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Transport simulations are very valuable for extracting physics information from heavy-ion-collision experiments. With the emergence of many different transport codes in recent years, it becomes important to estimate their robustness in extracting physics information from experiments. We report on the results of a transport-code-comparison project. Eighteen commonly used transport codes were included in this comparison: nine Boltzmann-Uehling-Uhlenbeck-type codes and nine quantum-molecular-dynamics-type codes. These codes have been asked to simulate Au + Au collisions using the same physics input for mean fields and for in-medium nucleon-nucleon cross sections, as well as the same impact parameter, the similar initialization setup, and other calculational parameters at 100 A and 400 A MeV incident energy. Among the codes we compare one-body observables such as rapidity and transverse flow distributions. We also monitor nonobservables such as the initialization of the internal states of colliding nuclei and their stability, the collision rates, and the Pauli blocking. We find that not completely identical initializations may have contributed partly to different evolutions. Different strategies to determine the collision probabilities and to enforce the Pauli blocking also produce considerably different results. There is a substantial spread in the predictions for the observables, which is much smaller at the higher incident energy. We quantify the uncertainties in the collective flow resulting from the simulation alone as about 30% at 100 A MeV and 13% at 400 A MeV, respectively. We propose further steps within the code comparison project to test the different aspects of transport simulations in a box calculation of infinite nuclear matter. This should, in particular, improve the robustness of transport model predictions at lower incident energies, where abundant amounts of data are available. more...

The velocity dependence of the thermal width of heavy quarkonia traveling with respect to the quark gluon plasma is calculated up to the NLO in perturbative QCD. At the LO, the width decreases with increasing speed, whereas at the NLO it increases with a magnitude approximately proportional to the expectation value of the relative velocity between the quarkonium and a parton in thermal equilibrium. Such an asymptotic behavior is due to the NLO dissociation cross section converging to a nonvanishing value in the high energy limit., Comment: 8 pages, 4 figures, references addes. version to be published in Phys. Lett. B more...

We study charm production in $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{{s}_{NN}}=2.76$ TeV in the parton-hadron-string-dynamics (PHSD) transport approach and the charm dynamics in the partonic and hadronic medium. The charm quarks are produced through initial binary nucleon-nucleon collisions by using the pythia event generator, taking into account the (anti-)shadowing incorporated in the eps09 package. The produced charm quarks interact with off-shell massive partons in the quark-gluon plasma and are hadronized into $D$ mesons through coalescence or fragmentation close to the critical energy density, and then interact with hadrons in the final hadronic stage with scattering cross sections calculated in an effective Lagrangian approach with heavy-quark spin symmetry. The PHSD results show a reasonable ${R}_{\mathrm{AA}}$ and elliptic flow of $D$ mesons in comparison to the experimental data for $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{{s}_{NN}}=2.76$ TeV from the ALICE Collaboration. We also study the effect of temperature-dependent off-shell charm quarks in relativistic heavy-ion collisions. We find that the scattering cross sections are only moderately affected by off-shell charm degrees of freedom. However, the position of the peak of ${R}_{\mathrm{AA}}$ for $D$ mesons depends on the strength of the scalar partonic forces which also have an impact on the $D$ meson elliptic flow. The comparison with experimental data on the ${R}_{\mathrm{AA}}$ suggests that the repulsive force is weaker for off-shell charm quarks as compared to that for light quarks. Furthermore, the effects from radiative charm energy loss appear to be low compared to the collisional energy loss up to transverse momenta of $\ensuremath{\sim}15$ GeV/$c$. more...

Heavy quarks (charm and bottoms) are one of the few probes which are sensitive to the degrees of freedom of a Quark Gluon Plasma (QGP), which cannot be revealed by lattice gauge calculations in equilibrium. Due to the rapid expansion of the QGP energetic heavy quarks do not come to an equilibrium with the QGP. Their energy loss during the propagation through the QGP medium depends strongly on the modelling of the interaction of the heavy quarks with the QGP quarks and gluons, i.e. on the assuption of the degrees of freedom of the plasma. Here we compare the results of different models, the pQCD based Monte-Carlo (MC@sHQ), the Dynamical Quasi Particle Model (DQPM) and the effective mass approach, for the drag force in a thermalized QGP and discuss the sensitivity of heavy quark energy loss on the properties of the QGP as well as on non-equilibrium dynamics, Comment: proceedings symposion "New Horizons" Makutsi, South Africa, Nov 2015 more...

The authors have studied a superconducting induction motor with Bi-2223/Ag HTS secondary conductors in the rotor. If the superconductor is applied to an induction motor, a higher efficiency and a higher power and a higher starting torque can be expected. The authors remodelled the rotor of a commercial 200 W (4 pole) induction motor and made an experimental HTS induction motor. The cast aluminum in the rotor slots were cut-in by 5 mm in depth and HTS tapes were put in the slots. Thus, the original conventional 200 W induction motor was remodeled to a HTS induction motor. The experimental motor was immersed in a liquid nitrogen bath. And, a no-load test, a locked test, a variable frequency locked test, and a load test of the HTS induction motor were carried out in liquid nitrogen bath. The experimental results are presented together with some theoretical analysis. more...

