3,479 research outputs found
Quarkonium studies in p+p and Pb+Pb collisions with CMS
The collisions of Pb nuclei at the LHC will create strongly interacting matter at unprecedented energy densities, allowing us to probe QCD at extreme temperatures and very low parton momentum fractions. This paper presents the capabilities of the CMS experiment to study the production of quarkonium states in and Pb+Pb collisions. The very good acceptance and excellent dimuon mass resolution will allow us to do with the three states (1S, 2S, 3S) the exciting measurements previously performed with the and states, at the SPS and RHIC
Measurement of photons via conversion pairs in \sqrt{s_{NN}} = 200 GeV Au+Au collisions with the PHENIX experiment at RHIC
Thermal photons can provide information on the temperature of the new state
of matter created at RHIC. In the p_T region of 1--3 GeV/c thermal photons are
expected to be the dominant direct photon source. Therefore, a possible excess
compared to a pure decay photon signal due to a thermal photon contribution
should be seen in the double ratio
(\gamma/\gamma(\pi^{0}))_{Measured}/(\gamma/\gamma(\pi^{0}))_{Simulated}, if
sufficient accuracy can be reached. We present a method to reconstruct direct
photons by measuring e^{+}e^{-}--pairs from external photon conversions.Comment: 4 pages, 7 figures. To appear in the proceedings of Hot Quarks 2006:
Workshop for Young Scientists on the Physics of Ultrarelativistic
Nucleus-Nucleus Collisions, Villasimius, Italy, 15-20 May 200
Heavy-flavor dynamics in nucleus-nucleus collisions: from RHIC to LHC
The stochastic dynamics of c and b quarks in the fireball created in
nucleus-nucleus collisions at RHIC and LHC is studied employing a relativistic
Langevin equation, based on a picture of multiple uncorrelated random
collisions with the medium. Heavy-quark transport coefficients are evaluated
within a pQCD approach, with a proper HTL resummation of medium effects for
soft scatterings. The Langevin equation is embedded in a multi-step setup
developed to study heavy-flavor observables in pp and AA collisions, starting
from a NLO pQCD calculation of initial heavy-quark yields, complemented in the
nuclear case by shadowing corrections, k_T-broadening and nuclear geometry
effects. Then, only for AA collisions, the Langevin equation is solved
numerically in a background medium described by relativistic hydrodynamics.
Finally, the propagated heavy quarks are made hadronize and decay into
electrons. Results for the nuclear modification factor R_AA of heavy-flavor
hadrons and electrons from their semi-leptonic decays are provided, both for
RHIC and LHC beam energies.Comment: 4 pages, 2 figures (3 eps files); submitted for publication in the
proceedings of "Quark Matter 2011", 23-28 May 2011, Annecy (France
Direct photons ~basis for characterizing heavy ion collisions~
After years of experimental and theoretical efforts, direct photons become a
strong and reliable tool to establish the basic characteristics of a hot and
dense matter produced in heavy ion collisions. The recent direct photon
measurements are reviewed and a future prospect is given.Comment: 8 pages, 8 figures, Invited plenary talk at Quark Matter 200
Synchronisation in networks of delay-coupled type-I excitable systems
We use a generic model for type-I excitability (known as the SNIPER or SNIC
model) to describe the local dynamics of nodes within a network in the presence
of non-zero coupling delays. Utilising the method of the Master Stability
Function, we investigate the stability of the zero-lag synchronised dynamics of
the network nodes and its dependence on the two coupling parameters, namely the
coupling strength and delay time. Unlike in the FitzHugh-Nagumo model (a model
for type-II excitability), there are parameter ranges where the stability of
synchronisation depends on the coupling strength and delay time. One important
implication of these results is that there exist complex networks for which the
adding of inhibitory links in a small-world fashion may not only lead to a loss
of stable synchronisation, but may also restabilise synchronisation or
introduce multiple transitions between synchronisation and desynchronisation.
To underline the scope of our results, we show using the Stuart-Landau model
that such multiple transitions do not only occur in excitable systems, but also
in oscillatory ones.Comment: 10 pages, 9 figure
Examining the thermal properties of unirradiated nuclear grade graphite between 750 and 2500 K
This study presents the first high temperature measurements (between 750 K and 2500 K) of thermal conductivity, thermal diffusivity, specific heat and spectral emissivity of virgin graphite samples (type IM1-24) from advanced gas-cooled reactor (AGR) fuel assembly bricks. Scanning electron microscope (SEM) and X-ray computed tomography (XRT) techniques were used to verify the presence of Gilsocarbon filler particles (a characteristic microstructural feature of IM1-24 graphite). All thermal properties were investigated in two orthogonal directions, which showed the effective macroscopic thermal conductivity to be the same (to within experimental error). This can be linked to the morphology of the filler particles that consist of concentrically aligned graphitic platelets. The resulting spherical symmetry allows for heat to flow in the same manner in both macroscopic directions. The current thermal conductivity results were compared to other isotropic grade graphite materials. The significant discrepancies between the thermal conductivities of the individual grades are likely the result of different manufacturing processes yielding variations in the microstructure of the final product. Differences were identified in the filler particle size and structure, and possibly the degree of graphitization compared to other reported nuclear graphites
Dynamics of fully coupled rotators with unimodal and bimodal frequency distribution
We analyze the synchronization transition of a globally coupled network of N
phase oscillators with inertia (rotators) whose natural frequencies are
unimodally or bimodally distributed. In the unimodal case, the system exhibits
a discontinuous hysteretic transition from an incoherent to a partially
synchronized (PS) state. For sufficiently large inertia, the system reveals the
coexistence of a PS state and of a standing wave (SW) solution. In the bimodal
case, the hysteretic synchronization transition involves several states.
Namely, the system becomes coherent passing through traveling waves (TWs), SWs
and finally arriving to a PS regime. The transition to the PS state from the SW
occurs always at the same coupling, independently of the system size, while its
value increases linearly with the inertia. On the other hand the critical
coupling required to observe TWs and SWs increases with N suggesting that in
the thermodynamic limit the transition from incoherence to PS will occur
without any intermediate states. Finally a linear stability analysis reveals
that the system is hysteretic not only at the level of macroscopic indicators,
but also microscopically as verified by measuring the maximal Lyapunov
exponent.Comment: 22 pages, 11 figures, contribution for the book: Control of
Self-Organizing Nonlinear Systems, Springer Series in Energetics, eds E.
Schoell, S.H.L. Klapp, P. Hoeve
Overview of experimental results in PbPb collisions at sqrt{s_NN} = 2.76 TeV by the CMS Collaboration
The CMS experiment at the LHC is a general-purpose apparatus with a set of
large acceptance and high granularity detectors for hadrons, electrons, photons
and muons, providing unique capabilities for both proton-proton and ion-ion
collisions. The data collected during the November 2010 PbPb run at sqrt{s_NN}
= 2.76 TeV was analyzed and multiple measurements of the properties of the hot
and dense matter were obtained. Global event properties, detailed study of jet
production and jet properties, isolated photons, quarkonia and weak bosons were
measured and compared to pp data and Monte Carlo simulations.Comment: 8 pages, 10 figures, proceedings for Quark Matter 2011, Annecy,
France, May 23-28, 201
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