An overview of recent STAR results

1. What have we learnt this past year? An overview of recent STAR results

2. The data Run Year Species √s[GeV ] Ldt 01 2000 Au+Au 130 1 b-1 02 2001/2 Au+Au 200 24 b-1 p+p 200 0.15 pb-1 03 2002/3 d+Au 200 2.74 nb-1 p+p 200 0.35 pb-1 04 2003/4 Au+Au 200 241 b-1 Au+Au 62 9 b-1 05 2004/5 Cu+Cu 200 3 nb-1 Cu+Cu 62 0.19 nb-1 Cu+Cu 22.5 2.7 b-1 p+p 200 3.8 pb-1

4. Chemical freeze-out Tch short lived resonances STAR white paper Nucl Phys A757 (05) 102 gs • Tch ≈ TC ≈ 165 ± 10 MeVChemical freezeout ≈ hadronization. • s ~ u, d Strangeness is chemically equilibrated.

5. Lifetime and size resonance decays and regeneration: measure kinetic freezeout – life time. HBT: measures freeze-out source sizes (marked by collective flow). Npart HBT size (low kT): x2 expansion initial  final in Au+Au. What is the size at chemical freeze-out? may be assessed via p-X correlations. Re-scattering and regeneration needed! Finite time span from Tch to Tfo

6. Radial Flow 0.13 Most Central Collisions • Temperature Tkinetic is higher for baryons with higher strange quark content for Blast-wave fits. • Spectral shapes are different. T=100 MeV T=132 MeV • p,K, p <T> 200 GeV > 62 GeV Tkin 200 GeV = 62 GeV • X, W<T> 200 GeV = 62 GeV Tkin 200 GeV > 62 GeV Tkinetic from a Blast-Wave is not same as the Temperature from a Hydro Model.

7. Baryon/Meson ratios Au+Au 0-10% p+p Baryon stopping has strong effect Shape driven by flow?

8. Elliptic flow Almond shape overlap region in coordinate space Interactions/ Rescattering Anisotropy in momentum space t2 t3 t1 t4 Elliptic flow observable sensitive to early evolution of system Mechanism is self-quenching Large v2 is an indication of early thermalization dN/df ~ 1+2 v2(pT)cos(2f) + …. f = atan(py/px) v2= cos2f v2: 2nd harmonic Fourier coefficient in dN/d with respect to the reaction plane Au+Au at b=7 fm P. Kolb, J. Sollfrank, and U. Heinz Equal energy density lines

9. Elliptic flow v2 PRC 72 (05) 014904 200 GeV Au+Au min-bias Hydro by Huovinen et al. hydro tuned to fit central spectra data. large v2 (even f, X, W): strong interactions at early stage large v2 of f, X, W(low hadronic x-sections): partonic collectivity at RHIC. First time hydro works: suggests early thermalization - t = 0.6 fm/c e = 20 GeV/fm3 Soft (QGP) EOS favored: sub-hadronic DOF.

10. Significantly smaller v2 in Cu-Cu than in Au-Au for given centrality Scales with v2(Npart) Large non-flow effects at high pT v2 – Cu-Cu vs Au-Au Greater non-flow effects in Cu-Cu.

11. Constituent quark scaling solid: STAR open: PHENIX PRL91(03) STAR Preliminary Au+Au √sNN=62 GeV The complicated observed flow pattern in v2(pT) for hadrons is predicted to be simple at the quark level underpT → pT /n v2 → v2 / n , n = (2, 3) for (meson, baryon) Works for p, (p), K0s, , , W v2s ~ v2u,d ~ 7% Constituent quark DOF – deconfinement?

12. Collision energy dependencies STAR Preliminary Pb+Pb Au+Au STAR Preliminary • s-Baryon production is ~constant at mid-rapidity. • s-Baryon rises smoothly at mid-rapidity. What determines the overall yields?

13. Strangeness enhancement K. Redlich – private communication Solid – STAR Open – NA57 Correlation volume: V= AaNN·V0 ANN = Npart/2 V0 = 4/3p·R03 R0 = 1.1 fm proton radius/ strong interactions T= 170-177 MeV a= 1 STAR Preliminary Particle ratios indicate T= 165 MeV STAR Preliminary a = 1/3 fits best, very sensitive to T

14. Flavor dependence of scalings PHENIX D’s Participant scaling for light quark hadrons Binary scaling for heavy flavor quark hadrons Hadrons with strange quarks an add-mixture of Npart and Nbin?

15. Motivation from h- PHOBOS: Phys. Rev. C70, 021902(R) (2004) There’s a correlation between dNch/dh and Npart/2 small dotted lines are: dNch/dh = npp(1-x)Npart/2 + xNbin npp= Yield in pp = 2.29 ( 1.27) x = 0.13 N.B.: SPS energy only 17 GeV If know npp can predict yield at any Npart

16. Strangeness and dNch/dh Look at yields relative to pp SPS and RHIC data follows same curves as a func. of dNch/dη HBT radii show similar scaling with dNch/dη dNch/dη- strongly correlated to the entropy of the system! Entropy alone seems to drive much of the soft physics

17. High pT suppression Binary coll. scaling p+p reference J. Adams et al, Phys. Rev. Lett. 91 (2003) 072304 • Central Au+Au collisions: factor ~4-5 suppression. • pT >5 GeV/c: suppression ~ independent of pT. • pQCD describes data only when energy loss included. RAA << 1; RdAu > 1 Confirms final state effectspresent

18. Confirming the probe Photons - unsuppressed Hadrons - suppressed Direct g Survival Probability p0, h We have an understood and calibrated probe

19. Geometrical dependence of RAA • RAA scales smoothly from Au+Au  Cu+Cu  p+p Scaling prefers Npart1/3, though Npart2/3 not strongly excluded

20. Nuclear modification factors - RCP √sNN=62 GeV 0-5% 40-60% 0-5% 40-60% √sNN=17.3 GeV NA57, PLB in print, nucl-ex/0507012 √sNN=200 GeV First time differences between L and L B absorption? Recombination or different “Cronin” for L and K at SPS?

