Multi-Parton Dynamics at RHIC Huan Zhong Huang Department of Physics and Astronomy University of California Los University Oct

Outline 1)Experimental Observations at Intermediate p T 2)Multi-parton Dynamics -- coalescence/recombination picture -- possible gluon junction interaction 3)Hydrodynamics and pQCD 4)Mass Dependence in Cronin Effect 5)Outlook

Intermediate p T Region Volcanic mediate p T – Spatter (clumps)

Elliptic Flow Parameter v 2 y x pypy pxpx coordinate-space-anisotropy  momentum-space-anisotropy Initial/final conditions, dof, EOS

y Dynamical Origin of Elliptic Flow STAR Preliminary Au+Au 200 GeV V 2 in the intermediate p T region: Dynamics for Saturation ? Particle Dependence of v 2 ? Collective Pressure High pressure gradient Large expansion velocity Small expansion velocity p T dependent ! Surface Geometrical Phase Space Surface Emission Pattern High particle density Low particle density p T independent ! or p T dependence may come from surface thickness (p T ) x

What Determines the p T Dependence ? v2v2 Particle production steep func of p T V 2 little p T dependence 2<p T <5 GeV/c Charged hadron elliptic flow

STAR PHENIX What Determines the Particle Dependence ? Baryon Meson Why saturation at intermediate p T ? Why baryon and meson difference ?

So Many Baryons !! Two component shape evident in the K S spectra. The Λ yield exceeds the K S yield at intermediate p T. The Λ yield is most enhanced in central collision.

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

Surface Model Alone Does not Work more opaque: fewer particles less opaque: more particles Neither Woods-Saxon nor Hard-Sphere distribution can match the v 2 magnitude readily with standard fragmentation for particle formation !

Multi-Parton Dynamics K S – two quark coalescence  – three quark coalescence from the partonic matter surface?! Particle v 2 may be related to quark matter anisotropy !! p T < 1 GeV/c may be affected by hydrodynamic flow ! Hadronization Scheme for Bulk Partonic Matter: Quark Coalescence – (ALCOR-J.Zimanyi et al, AMPT-Lin et al, Molnar+Voloshin …..) Quark Recombination – (R.J. Fries et al….) STAR+PHENIX

Nuclear Modification Factor R AA R CP Multi-parton dynamics predict baryon yield increases with centrality FASTER than mesons! Yield ~  n and n  >n K  a feature not present in single parton fragmentation ! Multi-parton dynamics: coalescence, recombination and gluon junctions. R CP R CP = [yield/N-N] central [yield/N-N] peripheral

Strangeness from Bulk Partonic Matter Strangeness enhancement is most prominent at intermediate p T from quark coalescence in an equilibrated bulk matter !  

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

Interesting Measurements C. Nonaka et al nucl-th/ hydro  at high p T !! Open Charm !! STAR TOF Upgrade !

Intermediate p T Dynamics Identified particle spectra and elliptic flow at intermediate p T 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 p T can be the key to a phenomenological hadronization description of bulk partonic matter!

The  to  Many more  s Than  s !!

Scenarios of Baryon Number Transport Direct Transport Through Gluon Junctions …  X) Indirect Transport Through Pair Production Modified by Baryon Chemical Potential …  and  K  and  K  and  p / n ) K Net Baryon Density Increases the Associated Production and Transfers net baryon number to multiply-strange baryons !

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

Hydrodynamics at Intermediate p T ?  At intermediate p T, R CP of K 0 S is lower than that of Lambda  Hydro/p-QCD: mass effect  Quark coalescence: Particle type effect  Need  !!!  R CP of  close to that of K 0 S other than that of Lambda  Particle production at intermediate p T region is driven by the particle’s type, not the mass Hydrodynamics fails at intermediate p T no v 2 saturation Particle dependence of v 2 and R AA (R CP ) Higher statistics  data from d+Au is being analyzed by Xiangzhou Cai from SINR. Future Au+Au data + TOF upgrade !!

Particle Dependence in Cronin Effect Significant at Low Energy P.B. Straub et al., PRL (1992) p+A collisions at sqrt(s) = 38.8 GeV 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 ! pp K+K+ K-K-   R W/Be

Traditional Cronin Effect is not the whole story at RHIC STAR d+Au from TOFr analysis (USTC+BNL+RICE) Results on K S,  and  will reach higher p T (SINR+UCLA)

Nuclear Modification Factor Rcp  At intermediate p T, R CP of K 0 S is lower than that of Lambda  p-QCD: mass effect  Quark coalescence: Particle type effect  R CP of  is closer to K 0 S than Lambda  Particle production at intermediate p T region is dividing by the particle’s type, not the mass The ratio of central (top 20%) over peripheral (100-40%) (R CP ) normalized by, vs. transverse momentum. |cent=14.18; |periph=3.34 STAR Preliminary Xiangzhou Cai

Outlook Intermediate p T 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 !! (  J/ , and D mesons) STAR TOF/microSVT detector upgrade essential !