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Yichun Xu University of Science and Technology of China Brookhaven National Laboratory

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. Outline. Motivation In p+p, extend identified spectra study up to p T ~15 GeV/c

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Yichun Xu University of Science and Technology of China Brookhaven National Laboratory

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  1. Measurements of identified meson and baryon production at high pT in p+p and Au+Au collisions at STAR Yichun Xu University of Science and Technology of China Brookhaven National Laboratory April 27-29, Hangzhou, CHINA

  2. Outline • Motivation • In p+p, extend identified spectra study up to pT~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/p), color charge effect • recent prediction (K), jet conversion • Data analysis • Identify charge p, K, p and pbar by dE/dx using re-calibration method • Reconstruct neutral kaon with one triggered daughter • Results • Summary April 27-29, Hangzhou, CHINA

  3. [1] Phys. Lett. B 637 (2006) 161 [2] Phys. Rev. Lett. 97 (2006) 152301 Motivation 1—high pT spectra in p+p Extend the identified hadron spectra study to higher pT in p+p collisions. • Test the applicability of pQCD in p+p collisions. • Provide baseline for Nuclear Modification Factor (RAB) in heavy ion collisions. Proton spectra was limited to 7GeV/c with current statistics from minbias p+p @ STAR.[1] In Au+Au, it have been extended to 12GeV/c. [2] April 27-29, Hangzhou, CHINA

  4. arXiv: 0804.4760 QM08 2 AB 1 d N / dp d h path length L Eg T R hard parton = AB N 2 pp d / dp d STAR preliminary  h ~ 9/4 In pQCD: bin T Quark Eq Quark Motivation 2—energy loss Color charge effect of parton energy loss in heavy ion collisions. A popular theoretical explanation RAAsuppression—Energy Loss when jet pass the medium, which is characterized bym2/l (squared momentum transfer per collision and the mean free path l. Suppression for proton > p April 27-29, Hangzhou, CHINA

  5. path length L hard parton gluon Quark Motivation 3—Jet Conversion Jet Conversion in heavy ion collisions. Another predictions recently, Jet Conversion: The flavor of jet can be converted through the interaction with the medium. W. Liu, R.J. Fries, Phys. Rev. C77 (2008) 054902 April 27-29, Hangzhou, CHINA

  6. arXiv:nucl-ex/0505026v2 Focus STAR preliminary p±/K±/p(p) with dE/dx - + Where Bπis the expected mean dE/dx of p from Bichsel function of ionization energy loss in TPC. arXiv:0807.4303v1 April 27-29, Hangzhou, CHINA

  7. Barrel Electro-Magnetic Calorimeter Triggered by tower p K0S STAR preliminary STAR preliminary K0S with triggered p An independent way to reconstruct K0S with one daughter triggered by the BEMC through K0S→p++p- for cross-checking credibility of PID in triggered events. April 27-29, Hangzhou, CHINA

  8. STAR preliminary STAR preliminary 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 April 27-29, Hangzhou, CHINA

  9. Constraint for pQCD calculation 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, pT<5 GeV/c). [1] arXiv:0803.2768 , [2] Phys. Rev. Lett. 98, 252001 (2007) April 27-29, Hangzhou, CHINA

  10. STAR preliminary Particles Ratios in p+p collisions • Experimental data: • (Consistent with published data) • p-/p+: decrease with pT • p/p: decrease with pT indicates a significant quark jet contribution to baryon. • p/p and p/p: p/p+~0.2, and p/p-~0.1 • Compare to models: • PYTHIA(v6.205) describe ratios reasonably. • DSS over-predicts anti-protons relative to pions and protons. PLB 637 (2006) 161 April 27-29, Hangzhou, CHINA

  11. QM08 STAR preliminary p/ (Au+Au)>p/ (p+p & d+Au) p/p (Au+Au)>p/p (p+p & d+Au) STAR preliminary Ratios in p+p and A+A STAR preliminary PRL 97, 152301 (2006) K/ (Au+Au) >K/ (p+p) April 27-29, Hangzhou, CHINA

  12. STAR preliminary pT (GeV/c) RAA for p, K and p RAA(proton)>RAA(pion) at high pT 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. RAA(K) ~ 0.4 at high pT > 5.0 GeV/c consistent with the prediction of jet conversion by interaction with the medium in Au+Au. RAA(p) ~ RAA(r0) at high pT See more RAA Vs Npartin Anthony ’s talk in 6C session. April 27-29, Hangzhou, CHINA

  13. _ 7<pT<8 GeV/c STAR preliminary L with triggered p L 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. 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 pT . • Color charge effectcan’t explain suppression for pion and proton from RAA measurements. • RAA(K) ~ 0.4 shows consistence with the prediction of Jet Conversion in the medium created in Au+Au collisions. April 27-29, Hangzhou, CHINA

  15. Thanks! April 27-29, Hangzhou, CHINA

  16. Experiment and Data set Data set: EMC Triggers in run5 pp @ 200GeV Jet Patch trigger: ETtot>7.8 GeV High Tower trigger: ETot>2.5 GeV ETot>3.6 GeV Central trigger in run4 AuAu@200GeV • Time Projection Chamber (TPC) • Electro-Magnetic Calorimeter (EMC) • Shower Maximum Detector (SMD) April 27-29, Hangzhou, CHINA

  17. STAR preliminary STAR preliminary 4.0<pT<4.5GeV/c w/ EMC cut arXiv:0807.4303v1 dE/dx re-calibration EMC cut:0.3<p/E<1.5, nh>=2, nf>=2, |zdist|<2, |fdist|<0.01 April 27-29, Hangzhou, CHINA

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