Inorganic–organic nanocomposites of CdSe nanocrystals surface-modified with oligo- and poly(fluorene) moieties

We report a facile grafting-from strategy towards the synthesis of inorganic–organic composites of semiconductor nanocrystals and wide-bandgap polymers. Amino-functional fluorenes have been used as co-ligands for CdSe nanocrystals, thus enabling us to design their surface directly during the synthesis. Highly monodisperse, strongly emitting CdSe nanocrystals have been obtained. Subsequently, a straightforward Yamamoto C–C coupling protocol was used to carry out surface polymerisation, hence modifying CdSe nanocrystals with oligo- and poly(fluorene) moieties. Both amino-fluorene capped CdSe nanocrystals and the resulting nanocrystal–polymer composites were characterized in detail by optical and FT-IR spectroscopy, TEM, AFM, and gel permeation chromatography, showing their potential as novel functional inorganic–organic hybrid materials

Pion damping width from SU(2) x SU(2) NJL model

Within the framework of the NJL model, we investigate the modification of the pion damping width in a hot pion gas for temperatures ranging from 0 to 180 MeV. The pion is found to broaden noticeably at T > 60 MeV. Near the chiral phase transition T ~ 180 MeV, the pion width is saturated and amounts to 70 MeV. The main contribution to the width comes from pion-pion collisions. Other contributions are found negligibly small.Comment: LaTeX2e, 13 pages, 2 figure

Properties of ρ\rho and ω\omega Mesons at Finite Temperature and Density as Inferred from Experiment

The mass shift, width broadening, and spectral density for the $\rho$ and $\omega$ mesons in a heat bath of nucleons and pions are calculated using a general formula which relates the self-energy to the real and imaginary parts of the forward scattering amplitude. We use experimental data to saturate the scattering amplitude at low energies with resonances and include a background Pomeron term, while at high energies a Regge parameterization is used. The real part obtained directly is compared with the result of a dispersion integral over the imaginary part. The peaks of the spectral densities are little shifted from their vacuum positions, but the widths are considerably increased due to collisional broadening. Where possible we compare with the UrQMD model and find quite good agreement. At normal nuclear matter density and a temperature of 150 MeV the spectral density of the $\rho$ meson has a width of 345 MeV, while that for the $\omega$ is in the range 90--150 MeV.Comment: 21 pages revtex + 9 postscript figure

New method for measuring azimuthal distributions in nucleus-nucleus collisions

The methods currently used to measure azimuthal distributions of particles in heavy ion collisions assume that all azimuthal correlations between particles result from their correlation with the reaction plane. However, other correlations exist, and it is safe to neglect them only if azimuthal anisotropies are much larger than 1/sqrt(N), with N the total number of particles emitted in the collision. This condition is not satisfied at ultrarelativistic energies. We propose a new method, based on a cumulant expansion of multiparticle azimuthal correlations, which allows to measure much smaller values of azimuthal anisotropies, down to 1/N. It is simple to implement and can be used to measure both integrated and differential flow. Furthermore, this method automatically eliminates the major systematic errors, which are due to azimuthal asymmetries in the detector acceptance.Comment: final version (misprints corrected), to be published in Phys.Rev.

The universal psi-prime-prime to psi-prime ratio as unambiguous signature for hard physics in nuclear reactions and in decays of beauty hadrons

We suggest the ratio of the $\psi''(3770)/\psi'(3686)$ production cross sections as an unambiguous probe of the dominance of hard, point-like physics in charmonium production. If hard physics dominates the charmonium production the ratio : ${\sigma(\psi'')\over\sigma(\psi')}\approx {\Gamma(\psi''\to l^+l^-)\over \Gamma(\psi'\to l^+l^-)} \approx 0.1$ is independent of the process. We argue that since the dominant $D\bar D$ decay mode of the $\psi''$-meson can be detected with a high efficiency at the current facilities the effective counting rate for the $\psi''$ production should be comparable to that of the $\psi'$ and hence it could be observed at the $B$-factories. Even in hadron induced processes the ratio will not be changed significantly by final state interactions due to the similar mass and size of these two charmonium states. A possible exception are the charmonium state interactions with low energy particles -- comovers -- which are especially relevant for the heavy ion collisions.Comment: final version, 9 page

Flow and non-flow event anisotropies at the SPS

A study of differential elliptic event anisotropies (v_2) of charged particles and high-pt pions in 158 AGeV/c Pb+Au collisions is presented. Results from correlations with respect to the event plane and from two-particle azimuthal correlations are compared. The latter give systematically higher v_2 values at pt>1.2GeV/c providing possibly an evidence of a non-flow semihard component.Comment: 4 pages, 6 figures, Quark Matter 2002, Nantes, to appear in Nucl. Phys.

Thermal rho and sigma mesons from chiral symmetry and unitarity

We study the temperature evolution of the rho and sigma mass and width, using a unitary chiral approach. The one-loop pion-pion scattering amplitude in Chiral Perturbation Theory at finite temperature is unitarized via the Inverse Amplitude Method. Our results predict a clear increase with T of both the rho and sigma widths. The masses decrease slightly for high T, while the rho-pion-pion coupling increases. The rho behavior seems to be favored by experimental results. In the sigma case, it signals chiral symmetry restoration.Comment: 5 pages, 5 figures, revtex. References and brief comments added. Final version to appear in Phys. Rev.

Event-by-event fluctuations at SPS

Results on event-by-event fluctuations of the mean transverse momentum and net charge in Pb-Au collisions, measured by the CERES Collaboration at CERN-SPS, are presented. We discuss the centrality and beam energy dependence and compare our data to cascade calculations.Comment: 4 pages, 4 figures, proceedings to INPC2004 Goteborg, Swede

Is the analysis of flow at the CERN SPS reliable?

Several heavy ion experiments at SPS have measured azimuthal distributions of particles with respect to the reaction plane. These distributions are deduced from two-particle azimuthal correlations under the assumption that they result solely from correlations with the reaction plane. In this paper, we investigate other sources of azimuthal correlations: transverse momentum conservation, which produces back-to-back correlations, resonance decays, HBT correlations and final state interactions. These correlations increase with impact parameter: most of them vary with the multiplicity N like 1/N. When they are taken into account, the experimental results of the NA49 collaboration at SPS are significantly modified. These correlations might also explain an important fraction of the pion directed flow observed by WA98. Data should be reanalyzed taking into account carefully these non--flow correlations.Comment: Revised version (minor corrections), 13 pages, LaTeX, 6 Postscript figures included. Submitted to Physical Review

Event-by-event fluctuations of the mean transverse momentum in 40, 80, and 158 A GeV/c Pb-Au collisions

Measurements of event-by-event fluctuations of the mean transverse momentum in Pb-Au collisions at 40, 80, and 158 A GeV/c are presented. A significant excess of mean p_T fluctuations at mid-rapidity is observed over the expectation from statistically independent particle emission. The results are somewhat smaller than recent measurements at RHIC. A possible non-monotonic behaviour of the mean p_T fluctuations as function of collision energy, which may have indicated that the system has passed the critical point of the QCD phase diagram in the range of mu_B under investigation, has not been observed. The centrality dependence of mean p_T fluctuations in Pb-Au is consistent with an extrapolation from pp collisions assuming that the non-statistical fluctuations scale with multiplicity. The results are compared to calculations by the RQMD and UrQMD event generators.Comment: 28 pages, 10 figure