Identified baryon and meson spectra at intermediate and

Identified baryon and meson spectra at intermediate and high p. T in 200 Ge. V Au+Au Collisions Lijuan Ruan (for the STAR Collaboration) (Lawrence Berkeley National Laboratory) Outline: • Motivation • Intermediate p. T particle production mechanism at mid-rapidity • High p. T charged & p spectra up to 12 Ge. V/c from STAR RCP, particle ratios • Summary and Outlook 03/14/2006 WWND 2006 at La Jolla 1

Particle production at p. T>2 Ge. V/c in p+p collisions Convolution of PDF p. QCD FF PDF (parton distribution function): derived from e-h deep inelastic scattering. p. QCD (parton-parton interaction cross section from p. QCD calculation) FF (fragmentation function): derived from e+e- collisions. 03/14/2006 WWND 2006 at La Jolla 2

p+p collisions and p. QCD (AKK) NLO p. QCD calculations with AKK FF are consistent with pion data at high p. T (> 2 Ge. V/c) NLO p. QCD calculations only with AKK FF (Nucl. Phys. B 725: 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 03/14/2006 WWND 2006 at La Jolla 3

from p+p Au+Au collisions p + p collisions Au + Au collisions Soft particle production region: p. T<2 Ge. V/c Hot, dense, strongly interacting matter created Hard particle production region: p. T>2 Ge. V/c, which can be described by NLO p. QCD calculations. p(pbar)/ >=1 at p. T=2 Ge. V/c, which cannot be reproduced by p. QCD 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. 03/14/2006 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. WWND 2006 at La Jolla 4

hydro+jet: Interplay between Soft and Hard Au+Au at b=2 fm (1/p. T)(d. N/dp. T) T. Hirano & Y. Nara(’ 03), PRC 69(2004)034908 NSOFT~NHARD 03/14/2006 PT, cross~ 1. 8 Ge. V/c for 2. 7 Ge. V/c for K 3. 7 Ge. V/c for p Hydrodynamic afterburner soft hard Crossing p. T moves toward high p. T Jet quenching p. T Interesting region Intermediate p. T (2<p. T<3. 5 Ge. V/c) Pion hard, Proton soft WWND 2006 at La Jolla 5

Consequence from hadron species dependent p. T, cross Hydro+Jet T. Hirano & Y. Nara(’ 03), PRC 69(2004)034908 03/14/2006 WWND 2006 at La Jolla 6

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 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. 03/14/2006 WWND 2006 at La Jolla 7

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. 03/14/2006 WWND 2006 at La Jolla 8

Centrality Dependence: Rcp in Au+Au STAR: Nucl. Phys. A 757 (2005) 102 X. Cai QM 05, STAR Preliminary Two groups (2<p. T<6 Ge. V/c): - , Ks, K , K*, Φ mesons - p, Λ, Ξ, Ω baryons 03/14/2006 WWND 2006 at La Jolla 9

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 RCP shows baryon/meson difference. • No precise measurements of identified baryon and meson spectra at high p. T (p. T>6 Ge. V/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) 03/14/2006 WWND 2006 at La Jolla 10

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. 03/14/2006 WWND 2006 at La Jolla 11

Color charge dependence of energy loss X. N. Wang: PRC 58(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. 03/14/2006 WWND 2006 at La Jolla 12

STAR Detector: TPC & MRPC-TOF • RHIC run 4 (2004) 200 Ge. V Au+Au data • ~14 M minbias events after |z_vertex|<30 cm • ~7. 8 M TOF matched events A new technology ---Multi-gap Resistive Plate Chamber (MRPC) adopted from CERN-Alice. ØA prototype detector of time-of-flight (TOF) was installed in year 4 ØIntrinsic timing resolution: 85 ps in STAR. 03/14/2006 WWND 2006 at La Jolla 13

Spectra STAR Preliminary 03/14/2006 WWND 2006 at La Jolla 14

Nuclear Modification Factors RCP STAR Preliminary In central Au+Au collisions: • At 4<p. T<12 Ge. V/c, both and p are strongly suppressed in RCP. • At 1. 5<p. T<7 Ge. V/c, RCP(p+pbar) > RCP( ) , RCP(p+pbar) shows obvious decreasing trend, not consistent with the binary scaling at intermediate p. T. I. Vitev, nucl-ex/0603010. 03/14/2006 WWND 2006 at La Jolla 15

Anti-particle to particle ratios STAR Preliminary 1. 2. -/ + are consistent with flat at unity in all p. T, 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). 03/14/2006 WWND 2006 at La Jolla 16

Proton over pion ratios STAR Preliminary 1. 2. 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 p. T~23 Ge. V/c, approach the corresponding ratios in p+p, d+Au collisions at p. T>5 Ge. V/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). 03/14/2006 WWND 2006 at La Jolla 17

Discussion • In Au+Au collisions, at p. T>6 Ge. V/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. 03/14/2006 WWND 2006 at La Jolla 18

Summary • The spectra of and p (pbar) from 200 Ge. V Au+Au collisions are analyzed up to p. T=12 Ge. V/c. • At central Au+Au collisions, at intermediate p. T, RCP(p+pbar) > RCP( ) , RCP(p+pbar) decreasing trend with p. T, not consistent with binary scaling; the p(pbar)/ ratio~1 at p. T 2~3 Ge. V/c. • In central Au+Au collisions, at high p. T, 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: p. T>6 Ge. V/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. 03/14/2006 WWND 2006 at La Jolla 19

Discussion: energy loss in QCD matter • S. Wicks et al. , nucl-th/0512076 Color charge dependence: g vs q. experimentally, p and pbar at high p. T. STAR Preliminary 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) nonphotonic electrons have similar energy loss. 03/14/2006 WWND 2006 at La Jolla 20

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

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