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03/14/2006WWND2006 at La Jolla1 Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions Outline: Motivation Intermediate.

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Presentation on theme: "03/14/2006WWND2006 at La Jolla1 Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions Outline: Motivation Intermediate."— Presentation transcript:

1 03/14/2006WWND2006 at La Jolla1 Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions Outline: Motivation Intermediate p T  particle production mechanism at mid-rapidity High p T  charged  & p spectra up to 12 GeV/c from STAR  R CP, particle ratios Summary and Outlook Lijuan Ruan (for the STAR Collaboration) (Lawrence Berkeley National Laboratory)

2 03/14/2006WWND2006 at La Jolla2 Particle production at p T >2 GeV/c in p+p collisions Convolution of PDF  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.

3 03/14/2006WWND2006 at La Jolla3 p+p collisions and pQCD (AKK) NLO pQCD calculations with AKK FF are consistent with pion data at high p T (> 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

4 03/14/2006WWND2006 at La Jolla4 from p+p  Au+Au collisions Soft particle production region: p T <2 GeV/c Hard particle production region: p T >2 GeV/c, which can be described by NLO pQCD calculations. pQCD approach  p/  ratio 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 p T =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 p T. p + p collisionsAu + Au collisions

5 03/14/2006WWND2006 at La Jolla5 hydro+jet: Interplay between Soft and Hard N SOFT ~N HARD pTpTpTpT (1/p T )(dN/dp T ) Hydrodynamicafterburner Jetquenching Interesting region  Intermediate p T (2<p T <3.5 GeV/c) Pion  hard, Proton  soft T.Hirano & Y.Nara(’03), PRC69(2004)034908 Crossing p T moves toward high p T soft hard Au+Au at b=2 fm P T, cross~ 1.8 GeV/c for  2.7 GeV/c for K 3.7 GeV/c for p

6 03/14/2006WWND2006 at La Jolla6 Consequence from hadron species dependent p T,cross Hydro+Jet T.Hirano & Y.Nara(’03), PRC69(2004)034908

7 03/14/2006WWND2006 at La Jolla7 Recombination models Recombination models predict that a scale according to the number of constituent quarks in a hadron seems to govern the particle production at intermediate p T. 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 models:

8 03/14/2006WWND2006 at La Jolla8 Centrality Dependence: R cp in Au+Au 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. STAR: Phys. Rev. Lett. 92 (2004) 052302 PHENIX: Phys. Rev. Lett. 91 (2003) 172301

9 03/14/2006WWND2006 at La Jolla9 Centrality Dependence: R cp in Au+Au Two groups (2<p T <6GeV/c): - , K s, K , K*, Φ  mesons - p, Λ, Ξ, Ω  baryons STAR: Nucl. Phys. A 757 (2005) 102 X. Cai QM05, STAR Preliminary

10 03/14/2006WWND2006 at La Jolla10 From intermediate p T  high p T region The interplay between soft and hard plays an important role for particle production at intermediate p T. The R CP shows baryon/meson difference. No precise measurements of identified baryon and meson spectra at high p T (p T >6 GeV/c). The high p T PID spectra will be presented to address The transition between coalescence and jet fragmentation. Possible color charge dependence of energy loss (g/q)

11 03/14/2006WWND2006 at La Jolla11 g/q jet contribution to particle production Gluon jet contribution to protons is significantly larger than to pions at high p T in p+p collisions at RHIC.

12 03/14/2006WWND2006 at La Jolla12 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.

13 03/14/2006WWND2006 at La Jolla13 STAR Detector: TPC & MRPC-TOF 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. RHIC run4 (2004) 200 GeV Au+Au data ~14 M minbias events after |z_vertex|<30cm ~7.8 M TOF matched events

14 03/14/2006WWND2006 at La Jolla14 Spectra STAR Preliminary

15 03/14/2006WWND2006 at La Jolla15 Nuclear Modification Factors R CP In central Au+Au collisions: At 4<p T <12 GeV/c, both  and p are strongly suppressed in R CP. At 1.5 R CP (  ), R CP (p+pbar) shows obvious decreasing trend, not consistent with the binary scaling at intermediate p T. I. Vitev, nucl-ex/0603010. STAR Preliminary

16 03/14/2006WWND2006 at La Jolla16 Anti-particle to particle ratios 1.  - /  + are consistent with flat at unity in all p T, no significant centrality dependence. 2. pbar/p ratio: no significant centrality dependence, not consistent with the jet quenching prediction ( X.N. Wang, PRC 58 (2321) 1998). STAR Preliminary

17 03/14/2006WWND2006 at La Jolla17 Proton over pion ratios 1.The p(pbar)/  ratios in Au+Au collisions show strong centrality dependence. 2.In central Au+Au collisions, the p(pbar)/  ratios reach maximum value at p T ~2- 3 GeV/c, approach the corresponding ratios in p+p, d+Au collisions at p T >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). STAR Preliminary

18 03/14/2006WWND2006 at La Jolla18 Discussion In Au+Au collisions, at p T >6 GeV/c: R CP (p+pbar) ~ R CP (  ); 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;  R CP (p+pbar)<R CP (  ); 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.

19 03/14/2006WWND2006 at La Jolla19 Summary The spectra of  and p (pbar) from 200 GeV Au+Au collisions are analyzed up to p T =12 GeV/c. At central Au+Au collisions, at intermediate p T, R CP (p+pbar) > R CP (  ), R CP (p+pbar) decreasing trend with p T, not consistent with binary scaling; the p(pbar)/  ratio~1 at p T 2~3 GeV/c. In central Au+Au collisions, at high p T, R CP (p+pbar) ~ R CP (  ) the p(pbar)/  ratios approach the ratios in p+p and d+Au collisions.  In Au+Au collisions, jet fragmentation mechanism region: p T >6 GeV/c. The  - /  + and pbar/p ratios, no significant centrality or p T dependence.  Indicate that the partonic sources of protons and pions have similar energy loss.

20 03/14/2006WWND2006 at La Jolla20 Discussion: energy loss in QCD matter Color charge dependence: g vs q.  experimentally, p and pbar at high p T. 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 STAR Preliminary

21 03/14/2006WWND2006 at La Jolla21 Outlook: A Heavy-Flavor Tracker for STAR

22 03/14/2006WWND2006 at La Jolla22 Outlook: A Heavy-Flavor Tracker for STAR The energy loss of heavy flavor will be measured from open charm directly!!!

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