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We update our former analysis of the Nuclear Modification Factors (NMF) for different hadron species at RHIC and LHC. This update is motivated by the new experimental data from STAR which presents differences with the preliminary data used to fix some of the parameters in our model. The main change is the use of AKK fragmentation functions for the hard part of the spectrum and minor adjustments of the coalescence (soft) contribution. We confirm that observation of the NMF for the f_0 meson can shed light on its quark composition.
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We update results presented at Lattice 2005 on charmonium masses. New ensembles of gauge configurations with 2+1 flavors of improved staggered quarks have been analyzed. Statistics have been increased for other ensembles. New results are also available for P-wave mesons and for bottomonium on selected ensembles.
The impact of large-distance contributions on the behaviour of the slopes of the spin-non-flip and of the spin-flip amplitudes is analysed. It is shown that the long tail of the hadron potential in impact parameter space leads to a larger value of the slope for the spin-flip amplitude (without the kinematic factor sqrt(|t|)) than for the spin-non-flip amplitude. This effect is taken into account in the calculation of the analysing power in proton-nucleus reactions at high energies.
We evaluate drag and diffusion transport coefficients comparing a quasi-particle approximation with on-shell constituents of the QGP medium and a dynamical quasi-particles model with off-shell bulk medium at finite temperature T. We study the effects of the width $gamma$ of the particles of the bulk medium on the charm quark transport properties exploring the range where $gamma < M_{q,g}$. We find that off-shell effects are in general quite moderate and can induce a reduction of the drag coefficient at low momenta that disappear already at moderate momenta, $p gtrsim 2-3, rm GeV$. We also observe a moderate reduction of the breaking of the Fluctuation-Dissipation theorem (FDT) at finite momenta. Moreover, we have performed a first study of the dynamical evolution of HQ elastic energy loss in a bulk medium at fixed temperature extending the Boltzmann (BM) collision integral to include off-shell dynamics. A comparison among the Langevin dynamics, the BM collisional integral with on-shell and the BM extension to off-shell dynamics shows that the evolution of charm energy when off-shell effects are included remain quite similar to the case of the on-shell BM collision integral.
We develop a non-perturbative model for valence parton distribution functions (PDFs) based on the quark interactions in the mean field of the nucleonic interior. The main motivation for the model is to obtain a mean field description of the valence quarks as a baseline to study the short range quark-quark interactions that generate high $x$ tail of valence quark distributions. The model is based on the separation of valence three-quark system from the residual nucleon system which is the source of the mean field. The nucleon structure function is calculated within effective light-front diagrammatic approach which allows to introduce light-front valence quark and residual wave functions. The model allows us to obtain a new relation between the position of the peak of $xq_V(x)$ distribution of the valence quark and the effective mass of the residual system, $m_R$: $x_{peak} approx {1over 4} (1-{m_Rover m_N})$ and naturally explains the difference in the peak positions for d- and u- quarks due to expected larger residual mass in the case of valence d- quark distribution. The parameters of the model are fixed by fitting the calculated valence quark distributions to the phenomenological parameterizations. This allowed us to estimate the total contribution due to quark-quark correlations which are expected to dominate at high x. The fit allowed also to obtain the $Q^2$ dependence of the mass of the residual system and its effective size which gives a new insight on the effects of the QCD evolution on strongly interacting mean field of the nucleon. Finally, the evaluated parameters of non-perturbative wave functions of valence 3q- and residual system allow them to be used in calculations of other observables such as nucleon form factors, generalized partonic and transverse momentum distributions.
Moments of the generalized parton distributions of the nucleon, calculated with a mixed action of domain wall valence quarks and asqtad staggered sea quarks, are presented for pion masses extending down to 359 MeV. Results for the moments of the unpolarized, helicity, and transversity distributions are given and compared to the available experimental measurements. Additionally, a selection of the generalized form factors are shown and the implications for the spin decomposition and transverse structure of the nucleon are discussed. Particular emphasis is placed on understanding systematic errors in the lattice calculation and exploring a variety of chiral extrapolations.
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