1. Latest Results From PHOBOS David Hofman University of Illinois at Chicago

2. Shanghai David Hofman - UIC QM’06PHOBOS 2 PHOBOS Collaboration Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard Bindel, Wit Busza (Spokesperson), Vasundhara Chetluru, Edmundo García, Tomasz Gburek, Joshua Hamblen, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Chia Ming Kuo, Wei Li, Willis Lin, Constantin Loizides, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed, Christof Roland, Gunther Roland, Joe Sagerer, Peter Steinberg, George Stephans, Andrei Sukhanov, Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter Walters, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Bolek Wysłouch ARGONNE NATIONAL LABORATORYBROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOWMASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWANUNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLANDUNIVERSITY OF ROCHESTER 9 ongoing Ph.D. theses

3. Shanghai David Hofman - UIC QM’06PHOBOS 3 PHOBOS Experiment PHOBOS

4. Shanghai David Hofman - UIC QM’06PHOBOS 4 Colliding Nuclei at RHIC

5. Shanghai David Hofman - UIC QM’06PHOBOS 5 Two “snapshots” of colliding nuclei at RHIC nuclei crossing times extremely fast RHIC: ~0.13 fm/c SPS: ~1.6 fm/c AGS: ~5.3 fm/c

6. Shanghai David Hofman - UIC QM’06PHOBOS 6 Well known: initial collision geometry matters Initial overlap eccentricity Visible in final measured particle azimuthal angular distributions Elliptic Flow Reaction Plane b Impact Parameter 00

7. Shanghai David Hofman - UIC QM’06PHOBOS 7 Well known: initial collision geometry matters  To first order: initial collision geometry drives magnitude of v 2 (of course, the density also matters) Elliptic Flow Initial Eccentricity Final Particle Distributions Initial overlap eccentricity Visible in final measured particle azimuthal angular distributions b Impact Parameter Reaction Plane 00  v2v2

8. Shanghai David Hofman - UIC QM’06PHOBOS 8 Is our first RHIC snapshot “in focus”? Lets focus on: the spatial distribution of the interaction points of participating nucleons Au+Au b

9. Shanghai David Hofman - UIC QM’06PHOBOS 9 Is our first RHIC snapshot “in focus”? for the same b, these interaction points will vary from event-to-event Lets focus on: the spatial distribution of the interaction points of participating nucleons bb Au+Au

10. Shanghai David Hofman - UIC QM’06PHOBOS 10 Is our first RHIC snapshot “in focus”? From PHOBOS @ Quark Matter 2005  explored much further since then and thus the relevant eccentricity for elliptic flow also varies event-by-event Lets focus on: the spatial distribution of the interaction points of participating nucleons for the same b, these interaction points will vary from event-to-event bb Au+Au 00 00

11. Shanghai David Hofman - UIC QM’06PHOBOS 11 Does using make a difference? YES Increasingly important for smaller systems “standard” calculation “participant” nucleons event-by-event calculation 200 GeV

12. Shanghai David Hofman - UIC QM’06PHOBOS 12 How robust is Glauber MC + calculation? calculation from Glauber MC is robust arXiv:nucl-ex/0610037 Submitted to PRL More recent studies have included variations in individual nucleon density profiles and different N part and N coll weighting. 90% CL bands on calculation Studied variations in: In collaboration with Ulrich Heinz min N-N separation  NN nuclear radius skin depth

13. Shanghai David Hofman - UIC QM’06PHOBOS 13 How robust is Glauber MC + calculation? arXiv:nucl-ex/0610037 Submitted to PRL 90% CL bands on calculation Studied variations in: Bhalerao, Ollitrault – PLB641 260, (2006) Ollitrault – private communications (2006) PHOBOS internal MC calculation from Glauber MC is robust More recent studies have included variations in individual nucleon density profiles and different N part and N coll weighting. In collaboration with Ulrich Heinz min N-N separation  NN nuclear radius skin depth

14. Shanghai David Hofman - UIC QM’06PHOBOS 14 Data: average v 2 in Cu+Cu and Au+Au Cu+Cu arXiv:nucl-ex/0610037 submitted PRL Au+Au: PRC 72 051901(R)

