(1) Di-hadron azimuthal correlation and Mach-like cone structure in parton/hadron transport model (Theory)

Guoliang Ma  (co-authors:S. Zhang, Y. G. Ma , H. Z. Huang, X. Z. Cai)

Shanghai Institute of Applied Physics ,P.R.CHINA


In a framework of a multi-phase transport model with both partonic  and hadronic interactions,  azimuthal correlations between trigger  particles and associated scattering particles ($3< p^{trig}_T< 6$  GeV/$c$ and $0.15< p_{T} < 3$ GeV/$c$, or  $2.5< p^{trig}_T<$ 4  GeV/$c$ and $1< p_{T} < 2.5$ GeV/$c$) in Au + Au collisions at  $\sqrt{s_{NN}}$ = 200 GeV/$c$ have been studied by the  mixing-event technique and the Mach-like structure has been  observed in correlation function for central collisions. By  comparing the scenarios with and without parton cascade/hadronic  rescattering, it is shown that both partonic and hadronic  dynamical mechanisms contribute to the Mach-like structure of the  scattered particle correlations. It was particularly  pointed out  that the contribution of hadronic dynamical process can not be  ignored in the emergence of Mach-like correlations between the  soft scattered associated hadrons. However, only hadronic  rescattering can not reproduce the amplitude of Mach-like cone on  away side, therefore parton cascade process is responsible to  enhance larger amplitude of Mach-like cone on away side. In  addition, it was found that both the associated multiplicity and  the magnitude sum of $p_{T}$ decrease with impact parameter but  $\langle p_{T} \rangle$ increases with impact parameter within  string melting (parton cascade) model.(Please see nucl-th/0601012 for the detail.)



(2) Parton Cascade: A tool for studying partonic dynamics in ultrarelativistic  heavy-ion reactions (Theory)

Zhe Xu  (co-authors:Andrej El, Jens Fiedler, Oliver Fochler, Kai Gallmeister and  Carsten Greiner)

Institut fuer Theoretische Physik, Johann Wolfgang Goethe Universitaet Frankfurt, Germany


We report the status of the present investigations of partonic dynamics in ultrarelativistic heavy-ion reactions using a microscopical 3+1 dimensional parton cascade including pQCD gluonic inelastic gg<->ggg scatterings. The major emphasis is put on the understanding of the dominant role of gg<->ggg scatterings in thermalization and its dependence on the choosen initial conditions of partons from the minijets production and a Color Glass Condensate. We also show the recent results concerning elliptic flow and jet-quenching for Au+Au collisions at RHIC energy.


(3) No sudden drop of J/psi in central Au+Au collisions at RHIC (Theory)

Xiao-Ming Xu  (co-authors:)

Shanghai University


J/psi's are dissociated by gluons in quark-gluon matter and hadrons  in hadronic matter. This causes suppression of J/psi observed in RHIC Au-Au collisions. However, the suppression does not attribute to a sudden drop of data in central collisions as shown   by the data in the two rapidity regions of PHENIX detectors. Such  behavior is a result of J/psi production from gluon matter which is so large in some momentum region as to compensate part of the J/psi amount reduced by the collisions of the gluons and the hadrons.



(4) Two-Particle Green's Functions in the Study of Heavy Ions Collisions (Theory)

Koshelkin  (co-authors:)

Moscow Institiute for Physics and Engineering


The formalism of two-particle Green's functions  is a natural tool  in the study of heavy ion collisions since the four-point Green's  functions carry direct information about the interaction and  correlation of two interacting particles in matter. The formalism  is developed  for the two-particle Green's functions in  non-equilibrium matter. The set of the exact equation determining  such functions is derived. The found equations is solved  in the  gas approximation. The obtained solution has the pole  corresponding to the bonding state of  two particle  in the  matter. The production of dileptons is calculated in two loops in  the developed method in the case of  equilibrium matrer. It is  shown that the rate of dileptons depends strongly on the  occurrence of bonding state of two particle in the matter at given  temperature.


(5) Influence of Interference Effects on Dielepton Production in Strong Interacting Matter (Theory)

Koshelkin  (co-authors:)

Moscow Institiute for Physics and Engineering


We study dilepton production by sets of interacting particles in  matter in the formalism of two-particle Green's functions. In the  framework of the certain models determining the interaction of the  particles in the matter the rate of dileptons is calculated. It is  shown the interference results in increasing the dilepton rate.  The magnitude of the  increasing depends strongly on both the  temperature of the matter and  the characteristics of the  interaction of particles therein. Particular, the mentioned  increasing appears to be strong when the interacting particles are  scattered on small angles while it not too dramatic in the case of  isotropic scattering of the particles in the matter.



(6) Extract charm cross section from its semileptonic decay at RHIC (Experiment)

Yifei Zhang  (co-authors:Haidong Liu*, Chen Zhong**, Zhangbu Xu***)



In relativistic heavy-ion collisions, charm quarks are believed to be produced at early stage via initial gluon fusions and their production cross section can be evaluated by perturbative QCD. The interactions of heavy quark with the medium provide a unique tool for probing the early stage of the hot and dense matter. The measurement of leptons from heavy-flavor hadron decays can provide information on heavy quark production and its subsequent reactions in such collisions. Study of the binary-collision scaling ($N_{bin}$) properties of the charm total cross section can test if heavy-flavor quarks as a probe are produced exclusively at the initial impact.       In this talk, we propose a sensitive measurement of the charm total cross section at RHIC through low momentum muon identification from charm semileptonic decay. The effects of the form factor of the charm semileptonic decay on extracting the total charm cross section and on the shape of the lepton spectra are also discussed.   *     USTC/BNL/LBNL  **    SINAP/BNL  ***   BNL


(7) The Rapidity Twist : A Tomographic Signature of Hydro Initial Conditions at RHIC (Theory)

Azfar Adil  (co-authors:Miklos Gyulassy, Tetsufumi Hirano)

Columbia University


Independent experimental constraints on the initial condition assumed in hydrodynamics to predict collective flow in Au+Au at 200 AGeV are essential to strengthen the case for the ``perfect fluid'' property of deconfined quark-gluon matter.  We propose a 3D jet tomographic test of possible novel initial surface geometries predicted by a Color Glass Condensate (CGC) model of initial conditions.  We show that high $p_T$ and rapidity, $\eta$,  differential directed flow $v_{1}(p_{T}>6,|\eta|>1)$ is sensitive to the generic rapidity twist of the bulk low $p_T$ matter in the %$(x_\perp,\eta)$ reaction plane and can differentiate between conventional diffuse Glauber surfaces and sharper surfaces possible in some parametrizations of the CGC.



(8) Heavy quark jet quenching with collisional plus radiative energy loss and path length fluctuations (Theory)

Simon Wicks  (co-authors:W Horowitz, M Djordjevic and M Gyulassy)

Columbia University


Radiative energy loss cannot account for the observed suppression of (single non-photonic) electrons, as long as the QGP opacity is computed perturbatively with the global entropy constraints imposed by the observed dNch/dy~1000. We show that perturbative collisional energy loss that was previously neglected is comparable to radiative loss for both light and heavy jets, and may in fact be the dominant mechanism for bottom quarks. Predictions taking into account both radiative and collisional losses  significantly reduce the discrepancy with data. In addition to elastic energy loss, it is critical to include jet path length fluctuations to account for the observed pion suppression as well.


(9) Elastic Energy Loss is Dead ... Long Live Elastic Energy Loss (Theory)

Azfar Adil  (co-authors:M. Gyulassy, W. Horowitz, S. Wicks)

Columbia University


We analyze the claim of Peigne et al. that elastic energy loss can be neglected in the calculation of jet energy loss in nuclear collisions.  We isolate the partial radiative and elastic energy  contributions in the classical formulas used. The finite formation time needed to build up medium resistance is discussed.



