876 research outputs found
Searching for the Critical Point of QCD: Theoretical Benchmark Calculations
We present a comprehensive study of event-by-event multiplicity fluctuations
in nucleon-nucleon and nucleus-nucleus interactions from AGS/FAIR to RHIC
energies within the UrQMD transport approach. The scaled variances of negative,
positive, and all charged hadrons are analysed. The scaled variance in central
Pb+Pb collisions increases with energy and behaves similar to inelastic p+p
interactions. We find a non-trivial dependence of multiplicity fluctuations on
the rapidity and transverse momentum interval used for the analysis and on the
centrality selection procedure. Quantitative predictions for the NA49
experiment are given, taking into account the acceptance of the detector and
the selection procedure of central events.Comment: 10 pages, 10 figure
Multiplicity Fluctuations in Limited Segments of Momentum Space in Statistical Models
Multiplicity fluctuations in limited segments of momentum space are
calculated for a classical pion gas within the statistical model. Results for
the grand canonical, canonical, and micro-canonical ensemble are obtained,
compared and discussed. We demonstrate that even in the large volume limit
correlations between macroscopic subsystems due to energy and momentum
conservation persist. Based on the micro-canonical formulation we make
qualitative predictions for the rapidity and transverse momentum dependence of
multiplicity fluctuations. The resulting effects are of similar magnitude as
the predicted enhancement due to a phase transition from a quark-gluon plasma
to a hadron gas phase, or due to the critical point of strongly interacting
matter, and qualitatively agree with recently published preliminary
multiplicity fluctuation data of the NA49 SPS experiment.Comment: 23 pages, 4 figure
Multiplicity fluctuations in relativistic nuclear collisions: statistical model versus experimental data
The multiplicity distributions of hadrons produced in central nucleus-nucleus
collisions are studied within the hadron-resonance gas model in the large
volume limit. The microscopic correlator method is used to enforce conservation
of three charges - baryon number, electric charge, and strangeness - in the
canonical ensemble. In addition, in the micro-canonical ensemble energy
conservation is included. An analytical method is used to account for resonance
decays. The multiplicity distributions and the scaled variances for negatively,
positively, and all charged hadrons are calculated along the chemical
freeze-out line of central Pb+Pb (Au+Au) collisions from SIS to LHC energies.
Predictions obtained within different statistical ensembles are compared with
the preliminary NA49 experimental results on central Pb+Pb collisions in the
SPS energy range. The measured fluctuations are significantly narrower than the
Poisson ones and clearly favor expectations for the micro-canonical ensemble.
Thus this is a first observation of the recently predicted suppression of the
multiplicity fluctuations in relativistic gases in the thermodynamical limit
due to conservation laws.Comment: 27 pages, 9 figures, corrected reference
Multiplicity fluctuations in relativistic nuclear collisions
Multiplicity distributions of hadrons produced in central nucleus-nucleus
collisions are studied within the hadron-resonance gas model in the large
volume limit. In the canonical ensemble conservation of three charges (baryon
number, electric charge, and strangeness) is enforced. In addition, in the
micro-canonical ensemble energy conservation is included. An analytical method
is used to account for resonance decays. Multiplicity distributions and scaled
variances for negatively charged hadrons are presented along the chemical
freeze-out line of central Pb+Pb (Au+Au) collisions from SIS to LHC energies.
Predictions obtained within different statistical ensembles are compared with
preliminary NA49 experimental results on central Pb+Pb collisions in the SPS
energy range. The measured fluctuations are significantly narrower than a
Poisson reference distribution, and clearly favor expectations for the
micro-canonical ensemble.Comment: 6 pages, 3 figure
Particle number fluctuations in nuclear collisions within excluded volume hadron gas model
The multiplicity fluctuations are studied in the van der Waals excluded
volume hadron-resonance gas model. The calculations are done in the grand
canonical ensemble within the Boltzmann statistics approximation. The scaled
variances for positive, negative and all charged hadrons are calculated along
the chemical freeze-out line of nucleus-nucleus collisions at different
collision energies. The multiplicity fluctuations are found to be suppressed in
the van der Waals gas. The numerical calculations are presented for two values
of hard-core hadron radius, fm and 0.5 fm, as well as for the upper
limit of the excluded volume suppression effects.Comment: 19 pages, 4 figure
Multiplicity Fluctuations in Nucleus-Nucleus Collisions: Dependence on Energy and Atomic Number
Event-by-event multiplicity fluctuations in central C+C, S+S, In+In, and
Pb+Pb as well as p+p collisions at bombarding energies from 10 to 160 AGeV are
studied within the HSD and UrQMD microscopic transport approaches. Our
investigation is directly related to the future experimental program of the
NA61 Collaboration at the SPS for a search of the QCD critical point. The
dependence on energy and atomic mass number of the scaled variances for
negative, positive, and all charged hadrons is presented and compared to the
results of the model of independent sources. Furthermore, the nucleus-nucleus
results from the transport calculations are compared to inelastic proton-proton
collisions for reference. We find a dominant role of the participant number
fluctuations in nucleus-nucleus reactions at finite impact parameter . In
order to reduce the influence of the participant numbers fluctuations on the
charged particle multiplicity fluctuations only the most central events have to
be selected. Accordingly, the samples of the 1% most central nucleus-nucleus
collisions with the largest numbers of the projectile participants are studied.
