2,824 research outputs found
Glueball production in hadron and nucleus collisions
We elaborate on the hypothesis that in high energy hadron hadron and nucleus
nucleus collisions the lowest mass glueballs are copiously produced from the
gluon rich environment especially at high energy density. We discuss the
particular glueball decay modes: and .Comment: 14 pages, six figure
Charm in nuclear reactions in sqrt(s)=17 and 19 GeV
Consequences resulting from the D Dbar excess derived indirectly by the NA50
experiment in S+U and Pb+Pb collisions at sqrt(s)=19, 17 GeV, relevant for the
identification of the QCD phase transition in these collisions, are discussed.
The dependence of open and closed charm yields in Pb+Pb collisions on the
number of participating nucleons (N) indicates non thermal charm production and
J/Psi dissociation, stronger than the absorption seen in any other elementary
hadron. The J/Psi in central Pb+Pb collisions could originate dominantly from c
cbar pair coalescence out of a hadronizing quark and gluon environment.
Furthermore, the J/Psi appears to be suppressed in S+U collisions at sqrt(s)=19
GeV, as opposed to current interpretations. A significant change in the
(J/Psi)/D Dbar ratio as well as in the number density of kaons is observed
above energy density approx. 1 GeV/fm^3, suggesting a change of phase at this
energy density, and underlining the importance of direct open charm
measurements.Comment: (23 pages, 7 figures
Evidence for diquarks in lattice QCD
Diquarks may play an important role in hadron spectroscopy, baryon decays and
color superconductivity. We investigate the existence of diquark correlations
in lattice QCD by considering systematically all the lowest energy diquark
channels in a color gauge-invariant setup. We measure mass differences between
the various channels and show that the positive parity scalar diquark is the
lightest. Quark-quark correlations inside the diquark are clearly seen in this
channel, and yield a diquark size of order 1 fm.Comment: Version as published in Phys. Rev. Lett.97, 222002,2006; 4 pages, 5
figure
Stable quark stars beyond neutran stars : can they account for the missing matter ?
The structure of a spherically symmetric stable dark 'star' is discussed, at
zero temperature, containing 1) a core of quarks in the deconfined phase and
antileptons 2) a shell of hadrons in particular , , and
and leptons or antileptons and 3) a shell of hydrogen in the
superfluid phase. If the superfluid hydrogen phase goes over into the
electromagnetic plasma phase at densities well below one atom / ,
as is usually assumed, the hydrogen shell is insignificant for the mass and the
radius of the 'star'. These quantities are then determined approximatively :
mass = 1.8 solar masses and radius = 9.2 km. On the contrary if densities of
the order of one atom / do form a stable hydrogen superfluid
phase, we find a large range of possible masses from 1.8 to 375 solar masses.
The radii vary accordingly from 9 to 1200 km.Comment: 5 pages, 2 figures, contribution to Strange Quark Matter conference,
Frankfurt, Germany, Sept. 200
Production of nuclei and antinuclei in pp and Pb-Pb collisions with ALICE at the LHC
We present first results on the production of nuclei and antinuclei such as
(anti)deuterons, (anti)tritons, (anti)3He and (anti)4He in pp collisions at
\s = 7 TeV and Pb-Pb collisions at \sNN = 2.76 TeV. These particles are
identified using their energy loss (dE/dx) information in the Time Projection
Chamber of the ALICE experiment. The Inner Tracking System gives a precise
determination of the event vertex, by which primary and secondary particles are
separated. The high statistics of over 360 million events for pp and 16 million
events for Pb-Pb collisions give a significant number of light nuclei and
antinuclei (Pb-Pb collisions: \sim30,000 anti-deuterons() and \sim4
anti-alpha()). The predictions of various particle ratios from the
THERMUS model is also discussed.Comment: 4 pages, 5 figures, parallel talk at Quark Matter 2011, May 23rd-28th
2011, Annecy, Franc
Experimental evaluation of joint designs for a space-shuttle orbiter ablative leading edge
The thermal performance of two types of ablative leading-edge joints for a space-shuttle orbiter were tested and evaluated. Chordwise joints between ablative leading-edge segments, and spanwise joints between ablative leading-edge segments and reusable surface insulation tiles were exposed to simulated shuttle heating environments. The data show that the thermal performance of models with chordwise joints to be as good as jointless models in simulated ascent-heating and orbital cold-soak environments. The suggestion is made for additional work on the joint seals, and, in particular, on the effects of heat-induced seal-material surface irregularities on the local flow
Hadronic centrality dependence in nuclear collisions
The kaon number density in nucleus+nucleus and p+p reactions is investigated
for the first time as a function of the initial energy density and
is found to exhibit a discontinuity around =1.3 GeV/fm. This
suggests a higher degree of chemical equilibrium for
1.3 GeV/fm. It can also be interpreted as reflection of the same
discontinuity, appearing in the chemical freeze out temperature (T) as a
function of . The dependence of (u,d,s) hadrons,
whith N the number of participating nucleons, also indicates a high degree of
chemical equilibrium and T saturation, reached at 1.3 GeV/fm.
Assuming that the intermediate mass region (IMR) dimuon enhancement seen by
NA50 is due to open charm (), the following observation can be made:
a) Charm is not equilibrated. b) suppression -unlike
- appears also in S+A collisions, above 1
GeV/fm. c) Both charm and strangeness show a discontinuity near the same
. d) could be formed mainly through coalescence.
e) The enhancement factors of hadrons with u,d,s,c quarks may be connected in a
simple way to the mass gain of these particles if they are produced out of a
quark gluon plasma (QGP). We discuss these results as possible evidence for the
QCD phase transition occuring near 1.3 GeV/fm.Comment: 4 pages, 4 figures, proceedings of Vth International Conference on
Strangeness in Quark Matter, 20-25 July 2000, Berkeley, California. To appear
in Journal of Physics G: Nuclear and Particle Physic
Exotic hadrons from dynamical clustering of quarks in ultrarelativistic heavy ion collisions
Results from a model study on the formation of exotic quark clusters at the
hadronization stage of a heavy ion collision are presented. The dynamical quark
molecular dynamics (qMD) model which is used is sketched, and results for
exotica made of up to six (anti-)quarks are shown. The second part focuses on
pentaquarks. The rapidity distribution are shown, and the distribution of
strangeness is found to yield an indicator of thermalization and homogenisation
of the deconfined quark system. Relative Theta^+ yields are found to be lower
than thermal model estimates.Comment: 4 pages, 5 figures, to appear in the proceedings of Strangeness in
Quark Matter 2004 (SQM2004), Cape Town, South Africa, 15-20 September 200
Conservation of information and the foundations of quantum mechanics
We review a recent approach to the foundations of quantum mechanics inspired
by quantum information theory. The approach is based on a general framework,
which allows one to address a large class of physical theories which share
basic information-theoretic features. We first illustrate two very primitive
features, expressed by the axioms of causality and purity-preservation, which
are satisfied by both classical and quantum theory. We then discuss the axiom
of purification, which expresses a strong version of the Conservation of
Information and captures the core of a vast number of protocols in quantum
information. Purification is a highly non-classical feature and leads directly
to the emergence of entanglement at the purely conceptual level, without any
reference to the superposition principle. Supplemented by a few additional
requirements, satisfied by classical and quantum theory, it provides a complete
axiomatic characterization of quantum theory for finite dimensional systems.Comment: 11 pages, contribution to the Proceedings of the 3rd International
Conference on New Frontiers in Physics, July 28-August 6 2014, Orthodox
Academy of Crete, Kolymbari, Cret
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