(10) Overcoming the Fragility of Radiative Energy Loss (Theory)

William Horowitz  (co-authors:Simon Wicks and Miklos Gyulassy)

Columbia University


Eskola et al. suggested that jet quenching becomes insensitive to the opacity of the quark-gluon plasma as the model-determined pion nuclear modification factor RAA is driven down to experimentally observed levels.  This has led to the pessimistic belief that high transverse momentum jets are a "fragile" hard probe of the medium.  We show, however, that this fragility occurs only when the dominant quenching mechanism is induced radiative energy loss coupled with geometric path length fluctuations; by including the previously neglected elastic energy loss with the DGLV radiative energy loss in a model with gluon number- and geometric path length-fluctuations one overcomes the fragility and is led to a rather robust sensitivity to the plasma opacity at RHIC RAA values.  Moreover, this combined approach results in a possible perturbative solution to the apparent entropy problem posed by the large suppression observed in the non-photonic electron RAA while preserving consistency with the pion quenching levels.  Higher order Fourier moments of the single inclusive suppression pattern and dijet correlations provide important additional consistency checks on this pQCD-based approach to jet tomography.


(11) Jet properties from di-hadron correlations in p+p collisions at \sqrt{s}=200 GeV (Experiment)

Jan Rak  (co-authors:PHENIX collaboration)

JYFL/HIP Finland and UNM USA


The properties of jets produced in p+p collisions at \sqrt{s}=200 GeV are measured using the method of two particle correlations. The trigger particle is a leading particle from a large transverse momentum jet while the associated particle comes from either the same jet or the away-side jet. The width of the away-side peak is shown to be a convolution of the jet fragmentation transverse momentum j_T with the fragmentation variable, z, and the partonic transverse momentum, k_T.  Extraction of these quantities from the combined analysis of the single inclusive and trigger associated distributions will be discussed.



(12) Quark-quark double scattering and modified (anti-)quark fragmentation funcitons (Theory)

Ben-Wei Zhang  (co-authors:Xin-Nian Wang and Andreas Schaefer)

Institute of Particle Physics, Central China Normal University


Quark-quark double scattering in nuclei and its contribution to quark and anti-quark fragmentation functions have been studied under the asumption of generalized factorization of the relevant twist-four  processes. It is shown that quark-quark double scattering processes will mix quark and gluon fragmentation functions and the resulting modifications to quark and anti-quark fragmentation functions are  different. We demonstrate that this difference may account for the  significant differences between the multiplicity ratios for positive and  negative hadrons as observed by HERMES.


(13) Two-particle azimuthal correlations at high transverse momentum in Pb-Au at 158 AGeV/c (Experiment)

Mateusz Ploskon  (co-authors:CERES Collaboration)

Frankfurt University, Germany


Two-particle azimuthal correlations at high transverse momentum in Pb-Au at 158 AGeV/c    The analysis of the two-particle azimuthal angular correlations at high transverse momentum from the Pb+Au collisions at 158 AGeV/c at SPS reveals substantial modifications of the away-side peak as compared to the Gaussian shaped distributions from the p+p reactions. The data recorded with the CERES Time-Projection Chamber, which provides excellent tracking efficiency, suggest that the observed significant modification of the back-to-back structure implies fairly large re-interactions of the scattered partons within the medium. It is most interesting that these findings at top SPS energy show features qualitatively similar to the results obtained by the PHENIX collaboration from Au+Au collisions at sqrt(200) GeV/c and Cu+Cu collisions at sqrt(62) GeV/c at RHIC [1]. We will discuss the centrality dependent (0-5%, 5-10%, 10-20% of the most central collisions) conditional (di-)jet yields reconstructed within the CERES acceptance for similar transverse  momentum windows as recently investigated by the RHIC experiments (1 > pt_assoc > 2.5 > pt_trigger > 4 GeV/c) [1,2,3].    [1] S. S. Adler (PHENIX Collaboration) [nucl-ex/0507004]  [2] M. McCumber and J. Frantz (PHENIX Collaboration) [nucl-ex/0511048]  [3] J. Adams et al. (STAR Collaboration) Phys.Rev.Lett. 95 152301 (2005) [nucl-ex/0501016]



(14) Perspectives on beauty production measurement in ALICE at the LHC (Experiment)

Rachid GUERNANE  (co-authors:)

Laboratoire de Physique Corpusculaire de Clermont-Ferrand, CNRS-IN2P3


Open heavy flavor production is considered to be a valuable probe for studying QCD properties of the dense medium formed in heavy ion collisions. Heavy quarks, once produced in the early stages of the collision, are expected to rescatter and lose energy from gluon radiations traversing the surrounding matter. In addition, heavy flavor production measurements in p-p and p-A will help to understand both perturbative and nonperturbative regimes of QCD in a novel kinematic region of high virtuality and small-x becoming accessible at LHC energies. LHC energy domain will provide a unique opportunity to measure beauty production in heavy ion collisions. The large expected production cross sections will ensure high statistics data samples enabling precise measurements. ALICE is a general-purpose experiment equipped to reconstruct, among other signals, both electrons and muons from heavy quark semileptonic decays in p-p, p-A and A-A collisions both in its central barrel and forward muon spectrometer. In this talk, we will review the most recent feasibility studies for ALICE measurements of beauty production in central Pb-Pb collisions at the LHC using semileptonic decays.


(15) Study of the medium modification of the away side jet in AuAu/CuCu collisions in PHENIX (Experiment)

Jiangyong Jia  (co-authors:)

Columbia University


Jiangyong Jia ,Columbia University, for the PHENIX Collaboration    Two particle correlations in relative azimuth and pseudorapidity are an excellent probe of the dense medium created in heavy-ion collisions. Modifications of away side jet shape and strength, relative to pp collisions, can give insight to the opacity of the medium and how the lost energy of the jet is redistributed into the medium. Detailed jet tomography study via hadron-hadron and photon-hadron at high pT are made possible with the large AuAu and CuCu datasets collected by PHENIX in 2004 and 2005    We present the results of the di-hadron correlation in \Delta\phi for both AuAu and CuCu collisions. We present the systematic evolution of both the shape and the yield of the away side jet as function of centrality,trigger pT and associated hadron pT, and discuss their implications on the roles of various proposed mechanisms. We then focus on the modifications of the away side jet yield (I_{AA}) at high pT. We find that the away side jet structures are clearly visible, but their magnitudes are suppressed in the  central AuAu and CuCu collisions.



(16) Identified baryon and meson transverse momentum distributions up to 12 GeV/$c$ from Au+Au collisions at $\sqrt{s_{_{NN}}} = 200$ GeV (Experiment)

Lijuan Ruan (for the STAR Collaboration)  (co-authors:)

Lawrence Berkeley National Laboratory


Ultra-relativistic heavy ion collisions provide a unique  environment to study properties of strongly interacting matter in  the extreme condition of high temperature and high energy density.  The bulk particle production is dominated by soft QCD processes  and the transverse momentum ($p_T$) distribution is well described  by hydrodynamical models at $p_T{}^{<}_{\sim}$~2 GeV/$c$. At  intermediate $p_T$ (2${}^{<}_{\sim}p_T{}^{<}_{\sim}$5~GeV/$c$),  distinct patterns of meson and baryon production have been  observed, which is consistent with the coalescence of constituent  quarks at hadronization from a collective partonic system.  Besides, when hard partons traverse the medium, they lose energy  and fragment into hadron at high $p_T$  ($p_T{}^{>}_{\sim}5$~GeV/$c$). Due to the color charge difference,  energetic gluons and quarks are expected to lose energy  differently in the medium. High $p_T$ protons ($p$) and pions  ($\pi^{\pm}$) at RHIC are believed to have significant  contributions from quark fragmentation while anti-protons  ($\bar{p}$) are mostly from gluon fragmentation. Therefore, the  system size dependence of $\bar{p}/p$ and $\bar{p}/\pi$ ratios in  different systems should shed light on the possible color charge  dependence of energy loss. In this talk, we present the $p_T$  distributions of $\pi^{\pm}$, $p$ and $\bar{p}$, their nuclear  modification factors and particle ratios from 200 GeV Au+Au  collisions up to 12~GeV/$c$. We discuss the possible transition  between jet dominant fragmentation and quark coalescence at  hadronization, the color charge dependence of the energy loss, and  the fragmentation functions at high $p_T$.


