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Some results obtained at the relativistic heavy ion collider

PHYSICS OF PARTICLES AND NUCLEI 2007年第2期38卷 204-231页

作者： Litvinenko, A. G. Joint Inst Nucl Res Dubna 141980 Moscow Oblast Russia

Some results obtained in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory are discussed. Along with observables studied at energies lower than those at RHIC (particle production ratios, soft spectra, flows, and so on), observables specific for RHIC energies related to the Jet Quenching effect and Color Glass Condensate (CGC) manifestation are discussed. Preliminary results and specifics of particular experiments at RHIC are not considered.

关键词： QUARK-GLUON PLASMA NUCLEUS-NUCLEUS COLLISIONS CHARGED-PARTICLE MULTIPLICITY LARGE TRANSVERSE-MOMENTUM PLUS AU COLLISIONS HIGH-DENSITY QCD HADRON-PRODUCTION PION INTERFEROMETRY MESON PRODUCTION fragmentation functions

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Pion and kaon production in nucleon-nucleon collisions

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INTERNATIONAL JOURNAL OF MODERN PHYSICS A 2007年第2-3期22卷 582-586页

作者： Tichoruk, Marta Szczurek, Antoni Jagiellonian Univ Inst Phys PL-31342 Krakow Poland Inst Nucl Phys PL-31342 Krakow Poland Univ Rzeszow PL-35959 Rzeszow Poland

Inclusive cross section for pion production in proton - proton collisions are calculated based on unintegrated parton distribution functions (uPDFs). In addition to purely gluonic terms the present approach includes also quark degrees of freedom. Phenomenological fragmentation functions from the literature are used. The new mechanisms are responsible for pi+ - pi- asymmetry. In contrast to standard collinear approach, application of 2 -> 1 k(t) - factorization approach can be extended towards much lower transverse momenta, both at mid and forward rapidity region. The results of the calculation are compared with SPS and RHIC data.

关键词： unintegrated parton distributions fragmentation functions inclusive cross section

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Jet modification in three dimensional fluid dynamics at next-to-leading twist

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Physical Review C 2007年第4期76卷 041902(R)-041902(R)页

作者： A. Majumder C. Nonaka S. A. Bass Department of Physics Duke University Durham North Carolina 27708 USA Department of Physics Nagoya University Nagoya 464-8602 Japan

The modification of the single inclusive spectrum of high transverse momentum (pT) pions emanating from an ultrarelativistic heavy-ion collision is investigated. The deconfined sector is modeled using a full three-dimensional (3-D) ideal fluid dynamics simulation. Energy loss of high pT partons and the ensuing modification of their fragmentation is calculated within perturbative QCD at next-to-leading twist, where the magnitude of the higher twist contribution is modulated by the entropy density extracted from the 3-D fluid dynamics simulation. The nuclear modification factor (RAA) for pions with a pT⩾8 GeV as a function of centrality as well as with respect to the reaction plane is calculated. The magnitude of contributions to the differential RAA within small angular ranges, from various depths in the dense matter, is extracted from the calculation and demonstrates the correlation of the length integrated density and the RAA from a given depth. The significance of the mixed and hadronic phase to the overall magnitude of energy loss is explored.

关键词： NUCLEUS-NUCLEUS COLLISIONS HEAVY-ION COLLISIONS QUARK-GLUON PLASMA PARTON ENERGY-LOSS fragmentation functions HADRON SPECTRA COLLABORATION FLUCTUATIONS PERSPECTIVE TOMOGRAPHY

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Densities, parton distributions, and measuring the nonspherical shape of the nucleon

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Physical Review C 2007年第6期76卷 065209-065209页

作者： Gerald A. Miller University of Washington Seattle Washington 98195-1560 USA

Spin-dependent quark densities, matrix elements of specific density operators in proton states of definite spin-polarization, indicate that the nucleon may harbor an infinite variety of nonspherical shapes. We show that these matrix elements are closely related to specific transverse-momentum-dependent (TMD) parton distributions accessible in the angular dependence of the semi-inclusive processes ep→eπX and the Drell-Yan reaction pp→ll¯X. New measurements or analyses would allow the direct exhibition of the nonspherical nature of the proton.

关键词： fragmentation functions LEPTOPRODUCTION POLARIZATION

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Jet conversions in a quark-gluon plasma

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Physical Review C 2007年第5期75卷 051901(R)-051901(R)页

作者： W. Liu C. M. Ko B. W. Zhang Texas A&amp M Univ Inst Cyclotron College Stn TX 77843 USA Texas A&amp M Univ Dept Phys College Stn TX 77843 USA

Quark and gluon jets traversing through a quark-gluon plasma not only lose their energies but also can undergo flavor conversions. The conversion rates via the elastic q(q¯)g→gq(q¯) and the inelastic qq¯↔gg scatterings are evaluated in the lowest order in QCD. Including both jet energy loss and conversions in the expanding quark-gluon plasma produced in relativistic heavy ion collisions, we have found a net of quark jets to gluon jets. This reduces the difference between the nuclear modification factors for quark and gluon jets in central heavy ion collisions and thus enhances the p/π+ and p¯/π− ratios at high transverse momentum. However, a much larger net quark-to-gluon jet conversion rate than the one given by the lowest order QCD is needed to account for the observed similar ratios in central Au+Au and p+p collisions at the same energy. Implications of our results are discussed.

