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Measurements of identified hadron production at high p T in p+p and Au+Au collisions at RHIC-STAR

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. Outline. Motivation

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Measurements of identified hadron production at high p T in p+p and Au+Au collisions at RHIC-STAR

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  1. Measurements of identified hadron production at high pT 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 Yichun Xu@HEP8th-Nanchang

  2. Outline • Motivation • In p+p, extend identified hadron spectra study up to pT~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 (RAA) • Color charge effect, Jet conversion, Jet hadrochemistry • Data analysis • Identify charged p, K, p and pbar by dE/dx • Reconstruct K0S with one triggered daughter • Results & Summary 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 Yichun Xu@HEP8th-Nanchang

  4. STAR: PRL97,152301(2006) 2 AB 1 d N / dp d h path length L Eg T R hard parton = AB N 2 pp d / dp d  h ~ 9/4 In pQCD: bin T Quark Eq Quark Energy loss and QCD Color charge effect of parton energy loss RAA(p)<RAA(p) Yichun Xu@HEP8th-Nanchang

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

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

  8. Barrel Electro-Magnetic Calorimeter Triggered by tower p K0S STAR preliminary STAR preliminary K0S with triggered p K0S→p++p-(trg) Yichun Xu@HEP8th-Nanchang

  9. 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. AKK: S. Albino, B. A. Kniehl, and G. Kramer, arXiv: 0803.2768v2 DSS: Daniel de Florian, Werner Vogelsang, and Federico Wagner, arXiv: 0708.3060v3 Phys. Rev. C 75 (2007) 64901 Yichun Xu@HEP8th-Nanchang

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

  11. STAR preliminary Particles Ratios in p+p collisions • Experimental data: • (Consistent with published data) • p-/p+, p/p: decrease with pT indicates a significant quark jet contribution not only to meson but also 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 Yichun Xu@HEP8th-Nanchang

  12. STAR preliminary pT (GeV/c) RAA for p, K and p 1. RAA(proton)>RAA(pion)@ 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? 2. 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. 3. RAA(p) ~ RAA(r0) at high pT Light quark mesons have no mass effect Yichun Xu@HEP8th-Nanchang

  13. RAA vs Npart • Integral RAA at pT>5.5 GeV/c, <pT>~6.2 GeV/c • RAA for kaon and pion are suppressed more in central collisions. • RAA for kaon > RAA for pion, even in peripheral collisions. • => Does jet chemistry change in small system? Yichun Xu@HEP8th-Nanchang

  14. Summary Thanks for your attention! 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 pT . Au+Au collisions: • No mass effectfrom RAA() ~ RAA() • Color charge effect cannot explain RAA(p) > RAA(p). • RAA(K)~0.4 in central Au+Au collisions is consistent with the prediction of Jet Conversion in the medium. Yichun Xu@HEP8th-Nanchang

  15. Yichun Xu@HEP8th-Nanchang

  16. _ 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. Yichun Xu@HEP8th-Nanchang

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

  18. STAR preliminary Triggered p and enhancement factor A factor of 100 enhancement Given pT=5 GeV/c,~5.6MHT1 triggered events are equivalent to L(0.64 pb-1)*s(30mb)*effTrg(3%)/effTrk(90%) ~600M minibias evts. Yichun Xu@HEP8th-Nanchang

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