We study charm production in ultra-relativistic heavy-ion collisions by using the Parton-Hadron-String Dynamics (PHSD) transport approach. The initial charm quarks are produced by the PYTHIA event generator tuned to fit the transverse momentum spectrum and rapidity distribution of charm quarks from Fixed-Order Next-to-Leading Logarithm (FONLL) calculations. The produced charm quarks scatter in the quark-gluon plasma (QGP) with the off-shell partons whose masses and widths are given by the Dynamical Quasi-Particle Model (DQPM), which reproduces the lattice QCD equation-of-state in thermal equilibrium. The relevant cross sections are calculated in a consistent way by employing the effective propagators and couplings from the DQPM. Close to the critical energy density of the phase transition, the charm quarks are hadronized into $D$ mesons through coalescence and/or fragmentation. The hadronized $D$ mesons then interact with the various hadrons in the hadronic phase with cross sections calculated in an effective lagrangian approach with heavy-quark spin symmetry. The nuclear modification factor $R_{AA}$ and the elliptic flow $v_2$ of $D^0$ mesons from PHSD are compared with the experimental data from the STAR Collaboration for Au+Au collisions at $\sqrt{s_{NN}}$ =200 GeV and to the ALICE data for Pb+Pb collisions at $\sqrt{s_{NN}}$ =2.76 TeV. We find that in the PHSD the energy loss of $D$ mesons at high $p_T$ can be dominantly attributed to partonic scattering while the actual shape of $R_{AA}$ versus $p_T$ reflects the heavy-quark hadronization scenario, i.e. coalescence versus fragmentation. Also the hadronic rescattering is important for the $R_{AA}$ at low $p_T$ and enhances the $D$-meson elliptic flow $v_2$., 8 pages, 3 figures, to be published in the Proceedings of the 15th International Conference on Strangeness in Quark Matter (SQM2015), 6-11 July 2015, JINR, Dubna, Russia more...

We study charm production in ultra-relativistic heavy-ion collisions by using the Parton-Hadron-String Dynamics (PHSD) transport approach. The initial charm quarks are produced by the Pythia event generator tuned to fit the transverse momentum spectrum and rapidity distribution of charm quarks from Fixed-Order Next-to-Leading Logarithm (FONLL) calculations. The produced charm quarks scatter in the quark-gluon plasma (QGP) with the off-shell partons whose masses and widths are given by the Dynamical Quasi-Particle Model (DQPM) which reproduces the lattice QCD equation-of-state in thermal equilibrium. The relevant cross section are calculated in a consistent way by employing the effective propagators and couplings from the DQPM. Close to the critical energy density of the phase transition, the charm quarks are hadronized into $D$ mesons through coalescence and/or fragmentation depending on transverse momentum. The hadronized $D$ mesons then interact with the various hadrons in the hadronic phase with cross sections calculated in an effective lagrangian approach with heavy-quark spin symmetry. Finally, the nuclear modification factor $\rm R_{AA}$ and the elliptic flow $v_2$ of $D^0$ mesons from PHSD are compared with the experimental data from the STAR Collaboration for Au+Au collisions at $\sqrt{s_{\rm NN}}$ =200 GeV. We find that in the PHSD the energy loss of $D$ mesons at high $p_T$ can be dominantly attributed to partonic scattering while the actual shape of $\rm R_{AA}$ versus $p_T$ reflects the heavy quark hadronization scenario, i.e. coalescence versus fragmentation. Also the hadronic rescattering is important for the $\rm R_{AA}$ at low $p_T$ and enhances the $D$-meson elliptic flow $v_2$., 15 pages, 13 figures more...

I first discuss the NLO QCD calculation for the dissociation cross section of J/ψ into open charm, which shows a large second order correction near the threshold. The large correction softens when effective thermal masses in the order of the binding energy are introduced for the quarks and gluons. Hence, with the thermal masses, the method is reliably applied to calculate the dissociation cross section of J/ψ, which according to recent lattice results seems to remain bound even up to 1.6 × Tc. The dominant contribution to the dissociation comes from the thermal gluons, while the effects due to thermal quarks are suppressed due to suppressed phase space. The relevance of this result is discussed in the context of RHIC and signature of QGP. more...

