Nonlinear corrections to the DGLAP equations; looking for the saturation limits

The effects of the first nonlinear corrections to the DGLAP equations are studied in light of the HERA data. Saturation limits are determined in the DGLAP+GLRMQ approach for the free proton and for the Pb nucleus.The effects of the first nonlinear corrections to the DGLAP equations are studied in light of the HERA data. Saturation limits are determined in the DGLAP+GLRMQ approach for the free proton and for the Pb nucleus.The effects of the first nonlinear corrections to the DGLAP equations are studied in light of the HERA data. Saturation limits are determined in the DGLAP+GLRMQ approach for the free proton and for the Pb nucleus

Production Associated to Rare Events in High Energy Hadron-Hadron Collisions

At very high energy the same universal relation between the multiparticle or the transverse energy distribution associated to a rare event $C$, $P_C$ and the corresponding minimum bias distribution P, $P_C(\nu)\equiv \nu/ P(\nu)$, $\nu\equiv n$ or $E_T$ works for nucleus-nucleus collisions as well as for hadron-hadron collisions. This suggests that asymptotically, all hadronic processes are similar.Comment: 9 pages, 4 Postscript figure

Counting valence quarks at RHIC and LHC

We consider the Nuclear Modification Ratios in heavy ion collisions, R_CP and R_AA, in the region of intermediate transverse momentum, and study the dependency upon the constituent quark composition of the observed hadron. Adopting a two component recombination/fragmentation model, validated by experimental information from STAR and PHENIX, we show that a clear distinction is predicted for the f0(980) between the assumptions of $s\bar s$ or diquark-antidiquark content.Comment: 14 pages, 11 eps figures, added figures and minor corrections, to appear in Phys. Lett.

Heavy-to-light ratios as a test of medium-induced energy loss at RHIC and the LHC

The ratio of nuclear modification factors of high-$p_T$ heavy-flavored mesons tolight-flavored hadrons (heavy-to-light ratio) is shown to be a sensitive tool to test medium-induced energy loss at RHIC and LHC energies. Heavy-to-light ratios of $D$ mesons at RHIC in the region $7<p_T<12$ GeV, and of $D$ and $B$ mesons at the LHC in the region $10<p_T<20$ GeV, are proposed for such a test. Finally, the different contributions to the nuclear modification factor for electrons at RHIC are analyzed. Preliminary PHENIX and STAR data are compatible with radiative energy loss provided the contribution of electrons from beauty decays is small compared to that from charm.Comment: 5 pages, latex, 4 eps figs included using graphicx; to appear in the proceedings of 18th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions: Quark Matter 2005 (QM 2005), Budapest, Hungary, 4-9 Aug 200

Deciphering the properties of the medium produced in heavy ion collisions at RHIC by a pQCD analysis of quenched large p⊥p_{\perp} π0\pi^0 spectra

We discuss the question of the relevance of perturbative QCD calculations for analyzing the properties of the dense medium produced in heavy ion collisions. Up to now leading order perturbative estimates have been worked out and confronted with data for quenched large $p_{\perp}$ hadron spectra. Some of them are giving paradoxical results, contradicting the perturbative framework and leading to speculations such as the formation of a strongly interacting quark-gluon plasma. Trying to bypass some drawbacks of these leading order analysis and without performing detailed numerical investigations, we collect evidence in favour of a consistent description of quenching and of the characteristics of the produced medium within the pQCD framework.Comment: 10 pages, 3 figure

High transverse momentum suppression and surface effects in Cu+Cu and Au+Au collisions within the PQM model

We study parton suppression effects in heavy-ion collisions within the Parton Quenching Model (PQM). After a brief summary of the main features of the model, we present comparisons of calculations for the nuclear modification and the away-side suppression factor to data in Au+Au and Cu+Cu collisions at 200 GeV. We discuss properties of light hadron probes and their sensitivity to the medium density within the PQM Monte Carlo framework.Comment: Comments: 6 pages, 8 figures. To appear in the proceedings of Hot Quarks 2006: Workshop for Young Scientists on the Physics of Ultrarelativistic Nucleus-Nucleus Collisions, Villasimius, Italy, 15-20 May 200