(17) Centrality Dependence of Nuclear Modification Factor (Theory)

D.C. Zhou and W.C. Xiang  (co-authors:)

Institute of Particle Physics Huazhong Normal University


Centrality dependence of nuclear modification factor at high pt above 4GeV/c is studied in nucleus-nucleus collisions at sqrt(s_NN)=200GeV. An factorial function, F(b), is introduced into the high pt distribution of neutral pions induced in nucleon-nucleon collisions, which makes the nuclear modification factor R_{AA}(pt,b) depending on colliding centrality. Our calculation results show that the value of R_{AA} is approximately independent of pt above 4GeV/c and moreover are good consistent with Phenix data in all centrality classes.




Victor Goncalves  (co-authors:M. V. T. Machado)



In this contribution we study the photoproduction of heavy quarks and vector mesons in the coherent proton-nucleus (pA) interactions for RHIC and LHC energies and analyze if these processes can be used to determine the QCD dynamics at high energies. The integrated cross section and rapidity distribution are estimated using the Color Glass Condensate (CGC) formalism. A comparison with the linear dynamics predictions is also presented. Our results indicate that the nonlinear dynamics can be proven in those reactions, which are well suited for studing saturation effects.


(19) Performances of the ALICE experiment at LHC for photon and photon-jet physics. (Experiment)

Christelle Roy  (co-authors:ALICE Collaboration)



The high transverse momentum performances of the ALICE experiment at LHC are illustrated through photon and photon-jet measurements. We discuss detector capabilities and their relevance to various aspects of physics. ALICE will be  equipped by two neutral particle detectors, PHOS, a high resolution photon spectrometer, and EMCal, a large acceptance electromagnetic calorimeter. The performances will be discussed in terms of pt reach, jet triggering, and jet correlations.



(20) What does the $rho$ do? Lessons from NA60's di-muon measurement. (Theory)

Joerg Ruppert  (co-authors:Thorsten Renk, Berndt Mueller)

Duke University


The NA60 experiment has studied low mass muon pair production in In-In collisions at 158 AGeV with unprecedented precision. We present a systematic study of various models proposed for in-medium changes of the $\rho$-meson in comparison with the data. We especially show that the NA60 measurements are a proof of considerable in-medium broadening effects of the $\rho$-meson. No such signals are seen for the $\phi$-meson. We also studied what the data tell about possible scaling laws of the $\rho$-meson mass with the chiral condensate  as e.g. Brown-Rho scaling. We argue that a more sophisticated application of BR scaling which is compatible with a QCD sum rule analysis is not  in striking disagreement with the data, contrary to what was present at QM 2005. Furthermore, we present simulations showing what new insights a measurement of low mass muon pair production in Pb-Pb collisions at 158 AGeV with the NA60 detector could provide.


(21) Heavy Quarkonia above Deconfinement (Theory)

Agnes Mocsy  (co-authors:P. Petreczky and J. Casalderey-Solana)



We analyze the heavy quarkonia correlators and spectral functions above deconfinement in potential models with a temperature dependent screened Cornell potential and with the lattice internal energy used as the potential. Our results show that while potential models reproduce qualitative features obtained on the lattice, such as the survival of the 1S state well above deconfinement, there is no agreement with the lattice correlators. The discrepancy is greater when using the lattice internal energy as the potential.    We then show in a simple model that the shift in the continuum with increasing temperature can compensate for the melting of higher excited states, reproducing the spectral functions and correlators from the lattice. We further discuss the detailed effect of the continuum as determined in a non-relativistic approach by evaluating Green s functions.



(22) Crystalline three flavor Quark Matter (Theory)

Rishi Sharma  (co-authors:Krishna Rajagopal)



The nature of cold three-flavor quark matter at the large (but not  asymptotic) densities relevant to neutron star phenomenology is  not resolved. The gapless CFL phase, which was previously believed to  have the lowest free energy, was recently shown to be unstable in the  sense that some phase must have lower free energy. The nature of the instability motivates the hypothesis that the stable phase is a crystalline color superconductor. In this talk, which reports on work done in collaboration with Krishna Rajagopal, I will present the calculation of the free energies of three-flavor crystalline color superconductors for realistic crystal structures in the Ginsburg-Landau approximation. All previous work on this subject neglected the strange quarks; we include them,  with qualitative consequences. We calculate free energies for many  crystal structures, and find two (based upon cubic symmetry) that have  lower free energy than the gapless CFL phase over the lower density half of the relevant parameter space.


(23) High pT Lambda and K short v2 from Au+Au collisions at RHIC (Experiment)

Yan Lu  (co-authors:)



High pT Lambda and K short v2 from Au+Au collisions at RHIC    Y. Lu* for the STAR Collaboration    Anisotropic flow, described by the parameter v1, v2, v4 and so on, develops at a relatively early stage of nuclear collisions. It is therefore very useful for studying partonic dynamics in collisions at RHIC. We will present STAR's measurements of the elliptic flow parameter v2 for Lambda and K short in Au+Au collisions at 200 GeV. The high statistics 200 GeV measurements have been extended up to transverse momentum pT ~ 8 GeV/c, which is highest transverse momentum ever reached for the identified v2 measurements.  We observe: (i) At low pT, the ordering of Lambda and K short v2 is consistent with that predicted by hydrodynamic models. At a given pT, the heavier the hadron, the smaller the value of v2. (ii) In the intermediate pT region (pT from 2-5 GeV/c), we observe departures from the hydrodynamic trend. There, the v2 of baryons is higher than that of mesons. The trend indicates scaling according to the number of constituent quarks. (iii) In the high pT region, all v2 values seem to decrease. These measurements indicate that 'collective flow' has developed prior to hadronization and the partons are interacting over distances much larger than the size of a nucleon.      In this talk, the centrality dependence of Lambda and K short v2 will also be presented. In addition, we will compare our v2 results with multi-strange hadrons Cascade and Omega. Finally, comparisons with zero-viscosity hydrodynamic calculations will be discussed.



(24) J/psi production relative to the reaction plane in Pb-Pb collisions at CERN SPS (Experiment)

F. Prino  (co-authors:NA50 collaboration)

INFN Torino


The results of a measurement of J/psi production in  Pb-Pb collisions at 158 GeV/nucleon as a function of  the J/psi azimuthal angle relative to the reaction plane  are presented.  Different physical mechanisms, such as nuclear absorption and  break-up on co-moving hadrons, are expected to introduce anisotropy in J/psi azimuthal distributions.  The present analysis has been performed on the data sample  collected in year 2000 by the NA50 Collaboration, under improved  experimental conditions with respect to previous years.  The reaction plane is estimated from the azimuthal distribution  of neutral transverse energy in the electromagnetic calorimeter.  The number of J/psi's in different bins of azimuthal angle  relative to the reaction plane as well as the Fourier coefficients  v1 and v2 are presented.


(25) Medium modification of dihadron fragmentation functions in Au-Au collisions (Experiment)

Oana Catu  (co-authors:STAR Collaboration)

Yale University


Medium modification of jet fragmentation functions is expected to occur in heavy ion collisions due to parton energy loss. From an experimental point of view, one way to investigate this phenomenon is to use azimuthal correlations of high transverse momentum (p_T) hadrons. The purpose of this work is to study the influence of the hot medium created at RHIC on the dihadron fragmentation function. We investigate the correlations as a function of p_T of the trigger particles and the associated ones in Au+Au collisions at sqrt(s_NN) = 200 GeV as measured in STAR. The effect on our measurement of the large delta eta correlations observed in heavy-ion collisions will also be explored. Since charge ordering is an intrinsic characteristic of parton fragmentation, we investigate the ratio of opposite-sign pairs to same-sign pairs in heavy-ion collisions as compared to Pythia simulations shown in previous studies to describe charge ordering in p-p collisions for lower p_T. This study of the  modification of jet properties in the hot medium will help put constraints on the nature and magnitude of energy loss and therefore provide information on the medium created in high energy heavy-ion collisions.