15. Shanghai David Hofman - UIC QM’06PHOBOS 15 Average v 2 / in Cu+Cu and Au+Au Standard Eccentricity 200 GeV arXiv:nucl-ex/0610037, submitted to PRL Cu+Cu Au+Au

16. Shanghai David Hofman - UIC QM’06PHOBOS 16 Average v 2 / in Cu+Cu and Au+Au Participant Eccentricity Standard Eccentricity 200 GeV arXiv:nucl-ex/0610037, submitted to PRL Cu+Cu Au+Au arXiv:nucl-ex/0610037, submitted to PRL Cu+Cu Au+Au

17. Shanghai David Hofman - UIC QM’06PHOBOS 17 Voloshin, Poskanzer, PLB 474 27 (2000); Heiselberg, Levy, PRC 59 2716, (1999) Average v 2 / in Cu+Cu and Au+Au Participant Eccentricity Standard Eccentricity 200 GeV arXiv:nucl-ex/0610037, submitted to PRL unifies average v 2 in Cu+Cu and Au+Au Related work: Miller, Snellings, Zhu, Bleicher, Stöcker Cu+Cu Au+Au Cu+Cu Au+Au

18. Shanghai David Hofman - UIC QM’06PHOBOS 18 Voloshin, Poskanzer, PLB 474 27 (2000); Heiselberg, Levy, PRC 59 2716, (1999) Average v 2 / in Cu+Cu and Au+Au Participant Eccentricity Standard Eccentricity 200 GeV arXiv:nucl-ex/0610037, submitted to PRL unifies average v 2 in Cu+Cu and Au+Au Related work: Miller, Snellings, Zhu, Bleicher, Stöcker Cu+Cu Au+Au Cu+Cu Au+Au

19. Shanghai David Hofman - UIC QM’06PHOBOS 19 New Data: p T dependence of v 2 / Au+Au and Cu+Cu at matched N part unifies midrapidity v 2 (p T ) in Cu+Cu and Au+Au

20. Shanghai David Hofman - UIC QM’06PHOBOS 20 scaling as a function of  The collision geometry controls the dynamical evolution of heavy ion collisions. Talk by Rachid Nouicer Cu+Cu and Au+Au at matched N part

21. Shanghai David Hofman - UIC QM’06PHOBOS 21 scaling as a function of  The collision geometry controls the dynamical evolution of heavy ion collisions. Talk by Rachid Nouicer Consequence: this implies that the initial event-by-event participant collision geometry appears relevant. Cu+Cu and Au+Au at matched N part

22. Shanghai David Hofman - UIC QM’06PHOBOS 22 Fluctuations in participant eccentricity What magnitude of fluctuations are expected? Expect large dynamical fluctuation in the participant eccentricity Quantify with  (  part )/

23. Shanghai David Hofman - UIC QM’06PHOBOS 23 New Analysis: event-by-event v 2 measurement Utilize Full Phase space coverage of PHOBOS (|  |<5.4,  ~2  ). Detailed modeling of detector response, statistical fluctuations and multiplicity dependence. –Method is described in arXiv:nucl-ex/0608025 Measure v 2 on an event-by-event basis. Take e-by-e result and average to compare to our other results. 200 GeV Au+Au measured event-by-event is in agreement with both hit and track based PHOBOS results.

24. Shanghai David Hofman - UIC QM’06PHOBOS 24 New Result: v 2 and  part Fluctuations Response of the measurement for MC events with no dynamical fluctuations Reminder: this analysis corrects for detector and multiplicity effects as well as statistical fluctuations  (v 2 )/ in 200 GeV Au+Au Collisions

25. Shanghai David Hofman - UIC QM’06PHOBOS 25 New Result: v 2 and  part Fluctuations band: 90% CL PHOBOS v 2 result MC with no fluctuations Observe significant dynamical v 2 fluctuations  (v 2 )/ in 200 GeV Au+Au Collisions

26. Shanghai David Hofman - UIC QM’06PHOBOS 26 New Result: v 2 and  part Fluctuations Poster by Burak Alver and talk by Constantin Loizides Magnitude of v 2 fluctuations is in agreement with  part fluctuations  (v 2 )/ and  (  part )/ in 200 GeV Au+Au Collisions PHOBOS  part prediction PHOBOS v 2 result MC with no fluctuations band: 90% CL

