the bulk or
leaves the matter to end up as a jet of hadrons. Essentially low
segments from inside the volume will constitute the bulk, high segments
(or segments very close to the surface) contribute to the jets. The latter ones
appear after the usual flux tube breaking via q-qbar production (Schwinger
mechanism). Interesting is the transition region: Intermediate segments
produced inside the matter close to the surface but having enough energy to
escape, are supposed to pick up q-qbar pairs from the thermal matter rather
than creating them via the Schwinger mechanism. This represents a communication
between jets and the flowing bulk matter (fluid-jet interaction). Also very
important is the interaction between jet hadrons and the soft hadrons from the
fluid freeze-out. We employ the new picture to investigate Pb-Pb collisions at
2.76 TeV. We discuss the centrality and dependence of particle
production and long range dihadron correlations at small and large
Production of Theta(1540) and Xi Pentaquark States in Proton-Proton Interactions
The production of strange pentaquark states (e.g. Theta baryons and Xi^--
states) in hadronic interactions within a Gribov-Regge approach is explored. In
this approach the Theta^+(1540) and the Xi Pentaquark are produced by
disintegration of remnants formed by the exchange of pomerons between the two
protons. We predict the rapidity and transverse momentum distributions as well
as the 4 pi multiplicity of the Theta^+, Xi^--, Xi^-, Xi^0 and Xi^+ for sqrt{s}
= 17 GeV (SPS) and 200 GeV (RHIC). For both energies more than 10^{-3} Theta^+
and more than 10^{-5} Xi per pp event should be observed by the present
experiments.Comment: Predictions for Xi Pentaquarks added. Phys. Lett. B in prin
First Order Calculation of the Inclusive Cross Section pp to ZZ by Graviton Exchange in Large Extra Dimensions
We calculate the inclusive cross section of double Z-boson production within
large extra dimensions at the Large Hadron Collider (LHC). Using perturbatively
quantized gravity in the ADD model we perform a first order calculation of the
graviton mediated contribution to the pp to ZZ cross section. At low energies
(e.g. Tevatron) this additional contribution is very small, making it virtually
unobservable, for a fundamental mass scale above 2500 GeV. At LHC energies
however, the calculation indicates that the ZZ-production rate within the ADD
model should differ significantly from the Standard Model if the new
fundamental mass scale would be below 15000 GeV. A comparison with the observed
production rate at the LHC might therefore provide direct hints on the number
and structure of the extra dimensions.Comment: 7 pages, 7 figures, accepted for publication in Phys. Rev.
On the Role of Initial Conditions and Final State Interactions in Ultrarelativistic Heavy Ion Collisions
We investigate the rapidity dependence of the elliptical flow in heavy ion
collisions at 200 GeV (cms), by employing a three-dimensional hydrodynamic
evolution, based on different initial conditions, and different freeze-out
scenarios. It will be shown that the form of pseudo-rapidity ()
dependence of the elliptical flow is almost identical to space-time-rapidity
() dependence of the initial energy distribution, independent of the
freeze-out prescriptions
The production of charm mesons from quark matter at CERN SPS and RHIC
We study the production of charm mesons and other charm baryons from quark
matter at CERN SPS and RHIC energies. Using quark coalescence models as
hadronization mechanism, we predict particle ratios, absolute yields and
transverse momentum spectra.Comment: 4 pages in Latex, 2 PS figure, to be published in the proceedings of
the SQM'2000 Conference, Berkeley, CA, July 20-25, 2000. Submitted to J.
Phys.
Validity of the Hadronic Freeze-Out Curve
We analyze hadro-chemical freeze-out in central Pb+Pb collisions at CERN SPS
energies, employing the hybrid version of UrQMD which models hadronization by
the Cooper-Frye mechanism, and matches to a final hadron-resonance cascade. We
fit the results both before and after the cascade stage using the Statistical
Hadronization Model, to assess the effect of the cascade phase. We observe a
strong effect on antibaryon yields except anti-{\Omega}, resulting in a shift
in T and {\mu}_B. We discuss the implications for the freeze-out curve.Comment: 5 pages, 8 figures. To appear in the proceedings of Quark Matter
2011, the XXII International Conference on Ultrarelativistic Nucleus-Nucleus
Collision
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