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Production of meson, baryon and light nuclei in Au+Au collisions at RHIC Haidong Liu Univ. of Science & Technology of China.

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Presentation on theme: "Production of meson, baryon and light nuclei in Au+Au collisions at RHIC Haidong Liu Univ. of Science & Technology of China."— Presentation transcript:

1 Production of meson, baryon and light nuclei in Au+Au collisions at RHIC Haidong Liu Univ. of Science & Technology of China

2 UC Davis, Aug 21, 2007Haidong Liu2 Outline Motivation and introductions Detectors and techniques Results (RHIC run 4 AuAu 200 GeV) Conclusions & Discussions

3 UC Davis, Aug 21, 2007Haidong Liu3 Motivations & Introductions

4 UC Davis, Aug 21, 2007Haidong Liu4 Heavy-ion collisions at RHIC Time initial state pre-equilibrium (high Q 2 interactions) QGP and hydrodynamic expansion hadronization freeze-out 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

5 UC Davis, Aug 21, 2007Haidong Liu5 Particles production Pions and protons production Low p T – hydrodynamic Intermediate p T – partonic coalescence High p T – jet fragmentation Light nuclei production Final-state coalescence

6 UC Davis, Aug 21, 2007Haidong Liu6 The success of hydrodynamic At low p T, hydrodynamical models successfully reproduce the spectra and v 2 STAR PRC.72 (2005) 014904

7 UC Davis, Aug 21, 2007Haidong Liu7 Coalescence at intermediate p T STAR PRC.72 (2005) 014904 NQ scaling of v 2 is a strong evidence Coalescence fragmenting parton: p h = z p, z<1 recombining partons: p 1 +p 2 =p h

8 UC Davis, Aug 21, 2007Haidong Liu8 STAR: Nucl. Phys. A 757 (2005) 102 The difference is not sensitive to the mass of the hadron, but rather depends on the number of valence quarks contained within it. Coalescence at intermediate p T

9 UC Davis, Aug 21, 2007Haidong Liu9 High p T – from pp to AuAu p+p collisions Parton Distribution Function (derived from e-h scattering) pQCD (parton-parton interaction cross section calculation) Fragmentation Function (derived from e + e - collisions) Au+Au collisions pp collisions + Nuclear effect We understand pp collisions

10 UC Davis, Aug 21, 2007Haidong Liu10 Jet fragmentation in pp collisions 1.Improved FF reasonably reproduces data 2.pbar/  ~ 0.2 at RHIC, <<0.1 at low energy pbar dominated by gluon FF PLB 637 (2006) 161

11 UC Davis, Aug 21, 2007Haidong Liu11 Jet quenching in Au+Au STAR: Nucl. Phys. A 757 (2005) 102 Significant suppression of inclusive charged hadron is observed in central Au+Au collisions: Fragmentation+parton energy loss

12 UC Davis, Aug 21, 2007Haidong Liu12 X.N. Wang: PRC58(2321)1998. Study the PID spectra and pbar/p ratios can help to further understand how the g/q jets interact with the medium Parton energy loss in HIJING HIJING calculation

13 UC Davis, Aug 21, 2007Haidong Liu13 pQCD: Color charge and flavor dependence of parton energy loss dE/dx(c/b)<dE/dx(uds)< dE/dx(g) S. Wicks et al., NPA 784(2007)426

14 UC Davis, Aug 21, 2007Haidong Liu14 The roles of energetic parton --- source of the meson/baryon production (1)In LEP e+e- experiment, identified charged particle spectra can be measured from 2 kinds of hadronic Z decays: quark jets and gluon jets (DELPHI EPJC 17 (2000) 207) (2) The anti-baryon phase space density can be accessed by measuring dbar/pbar F.Q. Wang, N. Xu, PRC 61 021904 (2000)

15 UC Davis, Aug 21, 2007Haidong Liu15 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!

16 UC Davis, Aug 21, 2007Haidong Liu16 Light nuclei formation – final-state coalescence Chemical Freeze-out Thermal Freeze-out Initial Collisions “QGP” “De-confinement” Hadronization Late stage scattering Due to the small binding energy, light nuclei cannot survive before thermal freeze-out. Therefore, light nuclei production and their elliptic flow are sensitive to the freeze-out conditions, such as temperature, particle density, local correlation volume and collective motion. Time

17 UC Davis, Aug 21, 2007Haidong Liu17 Final-state Coalescence R. Scheibl, U. Heinz, PRC 59 1585 (1999) Coalescence parameters B A Light nuclei v 2 – atomic mass number (A) scaling? (consequence of the final-state coalescence)

18 UC Davis, Aug 21, 2007Haidong Liu18 Detectors & Techniques

19 UC Davis, Aug 21, 2007Haidong Liu19 STAR detectors: TPC & TOF A new technology (TOF) ---- Multi-gap Resistive Plate Chamber 1.Good timing resolution (<100ps) 2.Two trays (TOFr+TOFp) for run 4, acceptance~0.01, 120 trays (TOFr) in the future Time Projection Chamber 1.Tracking 2.Ionization energy loss (dE/dx)