The results are compared with those for collisions at zero impact parameter. A
strong influence of the centrality selection criteria on the multiplicity
fluctuations is pointed out. Our findings are essential for an optimal choice
of colliding nuclei and bombarding energies for the experimental search of the
QCD critical point.Comment: 26 pages, 12 figures, extended version, to be published in Phys. Rev.
Energy dependence of transverse mass spectra of kaons produced in p+p and p+pbar interactions.A compilation
The data on m_T spectra of K0S K+ and K- mesons produced in all inelastic p+p
and p+pbar interactions in the energy range sqrt(s)NN=4.7-1800GeV are compiled
and analyzed. The spectra are parameterized by a single exponential function,
dN/(m_T*dm_T)=C exp(-m_T/T), and the inverse slope parameter T is the main
object of study. The T parameter is found to be similar for K0S, K+ and K-
mesons. It increases monotonically with collision energy from T~30MeV at
sqrt(s)NN=4.7GeV to T~220MeV at sqrt(s)NN=1800GeV. The T parameter measured in
p+p and p+pbar interactions is significantly lower than the corresponding
parameter obtained for central Pb+Pb collisions at all studied energies. Also
the shape of the energy dependence of is different for central Pb+Pb
collisions and p+p(pbar) interactions.Comment: more differential analysis adde
Regional variation in the flexural properties of the equine hoof wall
The equine hoof wall is a hard, keratinous structure that transmits forces generated when the hoof connects the ground to the skeleton of the horse. During locomotion the hoof capsule is known to deform, resulting in an inward curvature of the dorsal wall and expansion of the heels. However, while researchers have studied the tensile and compressive properties, there is a lack of data on the flexural properties of the hoof wall in different locations around the hoof capsule. In this study, the flexural properties and hydration status of the hoof wall were investigated in two orthogonal directions, in different locations around the hoof capsule. The hoof was divided into three regions: the dorsal-most aspect (toe), the medial and lateral regions (quarters) and the heels caudally. Beams were cut both perpendicular (transverse) and parallel (longitudinal) to the orientation of the tubules. Differences in the mechanical properties were then investigated using three-point bending tests. There were considerable differences in the flexural properties around the hoof capsule; transverse beams from the heel were 45% more compliant than those from the toe region. This corresponded with changes in the hydration of the hoof wall; beams from the heel region were more hydrated (28.2 ± 0.60%) than those from the toe (24.2 ± 0.44%; P < 0.01). Regional variation in the water content is thought to help explain differences in the flexural properties. Mechanical data are further discussed in relation to variation in the structure and loading of the hoof wall
Strangeness production time and the K+/pi+ horn
We construct a hadronic kinetic model which describes production of strange
particles in ultrarelativistic nuclear collisions in the energy domain of SPS.
We test this model on description of the sharp peak in the excitation function
of multiplicity ratio K+/pi+ and demonstrate that hadronic model reproduces
these data rather well. The model thus must be tested on other types of data in
order to verify the hypothesis that deconfinement sets in at lowest SPS
energies.Comment: proceedings of Hot Quarks 0
Strangeness and threshold of phase changes
We explore entropy and strangeness as signature of QGP for top AGS energy and
the energy scan at SPS. We find that the hadronization dynamics changes between
20 and 30 GeV projectile energy. The high energy results are consistent
with QGP.Comment: Presented at SQM07, to appear in JPG special issu
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