Identified particle transverse momentum distributions in 200 Ge

Identified particle transverse momentum distributions in 200 Ge. V Au+Au collisions at RHIC 刘海东 中国科技大学

Main contribution n n Identified charged hadron spectra n PRL 97 (2006) 152301 (cited by 61 articles ) nucl-ex 0606003 (cited by 26 articles) Light nuclei spectra and v 2 n n n J. Phys. G: Nucl. Part Phys. 34(2007) S 1087 -s 1091 (cited by 3 articles ) International Journal of Modern Physics E， Vol: 16 Issue: 10 (2007) Page: 3280 - 3285 Anti-baryon phase space density study n nucl-ex/0610035 Submitted to PLB Haidong Liu (USTC) 2

Outline n n n Motivation Detectors and measurement Results (RHIC run 4 Au. Au 200 Ge. V) 3

Heavy-ion collisions at RHIC Time initial state freeze-out QGP and hydrodynamic expansion pre-equilibrium (high Q 2 interactions) hadronization Physics: 1) Parton distributions in nuclei 2) Initial conditions of the collision 3) A new state of matter – Quark-Gluon Plasma and its properties 4) Hadronization and freeze-out Haidong Liu (USTC) 4

Particles production n Charged hadron (pions and protons) production n Low p. T – hydrodynamic Intermediate p. T – partonic coalescence High p. T – jet fragmentation Haidong Liu (USTC) 5

p. QCD: Color charge and flavor dependence of parton energy loss S. Wicks et al. , NPA 784(2007)426 d. E/dx(c/b)<d. E/dx(uds)< d. E/dx(g) Haidong Liu (USTC) 6

Parton energy loss in HIJING calculation Study the PID spectra and pbar/p ratios can help to further understand how the g/q jets interact with the medium X. N. Wang: PRC 58(2321)1998. Haidong Liu (USTC) 7

n n n Different mechanisms govern hadron formation in the different kinematic region Different hadron species may have different sources Those sources (g/q) may have different behavior when propagating the medium To study those behaviors, PID in large p. T range is required! Haidong Liu (USTC) 8

STAR detectors: TPC & TOFr Time Projection Chamber 1. 2. Tracking Ionization energy loss (d. E/dx) A new technology (TOF) ---Multi-gap Resistive Plate Chamber 1. 2. Good timing resolution (<100 ps) Two trays (TOFr+TOFp) for run 4, acceptance~0. 01, 120 trays (TOFr) in the future Haidong Liu (USTC) 9

PID – Hadrons Low & intermediate p. T 2. 5<p. T<3. 0 High performance of time resolution PID up to 12 Ge. V/c TPC High p. T Relativistic rising of d. E/dx Haidong Liu (USTC) 10

Pion & proton spectra STAR Collaboration PRL 97 (2006) 152301 PAs: H. Liu, O. Barannikova, L. Ruan and Z. Xu PID up to 12 Ge. V/c Haidong Liu (USTC) 11

Nuclear Modification factor In central Au+Au collisions: n n p. T At 1. 5<p. T<7 Ge. V/c, RCP(p+pbar) > RCP( ) , RCP(p+pbar) shows obvious decreasing trend. At 4<p. T<12 Ge. V/c, both and p are strongly suppressed. They approach to each other at about 0. 3 Curve: I. Vitev, PLB 639 (2006) 38. Haidong Liu (USTC) 12

Color charge and flavor dependence of parton energy loss High p. T Rcp measurements: , p(pbar), e , , 0 Nucl-ex/0607012 p. T PRL 96 (2006) 202301 Rcp(RAA)~0. 2 for all these particles! Haidong Liu (USTC) 13

Anti-particle to particle ratios 1. 2. -/ + are consistent with flat at unity in all p. T, no significant centrality dependence. pbar/p ratio: no significant centrality dependence, parton energy loss underpredicts the ratios (X. N. Wang, PRC 58 (2321) 1998). Haidong Liu (USTC) 14

Proton over pion ratios 1. 2. 3. 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~2 -3 Ge. V/c, approach the corresponding ratios in p+p, d+Au collisions at p. T>5 Ge. V/c. In general, parton energy loss models underpredict p/ ratios. 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). Haidong Liu (USTC) 15

B/M enhancement at intermediate p T STAR Nucl-ex/0601042 1) The relative baryon enhancement is clearly observed in the p/pi ratios at intermediate p. T, the similar behavior can also be seen in the /Ks 0 ratios. At the same p. T region, the NQ scaling of v 2 has also been observed. This can be explained by the parton coalescence phenomena. 2) In general, parton energy loss models underpredict p/ ratios. 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). Haidong Liu (USTC) 16

Summary n n n First time to extend PID pt range up to 12 Ge. V/c for charged pion, kaon and (anti)proton First time to observe the similar suppressions for high pt mesons and baryons, which challenges the standard parton energy loss model Further test the coalescence model in the intermediate pt range Haidong Liu (USTC) 17

Haidong Liu (USTC) 18