Multiplicity and Transverse Energy Distributions Associated to Rare Events in Nucleus-Nucleus Collisions

We show that in high energy nucleus-nucleus collisions the transverse energy or multiplicity distribution P_C, associated to the production of a rare, unabsorbed event C, is universally related to the standard or minimum bias distribution P by the equation $P_C(\nu)={\nu\over}P(\nu)$, with $\sum P(\nu)=1$ and $\nu\equiv E_T$ or n. Deviations from this formula are discussed, in particular having in view the formation of the plasma of quarks and gluons. This possibility can be distinguished from absortion or interaction of comovers, looking at the curvature of the $J/\Psi$ over Drell-Yan pairs as a function of E_T.Comment: 8 pages, 4 Postscript figure

Nuclear Parton Distributions - a DGLAP Analysis

Nuclear parton distributions $f_A(x,Q^2)$ are studied within a framework of the DGLAP evolution. Measurements of $F_2^A/F_2^D$ in deep inelastic $lA$ collisions, and Drell--Yan dilepton cross sections measured in $pA$ collisions are used as constraints. Also conservation of momentum and baryon number is required. It is shown that the calculated $Q^2$ evolution of $F_2^{\rm Sn}/F_2^{\rm C}$ agrees very well with the recent NMC data, and that the ratios $R_f^A=f_A/f$ are only moderately sensitive to the choice of a specific modern set of free parton distributions. For general use, we offer a numerical parametrization of $R_f^A(x,Q^2)$ for all parton flavours $f$ in $A>2$, and at $10^{-6}\le x \le 1$ and $2.25 {\rm GeV}^2\le Q^2\le 10^4 {\rm GeV}^2$.Comment: Talk in Quark Matter '99, 5 pages, includes 3 eps-figure

Multiplicity distributions inside parton cascades developing in a medium

The explanation of the suppression of high-pT hadron yields at RHIC in terms of jet-quenching implies that the multiplicity distributions of particles inside a jet and jet-like particle correlations differ strongly in nucleus-nucleus collisions at RHIC or at the LHC from those observed at e+e- or hadron colliders. We present a framework for describing the medium-induced modification, which has a direct interpretation in terms of a probabilistic medium-modified parton cascade, and which treats leading and subleading partons on an equal footing. We show that our approach can account for the strong suppression of single inclusive hadron spectra measured in Au-Au collisions at RHIC, and that this implies a characteristic distortion of the single inclusive distribution of soft partons inside the jet. We determine, as a function of the jet energy, to what extent the soft fragments within a jet can be measured above some momentum cut.Comment: 5 pages, 4 eps-figures; talk given at Hot Quarks 2006, Villasimius (Sardinia, Italy), May 15-20, 200

EPS09 - a New Generation of NLO and LO Nuclear Parton Distribution Functions

We present a next-to-leading order (NLO) global DGLAP analysis of nuclear parton distribution functions (nPDFs) and their uncertainties. Carrying out an NLO nPDF analysis for the first time with three different types of experimental input -- deep inelastic $\ell$+A scattering, Drell-Yan dilepton production in p+$A$ collisions, and inclusive pion production in d+Au and p+p collisions at RHIC -- we find that these data can well be described in a conventional collinear factorization framework. Although the pion production has not been traditionally included in the global analyses, we find that the shape of the nuclear modification factor $R_{\rm dAu}$ of the pion $p_T$-spectrum at midrapidity retains sensitivity to the gluon distributions, providing evidence for shadowing and EMC-effect in the nuclear gluons. We use the Hessian method to quantify the nPDF uncertainties which originate from the uncertainties in the data. In this method the sensitivity of $\chi^2$ to the variations of the fitting parameters is mapped out to orthogonal error sets which provide a user-friendly way to calculate how the nPDF uncertainties propagate to any factorizable nuclear cross-section. The obtained NLO and LO nPDFs and the corresponding error sets are collected in our new release called {\ttfamily EPS09}. These results should find applications in precision analyses of the signatures and properties of QCD matter at the LHC and RHIC.Comment: 34 pages, 16 figures. The version accepted for publicatio