Ralf Rapp

Diquark Bose condensates in high density matter and instantons

Instantons lead to strong correlations between up and down quarks with spin zero and antisymmetric color wave functions. In cold and dense matter, n{sub b}{gt}n{sub c}{approx_equal}1 fm {sup {minus}3} and T{lt}T{sub c}{approximately}50 thinspthinspMeV, these pairs Bose condense, replacing the usual {l_angle}{bar q}q{r_angle} condensate and restoring chiral symmetry. At high density, the ground state is a color superconductor in which diquarks play the role of Cooper pairs. An interesting toy model is provided by QCD with two colors: it has a particle-antiparticle symmetry which relates {l_angle}{bar q}q{r_angle} and {l_angle}qq{r_angle} condensates. {copyright} {ital 1998} {ital The American Physical Society}

Heavy-quark probes of the quark-gluon plasma and interpretation of recent data taken at the BNL Relativistic Heavy Ion Collider

Thermalization and collective flow of charm (c) and bottom (b) quarks in ultra-relativistic heavyion collisions are evaluated based on elastic parton rescattering in an expanding quark-gluon plasma (QGP). We show that resonant interactions in a strongly interacting QGP (sQGP), as well as parton coalescence, can play an essential role in the interpretation of recent data from the Relativistic HeavyIon Collider (RHIC), and thus illuminate the nature of the sQGP and its hadronization. Our main assumption, motivated by recent findings in lattice Quantum Chromodynamics, is the existence of Dand B-meson states in the sQGP, providing resonant cross sections for heavy quarks. Pertinent drag and diffusion coefficients are implemented into a relativistic Langevin simulation to compute transverse-momentum spectra and azimuthal asymmetries (v2) of band c-quarks in Au-Au collisions at RHIC. After hadronization into Dand B-mesons using quark coalescence and fragmentation, associated electron-decay spectra and v2 are compared to recent RHIC data. Our results suggest a reevaluation of radiative and elastic quark energy-loss mechanisms in the sQGP.

Rho meson propagation and dilepton enhancement in hot hadronic matter

A realistic model for the free rho meson with coupling to two-pion states is employed to calculate the rho propagator in a hot and dense hadron gas. The medium modifications are based on hadronic rescattering processes: intermediate two-pion states are renormalized through interactions with surrounding nucleons and deltas, and rho meson scattering is considered off nucleons, deltas, pions and kaons. Constraints from gauge invariance as well as the full off-shell dynamics of the interactions are accounted for. Within the vector dominance model we apply the resulting in-medium rho spectral function to compute e+e− production rates from π+π− annihilation. The calculation of corresponding e+e− spectra as recently measured in central collisions of heavy-ions at CERN/SpS energies gives reasonable agreement with the experimental data.

Medium modifications and production of charmonia at LHC

Abstract A previously constructed transport approach to calculate the evolution of quarkonium yields and spectra in heavy-ion collisions is applied to Pb Pb ( s = 2.76 A TeV ) collisions at the Large Hadron Collider (LHC). In this approach spectral properties of charmonia are constrained by Euclidean correlators from thermal lattice QCD and subsequently implemented into a Boltzmann equation accounting for both suppression and regeneration reactions. Based on a fair description of SPS and RHIC data, we provide predictions for the centrality dependence of J / ψ yields at LHC. The main uncertainty is associated with the input charm cross section, in particular its hitherto unknown reduction due to shadowing in nuclear collisions. Incomplete charm-quark thermalization and non-equilibrium in charmonium chemistry entail a marked reduction of the regeneration yield compared to the statistical equilibrium limit.

Hadronic production of thermal photons

We study the thermal emission of photons from hot and dense strongly interacting hadronic matter at temperatures close to the expected phase transition to the quark-gluon plasma (QGP). Earlier calculations of photon radiation from ensembles of interacting mesons are reexamined with additional constraints, including new production channels as well as an assessment of hadronic form factor effects. Whereas strangeness-induced photon yields turn out to be moderate, the hitherto not considered

Transverse flow and hadrochemistry in Au+Au collisions at (S(NN))**(1/2) = 200-GeV

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Medium modifications of the rho meson at CERN super proton synchrotron energies (200 GeV/nucleon).

-channel exchange of

Thermalization of heavy quarks in the quark-gluon plasma

\ensuremath{\omega}

Low-mass dileptons at the CERN-SpS: evidence for chiral restoration?

mesons is found to contribute appreciably for photon energies above

Nonperturbative heavy-quark diffusion in the quark-gluon plasma.

\ensuremath{\sim}1.5\phantom{\rule{0.3em}{0ex}}\text{GeV}