(26) Charmonium, charm and beauty production at HERA-B (Experiment)

Antonio Zoccoli  (co-authors:HERA-B Collaboration)

University of Bologna


HERA-B is a fixed target experiment at the 920 GeV HERA proton beam at DESY which uses a variety nuclear targets. A di-lepton trigger can select events containing leptonic $J/\psi$ decays. During the 2002/2003 HERA-B run, 150 million di-lepton triggers and 200 million minimum bias triggers were recorded.    About 300.000 leptonic $J/\psi$ decays ($\sim 170.000 J/\psi  \rightarrow \mu^+\mu^-$ and $\sim 130.000 J/\psi \rightarrow e^+e^-$)  were acquired with the di-lepton trigger. These samples allow for the first time the study of charmonium production (such as $J/\psi$,  $\psi$' and $\chi_c$ states) in the negative Feynman x region ($x_F$), and will provide important input for testing charmonium production mechanisms.  Moreover clean samples of $\mathrm{D0\rightarrow K^- \pi^+}$, $\mathrm{D^+ \rightarrow K^- \pi^+ \pi^+}$, $\mathrm{D^{*+} \rightarrow D0 \pi^+}$ and $\mathrm{J/\psi \rightarrow \mu^+ \mu^-}$  from the minimum bias sample have been reconstructed.    Results will be presented on the nuclear dependence of charmonium production, on $J/\psi$ polarization, on $\chi_c$ and $\psi$', on open charm production and on the determination of the $b \bar b$ cross section in proton-nucleus collisions.


(27) Direct Photon Production in Au+Au Collisions at RHIC-PHENIX (Experiment)

Tadaaki Isobe for the PHENIX collaboration  (co-authors:)

University of Tokyo


Since photons do not interact strongly, direct photons are a powerful probe to study the initial state of matter produced from relativistic heavy ion collisions.  They are emitted from all the states such as the initial state, the Quark-Gluon Plasma (QGP), and the final hadron-gas state.    We present a systematic study of direct photon production in Au+Au collisions. PHENIX recorded a high-statistics Au+Au data set in the 2004 Run. The new data set allows us to measure direct photons beyond pT=10GeV/c and also at intermediate pT where thermal photons and photons from jet-plasma interactions are important.



(28) Mach cones and dijets - jet quenching and fireball expansion dynamics (Theory)

Thorsten Renk  (co-authors:Kari Eskola, J rg Ruppert)

University of Jyv skyl


The angular correlations of hadrons associated with a triggered hard hadron show a rich pattern when going from low p_T to high p_T. Of prime interest is the fate of the away side parton with a trajectory through the medium of on average several fm. At low p_T, the pattern of associate hadrons can be understood in terms of Mach shocks excited by the energy lost from the away side parton. At high p_T, fluid dynamics is not applicable any more and the correlations become dominated by the punchtrough of the away side parton with subsequent fragmentation.    We present an analysis of these phenomena within a dynamical model of fireball evolution and a realistic simulation of the experimental trigger conditions. We find that the expansion dynamics of the medium is important in the understanding of long in-medium parton paths. Provided that the medium is modeled in a realistic way, we demonstrate that within a state-of-the-art radiative energy loss formalism the measured dijet yield can be explained without additional free parameters. Using information from lattice QCD about the EOS of hot QCD matter, we also demonstrate that the lower p_T correlation pattern can be understood in terms of Mach shocks induced by lost energy if the coupling of the hard parton to a sound mode is sufficiently strong. We conclude by presenting predictions for hard dihadron correlation measurements at LHC.


(29) Particle Species Dependence of Jet Fragmentation in Au+Au Collisions at PHENIX (Experiment)

Anne Sickles for the PHENIX Collaboration  (co-authors:)

Brookhaven National Lab


A surprising excess of protons at intermediate p_T, 2-5GeV/c, has been observed in Au+Au collisions at RHIC, for which the source is not known. In p+p collisions, particles at this p_T arise from jet fragmentation, however the observed baryon yield in central Au+Au collisions are not compatible with the usual jet fragmentation function.  Two particle \Delta\phi correlations are powerful probe for quantitatively understanding the modifications to jet fragmentation from interactions with the medium. Earlier studies have shown that the excess baryons do have jet-like partners, indicating a hard scattering origin. We present new results from a systematic study of two particle correlations as a function of trigger and partner particle species, charge, p_T and centrality from the high statistics Au+Au dataset. p+p collisions are also analyzed as a reference.



(30) From di-hadron correlations to parton intrinsic transverse momentum   in proton-proton collisions (Theory)

George Fai  (co-authors:P. Levai, G. Papp)

Kent State University


Jet structure has been extensively studied at RHIC recently, as a very valuable tool to explore the properties of the high-energy phase created in relativistic nuclear collisions. Two-jet events, in particular, allow the study of the centrality dependence of jet suppression (jet quenching) in d+Au and Au+Au collisions. Moreover, the width of the back-to-back peaks in the correlation between high transverse-momentum charged hadrons contains additional information already in proton-proton collisions. The width in azimuthal angle has been used at ISR and RHIC energies to learn about the fragmentation of jets initiated in hard parton collisions. Our focus here will be on the difference between the widths of the near-side and away-side peaks, which can be understood in terms of transverse momentum imbalance. This imbalance originates in the intrinsic transverse momenta of partons in the proton and in processes that complicate the 2 --> 2 skeleton kinematics. Such processes partially randomize the strong initial parton-parton correlations. We connect the measured di-hadron correlation widths to the width of the intrinsic transverse momentum distribution of partons in the proton. Our simple model is able to account for the trigger-dependence of the transverse momentum width observed in some data. We propose a new method to evaluate the data on near and away-side correlations. At $\sqrt{s} = 200$ GeV we find a value for the transverse momentum width of partons in the proton in good agreement with the value extracted from pion spectra.


(31) Formation time scaling and hadronization in cold nuclear matter (Theory)

Alberto Accardi  (co-authors:)

Iowa State U.


Hadron suppression in Deep Inelastic Scattering on nuclei (nDIS) is an important tool to study the space-time evolution of the hadronization process.  Two theoretical frameworks are presently competing to explain the observed hadron suppression: energy loss models, with hadron formation outside the nuclear medium, and hadron absorption, with hadronization starting inside the medium. Establishing the leading mechanism in nDIS is very important for a correct interpretation of jet quenching in heavy-ion collisions as a signature of the production of a Quark-Gluon Plasma.     I will show that the observed approximate A^{2/3} dependence of the hadron multiplicity ratio in nDIS cannot be used as a proof of the energy loss mechanism, as often done. More sensitive observables need to be devised.    I will then discuss a scaling behavior of the hadron multiplicity ratio. The proposed scaling variable is a function of the hadron fractional energy and of the virtual photon energy. Its functional form, which depends on a parameter $\lambda$, can be fixed by general theoretical considerations and encompasses both energy loss and hadron absorption models. The parameter $\lambda$ is fitted to HERMES experimental data and shown to favor absorption as a leading mechanism for hadron suppression as opposed to quark energy loss. Up to an overall normalization, the scaling variable can then be interpreted as a measure of the formation time of the prehadron, the color neutral precursor of the observed hadron.



(32) Heavy quark energy loss and electromagnetic response in strongly coupled super-Yang-Mills fluid (Theory)

Pavel Kovtun  (co-authors:C.Herzog, A.Karch, C.Kozcaz, A.Starinets, L.Yaffe)

KITP, UC Santa Barbara


Finite-temperature properties of certain strongly coupled  gauge theories can be analyzed by using a dual string  theory description (AdS/CFT correspondence). We present  results for energy loss by a heavy quark moving through  thermal equilibrium state of strongly coupled N=4  supersymmetric Yang-Mills (SYM) theory. The momentum drag  coefficient at strong coupling depends only weakly on the  energy of the heavy-quark probe, but depends non-trivially  on its mass. In addition, photon and dilepton emission  rates from the strongly coupled SYM fluid can be computed  by AdS/CFT methods with much less effort than is required  for weakly coupled plasmas.