关键词： HEAVY-ION COLLISIONS ABELIAN ENERGY-LOSS fragmentation functions HADRON SPECTRA COLLABORATION SCATTERING OPACITY NUCLEI

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Final state interactions and hadron quenching in cold nuclear matter

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Physical Review C 2007年第3期76卷 034902-034902页

作者： A. Accardi Department of Physics and Astronomy Iowa State University Ames Iowa 50011 USA

I examine the role of final state interactions in cold nuclear matter in modifying hadron production on nuclear targets with leptonic or hadronic beams. I demonstrate the extent to which available experimental data in electron-nucleus collisions can give direct information on final state effects in hadron-nucleus and nucleus-nucleus collisions. For hadron-nucleus collisions, a theoretical estimate based on a parton energy loss model tested in lepton-nucleus collisions shows a large effect on midrapidity hadrons at fixed target experiments. At energies currently available at the BNL Relativistic Heavy Ion Collider, the effect is large for negative rapidity hadrons but mild at midrapidity. This final state cold hadron quenching needs to be taken into account in jet tomographic analysis of the medium created in nucleus-nucleus collisions.

关键词： DEEP-INELASTIC SCATTERING PARTON ENERGY-LOSS LARGE TRANSVERSE-MOMENTUM QUARK-GLUON PLASMA DIMUON PRODUCTION fragmentation functions GLASS CONDENSATE D+AU COLLISIONS HADRONIZATION QCD

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Resolving the plasma profile via differential single inclusive suppression

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Physical Review C 2007年第2期75卷 021901(R)-021901(R)页

作者： A. Majumder Department of Physics Duke University Durham North Carolina 27708 USA

The ability of experimental signatures to resolve the spatiotemporal profile of an expanding quark-gluon plasma is studied. In particular, the single inclusive suppression of high-momentum hadrons versus the centrality of a heavy-ion collision and with respect to the reaction plane in noncentral collisions is critically examined. Calculations are performed in the higher twist formalism for the modification of the fragmentation functions. Radically different nuclear geometries are used. The influence of different initial gluon distributions as well as different temporal evolution scenarios on the single inclusive suppression of high-momentum pions are outlined. It is demonstrated that the modification versus the reaction plane is quite sensitive to the initial spatial density. Such sensitivity remains even in the presence of a strong elliptic flow.

关键词： QUARK-GLUON PLASMA PARTON ENERGY-LOSS fragmentation functions SCATTERING COLLISIONS NUCLEI COLLABORATION PERSPECTIVE RADIATION OPACITY

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Phenomenology of elastic energy loss

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Physical Review C 2007年第6期76卷 064905-064905页

作者： Thorsten Renk Univ Jyvaskyla Dept Phys FI-40014 Jyvaskyla Finland

The unexpectedly strong suppression of high pT heavy quarks in heavy-ion collisions has given rise to the idea that partons propagating through a medium in addition to energy loss by induced radiation also undergo substantial energy loss due to elastic collisions. However, the precise magnitude of this elastic energy-loss component is highly controversial. Although for a parton inside a medium it is surprisingly difficult to define the difference between elastic and radiative processes rigorously, the main phenomenological difference is in the dependence of energy loss on in-medium path length: in a constant medium radiative energy loss is expected to grow quadratically with path length, elastic energy loss linearly. In this article, we investigate a class of energy-loss models with such a linear path-length dependence and demonstrate that they are incompatible with measured data on hard hadronic back-to-back correlations where a substantial variation of path length is probed. This indicates that any elastic energy-loss component has to be small.

关键词： QUARK-GLUON PLASMA fragmentation functions HADRON SPECTRA COLLISIONS PARTONS NUCLEI

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Proton-antiproton suppression in 200A GeV Au-Au collisions

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Physical Review C 2007年第2期76卷 027901-027901页

作者： Thorsten Renk Kari J. Eskola Univ Jyvaskyla Dept Phys FIN-40014 Jyvaskyla Finland Univ Helsinki Helsinki Inst Phys FIN-00014 Helsinki Finland

We discuss the measured nuclear suppression of p+p¯ production in 200A GeV Au-Au collisions at the Relativistic Heavy Ion Collider (RHIC) within radiative energy loss. For the Albino-Kniehl-Kramer (AKK) set of fragmentation functions, proton production is dominated by gluons, giving rise to the expectation that the nuclear suppression for p+p¯ should be stronger than for pions due to the stronger coupling of gluons to the quenching medium. Using a hydrodynamical description for the soft matter evolution, we show that this is indeed seen in the calculation. However, the expected suppression factors for pions and protons are sufficiently similar that a discrimination with present data is not possible. In the high pT region above 6 GeV where the contributions of hydrodynamics and recombination to hadron production are negligible, the model calculation is in good agreement with the data on p+p¯ suppression.

关键词： fragmentation functions HADRON SPECTRA

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Evolution of Shower Parton Distributions in a Jet from Quark Recombination Model

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Chinese Physics Letters 2006年第2期23卷 332-335页

作者：谭志光杨纯斌 Institute of Particle Physics Huazhong Normal University Wuhan 430079

The evolution of shower parton distributions in a jet is investigated in the framework of a quark recombination model. The distributions are parameterized and the Q^2 dependence of the parameters is given by polynomia... 详细信息

关键词： INELASTIC EP SCATTERING fragmentation functions PERTURBATION-THEORY

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