21. Nuclear modification factors - RAA HIJING/BBar + KT ~ 1 GeV Strong Colour Field qualitatively describes RAA. SCF - long range coherent fields SCF behaviour mimicked by doubling the effective string tension SCF controlsqq and qqqq production rates and gs Topor Pop et al. hep-ph/0505210 SCF only produced in nucleus-nucleus collisions RAA≠ RCP Effects dominate out to high pT

22. Coupling of heavy quarks to the medium reduced due to mass Dead cone effect Djordjevic et al, nucl-th/0507019 See also Armesto et al, Phys. Rev. D71 (2005) 054027 Expectation: Little suppression for single e- from heavy flavor

23. In central Au+Au collisions, non-photonic electrons are very strongly suppressed at high pT Non-photonic e- RAA • Data agree with c  e predictions if the density is quite high • Butb  e should be there, too • Is our understanding of c and b production correct? • Is our understanding of partonic energy loss correct? • How strong are the in-medium interactions? • How dense is the medium? • Re-scattering significant?

24. Alternative scenario: collisional contribution Moore & Teaney, hep-ph/0412346 AMPT: (C.M. Ko) ← σ=10 mb ← σ=3 mb ← pQCD Large collisional interactions also produce suppression but also v2 v2 signal in e-

25. Jet quenching Jet correlations in proton-proton reactions. Strong back-to-back peaks. Jet correlations in central Gold-Gold. Away side jet disappears for particles pT > 2 GeV Jet correlations in central Gold-Gold. Away side jet reappears for particles pT>200 MeV Azimuthal Angular Correlations

26. conical flow? 3-particle correlation pTtrig=3-4, pTassoc=1-2 GeV/c 2-particle corr, bg, v2 subtracted near near d+Au min-bias Df2 p Dφ2=φ2-φtrig Medium Medium away away 0 0 p mach cone Df1 Au+Au 10% Df2 Dφ2=φ2-φtrig p dN2/dΔφ1dΔφ2/Ntrig 0 deflected jets 0 p Df1 Dφ1=φ1-φtrig Three regions on away side: center = (p, p) ±0.4 corner = (p+1,p+1) ±0.4 x2 cone = (p+1,p-1) ±0.4 x2 difference in Au+Au average signal per radian2: center – corner = 0.3 ± 0.3 (stat) ± 0.4 (syst) center – cone = 2.6 ± 0.3 (stat) ± 0.8 (syst) d+Au and Au+Au elongated along diagonal: kT effect, and deflected jets? Distinctive features of conical flow are not seen in present data.

27. Emergence of dijets 8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV STAR Preliminary No background subtraction! For the first time: clear jet-like peaks seen on near and away side in central Au-Au collisions

28. Centrality dependence of yields ≈ 5-7 GeV2/fm in central Au+Au @ RHIC Fit scaledby x2 8 < pT(trig) < 15 GeV/c • Near-side yields consistent within errors • Away-side yields decrease monotically with increasing NPart • Suppression pattern similar for two pT(assoc) ranges! IAA = Yield (AA)/ Yield(dAu) IAA ≈RAA ≈ 0.20-0.25

29. mT scaling STAR Preliminary p+p 200 GeV No complete mT scaling Au-Au Radial flow prevents scaling at low mT Seems to scale at higher mT p-p Appears to be scaling at low mT Baryon/meson splitting at higher mT – Gluon jets?

30. Gluon vs quark jets in p-p No absolute mT scaling – “data” scaled to match at mT~1 GeV/c Quark jets events display mass splitting Gluon jets events display baryon/meson splitting Way to explore quark vs gluon dominance

31. Changing the probe: towards g-jet STAR Preliminary • Correlations triggered on g: clear near and away-side peaks • Strong contamination remains from p0 decay daughters • Work in progress to separate out direct g • g does not couple to medium or fragment into jets • remove trigger surface bias and fragmentation uncertainty in Q2

32. Conclusions • We have successfully created • the Quark Gluon Plasma! • Now we have many exciting • properties that we are just • beginning to explore…. • low viscosity • rapid equilibration • novel hadron formation mechanisms • jet quenching and medium reaction • temperature determination • degrees of freedom

33. The STAR Collaboration STAR U.S. Labs: Argonne, Lawrence Berkeley, and Brookhaven National Labs U.S. Universities: UC Berkeley, UC Davis, UCLA, Caltech, Carnegie Mellon, Creighton, Indiana, Kent State, MIT, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale Brazil: Universidade de Sao Paolo China: IHEP - Beijing, IPP - Wuhan, USTC, Tsinghua, SINAP, IMP Lanzhou Croatia: Zagreb University Czech Republic: Nuclear Physics Institute England: University of Birmingham France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes Germany: Max Planck Institute – Munich University of Frankfurt India: Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC Netherlands: NIKHEF/Utrecht Poland: Warsaw University of Technology Russia: MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP – Protvino South Korea: Pusan National University Switzerland: University of Bern