361 research outputs found
Elliptic flow in nuclear collisions at the Large Hadron Collider
We use perfect-fluid hydrodynamical model to predict the elliptic flow
coefficients in Pb + Pb collisions at the Large Hadron Collider (LHC). The
initial state for the hydrodynamical calculation for central collisions
is obtained from the perturbative QCD + saturation (EKRT) model. The centrality
dependence of the initial state is modeled by the optical Glauber model. We
show that the baseline results obtained from the framework are in good
agreement with the data from the Relativistic Heavy Ion Collider (RHIC), and
show predictions for the spectra and elliptic flow of pions in Pb + Pb
collisions at the LHC. Also mass and multiplicity effects are discussed.Comment: 11 pages, 10 figure
Which probes are most useful when undertaking cognitive interviews?
This paper reports the use of verbal probes in cognitive interviews (CIs) undertaken to test the usefulness, validity and reliability of survey questions. Through examining the use of probes by three interviewers undertaking interviews as part the piloting of a cross-national crime survey, we examine which of the various types of probes used in CIs produce the most useful information. Other influences on interview quality are examined, including differences between interviewers and respondents themselves. The analyses rely on multi-level modelling and suggest that anticipated, emergent and conditional probes provide the most useful data. Furthermore, age, gender and educational levels appear to have no bearing on the quality of the data generated
Dynamical freeze-out condition in ultrarelativistic heavy ion collisions
We determine the decoupling surfaces for the hydrodynamic description of
heavy ion collisions at RHIC and LHC by comparing the local hydrodynamic
expansion rate with the microscopic pion-pion scattering rate. The pion
spectra for nuclear collisions at RHIC and LHC are computed by applying the
Cooper-Frye procedure on the dynamical-decoupling surfaces, and compared with
those obtained from the constant-temperature freeze-out surfaces. Comparison
with RHIC data shows that the system indeed decouples when the expansion rate
becomes comparable with the pion scattering rate. The dynamical decoupling
based on the rates comparison also suggests that the effective decoupling
temperature in central heavy ion collisions remains practically unchanged from
RHIC to LHC.Comment: 7 pages, 9 figure
Bremsstrahlung Radiation as Coherent State in Thermal QED
Based on fully finite temperature field theory we investigate the radiation
probability in the bremsstrahlung process in thermal QED. It turns out that the
infrared divergences resulting from the emission and absorption of the real
photons are canceled by the virtual photon exchange processes at finite
temperature. The full quantum calculation results for soft photons radiation
coincide completely with that obtained in the semi-classical approximation. In
the framework of Thermofield Dynamics it is shown that the bremsstrahlung
radiation in thermal QED is a coherent state, the quasiclassical behavior of
the coherent state leads to above coincidence.Comment: 8 pages, 2 figure
Thermal quark production in ultra-relativistic nuclear collisions
We calculate thermal production of u, d, s, c and b quarks in
ultra-relativistic heavy ion collisions. The following processes are taken into
account: thermal gluon decay (g to ibar i), gluon fusion (g g to ibar i), and
quark-antiquark annihilation (jbar j to ibar i), where i and j represent quark
species. We use the thermal quark masses, ,
in all the rates. At small mass (), the production is largely
dominated by the thermal gluon decay channel. We obtain numerical and analytic
solutions of one-dimensional hydrodynamic expansion of an initially pure glue
plasma. Our results show that even in a quite optimistic scenario, all quarks
are far from chemical equilibrium throughout the expansion. Thermal production
of light quarks (u, d and s) is nearly independent of species. Heavy quark (c
and b) production is quite independent of the transition temperature and could
serve as a very good probe of the initial temperature. Thermal quark production
measurements could also be used to determine the gluon damping rate, or