Using the relativistic Vlasov-Uehling-Uhlenbeck (RVUU) equation based on mean fields from the nonlinear relativistic $\text{NL}\ensuremath{\rho}$ and $\text{NL}\ensuremath{\rho}\ensuremath{\delta}$ models, which have same nuclear equation of state and symmetry energy but different symmetry energy slope parameters, we study the effect of medium modification of the pion-production threshold on the total pion yield and the ${\ensuremath{\pi}}^{\ensuremath{-}}/{\ensuremath{\pi}}^{+}$ ratio in Au+Au collisions. We find that the in-medium threshold effect enhances both the total pion yield and the ${\ensuremath{\pi}}^{\ensuremath{-}}/{\ensuremath{\pi}}^{+}$ ratio, compared to those without this effect. Furthermore, including the medium modification of the pion-production threshold leads to a larger ${\ensuremath{\pi}}^{\ensuremath{-}}/{\ensuremath{\pi}}^{+}$ ratio for the $\text{NL}\ensuremath{\rho}\ensuremath{\delta}$ model with a larger symmetry energy parameter than the $\text{NL}\ensuremath{\rho}$ model with a smaller symmetry energy parameter, opposite to that found without the in-medium threshold effect. To reproduce the total pion yield measured by the FOPI Collaboration, we introduce a density-dependent cross section for $\ensuremath{\Delta}$ baryon production from nucleon-nucleon collisions, which suppresses the total pion yield but hardly changes the ${\ensuremath{\pi}}^{\ensuremath{-}}/{\ensuremath{\pi}}^{+}$ ratio. Because of the small difference in the stiffness of their symmetry energies, the ${\ensuremath{\pi}}^{\ensuremath{-}}/{\ensuremath{\pi}}^{+}$ ratios obtained from both the $\text{NL}\ensuremath{\rho}$ and $\text{NL}\ensuremath{\rho}\ensuremath{\delta}$ models are consistent with the FOPI data within the experimental errors. more...

Using the color evaporation model, the cross section for charmonium production in p+p collision is calculated in quark-gluon plasma. The threshold energy for open charms is given by the free energy potential from lattice calculations, the initial charm quark pairs by the Pythia simulations, and their time evolution by solving the Langevin equation. It is found that the threshold energy which decreases with temperature reduces the cross section while the invariant mass of charm pair which decreases by collisions enhances it. As a result, charmonia production is suppressed by $30$\sim$50\%$ while $J/\psi$ production is similar or enhanced compared to in vacuum., Comment: 6 pages and 4 figures more...

Using the relativistic Vlasov-Uehling-Uhlenbeck (RVUU) equation based on mean fields from the nonlinear relativistic models, we study the effect of medium modification of pion production threshold on the total pion yield and the $\pi^-/\pi^+$ ratio in Au+Au collisions. We find that the in-medium threshold effect enhances both the total pion yield and the $\pi^-/\pi^+$ ratio, compared to those without this effect. Furthermore, including the medium modification of the pion production threshold in asymmetric nuclear matter leads to a larger $\pi^-/\pi^+$ ratio for the $NL\rho\delta$ model with a stiffer symmetry energy than the $NL\rho$ model with a softer symmetry energy, opposite to that found without the in-medium threshold effect. Experimental data from the FOPI Collaboration are reproduced after including a density-dependent cross section for $\Delta$ baryon production from nucleon-nucleon collisions, which suppresses the total pion yield but hardly changes the $\pi^-/\pi^+$ ratio. The large errors in the experimentally measured $\pi^-/\pi^+$ ratio prevent, however, the distinction between the predictions from the $NL\rho$ and $NL\rho\delta$ models., Comment: 9 pages, 6 figures more...

Using a partonic transport model based on the 3-flavor Nambu-Jona-Lasinio model and a relativistic hadronic transport model to describe, respectively, the evolution of the initial partonic and the final hadronic phase of heavy-ion collisions at energies carried out in the Beam-Energy Scan program of the Relativistic Heavy Ion Collider, we have studied the effects of both the partonic and hadronic mean-field potentials on the elliptic flow of particles relative to that of their antiparticles. We find that to reproduce the measured relative elliptic flow differences between nucleons and antinucleons as well as between kaons and antikaons requires a vector coupling constant as large as 0.5 to 1.1 times the scalar coupling constant in the Nambu-Jona-Lasinio model. Implications of our results in understanding the QCD phase structure at finite baryon chemical potential are discussed., Comment: 5 pages, 4 figures, discussions added, version accepted by Phys. Rev. Lett more...

Using a nonrelativistic potential model, we calculate the cross section for the leading-order gluon dissociation of J/psi by including the full gluon wave function. We find that the resulting cross section as a function of gluon energy is reduced by about a factor of three at its maximum value compared to that calculated in the dipole approximation that is usually adopted in theoretical studies. The effect of the reduced cross section on the J/psi dissociation width at finite temperature is also discussed., Comment: 8 pages, 8 figures more...

