1. Production and Flow of Identified Hadrons at RHIC Julia Velkovska XXXIV International Symposium on Multiparticle Dynamics Sonoma State University, 2004

2. July 27,2004, ISMDJ.Velkovska2 RHIC Specifications 3.83 km circumference Two independent rings 120 bunches/ring 106 ns crossing time Capable of colliding ~any nuclear species on ~any other species Energy: è 500 GeV for p-p è 200 GeV for Au-Au (per N-N collision) Luminosity Au-Au: 2 x 10 26 cm -2 s -1 p-p : 2 x 10 32 cm -2 s -1

3. July 27,2004, ISMDJ.Velkovska3 Summary of RHIC runs so far p+p : 200 GeV, baseline measurement d+Au : 200 GeV, study cold nuclear matter Au+Au : 200 GeV, Run2, Run4 : 130 GeV, Run1 : 62.4 GeV ( match top ISR energy) Run4 : very short 56 GeV, 19 GeV Data in this talk: mostly from 200 GeV runs Mostly from PHENIX

4. July 27,2004, ISMDJ.Velkovska4 Particle production at RHIC energies Bulk of particle production Collective phenomena pQCD Soft (hydro) 0 1 2 3 4 5 6 7 8 9 10 11 12 GeV/c Hard probes Modified by the medium Jet Quenching ? New physics This talk is focused at intermediate p T, but to get there we need to review both soft and hard particle production.

5. July 27,2004, ISMDJ.Velkovska5 pp and dAu identified hadron spectra: m T scaling Idenpendent of mass, strangeness,etc - approximately same m T slope

6. July 27,2004, ISMDJ.Velkovska6 Au+Au collisions Modifications to soft processes from the nuclear medium 1. Slopes depend on particle mass 2. Spectra are NOT exponential in m T T eff depends on fitting range Best to compare to full hydro calculations Very low m T data from PHOBOS – constrain the amount of flow needed to describe the data

7. July 27,2004, ISMDJ.Velkovska7 Example of Blast wave fits 0-10% central Au+Au 200 GeV Fit |m T –m 0 | < 1GeV Extrapolate  meson described by same T fo,  

8. July 27,2004, ISMDJ.Velkovska8 Soft processes: Summary m T “ scaling” in pp and dAu collisions Radial flow in AuAu collisions. Protons and anti- protons spectra significantly affected due to their large mass

9. Hard probes

10. July 27,2004, ISMDJ.Velkovska10 Why study hard scattering ? (in Brief) The full pallet of QCD probes can be created and measured in the RHIC experiments q: fast color triplet g: fast color octet Q: slow color triplet QQbar: slow color singlet/octet Virtual photon: colorless Real photon: colorless Unknown Medium Induced gluon radiation? Energy Loss? Dissociation? Controls A main goal of relativistic heavy ion physics is to investigate high- temperature, high-density QCD, by creating and then studying the highly-excited medium produced in high-energy nuclear collisions. QCD probe in QCD probe out Excited medium (possible quark-gluon plasma?) Modification? One method of diagnosing a QCD medium is to shoot a QCD-sensitive probe through it, then look for any modifications due to the medium. (Most obvious possibilities: multiple scatterings, induced radiations, and energy loss.)

11. July 27,2004, ISMDJ.Velkovska11 Constrains Fragmentation Function D(Gluon-pi) Reference for Au+Au spectra  0 production in p+p Phys. Rev. Let 91, 241803 (2003)  AB  hX  f a/A (x a,Q 2 a )  f b/B (x b,Q 2 b )  a b  cd  D h/c (z c,Q 2 c ) Good agreement with NLO pQCD Factorization theorem: KKP Kretzer data vs pQCD 200 GeV - Run2

12. July 27,2004, ISMDJ.Velkovska12 If no “effects”:  R < 1 in regime of soft physics  R = 1 at high-p T where hard scattering dominates  A+B = A*B(p+p) Nuclear Modification Factor R AA /R CP Quantify deviations from expected behaviour in p+p collisions: /  inel p+p (Nuclear Geometry)

13. July 27,2004, ISMDJ.Velkovska13 Nuclear Modification factor R AA for   @ 200 GeV strong suppression Phys. Rev. Lett. 91, 072301 (2003) Jet quenching due to the dense medium No modification for Peripheral AuAu

14. July 27,2004, ISMDJ.Velkovska14 R AA for  0 in Central Collisions: Energy Dependence A.L.S.Angelis, PLB 185, 213 (1987) WA98, EPJ C 23, 225 (2002),[ Renormalization: D.d'E. nucl-ex/0403055] PHENIX, PRL 88 022301 (2002) ; PHENIX, PRL 91, 072303 (2003) Cronin enhancement at 17 GeV Suppression at 62 And 200 GeV Differences < 6 GeV/c Central AA

15. July 27,2004, ISMDJ.Velkovska15 Protons are not produced from colorless objects: but N coll scaling !

16. July 27,2004, ISMDJ.Velkovska16 Large!!! baryon/meson ratios Peripheral: consistent with standard fragmentation Central: a factor ~ 3 higher than peripheral, e + e - and ISR pp data p and pbar at p T 2-5 GeV/c : SOFT OR HARD ? Phys. Rev. Lett 91, 172301 (2003)Phys. Rev. Lett 91, 172301 (2003).

