Yichun Xu (USTC/BNL)April 27-29, Hangzhou, CHINA1 Measurements of identified meson and baryon production at high p T in p+p and Au+Au collisions at STAR Yichun Xu University of Science and Technology of China Brookhaven National Laboratory

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 2 Outline Motivation  In p+p, extend identified spectra study up to p T ~15 GeV/c Good constraints to pQCD calculation Baseline for study of nuclear modification factor in heavy ion collisions.  In Au+Au, study of nuclear modification factor previous results (  /p), color charge effect recent prediction (K), jet conversion Data analysis  Identify charge , K, p and pbar by dE/dx using re-calibration method  Reconstruct neutral kaon with one triggered daughter Results Summary

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 3 Motivation 1 — high p T spectra in p+p Extend the identified hadron spectra study to higher p T in p+p collisions.  Test the applicability of pQCD in p+p collisions.  Provide baseline for Nuclear Modification Factor (R AB ) in heavy ion collisions. Proton spectra was limited to 7GeV/c with current statistics from minbias STAR.[1] In Au+Au, it have been extended to 12GeV/c. [2] [1] Phys. Lett. B 637 (2006) 161 [2] Phys. Rev. Lett. 97 (2006)

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 4 Motivation 2 — energy loss A popular theoretical explanation R AA suppression—Energy Loss when jet pass the medium, which is characterized by    (squared momentum transfer per collision and the mean free path. Color charge effect of parton energy loss in heavy ion collisions.   ddpd d Nd N R T pp T AB bin AB / /1 2 2  QM08 arXiv: STAR preliminary EgEg EqEq ~ 9/4 In pQCD: Suppression for proton >  hard parton path length L Quark

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 5 Motivation 3 — Jet Conversion Another predictions recently, Jet Conversion: The flavor of jet can be converted through the interaction with the medium. Jet Conversion in heavy ion collisions. W. Liu, R.J. Fries, Phys. Rev. C77 (2008) hard parton path length L Quark gluon

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 6  ± /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. arXiv:nucl-ex/ v2 Focus STAR preliminary arXiv: v1 -+

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 7 K 0 S with triggered  An independent way to reconstruct K 0 S with one daughter triggered by the BEMC through K 0 S →     for cross-checking credibility of PID in triggered events. Barrel Electro- Magnetic Calorimeter K0SK0S  Triggered by tower STAR preliminary

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 8 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) STAR preliminary

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 9 Constraint for pQCD calculation [1] arXiv: , [2] Phys. Rev. Lett. 98, (2007) Simon, private communication Our data will provide a better constraint on Fragmentation Function! AKK 2008 [1] is constrained by BRAHMS pbar/p ratio [2] (y=2.95, p T <5 GeV/c).

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 10 Particles Ratios in p+p collisions Experimental data: (Consistent with published data)    + : decrease with p T 2.p/p: decrease with p T indicates a significant quark jet contribution to baryon. 3.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

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 11 Ratios in p+p and A+A QM08 STAR preliminary p/  (Au+Au)>p/  (p+p & d+Au) p/p (Au+Au)>p/p (p+p & d+Au) STAR preliminary K/  (Au+Au) > K/  (p+p) PRL 97, (2006)

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 12 R AA for , K and p R AA (proton)>R AA (pion) at high p T  Which is in contrast to the prediction of color charge dependence of Energy Loss.  how the gluon jet/quark jet interact with the medium created in Au+Au collisions. 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. R AA (  ) ~ R AA (   ) at high p T See more R AA Vs N part in Anthony ’s talk in 6C session. p T (GeV/c) STAR preliminary

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 13  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

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 14 Summary Extend identified hadron spectra up to 15GeV/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.  Color charge effect can’t explain suppression for pion and proton from R AA measurements.  R AA (K) ~ 0.4 shows consistence with the prediction of Jet Conversion in the medium created in Au+Au collisions.

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 15 Thanks!

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 16 Experiment and Data set Time Projection Chamber (TPC) Electro-Magnetic Calorimeter (EMC) Shower Maximum Detector (SMD) Data set: EMC Triggers in run5 200GeV Jet Patch trigger: E Ttot >7.8 GeV High Tower trigger: E Tot >2.5 GeV E Tot >3.6 GeV Central trigger in run4

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 17 dE/dx re-calibration EMC cut: 0.3 =2, n  >=2, |z dist |<2, |  dist |<0.01 arXiv: v1 STAR preliminary 4.0<p T <4.5GeV/c w/ EMC cut STAR preliminary