(33) Away-side distribution in a parton multiple-scattering model and a background-suppressed measure (Theory)

Charles B. Chiu  (co-authors:Rudolph C. Hwa)

University of Texas at Austin


In the first part of this presentation, a model of parton multiple scattering in a dense and expanding medium is described. The trajectory of the parton recoiling against a hard parton that generates a trigger particle is traced.The recoil parton can either be absorbed or emerge on the far side with diminished momentum and at various azimuthal angle in the transverse plane. The experimental dip-bump structure at the intermediate trigger momentum can be generated in the model. As the trigger momentum increases this structure evolves into a peak. In the model the multiplicity of the away-side jet is small relative to the statistical background which includes the thermalized particles induced by the quenched partons.     In the second part of the presentation, a new measure is proposed to quantify the azimuthal distribution with the virtue that it suppresses the statistical fluctuation event-by-event, while enhancing the event-structure. This new method of analysis distinguishes clearly the one-jet from two-jet structure on the away-side without background subtraction, which is conventionally done after summing over all events. The result of the present model is analyzed based on this new approach.



(34) Dielectron production in C+C collisions with HADES (Experiment)

P. Salabura  (co-authors:HADES collaboration)

M. Smoluchowski Institute of Physics Jagiellonian University


The HADES spectrometer installed at GSI Darmstadt is devoted to study production of di-electron pairs from proton, pion and nucleus induced reactions at 1-2 AGeV.   The main goal is to search for in-medium modifications of spectral functions of the light vector meson rho/omega at moderate temperatures and nuclear matter densities.      Spectroscopy of rare lepton pairs in reactions with abundant hadron production requires an efficient electron identification. In HADES it is achieved with a large geometrical acceptance (35% for pairs), fast electron identification in hadron blind RICH accompanied by set of Pre-Shower and TimeOfFlight counters and selective multistage trigger scheme. Particles momentum is measured by a tracking system surrounding a toroidal superconducting magnet.      The detector went into operational in 2002 and since then collected data from 12C+12C collisions at 2AGeV (2002), 1AGeV (2004) and proton-proton (2004) reactions at 2.2 GeV.  The main goal of the measurement with 12C+12C system is to investigate dielectron enhancement found in 12C+12C  and 40Ca+40Ca collisions at 1 AGeV in the pioneering experiments of DLS collaboration.  In the pp collisions we have focused on exclusive and inclusive   meson production which contributes to the invariant mass range of 140< Me+e- <550 MeV/c2.    In this contribution we would like to focus on the results obtained from 12C+12C collisions at 2 AGeV and 1 AGeV. Invariant mass, rapidity and transverse momentum distributions corrected for reconstruction efficiencies will be shown and compared with calculations based on the thermal (PLUTO) and microscopic (QMD, HSD,RQMD) transport models.


(35) Charm at ALICE: a probe of the density and thermalization of the partonic medium at LHC. (Experiment)

Andrea Dainese  (co-authors:for the ALICE Collaboration)



At LHC energy, heavy quarks will be abundantly produced  and the design of the ALICE detector will allow us to  study their production using several channels.  Hard partons are sensitive probes of the medium formed  in Pb-Pb collisions as they are expected to  lose energy while propagating through the medium itself.  The study of the charm particles quenching, compared  to that of the (mostly) gluon-originated light-flavoured particles,  should enable us to test the predicted color-charge  dependence of parton energy loss.  In addition, measuring the azimuthal anisotropy of  D mesons in non-central collisions  will provide insight on the degree of  thermalization of the partonic phase (at moderate and  intermediate pT), and on the path-length dependence  of energy loss (at high pT, above 7-8 GeV/c).  Available predictions for nuclear modification factors,  heavy-to-light ratios and azimuthal  anisotropy of heavy-flavour mesons will be reviewed.  The expected capability of the ALICE experiment for  measuring the observables using fully-reconstructed  D0 and D+ mesons will be discussed.



(36) High-p_T strange particle spectra and correlations in STAR (Experiment)

Jana Bielcikova  (co-authors:STAR Collaboration)

Yale University


The wealth of data collected by the STAR experiment in p+p, d+Au and  Au+Au collisions offers the possibility to investigate in detail  strangeness production in the intermediate and high p_T regime at RHIC and to provide additional information on jet quenching, anomalous    baryon production and particle production mechanisms in general. We will discuss the nuclear modification factors of strange baryons and mesons as well as the ratios of the strange particle yields up to high p_T in order to investigate the range of anomalous baryon production.  The medium modification of the fragmentation process is further    explored by studying the trigger and associated particle dependence of two particle correlations at high p_T in both azimuthal and pseudo-rapidity space for K0S, Lambda and Antilambda particles. The larger p_T reach of the new Au+Au data sample allows us to measure the associated yield differentially in p_T. These results are compared to the proton and  pion triggered correlations as well as to fragmentation and recombination models.


(37) Do we need a new term: Formation Time of strongly interacting Quark Gluon Plasma? (Experiment)

Vlad Pantuev  (co-authors:)

Stony Brook University


We demonstate that the existance of finite formation time of strongly interacting plasma at RHIC is inevitable conclusion from recent experimental data. The absence of jet suppression at early time interval of 2-3 fm/c and total absorption after that can explain most of seen experimental features at high pt: centrality behaviour of Raa and its angular dependence in reaction plane, high azimuthal assimetry v2, no change of forward and back jet fragmentation properties, identity of mesons and baryons Raa at high pt, appearence of charm quark v2 as a consequence of geometry effect.



(38) Direct Photon Production in pp and d+Au Collisions Measured with the PHENIX Experiment (Experiment)

D. Peressounko  (co-authors:PHENIX collaboration)

RRC "Kurchatov institute"


Direct photons escape freely from the hot and/or dense matter and provide the clearest probe of the initial state of the collision as well as of its subsequent evolution. Systematic measurement of the direct photon production  in pp and d+Au gives the possibility not only to test pQCD predictions but also to estimate modifications introduced by cold nuclear matter. In addition direct photon measurement in the pp and d+Au collisions provides necessary baseline for identifying direct photons emitted by hot matter in nucleus-nucleus collisions.    PHENIX has observed a significant signal of direct photons in d+Au and pp collisions. We will present results of the measurement of direct photon production in these collisions and compare them to the theoretical predictions.


(39) Di-jet Shape Modification in Hot QCD Matter at RHIC-PHENIX (Experiment)

Paul Constantin  (co-authors:PHENIX collaboration)

Los Alamos National Lab


By 2002, the RHIC experiments established several new exciting results in the area of hadronic jet modification in hot and dense QCD media formed at RHIC: final-state leading hadron suppression, di-jet away side disappearance at high $p_T$, strong modification of the di-jet away side at intermediate $p_T$.  The much higher statistics Au+Au and Cu+Cu RHIC runs in the last two  years allow a systematic study of these phenomena. We present preliminary results on the shape analysis of di-jet induced, intermediate $p_T$ (1-5 GeV/c), di-hadron azimuthal correlations with the PHENIX detector.  A qualitatively new feature, specific only to central and mid-central heavy-ion collisions, is the double-peaked away-side structure. A systematic study of its dependence on the collision centrality, orientation to reaction plane, collision energy, and system size will be shown.



(40) Why the xE distribution triggered by $\pi^0$ does not measure the fragmentation function (Experiment)

M. J. Tannenbaum  (co-authors:)

Brookhaven National Laboratory


Due to the steeply falling power-law transverse momentum spectrum of the scattered partons, the inclusive single particle (e.g. pizero) spectrum from jet fragmentation is dominated by trigger fragments with large $\mean{z_t}\sim 0.7-0.8$, where $z_t=p_{T_t}/p_{T{\rm jet}}$ is the fragmentation variable. However, it was generally assumed, following Feynman, Field and Fox, as shown by data from the CERN-ISR experiments, that the $p_{T_a}$ ``distribution of away side hadrons from a single particle trigger [with $p_{T_t}$], corrected for $\mean{z_t}$, would be the same as that from a jet-trigger and follow the same fragmentation function as observed in $e^+ e^-$  or DIS. An attempt by PHENIX to measure the fragmentation function from the away side $x_E\sim p_{T_a}/p_{T_t}$ distribution of charged particles triggered by a $\pi^0$ in p-p collisions showed by explicit calculation that the $x_E$ distribution was actually quite insensitive to the fragmentation function.  Illustrations of the original arguments and ISR results will be given. Then the lack of sensitivity to the fragmentation function will be  explained, and an analytic formula for the $x_E$ distribution given in terms of an incomplete Gamma function, for the case where the fragmentation function is exponential. The away-side distribution has the nice property that it both exhibits $x_E$ scaling and is directly sensitive to the ratio of the away jet $\hat{p}_{T_a}$ to that of the trigger jet, $\hat{p}_{T_t}$ and thus to the relative energy loss of the two jets escaping from the medium in RHI collisions.


