Jin-Hui Chen

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Parton distributions at hadronization from bulk
dense matter produced at RHIC
Jin-Hui Chen Shanghai Institute of Applied
Physics, CAS The 2nd Asian Triangle Heavy Ion
Conference Oct. 13-15, 2008 University of
Tsukuba Tsukuba, Japan In collaboration with
F. Jin (SINAP), D. Gangadharan (UCLA), X. Cai
(SINAP), H. Huang (UCLA) and Y. Ma (SINAP).
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Outline

• Introduction and Motivation
• Phenomena _at_ RHIC in favor of quark
  Coalescence/Recombination mechanism
• Results and Discussions
• Constituent quark pT distribution at
  hadronization
• s/d quark ratio at hadronization
• Parton freeze-out properties
• Dynamical model calculation
• Summary and Outlook

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pT dependence physical process

• pT dependence physical process at RHIC
• We will focus on the intermediate pT region, and
  lets visit the data again

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Intriguing phenomena at RHIC
---- large p/p ratio

• Unexpected large p/p ratio at intermediate pT in
  central AuAu collisions
• The hadronization scheme at RHIC must be
  different from ee- !

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Intriguing phenomena at RHIC
---- v2,RCP grouping

• V2 and RCP measurements for identified particles
  show a B/M grouping behavior at intermediate pT
• NCQ-scaling, partonic degrees of freedom?

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What can we learn from those phenomena?

• At RHIC intriguing experimental features
• enhanced baryon over meson production
• strong elliptic flow
• B/M type grouping behavior of v2 and RCP for
  indentified particles
• Hadronization of bulk dense matter created at
  RHIC must be different from ee- collisions!
• Evidence for quark Coal/Reco!

• ?The essential degrees of freedom at
  hadronization seem to be effective constituent
  quarks that have developed a collective flow
  during the partonic evolution.
• v2/nq represents the constituent quark v2, what
  about the constituent quark pT distribution?
• p,K,p large resonance decay and hadronic
  re-scattering effect.
• our approach is made possible because of high
  stat. W, f measurements.

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Focus on W and f
STAR RunIV AuAu _at_ 200 GeV

• W and f are mostly from bulk s quarks
• Bulk s quarks have collective flow.
• ? Extract the s quarks pT distributions from
  high stat. W f data?

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Parton pT distributions at hadronization
If baryons of pT are mostly formed from
coalescence of partons at pT/3 and mesons of pT
are mostly formed from coalescence of partons at
pT/2 1,2,3
1 R.C. Hwa et al., Phys. Rev. C 66, 025205
(2002) 2 V. Greco et al., Phys. Rev. Lett.
90, 202302 (2003) 3 R.J. Fries et al., Phys.
Rev. Lett. 90, 202303 (2003).

• W and f particles have no decay feed-down
  contribution.
• These particles will freeze-out earlier from the
  system and have small hadronic re-scattering
  cross sections.

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Strange and light quark distribution
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s/d quark ratio from primordial hyperon

• s/d ratio from hyperon X0(1530)
  feed-down1 46-14

1 R. Witt, J. Phys. G 34, S921 (2007)
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s/d ratio compared with Reco. model calculation
? Good agreement with the data? Large exp.
uncertainty

• Quark Reco. model predicted a consistent shape
  between s/d ratio and the hyperon ratio.

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Parton freeze-out properties

• Significant radial flow though with large
  uncertainty involved from the data
• ms 460 MeV
• md 260 MeV

R.J. Fries et al., Phys. Rev. C 68,044902
(2003) Phys. Rev.
Lett. 90,202303 (2003).
Thermal parton distribution function
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Constraints on the system evolution dynamics

• Theoretical model for particle production at
  RHIC typically involve initial conditions,
  partonic evolutions, hadronization and hadronic
  evolutions.
• Theoretical uncertainties due to
  hadronization scheme and hadronic evolution are
  major issues for quantitative description of
  properties of QCD medium created at RHIC.
• i.e. the hadronic evolution process have
  been added to the hydrodynamic models as an
  afterburner and have been shown to significantly
  alter the spectra shapes of ordinary hadrons1.
  1 T. Hirano et al., Phys. Rev.
  C 77, 044909 (2008)

Can our derived quark distributions, representing
a cumulative effect from initial conditions
through partonic evolution, be used to determine
the final-state hadron momentum distribution?
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Dynamical model calculation (1)

• A Multi-Phase Transport model1
• Initial condition HIJING
• Partonic evolution ZPC
• Hadronization coalescence
• Hadronic evolution ART

1 Z.W. Lin et al., Phys. Rev. C 72, 064901
(2005)
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Dynamical model calculation (2)

• Modified version
• Tuned the initial parton pT distribution
  inherited from HIJING string melting empirically,
  (vT0,Tth0)
• Requirement the tuned distributions after
  parton cascade match our derived s/d quark dis
• Coalescence scheme two nearest (in coordinate
  space) quarks ? meson while three nearest quarks
  ? baryon.

?An essential ingredient in Reco./Coa. model
calculation the distribution of effective
constituent quarks that readily turn into hadron.
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Summary

• Our analysis provided an empirical confirmation
  of recombination/ coalescence framework for
  hadronization of bulk partonic matter produced at
  RHIC. We derived transverse momentum
  distributions for effective constituent quarks at
  hadronization.
• Our results suggest that partons develop a
  significant collective radial flow during
  partonic evolution.
• The validity of our approach to explore quark
  transverse-momentum distributions at
  hadronization has been tested with independent
  particle ratios.
• Our approach in complement with the
  constituent quark number scaling in elliptic flow
  provides a means to measure quantitative parton
  distributions at hadronization.
• 
  c.f. Phys. Rev. C 78 (2008) 034907

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Outlook Extend PID Capability

• ?/K separation to 1.6 GeV/c (0.7 TPC)
• (?K)/p to 3 GeV/c (1.2 TPC)
• Clean electron ID down to 0.2 GeV

• ToF detector updated
• 90 (of 120) ToF trays to be installed for Run 9
  and will be completed before Run 10.
• This will allow a more precise quantitative
  measurement of multi-strange hadron production at
  RHIC.

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Quantify the parton distributions at hadronization

1. v2/nq vs. pT/nq distributions
2. pT/nq vs. pT/nq distributions

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extra slides
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Strange quark momentum difference in AMPT model