The effect of initial-state fluctuations on jet-energy loss in relativistic heavy-ion collisions is studied in a 2+1-dimensional ideal hydrodynamic model. Within the next-to-leading order perturbative QCD description of hard scatterings, we find that a jet loses slightly more energy in the expanding quark-gluon plasma if the latter is described by the hydrodynamic evolution with fluctuating initial conditions compared to the case with smooth initial conditions. A detailed analysis indicates that this is mainly due to the positive correlation between the fluctuation in the production probability of parton jets from initial nucleon-nucleon hard collisions and the fluctuation in the medium density along the path traversed by the jet. This effect is larger in noncentral than in central relativistic heavy ion collisions and also for jet-energy loss that has a linear than a quadratic dependence on its path length in the medium. more...

We study e^+e^- pair production in proton-proton and central Pb+Pb collisions at sqrt(s_NN)=2.76 TeV within two models: an extended statistical hadronization model (SHM) and the Parton-Hadron-String Dynamics (PHSD) transport approach. We find that the PHSD calculations roughly agree with the dilepton spectrum from hadronic sources with the 'cocktail' estimates from the statistical hadronization model matched to available data at LHC energies. The dynamical simulations within the PHSD show a moderate increase of the low mass dilepton yield essentially due to the in-medium modification of the rho-meson. Furthermore, pronounced traces of the partonic degrees of freedom are found in the PHSD results in the intermediate mass regime. The dilepton production from the strongly interacting quark-gluon plasma (sQGP) exceeds that from the semi-leptonic decays of open charm and bottom mesons. Additionally, we observe that a transverse momentum cut of 1 GeV/c further suppresses the relative contribution of the heavy meson decays to the dilepton yield, such that the sQGP radiation strongly dominates the spectrum for masses from 1 to 3 GeV, allowing a closer look at the electromagnetic emissivity of the partonic plasma in the early phase of Pb+Pb collisions. more...

Countries’ energy intensity levels are known to converge at both the world and the regional levels. We test convergence in energy intensity for the world using a more recent and larger data set: a 152-country sample during the period of 1980-2010. Furthermore, we use income, population and combination of income and population as subgroups to test convergence of energy intensity. We find the convergence of energy intensity for the world. We also find that energy intensity convergence takes place with substantially different patterns for different subgroups. Thus, effective energy policies may need to be customized for each subgroup of nations. more...

The quarkonium formation time in a quark-gluon plasma (QGP) is determined from the space-time correlator of heavy quark vector currents using the quarkonium in-medium mass and wave function obtained from heavy quark potentials extracted from the lattice QCD. It is found that the formation time of a quarkonium increases with the temperature of the QGP and diverges near its dissociation temperature. Also, the quarkonium formation time is longer if the heavy quark potential is taken to be the free energy from lattice calculations for a heavy quark pair, compared to that based on the more negative internal energy., Comment: 5 pages, 4 figures more...

The dynamics of partons and hadrons in ultra-relativistic nucleus-nucleus collisions is analyzed within the Parton-Hadron-String Dynamics (PHSD) transport approach, which is based on a dynamical quasiparticle model for the partonic phase (DQPM) including a dynamical hadronization scheme while reproducing lattice QCD results in thermodynamic equilibrium for the equation-of-state as well as transport coefficients like shear and bulk viscosities, the electric conductivity or the charm diffusion coefficient of the hot QCD medium. In this contribution we report on the recent results on the charm dynamics and elliptic flow in Au+Au collisions at RHIC and Pb+Pb reactions at the LHC as well as on the single electron spectra from D— and B—meson semileptonic decays in Au+Au collisions at √sNN =200 and 62.4 GeV. We find that the PHSD approach well describes the Raa and elliptic flow v2 of open charm mesons in Au+Au collisions at √sNN = 200 GeV (from STAR) and 2.76 TeV (from ALICE) as well as the elliptic flow of single electrons at √sNN = 200 and 62.4 GeV (from PHENIX), however, the large Raa at √sNN = 62.4 GeV is not reproduced at all which might indicate a new 'PHENIX puzzle'. more...

Using the two-component model that includes both initial production from nucleon-nucleon hard scattering and regeneration from produced quark-gluon plasma, 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 helpful for understanding the observed suppression of bottomonia production in experiments carried out at both the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider. more...

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 figures more...

The flow of charm is calculated in 2 $+$ 1 ideal hydrodynamics by introducing the charge of $c\overline{c}$ pair assuming that the number of $c\overline{c}$ pairs is conserved in relativistic heavy ion collisions. It is found that the mean radial flow velocity of charm quarks is smaller than that of bulk matter by 10 $\ensuremath{\sim}$ 15% and the measured ${v}_{2}$ of heavy-flavor electrons is reproduced up to ${p}_{T}^{e}=$ 1.5 GeV/$c$ in Au $+$ Au collisions at Relativistic Heavy Ion Collider (RHIC). The same flow is applied to regenerated $J/\ensuremath{\psi}$ and its ${v}_{2}$ is discussed. more...

