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Search Results: 1 - 10 of 454455 matches for " R. J. Fries "
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Hadron Chemistry at High-PT with Identified Particles
R. J. Fries
Physics , 2009, DOI: 10.1063/1.3293916
Abstract: We discuss mechanisms that change the hadron chemistry for high momentum particles emitted in high energy nuclear collisions. We argue that particle ratios naturally tend to be different from jets in the vacuum. We show results of computations in a model that propagates leading particles through a quark gluon plasma and permits elastic flavor changing processes. We predict less suppression for kaons compared to pions in central collision. We also discuss elliptic flow resulting from flavor changing processes.
Recombination Models
R. J. Fries
Physics , 2004, DOI: 10.1088/0954-3899/30/8/026
Abstract: We review the current status of recombination and coalescence models that have been successfully applied to describe hadronization in heavy ion collisions at RHIC energies. Basic concepts as well as actual implementations of the idea are discussed. We try to evaluate where we stand in our understanding at the moment and what remains to be done in the future.
Hadron Correlations from Recombination and Fragmentation
R. J. Fries
Physics , 2004, DOI: 10.1088/0954-3899/31/4/047
Abstract: We review the formalism of quark recombination applied to the hadronization of a quark gluon plasma. Evidence in favor of the quark recombination model is outlined. Recent work on parton correlations, leading to detectable correlations between hadrons, is discussed. Hot spots from completely quenched jets are a likely source of such correlations which appear to be jet-like. It will be discussed how such a picture compares with measurement of associated hadron yields at RHIC.
Higher Twist Effects in Nuclei
R. J. Fries
Physics , 2002,
Abstract: This talk serves as an introduction to higher twist effects in nuclei. We want to discuss how perturbative QCD can be applied to processes involving heavy nuclei by taking into account multiple scattering.
Resummation of nuclear enhanced higher twist in the Drell Yan process
R. J. Fries
Physics , 2002, DOI: 10.1103/PhysRevD.68.074013
Abstract: We investigate higher twist contributions to the transverse momentum broadening of Drell Yan pairs in proton nucleus collisions. We revisit the contribution of matrix elements of twist-4 and generalize this to matrix elements of arbitrary twist. An estimate of the maximal nuclear broadening effect is derived. A model for nuclear enhanced matrix elements of arbitrary twist allows us to give the result of a resummation of all twists in closed form. Subleading corrections to the maximal broadening are discussed qualitatively.
Elliptic Flow of Rare High-Momentum Probes in Nuclear Collisions
W. Liu,R. J Fries
Physics , 2008,
Abstract: In high energy nuclear collisions the leading parton of a jet can change flavor through interactions with the surrounding medium. This can considerably boost the relative yield of rare high momentum particles, like strange quarks and photons. We revisit these jet conversions and discuss implications for the azimuthal asymmetry $v_2$ of rare probes. We predict that the $v_2$ of kaons at RHIC falls significantly below that of pions and protons at high transverse momentum. Experimental information on the relative $v_2$ of strange hadrons could provide constraints on the mean free path of fast quarks and gluons in a quark gluon plasma.
Heavy Quark Production from Jet Conversions in a Quark-Gluon Plasma
W. Liu,R. J. Fries
Physics , 2008, DOI: 10.1103/PhysRevC.78.037902
Abstract: Recently, it has been demonstrated that the chemical composition of jets in heavy ion collisions is significantly altered compared to jets in the vacuum. This signal can be used to probe the medium formed in nuclear collisions. In this study we investigate the possibility that fast light quarks and gluons can convert to heavy quarks when passing through a quark gluon plasma. We study the rate of light to heavy jet conversions in a consistent Fokker-Planck framework and investigate their impact on the production of high-$p_T$ charm and bottom quarks at RHIC and LHC.
High-P_T Physics with Identified Particles
R. J Fries,W. Liu
Physics , 2009, DOI: 10.1016/j.nuclphysa.2009.09.057
Abstract: The suppression of high-P_T particles in heavy ion collisions was one of the key discoveries at the Relativistic Heavy Ion Collider. This is usually parameterized by the average rate of momentum-transfer squared to this particle, qhat. Here we argue that measurements of identified particles at high P_T can lead to complementary information about the medium. The leading particle of a jet can change its identity through interactions with the medium. Tracing such flavor conversions could allow us to constrain the mean free path. Here we review the basic concepts of flavor conversions and discuss applications to particle ratios and elliptic flow. We make a prediction that strangeness is enhanced at high P_T at RHIC energies while its elliptic flow is suppressed.
Probing Nuclear Matter with Jet Conversions
W. Liu,R. J. Fries
Physics , 2008, DOI: 10.1103/PhysRevC.77.054902
Abstract: We discuss the flavor of leading jet partons as a valuable probe of nuclear matter. We point out that the coupling of jets to nuclear matter naturally leads to an alteration of jet chemistry even at high transverse momentum $p_T$. In particular, QCD jets coupling to a chemically equilibrated quark gluon plasma in nuclear collisions, will lead to hadron ratios at high transverse momentum $p_T$ that can differ significantly from their counterparts in $p+p$ collisions. Flavor measurements could complement energy loss as a way to study interactions of hard QCD jets with nuclear matter. Roughly speaking they probe the inverse mean free path $1/\lambda$, while energy loss probes the average squared momentum transfer $\mu^2/\lambda$. We present some estimates for the rate of jet conversions in a consistent Fokker-Planck framework and their impact on future high-$p_T$ identified hadron measurements at RHIC and LHC. We also suggest some novel observables to test flavor effects.
Heavy Ions at LHC: Theoretical Issues
R. J. Fries,B. Muller
Physics , 2003, DOI: 10.1140/epjcd/s2004-04-026-6
Abstract: We give a brief overview of our current theoretical understanding of ultra-relativistic heavy ion collision and the properties of super-hot nuclear matter. We focus on several issues that have been discussed in connection with experimental results from the CERN SPS and from the Relativistic Heavy Ion Collider RHIC. We give an extrapolation of our current knowledge to LHC energies and ask which physics questions can be addressed at the LHC.
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