(41) Three-Particle Azimuthal Correlations from STAR (Experiment)

Jason Glyndwr Ulery  (co-authors:)

Purdue University


Two-particle azimuthal correlations have shown broadened and softened   away side correlations. This could be explained by different scenarios   such as: large angle gluon radiation, jets deflected by transverse   radial flow, and conical flow generated by hydrodynamic shock-waves.    Three-particle correlations are investigated to try to discriminate   between these different scenarios.  In this talk we present results for   3-article azimuthal angular correlations for a trigger particle of   $3<p_T<4$ GeV/c with two softer particles of $1<p_T<2$ GeV/c.  Results   are shown for $pp$, d+Au and Au+Au collisions at sqrt(s_NN)=200 GeV.   Implications of the results are discussed.



(42) Back-to-Back Azimuthal Correlations between Mid- and Forward-Rapidity Charged Hadrons (Experiment)

Levente Molnar for the STAR Collaboration  (co-authors:)

Purdue University


Mid-rapidity back-to-back azimuthal correlations probe di-jets originating mainly from gluon-gluon hard-scattering. Measurements of such correlations have revealed significant (gluon-)jet modification in central Au+Au collisions. Azimuthal correlations at forward-rapidity with a mid-rapidity high-pt hadron, on the other hand, are sensitive primarily to quark-gluon hard-scattering and may probe quark-jet modification in nuclear medium. In this talk, we will present new results from STAR on correlations of charged hadrons at forward rapidity in the Forward Time Projection Chambers (2.7 < |\eta| < 3.9, pT < 2 GeV/c) with high-pt charged hadrons at mid-rapidity from the main TPC (|\eta| < 0.7, pT > 3 GeV/c). Preliminary results from pp, d+Au, and Au+Au collisions at 200 GeV will be presented. Implications of the results and future perspective of such measurements will be discussed.


(43) Measurements of $\gamma$-hadron correlations at RHIC in p+p and d+Au collisions (Experiment)

Subhasis Chattopadhyay  (co-authors:STAR Collaboration)

Variable Energy Cyclotron Centre, Kolkata


One of the major results of the heavy ion program at RHIC is the discovery of jet quenching. A promising experimental probe to further explore jet-quenching is the production of hard photon-jet pairs, where the hard photon can be used to calibrate the jet energy. Gamma-jet measurements therefore hold promise to experimenatlly   access the details of medium-modified fragmentation.  Measurement of photon-tagged jets in pp and dAu collisions allow us to study the details of $\gamma$-tagged jets and serves as baseline for heavy ion collisions.                                                                                                                                  Azimuthal correlations between neutral showers produced in STAR Barrel Electromagnetic Calorimeter (BEMC) and charged particles measured using STAR-TPC have been measured. Efforts have been made to separate photon candidates from the showers produced by $\pi^0$ by using two-dimensional shower profile from Shower Maximum Detector in STAR-BEMC.                                                                                                                                  Direct photon candidates have a narrower shower profile than pi0 candidates. The near-side correlation strength can be further used to estimate the purity of the sample since direct   photons have zero associated yield. First results using this procedure on p+p and d+Au collisions will be presented and the sensitivity to the $\gamma$-jet process are explored.   Expected improvements in statistics from ongoing p+p runs and possibilities for application in Au+Au collisions will also be discussed.



(44) Hadron Correlation and Parton Recombination (Theory)

Rainer J. Fries  (co-authors:)

University of Minnesota


Recombination of quarks from a collectively expanding phase of partons has been a very successful picture to explain hadron yields, hadron ratios, and the elliptic flow measured at RHIC at intermediate transverse momentum. Recently, more and more data on hadron correlations in the same kinematic region has become available and has to be accomodated in this framework. In this talk I review the recombination model and recent efforts to describe how hadron correlations can emerge in this picture.


(45) Semi-exclusive Processes and Grey Track Production in Deep Inelastic Scattering  off  Nuclei (Theory)

C. Ciofi degli Atti  (co-authors:B. Z. Kopeliovich, Universidad Tecnica Federico Santamaria, Valparaiso, Chile)

Department of Physics University of Perugia, Perugia, Italy


Nuclear targets serve as a natural and unique analyzer of the space-time development of strong interactions at high energies. Due to Lorentz time dilation, projectile partons may keep their coherence for some time, but once they become incoherent  the cross section of final state interaction (FSI) increases. One way for experimental testing of theoretical models is the measurement of the nuclear modification factor for inclusive production of leading hadrons. The production of hadrons with large fraction  zh  of the initial parton momentum is a rare, nearly exclusive process, which has quite a specific time development. In the main bulk of events the jet energy is shared by many hadrons. We review two approaches which have been  recently pursued along this line, namely the  Semi- Exclusive DIS (SEDIS)  processes  A(e,e'B)X  [4,5], where   B is a  detected recoiling  hadron (e.g a nucleon if A=2) and   X  the   unobserved jets from hadronization,  and the  grey track  production in DIS off nuclei. Unlike the rare process of leading hadron production, both processes depend upon the   bulk  of the FSI of the nucleon debris with the  nuclear medium,  and turn out to be very sensitive to the  hadronization mechanism.  Their theoretical treatment  within a Glauber-like approach of FSI   requires an effective time-dependent nucleon debris-nucleon cross  section;  a recent model of the latter will be reviewed   and its use in the theoretical description of the two processes will be presented.



(46) Near-side Delta eta correlations of high-pt hadrons from STAR (Experiment)

Joern Putschke  (co-authors:STAR Collaboration)

Lawrence Berkeley National Laboratory


Systematic measurements of pseudorapidity (Delta eta) and azimuthal  (Delta phi) correlations between high-pt charged hadrons and  associated particles from the high statistics 200 GeV Au+Au and Cu+Cu  datasets will be presented. In previous measurements differences in  the near-side Delta Eta correlation between central Au+Au and the  lighter systems d+Au and p+p were observed, including an additional  long-range near-side correlation in Au+Au collisions.  Measurements to   characterize the properties of this long-range correlation (ridge) will be shown.   The underlying physics of these effects are not quite clear yet, and different   approaches to describe these phenomena are based on coupling of induced   radiation to longitudinal flow , on a combination of jet-quenching and strong   radial flow or on recombination of thermal partons. Systematic studies  of the dependence of the ridge properties on centrality, pt of the trigger and   associated particles as well as identified associated protons and pions  may help to distinguish between these models.



Vladymyr  Pastushenko  (co-authors:)



After creation of the Special Theory of the Relativity, the theory of gravitation in the General Theory of the Relativity has been created. After creation of the Quantum Theory of the Relativity, the theory of Quantum Gravitation has been created. The special case of Quantum Gravitation is the General Theory of the Relativity and the theory of Electro-strong Interaction. The special case of the theory of Electro-strong Interaction is equations of Maxwell. Works are represented on http://ic.km.ua/~pva .



