Anisotropic flow at RHIC from SPS to RHIC Raimond Snellings

Raimond Snellings; Moriond 2004 Introduction Heavy-Ion Collisions Study QCD at high temperature and density Establish and characterize properties of deconfined matter and the phase transition Requirement observables Provide information about the early, possibly deconfined phase Sensitive to the bulk properties Raimond Snellings; Moriond 2004

“Early” stage: high-pt probes Evidence of very dense system RAA, IAA Null experiment essential ! Raimond Snellings; Moriond 2004

Non-central heavy-ion collisions: coordinate system Raimond Snellings; Moriond 2004

Calculating flow using multi particle correlations Assumption all correlations between particles due to flow Non flow correlation contribute order (1/N), problem if vn≈1/√N Non flow correlation contribute order (1/N3), problem if vn≈1/N¾ N. Borghini, P.M. Dinh and J.-Y Ollitrault, Phys. Rev. C63 (2001) 054906 Raimond Snellings; Moriond 2004

Raimond Snellings; Moriond 2004 v2(pt) for high pt particles (self normalizing tomography of dense matter) M. Gyulassy, I. Vitev and X.N. Wang PRL 86 (2001) 2537 http://www.lbl.gov/nsd/annual/rbf/nsd1998/rnc/RNC.htm R17. Event Anisotropy as a Probe of Jet Quenching R.S and X.-N. Wang R.S, A.M. Poskanzer, S.A. Voloshin, STAR note, arXiv:nucl-ex/9904003 Raimond Snellings; Moriond 2004

Charged particle v2 at high-pt STAR preliminary PHENIX preliminary N. N. Ajitanand: Nucl.Phys. A715 (2003) 765-768 K. Filimonov: Nucl. Phys. A715 (2003) 737-740 Raimond Snellings; Moriond 2004

Raimond Snellings; Moriond 2004 Elliptic flow at higher pt, extracted using multi-particle correlations STAR Preliminary v2{2} v2{RP} v2{4} Significant v2 up to ~7 GeV/c in pt as expected from jet quenching. However at intermediate pt the magnitude is unexpectedly large A. Tang (STAR) QM 2004 Raimond Snellings; Moriond 2004

Raimond Snellings; Moriond 2004 More detailed information: v2(pt) for identified particles at higher-pt PHENIX STAR Preliminary ShinIchi Esumi: Nucl. Phys. A715 (2003) 599 P. Sorensen Raimond Snellings; Moriond 2004

Parton Coalescence/recombination? D. Molnar, S.A. Voloshin: Phys.Rev.Lett. 91 (2003) 092301 V. Greco, C.M. Ko and P. Levai: nucl-th/0305024 C. Nonaka, R.J. Fries, S.A. Bass nucl-th/0308051 J. Castillo (STAR preliminary) QM2004 M. Kaneta (PHENIX) QM2004 Raimond Snellings; Moriond 2004

Raimond Snellings; Moriond 2004 What about the bulk? y x coordinate space Coordinate space configuration anisotropic (almond shape) however, initial momentum distribution isotropic (spherically symmetric) Only interactions among constituents generate a pressure gradient, which transforms the initial coordinate space anisotropy into a momentum space anisotropy (no analogy in pp) Multiple interactions lead to thermalization -> limiting behavior ideal hydrodynamic flow py px Momentum space Raimond Snellings; Moriond 2004

Raimond Snellings; Moriond 2004 Time evolution SCIENCE Vol: 298 2179 (2002) Hydro calculation: P. Kolb, J. Sollfrank and U.Heinz Elliptic Flow reduces spatial anisotropy -> self quenching Raimond Snellings; Moriond 2004

Main contribution to elliptic flow develops early in the collision Zhang, Gyulassy, Ko, Phys. Lett. B455 (1999) 45 Raimond Snellings; Moriond 2004

