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Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions. L ijuan Ruan (for the STAR Collaboration) ( Lawrence Berkeley National Laboratory ). Outline: Motivation Intermediate p T  particle production mechanism at mid-rapidity High p T

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Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

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  1. Identified baryon and meson spectra at intermediate and high pTin 200 GeV Au+Au Collisions LijuanRuan (for the STAR Collaboration) (Lawrence Berkeley National Laboratory) Outline: • Motivation • Intermediate pT •  particle production mechanism at mid-rapidity • High pT •  charged  & p spectra up to 12 GeV/c from STAR • RCP, particle ratios • Summary and Outlook WWND2006 at La Jolla

  2. Particle production at pT>2 GeV/c in p+p collisions Convolution ofPDFpQCDFF PDF (parton distribution function): derived from e-h deep inelastic scattering. pQCD (parton-parton interaction cross section from pQCD calculation) FF (fragmentation function): derived from e+e- collisions. WWND2006 at La Jolla

  3. p+p collisions and pQCD (AKK) NLO pQCD calculations with AKK FF are consistent with pion data at high pT (> 2 GeV/c) NLO pQCD calculations only with AKK FF (Nucl.Phys.B725:181-206,2005) consistent with the p+pbar data AKK differ from KKP, in the way the light flavor FF are obtained OPAL Collaboration : Eur. Phys. J. C 17 (2000) 207 STAR Collaboration, nucl-ex/0601033 WWND2006 at La Jolla

  4. p + p collisions Au + Au collisions from p+p  Au+Au collisions Soft particle production region: pT<2 GeV/c Hard particle production region: pT>2 GeV/c, which can be described by NLO pQCD calculations. pQCD approach  p/ ratio <<1 due to D(q->p)/D(q->)<<1. At low energy, pbar/p (pbar/) ratio< 0.1, consistent with very low anti-baryon production from quark jets. Hot, dense, strongly interacting matter created p(pbar)/>=1 at pT=2 GeV/c, which cannot be reproduced by pQCD approach. Intrigue a lot of study for particle production mechanism: hydrodynamic, recombination/coalescence, gluon junction The medium pushes the soft particle production region up to higher pT. WWND2006 at La Jolla

  5. hydro+jet: Interplay between Soft and Hard Au+Au at b=2 fm soft T.Hirano & Y.Nara(’03), PRC69(2004)034908 hard Hydrodynamic afterburner Crossing pT moves toward high pT (1/pT)(dN/dpT) Jet quenching pT Interesting region Intermediate pT (2<pT<3.5 GeV/c) Pion hard,Protonsoft PT, cross~ 1.8 GeV/c for  2.7 GeV/c for K 3.7 GeV/c for p NSOFT~NHARD WWND2006 at La Jolla

  6. Consequence from hadron species dependent pT,cross Hydro+Jet T.Hirano & Y.Nara(’03), PRC69(2004)034908 WWND2006 at La Jolla

  7. Recombination models Recombination models: R.J. Fries, et al.,Phys. Rev. Lett. 90 202303 (2003). R. C. Hwa, et al., Phys. Rev. C 70, 024905 (2004). V. Greco, et al., Phys. Rev. C 68, 034904(2003). Recombination modelspredict that a scale according to the number of constituent quarks in a hadron seems to govern the particle production at intermediate pT. WWND2006 at La Jolla

  8. Centrality Dependence: Rcp in Au+Au STAR: Phys. Rev. Lett. 92 (2004) 052302 PHENIX: Phys. Rev. Lett. 91 (2003) 172301 Baryons (p, ) increase faster than mesons (, Ks, K) from peripheral to central collisions. consistent with the coalescence of constituent quarks at hadronization from a collective partonic system. WWND2006 at La Jolla

  9. X. Cai QM05, STAR Preliminary Centrality Dependence: Rcp in Au+Au STAR: Nucl. Phys. A 757 (2005) 102 Two groups (2<pT<6GeV/c): - , Ks, K, K*, Φ mesons - p, Λ,Ξ, Ω baryons WWND2006 at La Jolla

  10. From intermediate pT high pT region • The interplay between soft and hard plays an important role for particle production at intermediate pT. • The RCP shows baryon/meson difference. • No precise measurements of identified baryon and meson spectra at high pT (pT>6 GeV/c). The high pT PID spectra will be presented to address • The transition between coalescence and jet fragmentation. • Possible color charge dependence of energy loss (g/q) WWND2006 at La Jolla

  11. g/q jet contribution to particle production Gluon jet contribution to protons is significantly larger than to pions at high pT in p+p collisions at RHIC. WWND2006 at La Jolla