20 UC Davis, Aug 21, 2007Haidong Liu20 PID – Hadrons TPC Relativistic rising of dE/dx High p T High performance of time resolution Low & intermediate p T 2.5<p T <3.0 PID up to 12 GeV/c

21 UC Davis, Aug 21, 2007Haidong Liu21 Light Nuclei Identification PID Range (GeV/c): TOF

22 UC Davis, Aug 21, 2007Haidong Liu22 Feed-down correction for (anti-)protons Method 1: Primordial protons and the protons come from weak decays have different DCA distribution Primordial (MC) From decay (MC) Method 2: From the measurements of  and  spectra, we can estimate the FD contribution

23 UC Davis, Aug 21, 2007Haidong Liu23 Results (Au+Au 200 GeV) Pion and proton spectra: STAR Phys. Rev. Lett. 97 (2006) 152301 Nuclei spectra and v 2 : QM06 proceeding, J. Phys. G: Nucl. Part. Phys. 34 (2007) S1087-S1091

24 UC Davis, Aug 21, 2007Haidong Liu24 Pion & proton spectra PID up to 12 GeV/c STAR Collaboration PRL 97 (2006) 152301 PAs: O. Barannikova, H. Liu, L. Ruan and Z. Xu

25 UC Davis, Aug 21, 2007Haidong Liu25 Nuclear Modification factor In central Au+Au collisions: At 1.5 R CP (  ), R CP (p+pbar) shows obvious decreasing trend. At 4<p T <12 GeV/c, both  and p are strongly suppressed. They approach to each other at about 0.3 Curve: I. Vitev, PLB 639 (2006) 38. pTpT

26 UC Davis, Aug 21, 2007Haidong Liu26 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, parton energy loss underpredicts the ratios ( X.N. Wang, PRC 58 (2321) 1998).

27 UC Davis, Aug 21, 2007Haidong Liu27 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. 3.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).

28 UC Davis, Aug 21, 2007Haidong Liu28 Light Nuclei Spectra Deuteron Helium-3 QM06 proceeding: J. Phys. G: Nucl.Part. Phys. 34 (2007) S1087-S1091

29 UC Davis, Aug 21, 2007Haidong Liu29 Coalescence Parameters B 2 & B 3 B 2 & sqrt(B 3 ) are consistent Strong centrality dependence (anti-)proton spectra: STAR Phys. Rev. Lett. 97, 152301 (2006)

30 UC Davis, Aug 21, 2007Haidong Liu30 Coalescence Parameters B 2 & B 3 Compare to pion HBT results Beam energy dependence HBT parameters: STAR Phys. Rev. C71 (2005) 044906 Assuming a Gaussian shape in all 3 dimensions R. Scheibl et al.Phys.Rev.C59 (1999)1585

31 UC Davis, Aug 21, 2007Haidong Liu31 Scaled by A Baryon v 2 -- X.Dong et al, Phys. Lett. B597 (2004) 328-332 Light Nuclei v 2 This is the 1 st helium-3 v 2 measurement at RHIC Deuterons v 2 follows A scaling within error bars Helium-3 v 2 seems deviating from A scaling at higher p T (need more statistics) minBias

32 UC Davis, Aug 21, 2007Haidong Liu32 Low p T v 2 The 1 st observation of negative v 2 at RHIC No model can readily reproduce the data dbar centrality bins: 0~12%, 10~20%, 20~40%, 40~80% pbar v 2 : STAR Phys. Rev. C72 (2005) 014904 BW parameters: F. Retiere, M. Lisa, Phys.Rev. C70 (2004) 044907

33 UC Davis, Aug 21, 2007Haidong Liu33 Accessing anti-baryon density by & Source of anti-baryon production H. Liu & Z. Xu, nucl-ex/0610035 Submitted to PLB

34 UC Davis, Aug 21, 2007Haidong Liu34 In nucleus+nuclues collisions, the anti-baryon density increases with beam energy and reaches a plateau above ISR beam energy regardless the beam species (pp, pA, AA). It can be fitted to a thermal model : Anti-baryon Phase Space Density STAR preliminary F.Q. Wang, N. Xu, PRC 61 021904 (2000)

35 UC Davis, Aug 21, 2007Haidong Liu35 Anti-baryon Phase Space Density STAR preliminary ARGUS e + e - sqrt(s)=9.86(  ) ggg high sqrt(s)=10 q+qbar low

36 UC Davis, Aug 21, 2007Haidong Liu36 Anti-baryon Phase Space Density ARGUS e + e - sqrt(s)=9.86(  ) ggg high sqrt(s)=10 q+qbar low ALEPH(LEP) e + e - sqrt(s)=91(Z) q+qbar low STAR preliminary