(48) High-pt suppression and surface effects in nucleus-nucleus collisions (Theory)

Constantin Loizides  (co-authors:Andrea Dainese)



Parton energy loss effects in heavy-ion collisions are discussed within the Parton Quenching Model (PQM), constructed using the BDMPS quenching weights and a Glauber-based description of the collision geometry, in a scenario of longitudinal medium expansion.    The single parameter of the model is adjusted to describe the nuclear  modification factor measured in central Au-Au collisions at top RHIC energy. The model is then applied to other high-pt observables, as the  azimuthal anisotropy v2 and the two-particle correlations,  their evolution with centrality, and to other nucleus-nucleus colliding systems and centre-of-mass energies.    The inspection of production points and emission angles for primary partons within PQM reveals that, in central collisions, only the partons produced near the surface escape from the medium and contribute to the yield of high-pt hadrons. In the case of back-to-back parton pairs, this bias results in the "tangential emission" of the pair with respect to the surface: predominantly, those pairs escape in which both partons either have a small in-medium pathlength and/or dont traverse the high-density region.


(49) Quarkonium Spectral Function from Anisotropic Lattice (Theory)

Alexander Velytsky  (co-authors:Peter Petreczky)



Charmonia and bottomonia correlators and spectral functions are studied at zero and finite temperature. We use quenched approximation and employ standard Wilson action in the gauge sector with Fermilab anisotropic formulation for heavy quarks. We discuss the behaviour of the correlators and spectral functions above deconfinemnt and determine melting temperatures for different mesonic states.



(50) Suppression of  high $p_{T}$ non-photonic electrons in Au+Au collisions (Experiment)

Jaroslav Bielcik  (co-authors:(for the STAR Collaboration))



One of the most striking discoveries at RHIC is the observed strong suppression of high $p_{T}$ hadrons. This  has  been attributed to the radiative energy loss of the energetic partons  via induced gluon radiation in the hot and dense matter before fragmenting into hadrons. The study of heavy quark  production  extends our understanding of this scenario. Due to  the dead cone effect, the suppression of  heavy quark mesons at high  $p_{T}$ is expected to be smaller than that observed for charged hadrons at the same energy.       The measurement of  non-photonic single electrons up to high $p_{T}$ provides information on charm and beauty production.  The semi-leptonic decays of D and B mesons are the dominant contribution to the non-photonic electron spectra. The spectra from p+p, d+Au and Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV have been  extracted for  non-photonic electrons in the range $1.5 < p_{T}$ (GeV/c) $< 10$ at mid-rapidity.       The corresponding  nuclear modification factors ($R_{AA}$) are  presented. They  show a large  suppression in central Au+Au collisions, indicating an unexpectedly large energy loss for  heavy quarks in the hot and dense matter created at  RHIC. This observed suppression is compared to recent theoretical models.The radiative energy loss alone is not sufficient to explain the results and additional scenarios are   discussed.


(51) Indentified particle production in p+p and d+Au collisions at $\sqt{s_{NN}}$ = 200 GeV (Experiment)

Pawan Kumar Netrakanti (for STAR Collaboration)  (co-authors:)

Variable Energy Cyclotron Centre, India


Identified particle transverse momentum spectra in p+p and d+Au collisions  provide an important testing ground for perturbative Quantum Chromodynamics(pQCD).   They also provide a a better foundation for applications of jet quenching and quark recombination models to explain the phenomena in A+A collisions. The study of particle production in   d+Au collisions in forward and backward rapidities will   help in constraining he various particle production models  based on intial multiple partonic scattering,nuclear shadowing,  parton saturation,recombination and energy loss in cold nuclear matter.  In this talk we present the transverse momentum spectra   (0 < $p_{T}$ < 10 GeV/c) for pions,protons and   anti-protons at midrapidity (|y| < 1) in p+p and d+Au   collisions at $\sqrt{s_{NN}}$ = 200 GeV measured   in the STAR experiment at RHIC. The NLO pQCD calculations   describe the high $p_{\mathrm T}$ data for charged   pions reasonably well in $p$+$p$ collisions and $d$+Au  collisions. An improved description of experimental data in   RHIC's $p$+$p$ collisions by the AKK fragmentation   functions(FFs), comes from NLO pQCD fits to the recent flavour separated measurements in $e^{+}$+$e^{-}$ collisions.   Particle ratios as function of beam energy, beam species   and transverse momentum are found to reveal their dependence   on the FFs and the relative quark and gluon contributions.   The significant rapidity-asymmetry observed in the charged   pions and protons+anti-protons in d+Au collisions will   be discussed in terms of their centrality, rapidity,   and $p_{\mathrm T}$ dependence. The data will be compared   to various models to understand the relative contribution   of various physics process.



(52) High-pT azimuthal correlations at the NA49 Experiment at CERN (Experiment)

Marek Szuba  (co-authors:)

Warsaw University of Technology


Following successful attempts of observing jet pairs originating from lead-lead collisions at 158A GeV (top energy of the SPS) made by CERES, similar attempts are now in progress using data obtained by NA49. This presentation demonstrates results obtained so far in course of these attempts, especially showing already-obtained back-to-back structures and evaluating possible contamination of the results by acceptance effects of the NA49 detector.


(53) Elastic Energy Loss of High Energy Partons in a QCD Plasma (Theory)

Jan-e Alam  (co-authors:Abhee K. Dutt-Mazumder, Pradip Roy and Bikash Sinha)

Variable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata 700 064, India


The partonic energy loss has been calculated by taking both the hard  and soft contributions for all the $2 \rightarrow 2$ processes.  Cancellation of the  intermediate separation scale has been exhibited.  Subtleties related to the identical final state partons have properly  been taken into account.  The estimated collisional loss is compared with its radiative counter part.  We show that there exists a critical energy, E_c below which  the collisional loss is more than its radiative counterpart.  The energy loss due to elastic processes has been applied to study  the suppression of high energy jets produced in heavy ion collisions  at RHIC.



(54) Nuclear effects in dAu collisions from the final RHIC data (Theory)

P.  Levai  (co-authors:G. Barnafoldi, B. Cole, G. Fai, G. Papp)

RMKI Research Institute for Particle and Nuclear Physics, Budapest


Final PHENIX and STAR data on dAu collisions at s^1/2_{NN}=200 GeV at  mid-rapidity and forward/backward rapidities offer the possibility  for a critical review from the theoretical perspective. We have applied  different nuclear PDFs, shadowing functions, and fragmentation functions in a pQCD based parton model, and discuss the agreement/disagreement between data and theoretical descriptions. We aim to separate and extract the amplitude of different nuclear effects, and look forward to the existence of any non-conventional (beyond pQCD) initial and final state effects. We repeat our calculations at LHC energies to determine if the nuclear effects have measurable consequences at the higher energies.


(55) Quarkonium Production at PHENIX (Experiment)

Abigail Bickley  (co-authors:)

University of Colorado


Quarkonia provide a sensitive probe of the properties of the hot dense medium created in high energy heavy ion collisions.  Hard scattering processes result in the production of heavy quark pairs that interact with the collision medium during hadronization.  These in medium  interactions convey information about the fundamental properties of  the medium itself and can be used to examine the modification of the  QCD confining potential in the collision environment.  Baseline  measurements from the d+Au and p+p collision systems can be used to  distinguish cold nuclear matter effects while measurements from heavy  ion collision systems, Au+Au and Cu+Cu, can be used to quantify  in-medium effects.  PHENIX results for the production of the $J/\psi$  for a diverse set of collision systems and energies and for the $\Upsilon$ in p+p collisions will be presented.



(56) Coherent multiple scattering effect on hadron production in DIS (Theory)

Xiaofeng Guo  (co-authors:Jun Li)

Iowa State University


We present a QCD calculation of the coherent multiple scattering effect on single hadron production in semi-inclusive lepton-nucleus deeply inelastic scattering (DIS). We show that the destructive interference of coherent multiple scattering leads to suppression in hadron productions.  At leading pole approximation, when resummed to all powers, the suppression is equivalent to a shift in z for the fragmentation function D(z), which is very similar to the expectations of energy loss calculations. We compare our calculation with existing experimental data. We also discuss extensions of our approach to Drell-Yan and other other observables in hadronic collisions.