Using the two-component model that includes charmonium production from initial nucleon-nucleon hard scattering and regeneration in the produced quark-gluon plasma, we study $J/\psi$ production in heavy ion collisions at SPS, RHIC and LHC. For the expansion dynamics of produced hot dense matter, we use a schematic viscous hydrodynamic model with the specific shear viscosity taken, respectively, to be twice and ten times the lower bound of $1/4\pi$ suggested by the Ads/CFT correspondence in the quark-gluon plasma and in the hadron gas. For the initial dissociation and the subsequent thermal decay of charmonia in the hot dense matter, we use the screened Cornell potential to describe the properties of charmonia and the perturbative QCD to calculate their dissociation cross sections. Including regeneration of charmonia in the quark-gluon plasma via a kinetic equation with in-medium chamonium decay widths, we obtain a good description of measured nuclear modification factors at SPS and RHIC. A reasonable description of measured nuclear modification factor of $J/\psi$s of high transverse momenta in heavy ion collisions at LHC is also obtained if we include the contribution to the $J/\psi$ yield from the decay of bottomed hadrons. more...

Using the two-component model that includes charmonium production from both initial nucleon-nucleon hard scattering and regeneration in the produced quark-gluon plasma, we study $J/\ensuremath{\psi}$ production in heavy-ion collisions at the Super Proton Synchrotron (SPS), Relativistic Heavy Ion Collider (RHIC), and Large Hadron Collider (LHC). For the expansion dynamics of produced hot dense matter, we use a schematic viscous hydrodynamic model with the specific shear viscosity in the quark-gluon plasma and the hadronic matter taken, respectively, to be two and ten times the lower bound of $1/4\ensuremath{\pi}$ suggested by the anti-de Sitter/conformal field theory (AdS/CFT) correspondence. For the initial dissociation and the subsequent thermal decay of charmonia in the hot dense matter, we use the screened Cornell potential to describe the properties of charmonia and perturbative QCD to calculate their dissociation cross sections. Including regeneration of charmonia in the quark-gluon plasma via a kinetic equation with in-medium chamonium decay widths, we obtain a good description of measured $J/\ensuremath{\psi}$ nuclear modification factors in Pb $+$ Pb collisions at $\sqrt{{s}_{NN}}=1.73$ GeV at SPS and in Au $+$ Au collisions at $\sqrt{{s}_{NN}}=200$ GeV at RHIC. A reasonable description of the measured nuclear modification factor of high transverse momenta $J/\ensuremath{\psi}$ in Pb $+$ Pb collisions at $\sqrt{{s}_{NN}}=2.76$ TeV at LHC is also obtained. more...

Using a two-component model for charmonium production, which includes contributions from both the initial hard nucleon-nucleon scattering and from the regeneration in the quark-gluon plasma, we study the nuclear modification factor $R_{AA}$ and elliptic flow $v_2$ of $J/\psi$ in relativistic heavy ion collisions. For the expansion dynamics of produced hot dense matter, we introduce a schematic fireball model with its transverse acceleration determined from the pressure gradient inside the fireball and azimuthally anisotropic expansion parameterized to reproduce measured $v_2$ of light hadrons. We assume that light hadrons freeze out at the temperature of 120 MeV while charmonia at 160 MeV, similar to the kinetic and chemical freeze-out temperatures in the statistical model, respectively. For the properties of charmonia in the quark-gluon plasma, we use the screening mass between their charm and anticharm quarks and their dissociation cross sections given by the perturbative QCD (pQCD) in the leading order and up to the next-to-leading order, respectively. For the relaxation time of charm and anticharm quarks in the quark-gluon plasma, we also use the one calculated in the leading order of pQCD. Modeling the effect of higher-order corrections in pQCD by introducing multiplicative factors to the dissociation cross section of charmonia and the elastic scattering cross sections of charm and anticharm quarks, we find that this effect is small for the $R_{AA}$ of $J/\psi$ as they suppress the number of initially produced $J/\psi$ but enhance the number of regenerated ones. The higher-order corrections increase, however, the $v_2$ of $J/\psi$. Our results suggest that the $v_2$ of $J/\psi$ can play an important role in discriminating between $J/\psi$ production from the initial hard collisions and from the regeneration in the quark-gluon plasma., Comment: 15 pages, 14 figures more...

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 ten 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., Comment: 11 pages, 6 figures more...