Integrated Elliptic Flow PHOBOS: Phys. Rev. Lett. 89, 222301 (2002)  PHENIX: Phys. Rev. Lett. 89, 212301 (2002) STAR: Phys. Rev. Lett. 86, 402 (2001) Hydrodynamic limit STAR PHOBOS Compilation and Figure from M. Kaneta RQMD First time in Heavy-Ion Collisions a system created which at low pt is in quantitative agreement with hydrodynamic model predictions for v2 up to mid-central collisions Raimond Snellings; Moriond 2004

Elliptic flow at lower energies P. Kolb, J. Sollfrank, and U. Heinz, Phys. Rev. C. C62 054909 (2000). Raimond Snellings; Moriond 2004

Raimond Snellings; Moriond 2004 Identified particle v2 Fluid cells expand with collective velocity v, different mass particles get different Dp Hydro: P. Huovinen, P. Kolb, U. Heinz Typical pt dependence for different masses Heavy particles more sensitive to velocity distribution (less effected by thermal smearing) therefore put better constrained on EOS STAR Raimond Snellings; Moriond 2004

Raimond Snellings; Moriond 2004 v2(pt,mass) All particles reasonably described at low-pt with common set of parameters PHENIX (squares) and STAR agree well STAR, PHENIX preliminary Raimond Snellings; Moriond 2004

Raimond Snellings; Moriond 2004 Everything flows? J. Castillo (STAR) QM2004 What about charm? M. Kaneta (PHENIX) QM2004 Raimond Snellings; Moriond 2004 pT [GeV/c]

Raimond Snellings; Moriond 2004 Conclusion Consistent measurements of elliptic flow from PHENIX, PHOBOS and STAR Elliptic flow for all measured particles at low-pt well described by boosted thermal particle distributions Flow is large; indicative of strong partonic interactions at early stage of the collision In ideal hydro; thermalization time < 1 fm/c to describe the flow Up to pt = 7 GeV/c sizable elliptic flow, consistent with parton energy loss Parton coalescence/recombination does a good job at intermediate pt; important tests the precise v2 of the f-meson and the W 0 1 2 3 4 5 6 7 8 9 10 11 12 GeV/c Hydro ReCo R. Fries QM2004 pQCD Raimond Snellings; Moriond 2004

Raimond Snellings; Moriond 2004 What have we learned from elliptic flow so far (according to theorists)? U. Heinz: Resulting in a well-developed quark-gluon plasma with almost ideal fluid-dynamical collective behavior and a lifetime of several fm/c (arXiv:hep-ph/0109006). E. Shuryak: Probably the most direct signature of QGP plasma formation, observed at RHIC (arXiv:nucl-th/0112042). L. McLerran: one needs very strong interactions amongst the quark and gluons at very early times in the collision (arXiv:hep-ph/0202025). M. Gyulassy: The most powerful probe of the QGP equation of state: the mass dependence of v2; One of the three lines of evidence for the QGP at RHIC (arXiv:nucl-th/0403032). Raimond Snellings; Moriond 2004

Raimond Snellings; Moriond 2004 Backup Raimond Snellings; Moriond 2004

Raimond Snellings; Moriond 2004 v2(pt) SPS-RHIC Integrated v2 depends on slope and <pt> <pt> pions 17 GeV ≈ 400 MeV/c, 130 GeV charged particles <pt> ≈ 500 MeV/c NA49: Phys. Rev. C68 (2003) 034903; CERES: Phys. Rev. Lett. 92 (2004) 032301 Raimond Snellings; Moriond 2004

Elliptic flow; excitation function NA49 STAR NA49 Phys.Rev. C68 (2003) 034903 Raimond Snellings; Moriond 2004

Integrated v2 from cumulants About 20% reduction from v2{2} to v2{4} v2{4} ≈ v2{6} A. Tang (STAR), AIP Conf. Proc. 698:701, 2004; arXiv:nucl-ex/0308020 Raimond Snellings; Moriond 2004

Raimond Snellings; Moriond 2004 Higher moments <v2n> ≠ <v2>n Raimond Snellings; Moriond 2004

The possible fluctuation contribution “standard” v2{2} overestimates v2 by 10%, higher order cumulant underestimate v2 by 10% at intermediate centralities M. Miller and RS, arXiv:nucl-ex/0312008 Raimond Snellings; Moriond 2004

