Thermal Recombination: Beyond the Valence Quark Approximation

Quark counting rules derived from recombination models agree well with data on hadron production at intermediate transverse momenta in relativistic heavy-ion collisions. They convey a simple picture of hadrons consisting only of valence quarks. We discuss the inclusion of higher Fock states that add sea quarks and gluons to the hadron structure. We show that, when recombination occurs from a thermal medium, hadron spectra remain unaffected by the inclusion of higher Fock states. However, the quark number scaling for elliptic flow is somewhat affected. We discuss the implications for our understanding of data from the Relativistic Heavy Ion Collider.Comment: 5 pages, 5 figure

Polarized rho mesons and the asymmetry between Delta d^bar(x) and Delta u^bar(x) in the sea of the nucleon

We present a calculation of the polarized rho meson cloud in a nucleon using time-ordered perturbation theory in two different variants advocated in the literature. We calculate the induced difference between the distributions Delta d^bar(x) and Delta u^bar(x). We use a recent lattice calculation to motivate an ansatz for the polarized valence quark distribution of the rho meson. Our calculations show that the two theoretical approaches give vastly different results. We conclude that Delta d^bar(x) - Delta u^bar(x) can be of relevant size with important consequences for the combined fits of polarized distribution functions.Comment: 14 pages LaTeX, 8 figures; v3: some minor changes; this preprint supports the version to appear in Phys. Lett. B with an additional appendi

Correlations in the Parton Recombination Model

We describe how parton recombination can address the recent measurement of dynamical jet-like two particle correlations. In addition we discuss the possible effect realistic light-cone wave-functions including higher Fock-states may have on the well-known elliptic flow valence-quark number scaling law.Comment: 4 pages, two figures, proceedings of the 18th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions: Quark Matter 2005 (QM 2005), Budapest, Hungary, 4-9 Aug 200

Resummation of nuclear enhanced higher twist in the Drell Yan process

We investigate higher twist contributions to the transverse momentum broadening of Drell Yan pairs in proton nucleus collisions. We revisit the contribution of matrix elements of twist-4 and generalize this to matrix elements of arbitrary twist. An estimate of the maximal nuclear broadening effect is derived. A model for nuclear enhanced matrix elements of arbitrary twist allows us to give the result of a resummation of all twists in closed form. Subleading corrections to the maximal broadening are discussed qualitatively.Comment: 10 pages, 5 figures; v2: minor changes in text, acknowledgement added; v3: mistake in fig. 1 correcte

Strange prospects for LHC energies

Strange quark and hadron production will be studied at the Large Hadron Collider (LHC) energies in order to explore the properties of both pp and heavy-ion collisions. The ALICE experiment will be specifically efficient in the strange sector with the identification of baryons and mesons over a wide range of transverse momentum. Dedicated measurements are proposed for investigating chemical equilibration and bulk properties. Strange particles can also help to probe kinematical regions where hard processes and pQCD dominate. We try to anticipate here several ALICE analyses to be performed as the first Pb--Pb and pp data will be available.Comment: 5 pages, 2 figures. To appear in the proceedings of Hot Quarks 2006, Villasimius, Italy, 15-20 May 200

Search for the onset of baryon anomaly at RHIC-PHENIX

The baryon production mechanism at the intermediate $p_T$ (2 - 5 GeV/$c$) at RHIC is still not well understood. The beam energy scan data in Cu+Cu and Au+Au systems at RHIC may provide us a further insight on the origin of the baryon anomaly and its evolution as a function of $\sqrt{s_{NN}}$. In 2005 RHIC physics program, the PHENIX experiment accumulated the first intensive low beam energy data in Cu+Cu collisions. We present the preliminary results of identified charged hadron spectra in Cu+Cu at $\sqrt{s_{NN}}$ = 22.5 and 62.4 GeV using the PHENIX detector. The centrality and beam energy dependences of (anti)proton to pion ratios and the nuclear modification factors for charged pions and (anti)protons are presented.Comment: 5 pages, 9 figures, proceedings for Hot Quarks 2006 workshop, Villasimius, Sardinia, Italy, May 15 - 20, 2006. Proceedings of the conference will be published in The European Physical Journal

Universal behavior of baryons and mesons' transverse momentum distributions in the framework of percolation of strings

In the framework of percolation of strings, we present predictions for the $R_{AA}$ and $R_{CP}$ for mesons and baryons and for $\bar{p}/\pi^{0}$ ratios at LHC energies.Comment: Presented at "Heavy Ion Collisions at the LHC: last call for predictions", Geneva Switzerland, May 14th-June 8t

Bulk matter physics and its future at the Large Hadron Collider

Measurements at low transverse momentum will be performed at the LHC for studying particle production mechanisms in $pp$ and heavy-ion collisions. Some of the experimental capabilities for bulk matter physics are presented, focusing on tracking elements and particle identification. In order to anticipate the study of baryon production for both colliding systems at multi-TeV energies, measurements for identified species and recent model extrapolations are discussed. Several mechanisms are expected to compete for hadro-production in the low momentum region. For this reason, experimental observables that could be used for investigating multi-parton interactions and help understanding the "underlying event" content in the first $pp$ collisions at the LHC are also mentioned.Comment: 6 pages, 7 figures. To appear in the proceedings of Hot Quarks 2008, Estes Park, Colorado, 18-23 August 200

Jet hadrochemistry as a characteristics of jet quenching

Jets produced in nucleus-nucleus collisions at the LHC are expected to be strongly modified due to the interaction of the parton shower with the dense QCD matter. Here, we point out that jet quenching can leave signatures not only in the longitudinal and transverse jet energy and multiplicity distributions, but also in the hadrochemical composition of the jet fragments. In particular, we show that even in the absence of medium effects at or after hadronization, the medium-modification of the parton shower can result in significant changes in jet hadrochemistry. We discuss how jet hadrochemistry can be studied within the high-multiplicity environment of nucleus-nucleus collisions at the LHC.Comment: 15 pages, 7 figures, LaTe

Initial-State Interactions in the Unpolarized Drell-Yan Process

We show that initial-state interactions contribute to the $\cos 2 \phi$ distribution in unpolarized Drell-Yan lepton pair production $p p$ and $p \bar p \to \ell^+ \ell^- X$, without suppression. The asymmetry is expressed as a product of chiral-odd distributions $h_1^\perp(x_1,\bm{p}_\perp^2)\times \bar h_1^\perp(x_2,\bm{k}_\perp^2)$, where the quark-transversity function $h_1^\perp(x,\bm{p}_\perp^2)$ is the transverse momentum dependent, light-cone momentum distribution of transversely polarized quarks in an {\it unpolarized} proton. We compute this (naive) $T$-odd and chiral-odd distribution function and the resulting $\cos 2 \phi$ asymmetry explicitly in a quark-scalar diquark model for the proton with initial-state gluon interaction. In this model the function $h_1^\perp(x,\bm{p}_\perp^2)$ equals the $T$-odd (chiral-even) Sivers effect function $f^\perp_{1T}(x,\bm{p}_\perp^2)$. This suggests that the single-spin asymmetries in the SIDIS and the Drell-Yan process are closely related to the $\cos 2 \phi$ asymmetry of the unpolarized Drell-Yan process, since all can arise from the same underlying mechanism. This provides new insight regarding the role of quark and gluon orbital angular momentum as well as that of initial- and final-state gluon exchange interactions in hard QCD processes.Comment: 22 pages, 6 figure