  12. Color charge dependence of energy loss X.N. Wang: PRC58(2321)1998. PID spectra, centrality dependence of pbar/p and pbar/ ratios, address the color charge dependence of energy lossTo further understand how the gluon jet/quark jet interact with the medium created in Au+Au. collisions. WWND2006 at La Jolla

  13. STAR Detector: TPC & MRPC-TOF • RHIC run4 (2004) 200 GeV Au+Au data • ~14 M minbias events after |z_vertex|<30cm • ~7.8 M TOF matched events • A new technology ---- • Multi-gap Resistive Plate Chamber (MRPC) • adopted from CERN-Alice. • A prototype detector of time-of-flight (TOF) was installed in year4 • Intrinsic timing resolution: 85 ps in STAR. WWND2006 at La Jolla

  14. Spectra STAR Preliminary WWND2006 at La Jolla

  15. Nuclear Modification Factors RCP STAR Preliminary In central Au+Au collisions: • At 4<pT<12 GeV/c, both  and p are strongly suppressed in RCP. • At 1.5<pT<7 GeV/c, RCP(p+pbar) > RCP() , RCP(p+pbar) shows obvious decreasing trend, not consistent with the binary scaling at intermediate pT. I. Vitev, nucl-ex/0603010. WWND2006 at La Jolla

  16. Anti-particle to particle ratios STAR Preliminary -/+ are consistent with flat at unity in all pT, no significant centrality dependence. pbar/p ratio: no significant centrality dependence, not consistent with the jet quenching prediction (X.N. Wang, PRC 58 (2321) 1998). WWND2006 at La Jolla

  17. STAR Preliminary Proton over pion ratios The p(pbar)/ ratios in Au+Au collisions show strong centrality dependence. In central Au+Au collisions, the p(pbar)/ ratios reach maximum value at pT~2-3 GeV/c, approach the corresponding ratios in p+p, d+Au collisions at pT>5 GeV/c. R.J. Fries, et al., Phys. Rev. Lett. 90 202303 (2003); R. C. Hwa, et al., Phys. Rev. C 70, 024905 (2004); DELPHI Collaboration, Eur. Phy. J. C 5, 585 (1998), Eur. Phy. J. C 17, 207 (2000). WWND2006 at La Jolla

  18. Discussion • In Au+Au collisions, at pT>6 GeV/c:RCP(p+pbar) ~ RCP(); p(pbar)/ ~ p(pbar)/ (d+Au,p+p); pbar/p ~ pbar/p (d+Au). Indicate that partonic sources of p(pbar) and  have similar energy loss. • Gluon contribution to p(pbar) is significantly larger than to (p); Gluons lose twice as much energy as quarks;  RCP(p+pbar)<RCP(); p(pbar)/ < p(pbar)/ (d+Au,p+p); pbar/p < pbar/p (d+Au). • With the addition of collisional energy loss in the recent calculation, the gluon jet quenching is a factor of 3 higher than quark jet quenching (S. Wicks et al.,nucl-ex/0512076). • There is no model to readily explain these measurements. Direct comparisons to the measurements require proper fragmentation functions. WWND2006 at La Jolla

  19. Summary • The spectra of and p (pbar) from 200 GeV Au+Au collisions are analyzed up to pT=12 GeV/c. • At central Au+Au collisions, at intermediate pT, RCP(p+pbar) > RCP() , RCP(p+pbar) decreasing trend with pT, not consistent with binary scaling; the p(pbar)/ ratio~1 at pT 2~3 GeV/c. • In central Au+Au collisions, at high pT, RCP(p+pbar) ~ RCP() the p(pbar)/ ratios approach the ratios in p+p and d+Au collisions.  In Au+Au collisions, jet fragmentation mechanism region: pT>6 GeV/c. • The -/ + and pbar/p ratios, no significant centrality or pT dependence. • Indicate that the partonic sources of protons and pions have similar energy loss. WWND2006 at La Jolla

  20. STAR Preliminary Discussion: energy loss in QCD matter • Color charge dependence: g vs q. experimentally, p and pbar at high pT. In order to systematically study this effect  measure p(pbar)/, pbar/p ratio in different energy by changing the g/q relative contribution to particle production. • Flavor dependence: u, d quarks vs c, b quarks. go to charm. • The partonic sources of , protons, and (D,B to) non-photonic electrons have similar energy loss. S. Wicks et al., nucl-th/0512076 WWND2006 at La Jolla

  21. Outlook: A Heavy-Flavor Tracker for STAR WWND2006 at La Jolla

  22. Outlook: A Heavy-Flavor Tracker for STAR The energy loss of heavy flavor will be measured from open charm directly!!! WWND2006 at La Jolla

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