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Multi-Parton Dynamics at RHIC

This presentation explores the experimental observations of multi-parton dynamics at RHIC, focusing on intermediate pT regions and their implications for particle production. Key topics include coalescence and recombination mechanisms, hydrodynamics, and the Cronin effect. The dynamics of elliptic flow and the mass dependence of baryon-meson yields are analyzed, emphasizing differences in particle behavior under various collision centralities. The results reveal essential insights into the hadronization process and strangeness enhancement, suggesting a link between quark dynamics and observed phenomena.

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Multi-Parton Dynamics at RHIC

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  1. Multi-Parton Dynamics at RHIC Huan Zhong Huang Department of Physics and Astronomy University of California Los Angeles @ShanDong University Oct. 17 2003

  2. Outline • Experimental Observations at Intermediate pT • Multi-parton Dynamics -- coalescence/recombination picture -- possible gluon junction interaction • Hydrodynamics and pQCD • Mass Dependence in Cronin Effect • Outlook

  3. Volcanic mediate pT – Spatter (clumps) Intermediate pT Region

  4. coordinate-space-anisotropy  momentum-space-anisotropy y py px x Initial/final conditions, dof, EOS Elliptic Flow Parameter v2

  5. y Small expansion velocity Collective Pressure High pressure gradient Large expansion velocity pT dependent ! Low particle density Surface Geometrical Phase Space Surface Emission Pattern High particle density pT independent ! or pT dependence may come from surface thickness (pT) Dynamical Origin of Elliptic Flow STAR Preliminary Au+Au 200 GeV x V2 in the intermediate pT region: Dynamics for Saturation ? Particle Dependence of v2 ?

  6. What Determines the pT Dependence ? v2 Charged hadron elliptic flow Particle production steep func of pT V2 little pT dependence 2<pT<5 GeV/c

  7. STAR PHENIX What Determines the Particle Dependence ? Baryon Meson Why saturation at intermediate pT ? Why baryon and meson difference ?

  8. So Many Baryons !! • Two component shape evident in the KS spectra. • The Λ yield exceeds the KS yield at intermediate pT. • The Λ yield is most enhanced in central collision.

  9. [yield/N-N]central RCP= [yield/N-N]peripheral What Determines the Baryon-Meson Yield? RCP ~ 1 particle production proportional to the number of binary nucleon-nucleon collisions – superposition of independent of n-n collisions. Intermediate pT region special !!

  10. less opaque: more particles more opaque: fewer particles Surface Model Alone Does not Work Neither Woods-Saxon nor Hard-Sphere distribution can match the v2 magnitude readily with standard fragmentation for particle formation !

  11. Multi-Parton Dynamics STAR+PHENIX Hadronization Scheme for Bulk Partonic Matter: • KS – two quark coalescence • – three quark coalescence from the partonic matter surface?! Particle v2 may be related to quark matter anisotropy !! pT < 1 GeV/c may be affected by hydrodynamic flow ! Quark Coalescence – (ALCOR-J.Zimanyi et al, AMPT-Lin et al, Molnar+Voloshin …..) Quark Recombination – (R.J. Fries et al….)

  12. [yield/N-N]central RCP= [yield/N-N]peripheral Nuclear Modification Factor RAA RCP RCP Multi-parton dynamics predict baryon yield increases with centrality FASTER than mesons! Yield ~ rn and nL>nK  a feature not present in single parton fragmentation ! Multi-parton dynamics: coalescence, recombination and gluon junctions.

  13. Strangeness from Bulk Partonic Matter Strangeness enhancement is most prominent at intermediate pT from quark coalescence in an equilibrated bulk matter ! L X W

  14. Recombination versus Coalescence Standard Fragmentation Scheme – leading parton fragments into hadrons quarks from pair production out of vacuum. Recombination Model -- R. Hwa et al … original recombination idea -- Recent Fries et al… for heavy ion collisions leading parton from pQCD processes recombined with soft partons from thermalized quarks/gluons. Coalescence Model thermalized quarks (gluons) coalescence form hadrons. Flavor Correlations and Dynamical Transition

  15. Interesting Measurements hydro • L X W at high pT !! Open Charm !! • STAR TOF Upgrade ! C. Nonaka et al nucl-th/0308051

  16. Intermediate pT Dynamics • Identified particle spectra and elliptic flow at intermediate pT are unique probes of multi-parton dynamics for particle formation – clustering of quarks! • Strangeness equilibration of the bulk partonic matter may also reflect in the enhanced strange baryon production from quark clusterings. The dynamics at the intermediate pT can be the key to a phenomenological hadronization description of bulk partonic matter!

  17. @mid-rapidity Pb+Pb @SPS Many more Ws Than Ws !! The W to W Ratio

  18. Scenarios of Baryon Number Transport Direct Transport Through Gluon Junctions … W + K + K + K + (X) Indirect Transport Through Pair Production Modified by Baryon Chemical Potential … • W and W X K • X and X (L / S) K • L and L (p / n ) K Net Baryon Density Increases the Associated Production and Transfers net baryon number to multiply-strange baryons !

  19. q q Anti-Baryon Baryon q q q q Multi-parton Dynamics and Baryon Production Baryon (Hyperon) Production may be Enhanced by Gluon-Junction Interaction Dynamics: Gluon Junction Mechanism -- (Kharzeev, Gyulassy and Vance ….) Junction Measure local baryon and anti-baryon quantum number correlations in DpT-Dy space ! Event-by-Event STAR Hyperon Correlations Doable with STAR TOF and SVT Upgrade !

  20. Hydrodynamics at Intermediate pT? Hydrodynamics fails at intermediate pT no v2 saturation Particle dependence of v2 and RAA(RCP) • At intermediate pT, RCP of K0S is lower than that of Lambda • Hydro/p-QCD: mass effect • Quark coalescence: Particle type effect • Need f!!! • RCP of f close to that of K0S other than that of Lambda • Particle production at intermediate pT region is driven by the particle’s type, not the mass Higher statistics f data from d+Au is being analyzed by Xiangzhou Cai from SINR. Future Au+Au data + TOF upgrade !!

  21. p+ p- RW/Be K+ K- p p Particle Dependence in Cronin Effect Significant at Low Energy Strong particle dependence proton > kaon > pion No significant particle and anti-particle difference ! no valence quark effect ! The Cronin effect is expected to decrease with beam energy ! P.B. Straub et al., PRL 68 452 (1992) p+A collisions at sqrt(s) = 38.8 GeV

  22. Traditional Cronin Effect is not the whole story at RHIC STAR d+Au from TOFr analysis (USTC+BNL+RICE) Results on KS, L and f will reach higher pT (SINR+UCLA)

  23. Nuclear Modification Factor Rcp • At intermediate pT, RCP of K0S is lower than that of Lambda • p-QCD: mass effect • Quark coalescence: Particle type effect • RCP of f is closer to K0S than Lambda • Particle production at intermediate pT region is dividing by the particle’s type, not the mass STAR Preliminary The ratio of central (top 20%) over peripheral (100-40%) (RCP) normalized by <Nbin>, vs. transverse momentum. <Nbin>|cent=14.18; <Nbin>|periph=3.34 Xiangzhou Cai

  24. Outlook Intermediate pT very special !! Multi-parton dynamics --- coalescence --- recombinations --- gluon junction interactions Hadronization phenomenology of bulk partonic matter Particle dependence of Cronin effect Identified Particle Spectra and Elliptic Flow !! (f, L, X, W, J/y, and D mesons) STAR TOF/microSVT detector upgrade essential !

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