Charmonium production from nonequilibrium charm and anticharm quarks in quark-gluon plasma

Parameterizing the charm and anticharm quark momentum distributions by the Tsallis distribution, we study the nonequilibrium effect on the charmonium production rate in a quark-gluon plasma up to the next-to-leading order in perturbative QCD. We find that nonequilibrium charm and anticharm quarks suppress the charmonium production rate compared to that from equilibrated ones. We further show that the suppression factor calculated with the charm quark relaxation time, which has been frequently used in the literature, is close to our results.Comment: 8 pages, 5 figure

Jet Fragmentation via Recombination of Parton Showers and Its Medium Modification in Heavy Ion Collisions

For jets produced in relativistic heavy ion collisions, the presence of the quark-gluon plasma (QGP) formed in the collisions not only affects their energies but is also expected to affect their hadronization. In this dissertation, we have studied the influence of the QGP on jets by treating the jet as shower partons, which are then converted to hadrons via their recombination among themselves as well as with the thermal partons in the quark-gluon plasma. To verify the feasibility of treating the hadronization of energetic jets by recombination of shower partons, we have computed hadron spectra in e^+ + e^− collisions. Including contributions from resonance decays and from the string fragmentation of the remnant partons left after the recombination by using a subroutine of PYTHIA, we have found that the resulting spectra of longitudinal momentum fractions and transverse momenta for pion, kaon, nucleon, and Λ reproduce reasonably those from the string fragmentation obtained in PYTHIA. The medium effect on the conversion of jets to hadrons is then studied for heavy ion collisions at both RHIC and LHC by using the blast-wave model for generating the thermal partons in the QGP. In obtaining the shower partons from jets, we have included their energy loss due to interactions with thermal partons in QGP. We have found that including hadron production from the recombination of shower partons with thermal partons leads to a significant enhancement in the production of hadrons with intermediate transverse momenta at both RHIC and LHC. Our results show that the recombination model can reproduce well the experimental measurements conducted at both RHIC and LHC, thus suggesting the importance of medium modifications in the conversion of jets to hadrons in the presence of a QGP

Jet fragmentation via recombination of parton showers

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Dilepton production in schematic causal viscous hydrodynamics

Journals published by the American Physical Society can be found at http://publish.aps.org/Assuming that in the hot dense matter produced in relativistic heavy-ion collisions, the energy density, entropy density, and pressure as well as the azimuthal and space-time rapidity components of the shear tensor are uniform in the direction transversal to the reaction plane, we derive a set of schematic equations from the Isreal-Stewart causal viscous hydrodynamics. These equations are then used to describe the evolution dynamics of relativistic heavy-ion collisions by taking the shear viscosity to entropy density ratio of 1/4 pi for the initial quark-gluon plasma (QGP) phase and of 10 times this value for the later hadron-gas (HG) phase. Using the production rate evaluated with particle distributions that take into account the viscous effect, we study dilepton production in central heavy-ion collisions. Compared with results from the ideal hydrodynamics, we find that although the dilepton invariant mass spectra from the two approaches are similar, the transverse momentum spectra are significantly enhanced at high transverse momenta by the viscous effect. We also study the transverse momentum dependence of dileptons produced from QGP for a fixed transverse mass, which is essentially absent in the ideal hydrodynamics, and find that this so-called transverse mass scaling is violated in the viscous hydrodynamics, particularly at high transverse momenta

The genome sequence of Xanthomonas oryzae pathovar oryzae KACC10331, the bacterial blight pathogen of rice

The nucleotide sequence was determined for the genome of Xanthomonas oryzae pathovar oryzae (Xoo) KACC10331, a bacterium that causes bacterial blight in rice (Oryza sativa L.). The genome is comprised of a single, 4 941 439 bp, circular chromosome that is G + C rich (63.7%). The genome includes 4637 open reading frames (ORFs) of which 3340 (72.0%) could be assigned putative function. Orthologs for 80% of the predicted Xoo genes were found in the previously reported X.axonopodis pv. citri (Xac) and X.campestris pv. campestris (Xcc) genomes, but 245 genes apparently specific to Xoo were identified. Xoo genes likely to be associated with pathogenesis include eight with similarity to Xanthomonas avirulence (avr) genes, a set of hypersensitive reaction and pathogenicity (hrp) genes, genes for exopolysaccharide production, and genes encoding extracellular plant cell wall-degrading enzymes. The presence of these genes provides insights into the interactions of this pathogen with its gramineous host

Bottomonia suppression in relativistic heavy-ion collisions

Using the two-component model that includes both initial production from nucleon-nucleon hard scattering and regeneration from produced quark-gluon plasma (QGP), we study the effect of medium modifications of the binding energies and radii of bottomonia on their production in heavy-ion collisions. We find that the contribution to bottomonia production from regeneration is small and the inclusion of medium effects is generally helpful for understanding the observed suppression of bottomonia production in experiments carried out at both the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC).Comment: 6 pages, 4 figure