37 UC Davis, Aug 21, 2007Haidong Liu37 Anti-baryon Phase Space Density ARGUS e + e - sqrt(s)=9.86(  ) ggg high sqrt(s)=10 q+qbar low ALEPH(LEP) e + e - sqrt(s)=91(Z) q+qbar low AGS, SPS, RHIC, ISR, Tevatron nucleus+nucleus (AA, pA, pp, p+pbar) sqrt(s NN )>50 q+g, qbar+g high sqrt(s NN )<20 q+g, q+q low STAR preliminary

38 UC Davis, Aug 21, 2007Haidong Liu38 Anti-baryon Phase Space Density ARGUS e + e - sqrt(s)=9.86(  ) ggg high sqrt(s)=10 q+qbar low ALEPH(LEP) e + e - sqrt(s)=91(Z) q+qbar low AGS, SPS, RHIC, ISR, Tevatron nucleus+nucleus (AA, pA, pp, p+pbar) sqrt(s NN )>50 q+g, qbar+g high sqrt(s NN )<20 q+g, q+q low H1(HERA)  p W  p =200 qqbar+g high STAR preliminary

39 UC Davis, Aug 21, 2007Haidong Liu39 ARGUS e + e - sqrt(s)=9.86(  ) ggg high sqrt(s)=10 q+qbar low ALEPH(LEP) e + e - sqrt(s)=91(Z) q+qbar low AGS, SPS, RHIC, ISR, Tevatron nucleus+nucleus (AA, pA, pp, p+pbar) sqrt(s NN )>50 q+g, qbar+g high sqrt(s NN )<20 q+g, q+q low H1(HERA)  p W  p =200 qqbar+g high In e + e -, the density through qqbar processes is a factor of strong coupling constant less than that through ggg processes (  s =0.12) (q+qbar->q+qbar+g) ss STAR preliminary Anti-baryon Phase Space Density H. Liu, Z. Xu nucl-ex/0610035

40 UC Davis, Aug 21, 2007Haidong Liu40 Where does (anti-)baryon come from? In short, anti-baryon phase space density from collisions involving a gluon is much higher than those without gluons Conclusions: (1) Collisions which contain ggg, qbar+g or qqbar+g processes have higher anti-baryon phase space density (2) Processes q+qbar create few anti- baryons (3) Processes q+g create few anti- baryons at low energy – energy too low? STAR preliminary

41 UC Davis, Aug 21, 2007Haidong Liu41 Conclusions & Discussions

42 UC Davis, Aug 21, 2007Haidong Liu42 B/M enhancement at intermediate p T 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  /K s 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. STAR Nucl-ex/0601042

43 UC Davis, Aug 21, 2007Haidong Liu43 Freeze-out volumes B 2 and B 3 have strong centrality dependence, the system has larger freeze-out volumes in more central collisions. B 2 and sqrt(B 3 ) have similar values in different centrality collisions, which indicates that the deuteron and helium-3 have similar freeze-out volume. B 2 has little beam energy dependence when sqrt(s NN )>20 GeV, which indicates that the freeze-out volume won’t change with the beam energy.

44 UC Davis, Aug 21, 2007Haidong Liu44 Light nuclei v 2 At intermediate p T, deuteron v 2 follows A scaling within errors while helium-3 v 2 seems deviates from this scaling, we need more statistics to draw further conclusion. At low p T, the dbar v 2 is found to be negative. The BW model, which includes large radial flow scenario, also shows a negative flow prediction. But the BW model fails to reproduce our data since there is only mass input for light nuclei.

45 UC Davis, Aug 21, 2007Haidong Liu45 Color charge and flavor dependence of parton energy loss High p T Rcp measurements:  , p(pbar), e , ,  0 pTpT Nucl-ex/0607012 PRL 96 (2006) 202301 Rcp(R AA )~0.2 for all these particles!

46 UC Davis, Aug 21, 2007Haidong Liu46 Color charge and flavor dependence of parton energy loss The partonic source:  , ,  0 – light quarks p(pbar) – glouns e  – heavy quarks pQCD calculations dE/dx(c/b)<dE/dx(uds)< dE/dx(g) S. Wicks et al., NPA 784(2007)426 Rcp(R AA )~0.2 for all these particles! ???

47 UC Davis, Aug 21, 2007Haidong Liu47 Physics possible: g/q jets conversion in the medium soft q(qbar) + hard g hard q(qbar) + soft g Compton-like scattering: W. Liu et al., nucl-th/0607047 A much larger cross-section is needed to explain our data

48 UC Davis, Aug 21, 2007Haidong Liu48 The future – a good time for discovery Inv. Yield~ Anti- 3 He : dbar : pbar 1 : 1K : 1M In the RHIC upcoming high statistics AuAu runs, with STAR large acceptance detector TPC/TOF, we should try to search for anti- , which has never been observed before. And, there is also possible to discover Antihypernucleus STAR Phys. Rev. Lett. 87 (2001) 262301 E864 Phys. Rev. Lett. 85 (2000) 2685 Thanks!

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