Yu-Gang Ma Shanghai Institute of Applied Physics, Chinese Academy of Sciences

1. Parton transverse momentum distributions at hadronization in RHIC energy Yu-Gang Ma Shanghai Institute of Applied Physics, Chinese Academy of Sciences In collaboration with J. H. Chen, F. Jin, D. Gangadharan, X. Z. Cai and H. Z. Huang “RHIC-STAR Asia Meeting 2009”, Pusan Nat Univ, Pusan, May 6-9, 2009

2. 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 Parton dynamical model calculation Summary and Outlook Outline

3. STAR RunII Au+Au @ 200 GeV RCP 0 1 2 3 4 5 6 7 8 9 10 11 12 GeV/c Hydro ReCo pQCD pT dependent physical process • pT dependence of physical process at RHIC • We will focus on the intermediate pT region, and let’s recall the data again…

4. Intriguing phenomena at RHIC ----large p/p ratio • Unexpected large p/p ratio at intermediate pT in central Au+Au collisions • The hadronization scheme at RHIC must be different from e+e- !

5. NCQ=3 NCQ=2 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?

6. 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 e+e- 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/ncq 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.

7. Focus onW and f STAR Run 4 Au+Au @ 200 GeV • W and fare mostly from bulk s quarks; • Bulk s quarks have collective flow.  Extract the s quarks pT distributions from high stat. W f data?

8. STAR Run7 data: S quark flows S. S. Shi, QM09

9. Parton pT distributions at hadronization If baryons at pT are mostly formed from coalescence of partons at pT/3 and mesons at 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.

10. The constitute quark pT distributions have been extracted from the multi-strange data; • The s-quark shows a flatter pTdistribution than the d-quark. • The s-quark and d-quark have a similar KET distribution: partons have undergone a partonic evolution possibly described by hydrodynamics. Strange and light quark distribution

11. Consistent s/d ratio derived from primordial hyperon data • Sfeed-down: • S(1385)[2]: 26%+-5.9%; • S0: no data available yet • THERMUS[3]: 36% • String frag[4]: 25% [2] B.I. Abelev et al., Phys. Rev. Lett. 97, 132301 (2006); [3] S. Wheaton and J. Cleymans, J. Phys. G 31, S1069 (2005); [4] M. Bleicher et al., J. Phys. G 25, 1859 (1999); H.J. Drescher et al., Phys. Rep. 350, 93 (2001). s/d quark ratio from primordial hyperon • s/d ratio from hyperonX0(1530) feed-down[1]: 46%+-14% [1] R. Witt, J. Phys. G 34, S921 (2007);

12. 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.

13. Fit parameter of quark mass Can we put constrains on the constitute quark mass parameter ?

14. 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. eg., 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 hadrons[1].[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?

15. Original version failed to reproduce the spectra data: • Insufficiency parton cascading cross sections in the ZPC model where only pQCD processes have been included? • Wrong choice of hadronization scheme? Dynamical model calculation (1) • A Multi-Phase Transport model[1] • Initial condition: HIJING • Partonic evolution: ZPC • Hadronization: coalescence • Hadronic evolution: ART [1] Z.W. Lin et al., Phys. Rev. C 72, 064901 (2005)

16. It can faithfully reproduce the data at intermediate pT. 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.

17. 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 composition 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

18. 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.

19. Quantify the parton distributions at hadronization • v2/nq vs. pT/nq distributions • pT/nq vs. pT/nq distributions

20. How about the parton v2 ? parton v2 extracted from the NCQ scaled hadron v2

21. extra slides

22. Strange quark momentum difference in AMPT model

23. Parton freeze-out properties • Significant radial flow though with large uncertainty involved from the data: • ms = 460 MeV • md = 260 MeV Thermal parton distribution function: R.J. Fries et al.,Phys. Rev. C 68,044902 (2003); Phys. Rev. Lett. 90,202303 (2003).