Jin-Hui Chen Shanghai Institute of Applied Physics, CAS In collaboration with F. Jin, D. Gangadharan, X. Cai, H. Huang and Y. Ma Parton distributions at hadronization from bulk dense matter produced at RHIC

2 Outline Introduction and Motivation – RHIC in favor of quark Coalescence/Recombination mechanism Results and Discussions – Constituent quark p T distribution at hadronization – s/d quark ratio at hadronization – Parton freeze-out properties – Dynamical model calculation Summary and Outlook

3 p T dependence physical process GeV/c pQCD ReCo Hydro R CP STAR RunII 200 GeV p T dependence physical process at RHIC We will focus on the intermediate p T region, and let’s visit the data again…

4 Intriguing phenomena at RHIC ---- large p/  ratio Unexpected large p/  ratio at intermediate p T in central Au+Au collisions – The hadronization scheme at RHIC must be different from e + e - !

5 Intriguing phenomena at RHIC ---- v 2, R CP grouping V 2 and R CP measurements for identified particles show a B/M grouping behavior at intermediate p T – NCQ-scaling, partonic degrees of freedom? NCQ=3 NCQ=2

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 v 2 and R CP 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. – v 2 /nq represents the constituent quark v 2, what about the constituent quark p T distribution? –  p: large resonance decay and hadronic re-scattering effect. – our approach is made possible because of high stat.  measurements.

7 Focus on  and   and  are mostly from bulk s quarks; Bulk s quarks have collective flow.  Extract the s quarks p T distributions from high stat.  data? STAR RunIV 200 GeV

8 Parton p T distributions at hadronization If baryons of p T are mostly formed from coalescence of partons at p T /3 and mesons of p T are mostly formed from coalescence of partons at p T /2 [1,2,3]  and  particles have no decay feed-down contribution. These particles will freeze-out earlier from the system and have small hadronic re-scattering cross sections. [1] R.C. Hwa et al., Phys. Rev. C 66, (2002); [2] V. Greco et al., Phys. Rev. Lett. 90, (2003); [3] R.J. Fries et al., Phys. Rev. Lett. 90, (2003).

9 The constitute quark p T distributions have been extracted from the multi- strange data; The s-quark shows a flatter p T distribution than the d- quark. Strange and light quark distribution The s-quark and d-quark have a similar KE T distribution: partons have undergone a partonic evolution possibly described by hydrodynamics.

10 s/d quark ratio from primordial hyperon s/d ratio from hyperon  0 (1530) feed-down [1] : 46%+- 14% Consistent s/d ratio derived from primordial hyperon data [2] B.I. Abelev et al., Phys. Rev. Lett. 97, (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). –  feed-down: –  (1385) [2] : 26%+-5.9%; –  0 : no data available yet – THERMUS [3] : 36% – String frag [4] : 25% [1] R. Witt, J. Phys. G 34, S921 (2007);

11 s/d ratio compared with Reco. model calculation Quark Reco. model predicted a consistent shape between s/d ratio and the hyperon ratio.  Good agreement with the data;  Large exp. uncertainty;

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

13 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 hadrons [1]. [1] T. Hirano et al., Phys. Rev. C 77, (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?

14 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, (2005)

15 Modified version: – Tuned the initial parton p T distribution inherited from HIJING string melting empirically, (v T0,T th0 ); – 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. Dynamical model calculation (2)  An essential ingredient in Reco./Coa. model calculation: the distribution of effective constituent quarks that readily turn into hadron. It can faithfully reproduce the data at intermediate p T.

16 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)

17  /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. Outlook: Extend PID Capability

18 Quantify the parton distributions at hadronization 1.v 2 /n q vs. p T /n q distributions 2.p T /n q vs. p T /n q distributions

19 extra slides

20 Strange quark momentum difference in AMPT model