Charged particle directed flow in Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV measured with ALICE at the LHC

Charged particle directed flow at midrapidity, |eta|<0.8, and forward rapidity, 1.7 < |eta|<5.1, is measured in Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV with ALICE at the LHC. Directed flow is reported as a function of collision centrality, charged particle transverse momentum, and pseudo-rapidity. Results are compared to measurements at RHIC and recent model calculations for LHC energies.Comment: Talk given at the XXII International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2011), 23-28 May 2011, Annecy, France; 4 pages, 3 figure

Hydrodynamic predictions for mixed harmonic correlations in 200 GeV Au+ Au collisions

Recent measurements at the Large Hadron Collider involve the correlation of different azimuthal flow harmonics vn. These new observables add constraints to theoretical models and probe aspects of the system that are independent of traditional single-harmonic measurements such as two-particle and multiparticle cumulants vn{m}. Many of these new observables have not yet been measured at the Relativistic Heavy Ion Collider (RHIC), leaving an opportunity to make predictions as a test of models across energies. We make predictions using NEXSPHERIO, a hydrodynamical model which has accurately reproduced a large set of single-harmonic correlations in a large range of transverse momenta and centralities at RHIC. Our predictions thus provide an important baseline for comparison to correlations of flow harmonics, which contain nontrivial information about the initial state as well as quark-gluon plasma transport properties. We also point out significant biases that can appear when using wide centrality bins and nontrivial event weighting, necessitating care in performing experimental analyses and in comparing theoretical calculations to these measurements

Hydrodynamic predictions for mixed harmonic correlations in 200 GeV Au+ Au collisions

Recent measurements at the Large Hadron Collider involve the correlation of different azimuthal flow harmonics vn. These new observables add constraints to theoretical models and probe aspects of the system that are independent of traditional single-harmonic measurements such as two-particle and multiparticle cumulants vn{m}. Many of these new observables have not yet been measured at the Relativistic Heavy Ion Collider (RHIC), leaving an opportunity to make predictions as a test of models across energies. We make predictions using NEXSPHERIO, a hydrodynamical model which has accurately reproduced a large set of single-harmonic correlations in a large range of transverse momenta and centralities at RHIC. Our predictions thus provide an important baseline for comparison to correlations of flow harmonics, which contain nontrivial information about the initial state as well as quark-gluon plasma transport properties. We also point out significant biases that can appear when using wide centrality bins and nontrivial event weighting, necessitating care in performing experimental analyses and in comparing theoretical calculations to these measurements

Temporal evolution of tubular initial conditions and their influence on two-particle correlations in relativistic nuclear collisions

Relativistic nuclear collisions data on two-particle correlations exhibit structures as function of relative azimuthal angle and rapidity. A unified description of these near-side and away-side structures is proposed for low to moderate transverse momentum. It is based on the combined effect of tubular initial conditions and hydrodynamical expansion. Contrary to expectations, the hydrodynamics solution shows that the high energy density tubes (leftover from the initial particle interactions) give rise to particle emission in two directions and this is what leads to the various structures. This description is sensitive to some of the initial tube parameters and may provide a probe of the strong interaction. This explanation is compared with an alternative one where some triangularity in the initial conditions is assumed. A possible experimental test is suggested.Comment: 6 pages, 6 figure

Feeding of the elliptic flow by hard partons

We propose that in nuclear collisions at the LHC the elliptic flow may get a contribution from leading hard and semihard partons which deposit energy and momentum into the hydrodynamic bulk medium. The crucial effect is that these partons induce wakes which interact and merge if they come together. The contribution to the integrated elliptic flow is estimated with the help of a toy model to about 25% of the observed value and shows strong event-by-event fluctuations.Comment: 9 pages, 3 figure

Influence of tubular initial conditions on two-particle correlations

A unified description of the near-side and away-side structures observed in two-particle correlations as function of delta eta-delta phi is proposed for low to moderate transverse momentum. It is based on the combined effect of tubular initial conditions and hydrodynamical expansion.Comment: 4 pages, 3 figures. Contribution to QM201