equivalently the magnetic mass.Comment: 14 pages (latex) plus 6 figures (uuencoded postscript files);
CERN-TH.7038/9
Heavy Ion Physics at the LHC with the ATLAS Detector
The ATLAS detector at CERN will provide a high-resolution
longitudinally-segmented calorimeter and precision tracking for the upcoming
study of heavy ion collisions at the LHC (sqrt(s_NN)=5520 GeV). The calorimeter
covers |eta|<5 with both electromagnetic and hadronic sections, while the inner
detector spectrometer covers |eta|<2.5. ATLAS will study a full range of
observables necessary to characterize the hot and dense matter formed at the
LHC. Global measurements (particle multiplicities, collective flow) will
provide access into its thermodynamic and hydrodynamic properties. Measuring
complete jets out to 100's of GeV will allow detailed studies of energy loss
and its effect on jets. Quarkonia will provide a handle on deconfinement
mechanisms. ATLAS will also study the structure of the nucleon and nucleus
using forward physics probes and ultraperipheral collisions, both enabled by
segmented Zero Degree Calorimeters.Comment: 9 pages, 8 figures, submitted to the Proceedings of Quark Matter
2006, Shanghai, China, November 14-20, 200
Correlation measurements in high-multiplicity events
Requirements for correlation measurements in high--multiplicity events are
discussed. Attention is focussed on detection of so--called hot spots,
two--particle rapidity correlations, two--particle momentum correlations (for
quantum interferometry) and higher--order correlations. The signal--to--noise
ratio may become large in the high--multiplicity limit, allowing meaningful
single--event measurements, only if the correlations are due to collective
behavior.Comment: MN 55455, 20 pages, KSUCNR-011-92 and TPI-MINN-92/47-T (revised).
Revised to correct typo in equation (30), and to fill in a few steps in
calculations. Now published as Phys. Rev. C 47 (1993) 232
Rapidity Distributions of Dileptons from a Hadronizing Quark-Gluon Plasma
It has been predicted that dilepton production may be used as a quark-gluon
plasma probe. We calculate the rapidity distributions of thermal dileptons
produced by an evolving quark-gluon plasma assuming a longitudinal scaling
expansion with initial conditions locally determined from the hadronic rapidity
density. These distributions are compared with Drell-Yan production and
semileptonic charm decays at invariant mass , 4, and 6 GeV.Comment: 17 pages (standard LaTeX), 6 figures (available as topdraw files or
printed versions upon request), GSI-93-6
Lepton pairs from thermal mesons
We study the net dielectron production rates from an ensemble of thermal
mesons, using an effective Lagrangian to model their interaction. The coupling
between the electromagnetic and the hadronic sectors is done through the vector
meson dominance approach. For the first time, a complete set of light mesons is
considered. We include contributions from decays of the type
V~(PS)~~PS~(V)~+~, where V is a vector meson and PS is a
pseudoscalar, as well as those from binary reactions PS~+~PS, V~+~V, and
V~+~PS~. Direct decays of the type V~
are included and shown to be important. We find that the dielectron invariant
mass spectrum naturally divides in distinct regions: in the low mass domain the
decays from vector and pseudoscalar mesons form the dominant contribution. The
pion--pion annihilation and direct decays then pick up and form the leading
signal in an invariant mass region that includes the complex
and extends up to the . Above invariant mass ~1~GeV other
two-body reactions take over as the prominent mechanisms for lepton pair
generation. These facts will have quantitative bearing on the eventual
identification of the quark--gluon plasma.Comment: In ReVTeX 3.0, 9 figs. available from above email address. McGill
93/8, TPI-MINN-93/19-
Non-Perturbative Dilepton Production from a Quark-Gluon Plasma
The dilepton production rate from the quark-gluon plasma is calculated from
the imaginary part of the photon self energy using a quark propagator that
contains the gluon condensate. The low mass dilepton rate obtained in this way
exhibits interesting structures (peaks and gaps), which might be observable at
RHIC and LHC.Comment: 16 pages, REVTEX, 8 PostScript figure
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