Compare fluctuations to data M. Miller and RS, arXiv:nucl-ex/0312008 Raimond Snellings; Moriond 2004

Why is v2 so large at higher-pt? Measured v2 values seem to be larger than the maximum values in the case of extreme quenching -> surface emission E. Shuryak: nucl-th/0112042 Raimond Snellings; Moriond 2004

Raimond Snellings; Moriond 2004 Hydro + Jet Quenching? T. Hirano and Y. Nara: nucl-th/0307015 X.-N. Wang: nucl-th/0305010 Coupling of hydro and parton energy loss gives a reasonable description of the data and also has a mass dependence at higher-pt Raimond Snellings; Moriond 2004

How has elliptic flow defined our view of physics at RHIC? Charged particle elliptic flow at low pt; one of the first papers from RHIC First time quantitative agreement with hydrodynamics -> suggestive of early thermalization, strongly interacting parton phase Identified particle elliptic flow at low pt QGP equation of state (phase transition) provides accurate description Charged particle elliptic flow at higher pt First indications of jet quenching (later RAA) Strongly dissipative system -> limiting surface emission (later back to back suppression). Suggested by Shuryak for high-pt v2, earlier already by Huovinen for whole pt range -> Not the whole answer at low pt shown by mass dependence of v2(pt) for p, K, p. Identified particle elliptic flow at higher pt Surface emission, not whole answer at higher pt either shown by mass dependence of v2 of pion, Kaon, proton and Lambda pion, Kaon, proton and Lambda v2 give indication for parton coalescence. First suggested at QM2002 by Voloshin (later also used for RAA intermediate pt mass dependence) Raimond Snellings; Moriond 2004

Raimond Snellings; Moriond 2004 v2 at LHC energy S. Radomski (PPR) ALICE simulations and reconstruction, show that we will be in a beautiful position to do this physics at LHC P. Kolb, J. Sollfrank, and U. Heinz, Phys. Rev. C. C62 054909 (2000). Raimond Snellings; Moriond 2004

Flow (radial, directed and elliptic) x y z Only type of transverse flow in central collision (b=0) is transverse flow. Integrates pressure history over complete expansion phase Elliptic flow, caused by anisotropic initial overlap region (b > 0). More weight towards early stage of expansion. Directed flow, sensitive to earliest collision stage (pre-equilibrium, b > 0) Raimond Snellings; Moriond 2004

v1 predictions (QGP invoked) L.P. Csernai, D. Rohrich: Phys. Lett. B 458 (1999) 454 J. Brachmann et al., Phys. Rev. C. 61 024909 (2000) Raimond Snellings; Moriond 2004

v1 predictions (more general, QGP interpretation not necessary) R.S., H. Sorge, S.A. Voloshin, F.Q. Wang, N. Xu: Phys. Rev. Lett 84 2803 (2000) M. Bleicher, H. Stocker: Phys. Lett. B 526 (2002) 309 (UrQMD) Raimond Snellings; Moriond 2004

Directed flow at the SPS (NA49) NA49: Phys.Rev. C68 (2003) 034903 Raimond Snellings; Moriond 2004

First measurement of v1 at RHIC Confirms v2 is in-plane at RHIC Suggestive of limiting fragmentation picture Consistent with theory predictions The data with current statistics shows no sign of a wiggle (also does not exclude the magnitude of the wiggle as predicted A. Tang, M. Oldenburg, A. Poskanzer, J. Putschke, RS, S. Voloshin Raimond Snellings; Moriond 2004

Is there boost invariance? PHOBOS v2(h) PHOBOS: Phys. Rev. Lett. 89, 222301 (2002)  Preliminary v2200 Final v2130 200 130 average over all centrality (Npart ~200) Raimond Snellings; Moriond 2004

Event Characterization How do we distinguish peripheral collisions from central collisions? b 5% Central STAR Ncoll Npart Impact Parameter (b) Raimond Snellings; Moriond 2004