Body composition and resting metabolic rate in obese adolescents

Objetivo: Analisar a composição corporal e taxa metabólica de repouso (TMR) de adolescentes com obesidade. Metodologia: Foram avaliados 58 adolescentes, entre 12 e 16 anos (13,7±1,2 anos), com obesidade. A composição corporal foi mensurada por meio da Absortiometria de Raios-x de Dupla Energia (DEXA). A taxa metabólica de repouso e a oxidação de glicose e lipídeos foram determinadas pela medida do oxigênio consumido e pela produção de dióxido de carbono. Foi utilizado teste t de Student para variáveis independentes, análise de regressão linear múltipla e correlação de Pearson, com significância de p&lt;5%. Resultados: Foram observadas diferenças na porcentagem de gordura corporal (p=0,01), porcentagem de massa corporal magra (MCM) (p=0,01), porcentagem de gordura do tronco (p=0,01), massa magra membro inferior (p=0,01) e taxa metabólica de repouso (p=0,04) entre os sexos masculino e feminino. No sexo masculino a MCM foi a melhor preditora de TMR (p=0,01). Houve correlação positiva entre TMR e MCM, assim como observada associação entre a oxidação lipídica e MCM. Conclusão: A composição corporal total e por segmento corporal influenciam a taxa metabólica de repouso e a oxida- ção de substratos. Além disso, a MCM pode ser considerada um fator de aumento do gasto energético de repouso de adolescentes com obesidade.Objective: Analyze body composition and resting metabolic rate (RMR) in obese adolescents. Methods: 58 obese adolescents were assessed between 12 and 16 years (13.7 ± 1.2 years). The body composition was measured dual-energy x-ray absorptiometry (DEXA). The resting metabolic rate and oxidation of glucose and lipids were determined by measuring the oxygen consumption and the production of carbon dioxide. Student t test was used for independent data, multiple linear regression and Pearson correlation, significance was set p &lt;5%. Results: Significant differences were observed in the percentage of body fat (p = 0.01), percentage of lean body mass (LBM) (p = 0.01), percentage body fat (p = 0.01), lower limb lean mass (p = 0.01) and resting metabolic rate (p = 0.04) between males and females. The LBM is highlighted as the best predictor of RMR (p = 0.01). There was a positive correlation between RMR and LBM, as observed association between lipid oxidation and LBM. Conclusion: Total body composition and segment influence the resting metabolic rate and substrate oxidation. In addition, the LBM can be considered a factor of increased resting energy expenditure in obese adolescents

A minimal quasiparticle approach for the QGP and its large-NcN_c limits

We propose a quasiparticle approach allowing to compute the equation of state of a generic gauge theory with gauge group SU($N_c$) and quarks in an arbitrary representation. Our formalism relies on the thermal quasiparticle masses (quarks and gluons) computed from Hard-Thermal-Loop techniques, in which the standard two-loop running coupling constant is used. Our model is minimal in the sense that we do not allow any extra ansatz concerning the temperature-dependence of the running coupling. We first show that it is able to reproduce the most recent equations of state computed on the lattice for temperatures higher than 2 $T_c$. In this range of temperatures, an ideal gas framework is indeed expected to be relevant. Then we study the accuracy of various inequivalent large-$N_c$ limits concerning the description of the QCD results, as well as the equivalence between the QCD$_{AS}$ limit and the ${\cal N}=1$ SUSY Yang-Mills theory. Finally, we estimate the dissociation temperature of the $\Upsilon$-meson and comment on the estimations' stability regarding the different considered large-$N_c$ limits.Comment: 19 pages, 6 figure

A systematic study of the sensitivity of triangular flow to the initial state fluctuations in relativistic heavy-ion collisions

Experimental data from the Relativistic Heavy Ion Collider (RHIC) suggests that the quark gluon plasma behaves almost like an ideal fluid. Due to its short lifetime, many QGP properties can only be inferred indirectly through a comparison of the final state measurements with transport model calculations. Among the current phenomena of interest are the interdependencies between two collective flow phenomena, elliptic and triangular flow. The former is mostly related to the initial geometry and collective expansion of the system whereas the latter is sensitive to the fluctuations of the initial state. For our investigation we use a hybrid transport model based on the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) transport approach using an ideal hydrodynamic expansion for the hot and dense stage. Using UrQMD initial conditions for an Au-Au collision, particles resulting from a collision are mapped into an energy density distribution that is evolved event-by-event with a hydrodynamic calculation. By averaging these distributions over different numbers of events, we have studied how the granularity/smoothness of the distribution affects the initial eccentricity, the initial triangularity, and the resulting flow components. The average elliptic flow in non central collisions is not sensitive to the granularity, while triangular flow is. The triangularity might thus provide a good measure of the amount of initial state fluctuations that is necessary to reproduce the experimental data.Comment: 10 pages, 7 figure