We build up a model to reproduce the experimentally measured ${R}_{\mathit{AA}}$ of $J/\ensuremath{\psi}$ near midrapidty in an $\mathrm{Au}+\mathrm{Au}$ collision at $\sqrt{{s}_{\mathit{NN}}}=200$ GeV. The model takes into account the $J/\ensuremath{\psi}$ suppression from the quark-gluon plasma and hadron gas as well as the nuclear absorption of primordial charmonia and the regeneration effects at the hadronization stage and hence is a generalization of the two-component model introduced by Grandchamp and Rapp. The improvements in this work are twofold; the addition of the initial local temperature profile and a consistent use of QCD next-to-leading order (NLO) formula for both the dissociation cross section in the hadron gas and the thermal decay widths in the quark-gluon plasma for the charmonium states. The initial local temperature profile is determined from the assumption that the local entropy density is proportional to a formula involving the number densities of the number of participants and of the binary collisions that reproduces the multiplicities of charged particles at chemical freeze-out. The initial local temperature profile brings about a kink in the ${R}_{\mathit{AA}}$ curve due to the initial melting of $J/\ensuremath{\psi}$. The initially formed fireball, composed of weakly interacting quarks and gluons with thermal masses that are extracted from lattice QCD, follows an isentropic expansion with cylindrical symmetry. The fit reproduces well the $\mathrm{Au}+\mathrm{Au}$ as well as the $\mathrm{Cu}+\mathrm{Cu}$ data. The same method is applied to predict the ${R}_{\mathit{AA}}$ expected from the $\mathrm{Pb}+\mathrm{Pb}$ collision at Large Hadron Collider (LHC) energy. more...

This study evaluated the effect of respiratory movement on field-in-field (FIF) forward intensity-modulated radiotherapy (IMRT) for the treatment of breast cancer. FIF forward IMRT was performed on ten patients receiving radiotherapy to the whole breast after conservation surgery. Assuming that breast motion follows a sophisticated cyclic function, the changes in hot and cold region, dose homogeneity index (DHI), and skin dose were examined at different respiration amplitudes of 1 cm, 2 cm, and 3 cm. FIF forward IMRT significantly improved the hot region, DHI, and skin dose, but slightly worsened the cold region, compared to the two wedged tangential technique (TWT). Interestingly, we found that the respiration amplitude affected the DHI and cold region but had no effect on the hot region and skin dose. The DHI was slightly improved at 1 cm of amplitude probably due to the blurring effect, remained unchanged at 2 cm of amplitude, and was worsened at 3 cm of amplitude. FIF forward IMRT significantly increased the cold region at 2 cm and 3 cm of respiration amplitude compared to the TWT. At 3 cm of respiration amplitude, an average cold region of 3.27 cm3 was observed. In summary, our data indicate that during FIF forward IMRT, respiration movement has an important effect on various endpoints depending on the respiration amplitude of the patient. more...

Recent lattice calculations showed that the quarkonia will survive beyond the phase transition temperature, and will dissolve at different temperatures depending on the type of the quarkonium. In this work, we calculate the thermal width of the quarkonium at finite temperature before it dissolves into open heavy quarks. The input of the calculation are the parton quarkonium dissociation cross section to NLO in QCD, the quarkonium wave function in a temperature-dependent potential from lattice QCD, and a thermal distribution of partons with thermal masses. We find that for the J/psi, the total thermal width above 1.4 Tc becomes larger than 100 to 250 MeV, depending on the effective thermal masses of the quark and gluon, which we take between 400 to 600 MeV. Such a width corresponds to an effective dissociation cross section by gluons between 1.5 to 3.5 mb and by quarks 1 to 2 mb at 1.4 Tc. However, at similar temperatures, we find a much smaller thermal width and effective cross section for the upsilon., 7 pages, 13 figures, 2 tables, version to be published in Phys. Rev. C more...

Motivated by the recent lattice data that $J/\psi$ will survive up to 1.6$T_c$, we calculate the thermal width of $J/\psi$ at finite temperature in perturbative QCD. The inputs of the calculation are the parton quarkonium dissociation cross sections at the NLO in QCD, which were previously obtained by Song and Lee, and a gaussian charmonium wave function, whose size were fitted to an estimate by Wong by solving the schrodinger equation for charmonium in a potential extracted from the lattice at finite temperature. We find that the total thermal width above 1.4$T_c$ becomes larger than 100 to 200 MeV, depending on the effective thermal masses of the quark and gluon, which we take it to vary from 600 to 400 MeV., Comment: 4 pages, Talk at Quark Matter 2006 more...

The next to leading order (NLO) quarkonium-hadron cross section is calculated in perturbative QCD. The corresponding leading order (LO) result was performed by Peskin more than 20 years ago using the operator product expansion (OPE). In this work, the calculation is performed using the Bethe-Salpeter amplitude and the factorization formula. The soft divergence appearing in the intermediate stages of the calculations are shown to vanish after adding all possible crossed terms, while the collinear divergences are eliminated by mass factorization. Applying the result to the Upsilon system, one finds that there are large higher order correction near the threshold. The relevance of the present result to the charmonium case is also discussed., Yonsei University. to be published in PRD more...

Based on a kinetic description of J/psi dissociation and production in an expanding quark-gluon plasma that is described by a 2+1 dimensional ideal hydrodynamics, we have studied the double ratio R_{p Pb}(psi')/R_{p Pb}(J/psi) of charmonia in p+Pb collisions at sqrt(s_NN)=5.02 TeV by including not only the cold nuclear matter effects but also the hot nuclear matter effects. We find that the double ratio of prompt charmonia is significantly suppressed in the most central collisions as a result of the hot nuclear matter effects. more...

