1. 2010/04/18Yichun Xu@HEP8th-Nanchang1 Measurements of identified hadron production at high p T in p+p and Au+Au collisions at RHIC-STAR 许依春 (Yichun Xu) Center for Particle Physics and Technology University of Science and Technology of China

2. 2010/04/18 Yichun Xu@HEP8th-Nanchang 2 Outline Motivation  In p+p, extend identified hadron spectra study up to p T ~15 GeV/c Good constraints to pQCD calculation. Baseline for study of nuclear modification factor in HIC.  In Au+Au, study of nuclear modification factor (R AA ) Color charge effect, Jet conversion, Jet hadrochemistry Data analysis  Identify charged , K, p and pbar by dE/dx  Reconstruct K 0 S with one triggered daughter Results & Summary

3. 2010/04/18 Yichun Xu@HEP8th-Nanchang 3 Extend Charged hadron spectra in p+p Proton spectra was limited to 7GeV/c with current statistics from minbias p+p @ STAR.[1] In Au+Au, it has been extended to 12GeV/c. [2] [1] Phys. Lett. B 637 (2006) 161[2] Phys. Rev. Lett. 97 (2006) 152301

4. 2010/04/18 Yichun Xu@HEP8th-Nanchang 4 Energy loss and QCD Color charge effect of parton energy loss   ddpd d Nd N R T pp T AB bin AB / /1 2 2  EgEg EqEq ~ 9/4 In pQCD: hard parton path length L Quark R AA (p)<R AA (  ) STAR: PRL97,152301(2006)

5. 2010/04/18 Yichun Xu@HEP8th-Nanchang 5 Jet Conversion hard parton path length L Quark gluon W. Liu, R.J. Fries, Phys. Rev. C77 (2008) 054902 q + qbar  g + g q(qbar) + g  g + q(qbar) W. Liu, C.M. Ko, B.W. Zhang, Phys. Rev. C 75, 051901 (2007).

6. 2010/04/18 Yichun Xu@HEP8th-Nanchang 6 Jet hadrochemistry Enhanced parton splitting in medium calculation for LHC. Mechanism may lead to higher p/  and K/  ratios in A+A jets. S.Sapeta and U.A. Wiedemann, arXiv:0707.3494

7. 2010/04/18 Yichun Xu@HEP8th-Nanchang 7  ± /K ± /p(p) with dE/dx Where B π is the expected mean dE/dx of  from Bichsel function of ionization energy loss in TPC. p T >3GeV STAR preliminary -+ Nucl. Instru. & Meth. A 614 (2010) 28–33 Nucl. Instr. & Meth. A 558 (2006) 419

8. 2010/04/18 Yichun Xu@HEP8th-Nanchang 8 K 0 S with triggered  K 0 S →     (trg) Barrel Electro- Magnetic Calorimeter K0SK0S  Triggered by tower STAR preliminary

9. 2010/04/18 Yichun Xu@HEP8th-Nanchang 9 Kaon in p+p collisions Charged and neutral kaons are extended up to 15 GeV/c in p+p collisions. Charged and neutral kaons are consistent. Phys. Rev. C 75 (2007) 64901 STAR preliminary AKK: S. Albino, B. A. Kniehl, and G. Kramer, arXiv: 0803.2768v2 DSS: Daniel de Florian, Werner Vogelsang, and Federico Wagner, arXiv: 0708.3060v3

10. 2010/04/18 Yichun Xu@HEP8th-Nanchang 10 Constraint for pQCD calculation [1] arXiv:0803.2768, [2] Phys. Rev. Lett. 98, 252001 (2007) Simon, private communication Our data will provide a better constraint on Fragmentation Function!

11. 2010/04/18 Yichun Xu@HEP8th-Nanchang 11 Particles Ratios in p+p collisions Experimental data: (Consistent with published data)    +, p/p: decrease with p T indicates a significant quark jet contribution not only to meson but also to baryon. 2.p/  and p/  : p/    ~0.2, and p/   ~0.1 Compare to models: 1.PYTHIA (v6.205) describe ratios reasonably. 2.DSS over-predicts anti- protons relative to pions and protons. PLB 637 (2006) 161 STAR preliminary

12. 2010/04/18 Yichun Xu@HEP8th-Nanchang 12 R AA for , K and p 1. R AA (proton)>R AA (pion) @ high p T  Which is in contrast to the prediction of color charge dependence of Energy Loss. H ow the gluon jet/quark jet interact with the medium created in Au+Au collisions? 2. R AA (K) ~ 0.4 at high p T > 5.0 GeV/c  Consistent with the prediction of jet conversion by interaction with the medium in Au+Au. 3. R AA (  ) ~ R AA (   ) at high p T  Light quark mesons have no mass effect p T (GeV/c) STAR preliminary

13. 2010/04/18 Yichun Xu@HEP8th-Nanchang 13 R AA vs Npart Integral R AA at p T >5.5 GeV/c, ~6.2 GeV/c  R AA for kaon and pion are suppressed more in central collisions.  R AA for kaon > R AA for pion, even in peripheral collisions. => Does jet chemistry change in small system?

14. 2010/04/18 Yichun Xu@HEP8th-Nanchang 14 Summary p+p collisions: Extend identified hadron spectra up to 15 GeV/c in p+p. Provide constraints for Fragmentation Function. Indicates a significant quark jet contribution to baryon from decrease of pbar/p with p T. Au+Au collisions:  No mass effect from R AA (  ) ~ R AA (  )  Color charge effect cannot explain R AA (p) > R AA (  ).  R AA (K)~0.4 in central Au+Au collisions is consistent with the prediction of Jet Conversion in the medium. Thanks for your attention!

15. 2010/04/18 Yichun Xu@HEP8th-Nanchang 15

16. 2010/04/18 Yichun Xu@HEP8th-Nanchang 16  with triggered p  can be extended up to 10 GeV/c in p+p collisions with the triggered data sample, which will provide additional probe for the jet conversion. _ 7<p T <8 GeV/c STAR preliminary

17. 2010/04/18 Yichun Xu@HEP8th-Nanchang 17 Experiment and Data set Time Projection Chamber (TPC) Electro-Magnetic Calorimeter (EMC) Data set: EMC Triggers in run5 pp @ 200GeV Jet Patch trigger: E Ttot >6.4 GeV High Tower trigger: E T >2.5 GeV E T >3.6 GeV Central trigger in run4 AuAu@200GeV

18. 2010/04/18 Yichun Xu@HEP8th-Nanchang 18 Triggered  and enhancement factor STAR preliminary Given p T =5 GeV/c, ~5.6M HT1 triggered events are equivalent to L(0.64 pb -1 )*  (30mb)*effTrg(3%)/effTrk(90%) ~ 600M minibias evts. A factor of 100 enhancement