17. July 27,2004, ISMDJ.Velkovska17 Scaling properties of  (1020)  meson: Similar mass as proton, but meson.  Ideal test particle whether the observed baryon anomaly is a mass effect or not. proton, pbar: PHENIX: PRL 91, 172301 (2003), PRC 69, 034909 (2004)  : PHENIX final data, will be submitted to PRC. p, pbar: low p T (< 1.5 GeV/c): different shape due to the radial flow, intermediate p T : Ncoll scaling  : does not scale with N coll

18. July 27,2004, ISMDJ.Velkovska18 R cp of p,   mesons are heavy, but follow  0, not p+pbar! Indicates the absence of suppression of proton at intermediate p T is not a mass effect.

19. July 27,2004, ISMDJ.Velkovska19 Compilation on R cp from STAR Presented by M. Lamont (QM04) Two distinct groups in R cp, i.e. meson and baryon, not by particle mass. Separate at p T ~ 2 GeV/c and come together at 5 GeV/c. baryon meson

20. July 27,2004, ISMDJ.Velkovska20 Bulk (Hydrodynamic) Matter Pressure gradient converts position space anisotropy to momentum space anisotropy. Jet Propagation Energy loss results anisotropy based on location of hard scattering in collision volume. y x y x low p T high p T Azimuthal Anisotropy of Particle Emission

21. July 27,2004, ISMDJ.Velkovska21 Elliptic Flow of baryons and mesons At low p T hydro works remarkably well Above ~ 2 GeV/c : A split between mesons and baryons v2 – too large to be attributed to jet absorption (geometric limit for surface emission exceeded)

22. July 27,2004, ISMDJ.Velkovska22 Universal behavior in flow per quark

23. July 27,2004, ISMDJ.Velkovska23 Recombination of quarks to explain the data describe Rcp particle ratios, spectra, v2: pT(baryons) >pT(mesons)>pT(quarks) Duke model, PRC 68, 044902 (2003) p/  R cp

24. July 27,2004, ISMDJ.Velkovska24 Jet correlations with identified mesons and baryons jet partner equally likely for trigger baryons & mesons flat centrality dependence (within errors) expected from purely thermal recombination (nucl-th/0306027) Need partons from jets to explain the data!! A. Sickles

25. July 27,2004, ISMDJ.Velkovska25 Jet correlations with identified particles: Star “jettiness” of intermediate p T baryons confirmed!

26. July 27,2004, ISMDJ.Velkovska26 Summary Au+Au collisions at RHIC form a bulk medium which exhibits collective effects Radial flow (mass dependent) Elliptic flow: descirbed by hydro at low p T, partonic description works at high p T Hard probes: Dense nuclear medium is responsible for jet quenching dAu collisions show it is a final state effect At intermediate p T baryons are not suppressed Is there a new production mechanism at p T = 2-5 GeV ? Recombination: success and challenges Hadron yields and elliptic flow scale with the number of quarks: Points to partonic degrees of freedom baryons show jettiness – recombination of shower partons is needed

27. July 27,2004, ISMDJ.Velkovska27 EXTRA

28. July 27,2004, ISMDJ.Velkovska28 New data: R AA @ 62.4 GeV : Charged hadron and   Common reference p+p  charged+X is used, instead of ISR  0 reference.  0 yield is divided by (charged reference)/1.6. Clear difference between charged and  0 at intermediate p T up to 4 GeV/c. Suggests a large proton contribution in this p T region, as seen in 200 GeV data. 00 charged 0-10%

29. July 27,2004, ISMDJ.Velkovska29 Cronin effect stronger for protons than for pions Not enough to account for factor of 3 increase of p/  in central AuAu

30. July 27,2004, ISMDJ.Velkovska30 The proton “bump” in the h/  ratios Expectation (pp, e + e - ): h/   1.6 Above 5 GeV/c and in peripheral collisions: recover standard fragmentation Au+Au @ 200AGeV nucl-ex/0310005

31. July 27,2004, ISMDJ.Velkovska31 But what about the Cronin effect ? Can Cronin effect produce the enhanced p/  ratio in AuAu ? Usual description: “Initial state multiple scattering leading to pt broadening.” Why is it different for protons and pions ? P.B.Straub et al., Phys.Rev.Lett., 68,452(1992) P.B. Straub et al., PRL 68 (1992) FNAL experiments measuring R (W / Be) for identified particles at sqrt(s) of 27.4 and 51.3 GeV.

32. July 27,2004, ISMDJ.Velkovska32 Direct photons: a colorless probe 1 + (  pQCD direct x N coll ) / (  phenix pp backgrd x N coll ) [w/ the real, suppressed background] PHENIX Preliminary PbGl / PbSc Combined AuAu 200 GeV Central 0-10% 1 + (  pQCD direct x N coll ) /  phenix backgrd Vogelsang NLO Built-in control experiment in the AuAu data. Direct photons are described by a curve that includes the measured suppressed    production in AuAu.

33. July 27,2004, ISMDJ.Velkovska33 Strange baryon/meson ratios The mid-pT anomaly not unique to p/  also seen for strange particles With a little higher p T reach:  K 0 s has a peak at ~ 3GeV/c Height depends on centrality Peripheral – above pp data

34. July 27,2004, ISMDJ.Velkovska34 R AA for  0 and charged hadron PHENIX AuAu 200 GeV  0 data: PRL 91 072301 (2003), nucl-ex/0304022. charged hadron (preliminary) : NPA715, 769c (2003).

35. July 27,2004, ISMDJ.Velkovska35 p/  in dAu, pp and AuAu HUGE nuclear effect Coming from the final state (hot nuclear matter)