1. Helen Caines Yale University Alice Week - Erice– Dec. 2005 An overview of recent STAR results What have we learnt this past year?

2. Helen Caines Alice Week - Erice – Dec. 2005 2 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 The data

3. Helen Caines Alice Week - Erice – Dec. 2005 3

4. Helen Caines Alice Week - Erice – Dec. 2005 4 short lived resonances T ch ss STAR white paper Nucl Phys A757 (05) 102 T ch ≈ T C ≈ 165 ± 10 MeV Chemical freezeout ≈ hadronization. s ~ u, d Strangeness is chemically equilibrated. Chemical freeze-out

5. Helen Caines Alice Week - Erice – Dec. 2005 5 Lifetime and size resonance decays and regeneration: measure kinetic freezeout – life time. Re-scattering and regeneration needed! Finite time span from T ch to T fo N part HBT: measures freeze-out source sizes (marked by collective flow). HBT size (low k T ): x2 expansion initial  final in Au+Au. What is the size at chemical freeze-out? may be assessed via  -  correlations.

6. Helen Caines Alice Week - Erice – Dec. 2005 6 p,K, p 200 GeV > 62 GeV T kin 200 GeV = 62 GeV  200 GeV = 62 GeV T kin 200 GeV > 62 GeV Radial Flow T kinetic from a Blast-Wave is not same as the Temperature from a Hydro Model. Temperature T kinetic is higher for baryons with higher strange quark content for Blast-wave fits. Spectral shapes are different. Most Central Collisions 0.13 T=100 MeV T=132 MeV

7. Helen Caines Alice Week - Erice – Dec. 2005 7 Baryon/Meson ratios Au+Au 0-10% p+p Baryon stopping has strong effect Shape driven by flow?

8. Helen Caines Alice Week - Erice – Dec. 2005 8 Elliptic flow Almond shape overlap region in coordinate space Anisotropy in momentum space Interactions/ Rescattering dN/d  ~ 1+2 v 2 (p T )cos(2  ) + ….  = atan(p y /p x ) v 2 =  cos2  v 2 : 2 nd harmonic Fourier coefficient in dN/d  with respect to the reaction plane P. Kolb, J. Sollfrank, and U. Heinz Au+Au at b=7 fm Equal energy density lines     Elliptic flow observable sensitive to early evolution of system Mechanism is self-quenching Large v 2 is an indication of early thermalization

9. Helen Caines Alice Week - Erice – Dec. 2005 9 Elliptic flow v 2 Hydro by Huovinen et al. hydro tuned to fit central spectra data. PRC 72 (05) 014904 200 GeV Au+Au min-bias large v 2 (even  ): strong interactions at early stage large v 2 of  (low hadronic x-sections): partonic collectivity at RHIC. First time hydro works: suggests early thermalization -  = 0.6 fm/c  = 20 GeV/fm 3 Soft (QGP) EOS favored: sub-hadronic DOF.

10. Helen Caines Alice Week - Erice – Dec. 2005 10 Significantly smaller v 2 in Cu-Cu than in Au-Au for given centrality Scales with v 2 (N part ) Large non-flow effects at high p T v 2 – Cu-Cu vs Au-Au Greater non-flow effects in Cu-Cu.

11. Helen Caines Alice Week - Erice – Dec. 2005 11 solid: STAR open: PHENIX PRL91(03) The complicated observed flow pattern in v 2 (p T ) for hadrons is predicted to be simple at the quark level under p T → p T /n v 2 → v 2 / n, n = (2, 3) for (meson, baryon) Works for p, ( , K 0 s, , ,  v 2 s ~ v 2 u,d ~ 7% Au+Au √s NN =62 GeV STAR Preliminary Constituent quark scaling Constituent quark DOF – deconfinement?

12. Helen Caines Alice Week - Erice – Dec. 2005 12 s-Baryon production is ~constant at mid-rapidity. STAR Preliminary  s-Baryon rises smoothly at mid-rapidity. Au+AuPb+Pb Collision energy dependencies What determines the overall yields? STAR Preliminary

13. Helen Caines Alice Week - Erice – Dec. 2005 13 Strangeness enhancement Correlation volume: V= A  NN ·V 0 A NN = N part /2 V 0 = 4/3  ·R 0 3 R 0 = 1.1 fm proton radius/ strong interactions T= 170-177 MeV  = 1 K. Redlich – private communication Particle ratios indicate T= 165 MeV  = 1/3 fits best, very sensitive to T STAR Preliminary Solid – STAR Open – NA57 STAR Preliminary

14. Helen Caines Alice Week - Erice – Dec. 2005 14 Flavor dependence of scalings Binary scaling for heavy flavor quark hadrons PHENIX D’s Participant scaling for light quark hadrons Hadrons with strange quarks an add-mixture of N part and N bin ?

15. Helen Caines Alice Week - Erice – Dec. 2005 15 Motivation from h - N.B.: SPS energy only 17 GeV There’s a correlation between dN ch /d  and N part /2 If know n pp can predict yield at any  N part  small dotted lines are: dN ch /d  n pp (1-x)N part /2 + xN bin n pp = Yield in pp = 2.29 ( 1.27) x = 0.13 PHOBOS: Phys. Rev. C70, 021902(R) (2004)

16. Helen Caines Alice Week - Erice – Dec. 2005 16 Strangeness and dN ch /d  SPS and RHIC data follows same curves as a func. of dN ch /d η dN ch /d η - strongly correlated to the entropy of the system! Look at yields relative to pp Entropy alone seems to drive much of the soft physics HBT radii show similar scaling with dNch/dη