(57) Systematic Study of Low- and Intermediate-$p_T$ Azimuthal Charged Di-Hadron Correlations in Au+Au Collisions at sqrt{s_{NN}}=200GeV from the STAR Experiment (Experiment)

Mark J. Horner  (co-authors:STAR Collaboration)

Lawrence Berkeley National Laboratory


Di-hadron correlations have proved to be a valuable technique to study the hot and dense medium created in AuAu collisions at RHIC through the interaction of jet fragments with the medium. Recent results have shown large modifications of the away-side correlation shapes indicating strong coupling of the "jet" fragments to the medium. Possible explanations include large angle gluon radiation, jets deflected by transverse radial flow, and conical flow generated by hydrodynamic shock-waves or even a combination of these effects. We present here the results of a systematic study of $h^{\pm}$ azimuthal di-hadron correlations in different ranges of associated $p_T$ correlated with a high $p_T$ trigger particle, to explore changes in shape with varying associated $p_T$. In addition, we show results for $<p_T>$ as a function of azimuthal angle with a trigger hadron in different $p_T$ ranges. The data presented are from the high statistics year-4 $\sqrt{s_{NN}}$=200GeV Au+Au dataset. The results will be discussed in the context of different theoretical interpretations.



(58) Baryon stopping in pA collisions (Theory)

Javier L. Albacete  (co-authors:Yuri Kovchegov)

Ohio State University


The large stopping suffered by nucleons entering nuclear collisions is reflected in a net baryon number production in the central rapidity region of the collision. From a perturbative approach, this is due to the softening of the energetic incoming valence quarks.   I will present a calculation for small Bjorken-x valence quark production cross section in proton-nucleus collisions at high energies. The calculation is performed in the framework of the Color Glass Condensate, resumming multiple interactions at a quasi-classical level first and implementing quantum effects via non-linear evolution in the limit of large number of colors (BK) afterwards. The energy, rapidity, transverse momentum and atomic number dependence is studied in detail.  The role of nuclear effects is studied through the nuclear modification factor. The existence of a Cronin type enhancement at central rapidity and its evolution towards larger rapidities will be discussed. Comparison with the analogous modification factor defined for inclusive gluon production is performed and their possible experimantal consequences discussed.


(59) Open Charm and J/Psi Prodution at large rapidity in dAu collisions at RHIC (Experiment)

Ming Liu  (co-authors:PHENIX Collaboration)

Los Alamos National Lab


We study heavy flavor production through prompt muon measurements in the forward and backward rapidities 1.2<|eta| < 2.4 in dAu collisions with the PHENIX muon detectors. The rapidity dependence of prompt muon yields is studied as a function of the transverse momentum of the muon. Open charm is predominantly produced through gluon-gluon interactions at RHIC energy, thus such measurements will shed new light on gluon (anti)shadowing in small (large) Bjorken "x" in the Au nucleus. We also compare open charm to J/Psi yields in the forward and backward rapidities in dAu collisions and study the origin of the large forward and backward asymmetry observed by the PHENIX experiment in J/Psi production in the dAu collisions. This will help us to understand various normal (cold) nuclear effects - such as parton shadowing, CGC, initial state energy loss and nuclear absorption - on open charm and J/Psi production at RHIC. The latest results of this study will be presented.



(60) Azimuthal correlations between non-photonic electrons and charged hadrons in p+p and d+Au collisions from STAR (Experiment)

Xiaoyan Lin  (co-authors:STAR Collaboration)

Utrecht University and UCLA


The large suppression of high-pT hadron yields and correlations measured in central Au+Au collisions at RHIC presents strong evidence for significant final state parton energy loss in the strongly interacting medium. Recently, the STAR collaboration has measured a similarly strong suppression in non-photonic electrons in the pT range where they are expected to be dominated by semi-leptonic decays of charm and bottom mesons. This suppression is larger than expected from pure radiative energy loss, but the theoretical interpretation is complicated by the large uncertainty in the respective contributions of bottom and charm decays to the electron spectrum.    We will present measurements of high-pT angular correlations of non-photonic electrons and charged hadrons in p+p and d+Au collisions. These measurements can help disentangle the contributions of the different heavy flavors, due to kinematic effects in decays and jet fragmentation. In addition, the measurements will provide reference data for similar measurements in Au+Au collisions, which will allow to study heavy quark energy loss in more detail. In this talk, we will present preliminary results on high-pT electron-charged hadron azimuthal correlation measurements in nuclear collisions. Two different methods to evaluate the photonic background contribution are applied and compared. The results are compared to PYTHIA simulations to estimate the charm and beauty decay contributions to the  non-photonic electron spectrum.


(61) Nuclear modification of light meson at forward rapidities in Au+Au collisions at $sqrt{s_{NN}}$=200 GeV in the PHENIX experiment at RHIC (Experiment)

WooJin Park  (co-authors:)

Korea University


We study high pT light meson production at forward rapidity as a function of centrality in Au-Au collisions. It is expected that the energy and parton density of the fireball created in Au+Au collisions would be smaller at a larger rapidity, thus reducing the   jet quenching effects   observed at central rapidity for light mesons. On the other hand, gluon saturation models predict a suppression of particle yields at small x, or at a large rapidity, for a given pT.    We perform a quantitative analysis of the nuclear modification factor $R_{CP}$ and $R_{AA}$ for high pT light mesons at forward rapidities in Au+Au collision at $sqrt{s_{NN}}$=200 GeV. Light meson yields are measured in the PHENIX muon spectrometers. The latest results from this analysis will be presented.



(62) Background studies for single muon measurements in Au+Au collisions at (Experiment)

KwangBok, Lee  (co-authors:WooJin, Park)

Korea University, for the PHENIX Collaboration


Single muon production is an important tool for studying charm production  via semi-leptonic decays of c-quarks. Open charm production is not only  important to study QCD, but also considered to be one of the most  important probes of the Quark Gluon Plasma, which is predicted to be  created in relativistic heavy ion collisions. Understanding the processes  that produce backgrounds for the prompt single muon measurement is crucial  for studying single muons from heavy flavor decay.  The PHENIX experiment at RHIC has the ability to detect muons over the  range of $1.2 < |\eta | < 2.4$ using its muon spectrometers. PHENIX  detector has recorded $241 \mub^{-1}$ Au+Au luminosity and $1.5\times  10^{9}$ minimum bias events at $\sqrt{s_{_{NN}}}$=200 GeV during RHIC  run-4. The systematic study of backgrounds and techniques for their  removal will be presented.


(63) Measurement of single muons at forward rapidities in Cu-Cu collisions in the PHENIX experiment at RHIC (Experiment)

Kim, Byungil  (co-authors:)

Korea University


The measurement of open charm production in various collision species at different energies is important to study the properties of matter formed in the early stage of relativistic heavy ion collisions, especially to understand charm energy loss and recombination systematically. The RHIC facility provided Cu-Cu collisions at both high and low energy in 2005. This lighter colliding system compared with Au-Au can give much better precision on the centrality measurement in the lower $N_{part}$ region, and the comparison between two different colliding energies may give us a better systematic understanding of charm production.    PHENIX detectors measure muons in the rapidity range $1.2 < | \eta |< 2.4$, thus enabling us to study open charm as well as light meson production at forward rapidity. The status of single muon measurements of the centrality, transverse momentum and rapidity dependence of semi-leptonic open charm decays and light meson production, in Cu+Cu collisions at $\sqrt{s_{NN}}$=200 GeV and 62.4GeV will be presented.



(64) Extraction of jet topology using three particle correlations (Experiment)

Nuggehalli Ajitanand  (co-authors:PHENIX Collaboration)

SUNY Stony Brook


Recent theoretical studies  have indicated that the spatial  distribution of  away side jet fragments can be expected to be significantly altered by  medium  induced effects. In particular if the QGP fluid has a very low viscosity, Mach Cone like effects can be  generated and sustained. On the other  hand it has been argued that the  large flow  fields  may deflect the   fragmentation direction producing  a significantly  differing type of  jet  topology. Simulation results will be presented which  demonstrate  that three particle correlations are able to distinguish between  different modification scenarios. The method will be applied to the RHIC  data at 200 Gev/c Au+Au and results  presented as a  function of  event centrality.