We reanalyze the dissociation process of the $J/\ensuremath{\psi}$ by $\ensuremath{\pi}$ and $\ensuremath{\rho}$ mesons into $D+\overline{D},$ ${D}^{*}+\overline{D},$ $D+{D}^{*},$ and ${D}^{*}+{D}^{*}$ within a meson exchange model. In addition to the dissociation mechanisms considered in the literature, we consider anomalous parity interactions, whose couplings are constrained by heavy quark spin symmetry and phenomenology. This opens new dissociation channels and adds new diagrams in the previously considered processes. Compared to the previous results, we find that these new additions have only a minor effect on the $\ensuremath{\rho}+J/\ensuremath{\psi}$ total inelastic cross section, but reduce the one for $\ensuremath{\pi}+J/\ensuremath{\psi}$ by about 50% near the threshold. more...

Using the screened Cornell potential and the next-to-leading order perturbative QCD to determine, respectively, the properties of bottomonia and their dissociation cross sections in a quark-gluon plasma, we have studied in a 2+1 ideal hydrodynamics the effect of initial fluctuations on bottomonia production in relativistic heavy-ion collisions. We have found that while initial fluctuations hardly affect the yield of the 1S ground state bottomonium, their effect on that of excited bottomonium states is not small. Compared to the case with smooth initial conditions, the survival probabilities of excited bottomonium states are reduced at low transverse momentum in the case of large initial fluctuations while they are increased in the case of small initial fluctuations as a result of the smearing effect introduced in solving the hydrodynamic equations. The observed suppression of excited bottomonia relative to the ground state bottomonium of an average transverse momentum of 6.25 GeV/c by the Compact Muon Solenoid (CMS) collaborations can, however, be described at present with both smooth and fluctuating initial conditions. more...

Within the next-to-leading order perturbative QCD description of hard scatterings and using a 2+1 dimension ideal hydrodynamic model, we have studied the effect of initial state fluctuations on jet energy loss in relativistic heavy-ion collisions. We find that a jet loses slightly more energy in the expanding quark-gluon plasma if the latter is described by the hydrodynamic evolution with fluctuating initial conditions compared to the case with smooth initial conditions. A detailed analysis indicates that this is mainly due to the positive correlation between the fluctuation in the production probability of parton jets from initial nucleon-nucleon hard collisions and the fluctuation in the medium density along the path traversed by the jet. This effect is larger in non-central than in central relativistic heavy ion collisions and also for a linear than a quadratic dependence of jet energy loss on its path length in the medium. more...

Using the two-component model for charmonium production, which includes contributions from both initial hard nucleon-nucleon scattering and from regeneration in the quark-gluon plasma, we have studied the nuclear modification factor RAA and elliptic flow ν2 of J/Ψ in relativistic heavy-ion collisions. For the expansion dynamics of produced hot dense matter, we have introduced a schematic fire-cylinder model with its transverse acceleration determined from the pressure gradient inside the fire-cylinder and azimuthally anisotropic expansion parameterized to reproduce measured ν2 of light hadrons. We have assumed that light hadrons freeze out at the temperature of 120 MeV while charmonia at 160 MeV, similar to the kinetic and chemical freeze-out temperatures in the statistical model, respectively. For the properties of charmonia in the quark-gluon plasma, we have used the screening mass between their charm and anticharm quarks and their dissociation cross sections given by the perturbative QCD (pQCD) in the leading order and up to the next-to-leading order, respectively. For the relaxation time of charm and anticharm quarks in the quark-gluon plasma, we have also used the one calculated in the leading order pQCD. Modeling the effect of higher-order corrections in pQCD by introducing multiplicative factors to the dissociation cross sections of charmonia and the elastic scattering cross sections of charm and anticharm quarks, we have found that this effect is small for the RAA of J/Ψ as they suppress the number of initially produced J/Ψ but enhance the number of regenerated ones. The higher-order corrections increase, however, the ν2 of J/Ψ. Our results thus suggest that the ν2 of J/Ψ can play an important role in discriminating between J/Ψ production from initial hard collisions and from regeneration in the quark-gluon plasma. more...

130.9 cGy. The TLD chips indicated that the surface dose was higher than these, but it was due to the finite thickness of the TLD chips. In the former case, 95% of the prescribed dose was obtained at a 2.1 mm depth, while the prescribed does was at 2.2 mm in the latter case. The maximum dose was about 110% of the prescribed dose. As the depth became deeper, the dose decreased rapidly. Accordingly, at a 2-cm depth, the dose was 20 % of the prescribed dose. Conclusion : Helical tomotherapy could be a useful application in the treatment of a wide area of the skin with curvature. However, for depths up to 2 mm, the planning system overestimated the superficial dose. For shallower targets, the use of a compensator such as a bolus is required. more...