17. Helen Caines Alice Week - Erice – Dec. 2005 17 High p T suppression J. Adams et al, Phys. Rev. Lett. 91 (2003) 072304 Binary coll. scalingp+p reference ♦ Central Au+Au collisions: factor ~4-5 suppression. ♦ p T >5 GeV/c: suppression ~ independent of p T. ♦ pQCD describes data only when energy loss included. R AA 1 Confirms final state effects present

18. Helen Caines Alice Week - Erice – Dec. 2005 18 Photons - unsuppressed Hadrons - suppressed Survival Probability Direct   0,  Confirming the probe We have an understood and calibrated probe

19. Helen Caines Alice Week - Erice – Dec. 2005 19 Geometrical dependence of R AA R AA scales smoothly from Au+Au  Cu+Cu  p+p Scaling prefers N part 1/3, though N part 2/3 not strongly excluded

20. Helen Caines Alice Week - Erice – Dec. 2005 20 Nuclear modification factors - R CP √s NN =200 GeV √s NN =62 GeV 0-5% 40-60% 0-5% 40-60% NA57, PLB in print, nucl-ex/0507012 √s NN =17.3 GeV First time differences between  and   B absorption? Recombination or different “Cronin” for  and K at SPS?

21. Helen Caines Alice Week - Erice – Dec. 2005 21 Nuclear modification factors - R AA HIJING/BBar + K T ~ 1 GeV Strong Colour Field qualitatively describes R AA. SCF - long range coherent fields SCF behaviour mimicked by doubling the effective string tension SCF controls  qq and qqqq production rates and  s Topor Pop et al. hep-ph/0505210 Effects dominate out to high p T SCF only produced in nucleus-nucleus collisions R AA ≠ R CP

22. Helen Caines Alice Week - Erice – Dec. 2005 22 Dead cone effect Coupling of heavy quarks to the medium reduced due to mass 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. Helen Caines Alice Week - Erice – Dec. 2005 23 Non-photonic e - R AA In central Au+Au collisions, non-photonic electrons are very strongly suppressed at high p T Data agree with c  e predictions if the density is quite high But b  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. Helen Caines Alice Week - Erice – Dec. 2005 24 Alternative scenario: collisional contribution AMPT: (C.M. Ko) ← σ=10 mb ← σ=3 mb ← pQCD Moore & Teaney, hep-ph/0412346 Large collisional interactions also produce suppression but also v 2 v 2 signal in e -

25. Helen Caines Alice Week - Erice – Dec. 2005 25 Jet correlations in proton-proton reactions. Strong back-to- back peaks. Jet correlations in central Gold-Gold. Away side jet disappears for particles p T > 2 GeV Jet correlations in central Gold-Gold. Away side jet reappears for particles p T >200 MeV Azimuthal Angular Correlations Jet quenching

26. Helen Caines Alice Week - Erice – Dec. 2005 26 Three regions on away side: center =( ,  ) ±0.4 corner =(  +1,  +1) ±0.4 x2 cone =(  +1,  - 1) ±0.4 x2 away near Medium mach cone Medium away near deflected jets  1  2   0 0  1  2  0 0  p T trig =3-4, p T assoc =1-2 GeV/c 2-particle corr, bg, v2 subtracted  φ 2 = φ 2 - φ trig d+Au min-bias dN 2 /d Δφ 1 d Δφ 2 /N trig  φ 1 = φ 1 - φ trig  φ 2 = φ 2 - φ trig Au+Au 10% difference in Au+Au average signal per radian 2 : center – corner = 0.3 ± 0.3 (stat) ± 0.4 (syst) center – cone = 2.6 ± 0.3 (stat) ± 0.8 (syst) conical flow? 3-particle correlation d+Au and Au+Au elongated along diagonal: k T effect, and deflected jets? Distinctive features of conical flow are not seen in present data.

27. Helen Caines Alice Week - Erice – Dec. 2005 27 Emergence of dijets For the first time: clear jet-like peaks seen on near and away side in central Au-Au collisions 8 < p T (trig) < 15 GeV/c STAR Preliminary p T (assoc)>6 GeV No background subtraction!

28. Helen Caines Alice Week - Erice – Dec. 2005 28 Centrality dependence of yields Near-side yields consistent within errors Away-side yields decrease monotically with increasing N Part –Suppression pattern similar for two p T (assoc) ranges! Fit scaled by x2 8 < p T (trig) < 15 GeV/c I AA ≈ R AA ≈ 0.20-0.25 ≈ 5-7 GeV 2 /fm in central Au+Au @ RHIC I AA = Yield (AA)/ Yield(dAu)

29. Helen Caines Alice Week - Erice – Dec. 2005 29 m T scaling STAR Preliminary p+p 200 GeV No complete m T scaling Au-Au Radial flow prevents scaling at low m T Seems to scale at higher m T p-p Appears to be scaling at low m T Baryon/meson splitting at higher m T – Gluon jets?

30. Helen Caines Alice Week - Erice – Dec. 2005 30 Gluon vs quark jets in p-p Quark jets events display mass splitting Gluon jets events display baryon/meson splitting No absolute m T scaling – “data” scaled to match at m T ~1 GeV/c Way to explore quark vs gluon dominance

31. Helen Caines Alice Week - Erice – Dec. 2005 31 STAR Preliminary Changing the probe: towards  -jet Correlations triggered on  : clear near and away-side peaks Strong contamination remains from  0 decay daughters –Work in progress to separate out direct   does not couple to medium or fragment into jets – remove trigger surface bias and fragmentation uncertainty in Q 2

32. Helen Caines Alice Week - Erice – Dec. 2005 32 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 Conclusions

33. Helen Caines Alice Week - Erice – Dec. 2005 33 STAR The STAR Collaboration 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 STAR