120972199
Do quarks propagate
Abstract Processes with coloured particles in the initial state are generally infrared divergent. We investigate the effect of this on processes with colourless particles in the initial state, when the amplitude is near an intermediate quark pole. The result is a characteristics logarithmic dependence on the “binding energy” (even though spectator interactions are taken into account), and the result is gauge-invariant. Summed to all orders, the logarithms could perhaps suppress the quark pole.
120475304
An eikonal line-integral model and factorization in QCD
We study an approximation to perturbative QCD in which all quarks (active and spectator) move along eikonal lines. These eikonal lines are described by matrix operatorsU defined by time-ordered and path-ordered integrals. All known examples of Bloch-Nordsieck cancellations follow simply from the unitary properties ofU. In particular, when the eikonal lines are space-like, the time-ordering can be omitted and the unitarity ofU is evident. In this model, it is possible to examine rather explicitly the soft and very-soft gluons whose effects must cancel if factorization is hold (to leading twist). We can show such cancellation if there is a smooth continuation from space-like eikonal lines to time-like ones. We give some examples relevant to this conjecture, but we are unable to prove it in general.
16160539
Searching for Superhorizon Fluctuations in Heavy-Ion Collisions
In this talk I discuss novel explanations for the azimuthal correlations observed in heavy-ion collisions. I review some ideas about correlations and the evolution of heavy-ion collisions. Some aspects of the correlations observed in heavy-ion collisions may be indicitive of the suppression of super-horizon fluctuations.
118375394
Coalescence Models for Hadron Formation from Quark-Gluon Plasma
We review hadron formation from a deconfined quark-gluon plasma (QGP) via coalescence or recombination of quarks and gluons. We discuss the abundant experimental evidence for coalescence from the R...
18221719
Evidence from identified particles for active quark and gluon degrees of freedom
Measurements of intermediate pT (1.5 < pT < 5.0 GeV/c) identified particle distributions in heavy-ion collisions at SPS and RHIC energies display striking dependences on the number of constituent quarks in the corresponding hadron. One finds that elliptic flow at intermediate pT follows a constituent quark scaling law as predicted by models of hadron formation through coalescence. In addition, baryon production is also found to increase with event multiplicity much faster than meson production. The rate of increase is similar for all baryons and seemingly independent of mass. This indicates that the number of constituent quarks determines the multiplicity dependence of identified hadron production at intermediate pT. We review these measurements and interpret the experimental findings.
14779676
SPECTRAL FEATURES OF PRESOLAR DIAMONDS IN THE LABORATORY AND IN CARBON STAR ATMOSPHERES
Laboratory analyses on ne-grained diamond residues from primitive meteorites have shown that nano- diamonds represent the most abundant form of presolar dust preserved in meteoritic samples. The presolar diamonds carry isotopic anomalies which indicate a very complex formation history. Several groups of diamonds may exist with origin in different types of stars. In order to identify the sites of for- mation observationally, we have extracted presolar diamonds from the Allende meteorite and measured the monochromatic absorption coefcient in a form which is useful for stellar atmo- sphere calculations. The monochromatic absorption coefcient was measured in the wavelength ranges 400{4000cm 1 (2.5{ 25m) and 12200{52600cm 1 (190{820nm). We have made identical laboratory measurements on CVD diamonds as on the meteoritic diamonds, in order to get a more solid basis for the interpretationofthediamondspectrum.Themonochromaticab- sorption coefcient for the presolar diamonds was incorporated in self-consistent carbon star photospheric models. The main influence of the diamond dust in our photospheric models is a heating of the upper photospheric layers and a reduction of the C2H2 abundance. Due to the relatively small absorption coef- cientofthediamondscomparedtootherstellardustgrains,their spectral appearance is weak. However, the weak interaction of the diamonds with the radiation eld may give them an impor- tant role in the dust nucleation process. The gas pressure will stay high and the gas will be much closer to hydrostatic equilib- rium during possible diamond nucleation than is normally the case in dust forming stellar regions, and therefore allow ample time for the nucleation process.
121208134
Dependence of the non-photonic electron spectrum on the charmed baryon-to-meson ratio
Abstract In this talk I argue that a substantial fraction of the non-photonic electron suppression in Au+Au collisions could arise as a result of an enhanced Λc/D ratio rather than purely from jet-quenching. At intermediate transverse momentum (2<pT<6 GeV/c), the baryon-to-meson ratio in Au+Au collisions is enhanced compared to p+p collisions. Since charm-baryon decays produce electrons less frequently than charm-meson decays, the non-photonic electron spectrum is sensitive to the Λc/D ratio. I show the dependence of the non-photonic electron spectrum on the baryon-to-meson ratio for charm hadrons. As an example, I assume that the Λc/D ratio is the same as the Λ/K0S ratio. I show that even if the total charm quark yield in Au+Au collisions scales with the number of binary nucleon-nucleon collisions (Nbin), the electron spectrum at 2<pT<5 GeV/c will be suppressed relative to Nbin scaled p+p collisions by as much as 20%.  