Purpose: To investigate the feasibility of helical tomotherapy on a wide superficial area, and its accuracy of calculation near the superficial region Method and Materials: Two types of treatment plans were made with the cylinder‐shaped “cheese phantom”. In the first plan, 2 Gy was prescribed to the 1 cm thick ring shaped target at the surface area. In the second plan, we expanded the surface by 5 mm so that the target includes the 5 mm thick air ring. The inner part of the phantom below depth 2 cm was selected as a complete block so that we can make sure only the surface area can be irradiated. To measure the surface dose and the depth dose profile, an EDR2 film was inserted into the phantom. The film measured doses and planned doses were compared. Results: After irradiation, the surface dose of the former case was about 120 cGy and the latter case was about 130 cGy. 95 % of the prescribed dose could be obtained from roughly at 2 mm depth in both cases. The maximum dose was about 110 % of the prescribed dose. As the depth became deeper, the dose decreased rapidly, and at 2 cm depth, it became 20 % of the prescribed dose. However, in the air region and up to 2 mm depth in the phantom, the planning system overestimated superficial dose. Conclusion: We found that helical tomotherapy could be applied usefully to treatment of wide area of the skin with curvature. However, to treat the more shallow regions, it is safe to bolus. Conflict of Interest: Research sponsored by TomoTherapy Corporation. more...

We study the changes in the partial decay widths of excited charmonium states into $D \bar{D}$, when the D meson mass decreases in nuclear matter, taking the internal structure of the hadrons into account. Calculations within the 3P0 model for $\psi(3686)$ and $\psi(3770)$ imply that naive estimates of the in-medium widths based only on phase space are grossly exaggerated. Due to nodes in the wave functions, these states may even become narrow at high densities, if the D meson mass is decreased by about 200 MeV. For the $\chi$ states, we generally expect stronger modifications of the widths. The relevance of the $\chi$ widths for $J/\psi$ suppression in heavy ion collision is discussed. These phenomena could be explored in experiments at the future accelerator facility at GSI., Comment: 12 pages, 3 figures; allowed for two independent oscillator parameters for the charmonium states and D mesons, results are not significantly modified and conclusions remains unaltered more...

We study how heavy quark dynamics is affected by the nature of the bulk evolution of the QCD matter, the initial condition of the system, and the treatment of elementary interactions between heavy quarks and the surrounding medium. For the same initial condition and the same QGP expansion scenario we discuss the consequences of the assumption of a local equilibrium by comparing the consequences for the nuclear modification factor and the elliptic flows of charm quarks. For this purpose we employ the parton-hadron-string dynamics (PHSD), which is an off-shell microscopic transport approach, as well as the linearized-Boltzmann (LB) scheme obtained by coarse graining the PHSD bulk and assuming local equilibrium for the interactions of the charm quarks with the bulk. The $R_{\rm AA}$ of charm quarks stemming from the later LB approach is also compared to a genuine fluid dynamics evolution initiated by the coarse grained PHSD, which allows to further assess the consequences of reducing the full n-body dynamics. We then proceed to a systematic comparison of PHSD with MC@HQ, another transport model for heavy flavors which also relies on LB approach. In particular, we investigate the consequences for the nuclear modification factor of charm quarks if we vary separately the initial heavy quark distribution function in matter, the expansion dynamics of the QGP and the elementary interactions of heavy quarks of these models. We find that the results for both models vary significantly depending on the details of the calculation. However, both models achieve very similar predictions for key heavy quark observables for certain combinations of initial condition, bulk evolution and interactions. We conclude that this ambiguity limits our ability to determine the different properties of the system based on the current set of observables., Comment: 18 pages, 10 figures more...

Using the screened Cornell potential and the next-to-leading order perturbative QCD to determine, respectively, the properties of bottomonia and their dissociation cross sections in a quark-gluon plasma, we study in a 2+1 ideal hydrodynamics the effect of initial fluctuations on bottomonia production in relativistic heavy-ion collisions. We find that while initial fluctuations hardly affect the yield of the 1S ground state bottomonium, their effect on that of excited bottomonium states is not small. Compared to the case with smooth initial conditions, the survival probability of excited bottomonia is reduced at low transverse momentum and increased at high transverse momentum. The observed suppression of the excited bottomonia relative to the ground state bottomonium by the Compact Muon Solenoid (CMS) collaborations at an average transverse momentum can, however, be described at present with both smooth and fluctuating initial conditions., Comment: 5 pages, 5 figures more...

The diffusion coefficients of heavy quarks from the coherent color electromagnetic fields which are generated in the early stage of relativistic heavy-ion collisions are calculated at midrapidity, and compared with those obtained from collisions within a thermalized quark-gluon plasma. The coherent color fields are modeled such that they are initially longitudinal and then become isotropic. We found that the diffusion coefficients from the coherent color fields are larger than those from collisions except for very fast heavy quarks, and the color fields are less effective for heavy-quark energy loss. The importance of coherent color fields for heavy-quark diffusion decreases as energy density decreases., 10 pages, 7 figures more...