1,202 research outputs found
Multiplicity fluctuations in hadron-hadron and nucleus-nucleus collisions and percolation of strings
We argue that recent NA49 results on multiparticle distributions and
fluctuations, as a function of the number of participant nucleons, suggest that
percolation plays an important role in particle production at high densities.Comment: 13 pages, 5 eps figures, late
Critical issues in ionospheric data quality and implications for scientific studies
Ionospheric data are valuable records of the behavior of the ionosphere, solar activity, and the entire Sun-Earth system. The data are critical for both societally important services and scientific investigations of upper atmospheric variability. This work investigates some of the difficulties and pitfalls in maintaining long-term records of geophysical measurements. This investigation focuses on the ionospheric parameters contained in the historical data sets within the National Oceanic and Atmospheric Administration National Geophysical Data Center and Space Physics Interactive Data Resource databases. These archives include data from approximately 100 ionosonde stations worldwide, beginning in the early 1940s. Our study focuses on the quality and consistency of ionosonde data accessible via the primary Space Physics Interactive Data Resource node located within the National Oceanic and Atmospheric Administration National Geophysical Data Center and the World Data Center for Solar-Terrestrial Physics located in Boulder, Colorado. We find that, although the Space Physics Interactive Data Resource archives contained an impressive amount of high-quality data, specific problems existed involving missing and noncontiguous data sets, long-term variations or changes in methodologies and analysis procedures used, and incomplete documentation. The important lessons learned from this investigation are that the data incorporated into an archive must have clear traceability back to the primary source, including scientific validation by the contributors, and that the historical records must have associated metadata that describe relevant nuances in the observations. Although this report only focuses on historical ionosonde data in National Oceanic and Atmospheric Administration databases, we feel that these findings have general applicability to environmental scientists interested in using long-term geophysical data sets for climate and global change research.Peer ReviewedPostprint (published version
Limiting fragmentation in heavy-ion collisions and percolation of strings
The observed limiting fragmentation of charged particle distributions in
heavy ion collisions is difficult to explain as it does not apply to the proton
spectrum itself. On the other hand, string percolation provides a mechanism to
regenerate fast particles, eventually compensating the rapidity shift (energy
loss) of the nucleons. However a delicate energy-momentum compensation is
required, and in our framework we see no reason for limiting fragmentation to
be exact. A prediction, based on percolation arguments, is given for the
charged particle density in the full rapidity interval at LHC energy .Comment: 9 pages, 2 figures (2 eps files), late
Particle production azimuthal asymmetries in a clustering of color sources model
The collective interactions of many partons in the first stage of the
collisions is the usual accepted explanation of the sizable elliptical flow.
The clustering of color sources provides a framework of partonic interactions.
In this scheme, we show a reasonable agreement with RHIC data for pT<1.5 GeV/c
in both the dependence of v2 transverse momentum and in the shape of the
nuclear modified factor on the azimuthal angle for different centralities. We
show the predictions at LHC energies for Pb-Pb. In the case of proton-proton
collisions a sizable v2 is obtained at this energy.Comment: To appear in Journal of Physics
Deconfinement and degrees of freedom in and collisions at LHC energies
We present the extraction of the temperature by analyzing the charged
particle transverse momentum spectra in lead-lead (Pb-Pb) and proton-proton
() collisions at LHC energies from the ALICE Collaboration using the
Color String Percolation Model (CSPM). From the measured energy density and the temperature T the dimensionless quantity is obtained to get the degrees of freedom (DOF), = DOF /30.
We observe for the first time a two-step behavior in the increase of DOF,
characteristic of deconfinement, above the hadronization temperature at
temperature 210 MeV for both Pb-Pb and collisions and a
sudden increase to the ideal gas value of 47 corresponding to three
quark flavors in the case of Pb-Pb collisions.Comment: 7 pages and 4 figure
Nuclear like effects in proton-proton collisions at high energy
We show that several effects considered nuclear effects are not nuclear in
the sense that they do not only occur in nucleus-nucleus and hadron-nucleus
collisions but, as well, they are present in hadron-hadron (proton-proton)
collisions. The matter creation mechanism in hh, hA and AA collisions is always
the same. The pT suppression of particles produced in large multiplicity events
compared to low multiplicity events, the elliptic flow and the Cronin effect
are predicted to occur in pp collisions at LHC energies as a consequence of the
obtained high density partonic medium
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