27. Expanding Differentially in Phase Space

28. Shanghai David Hofman - UIC QM’06PHOBOS 28 New Data: global charged particle emission Extended longitudinal scaling Midrapidity charged particlesMidrapidity charged particle spectra Highlights from QM05 Energy/Centrality factorization and “scaling laws” in global charged particle production Phys.Rev. C74 (2006) 021901 Phys.Rev.Lett. 94 (2005) 082304 Nucl.Phys. A774 (2006) 113-128

29. Shanghai David Hofman - UIC QM’06PHOBOS 29 New Analysis: two particle correlations PHOBOS Preliminary PHOBOS Preliminary h±h± h±h± -6 Cu+Cu @ 200 GeV 0-10% central p+p @ 200 GeV 6 -6 6

30. Shanghai David Hofman - UIC QM’06PHOBOS 30 New Analysis: two particle correlations PHOBOS Preliminary PHOBOS Preliminary h±h± h±h± -6 Cu+Cu @ 200 GeV 0-10% central 6 -6 6 p+p @ 200 GeV

31. Shanghai David Hofman - UIC QM’06PHOBOS 31 New Analysis: two particle correlations Study the short-range rapidity correlations PHOBOS Preliminary PHOBOS Preliminary h±h± h±h± -6 Cu+Cu @ 200 GeV 0-10% central 6 -6 6 p+p @ 200 GeV

32. Shanghai David Hofman - UIC QM’06PHOBOS 32 New Result: effective cluster size Talk by Wei Li On average, particles tend to be produced in clusters with a size of 2-3. Interesting centrality dependence – can compare to other systems K eff = effective cluster size p+p scale error 2

33. Shanghai David Hofman - UIC QM’06PHOBOS 33 New Data: antiparticle/particle ratios 200 GeV Cu+Cu and Au+Au Detailed measurement of antiparticle/particle ratios as function of centrality 200, 62.4 GeV Cu+Cu

34. Shanghai David Hofman - UIC QM’06PHOBOS 34 New Publication: identified particle spectra Talk by Gabor Veres First published identified spectra for 62.4 GeV Au+Au at RHIC (down to very low p T, a unique PHOBOS measurement) arXiv:nucl-ex/0610001 submitted to PRC blast-wave fits 62.4 GeV Au+Au

35. Shanghai David Hofman - UIC QM’06PHOBOS 35 PHOBOS Physics for QM06 New Analyses: –Elliptic flow fluctuations

36. Shanghai David Hofman - UIC QM’06PHOBOS 36 PHOBOS Physics for QM06 New Analyses: –Elliptic flow fluctuations –Two particle correlations

37. Shanghai David Hofman - UIC QM’06PHOBOS 37 PHOBOS Physics for QM06 New Analyses: –Elliptic flow fluctuations –Two particle correlations Extended Analyses: –Elliptic flow in Cu+Cu

38. Shanghai David Hofman - UIC QM’06PHOBOS 38 PHOBOS Physics for QM06 New Analyses: –Elliptic flow fluctuations –Two particle correlations Extended Analyses: –Elliptic flow in Cu+Cu –Charged particle multiplicity

39. Shanghai David Hofman - UIC QM’06PHOBOS 39 PHOBOS Physics for QM06 New Analyses: –Elliptic flow fluctuations –Two particle correlations Extended Analyses: –Elliptic flow in Cu+Cu –Charged particle multiplicity –Anti-particle/particle ratios

40. Shanghai David Hofman - UIC QM’06PHOBOS 40 PHOBOS Physics for QM06 New Analyses: –Elliptic flow fluctuations –Two particle correlations Extended Analyses: –Elliptic flow in Cu+Cu –Charged particle multiplicity –Anti-particle/particle ratios QM06 Primary Message: PHOBOS has measured large dynamical v 2 fluctuations in 200 GeV Au+Au collisions. This suggests that the initial state thermalizes very rapidly, taking a detailed snapshot, which is propagated by the subsequent hydrodynamic evolution.

41. Shanghai David Hofman - UIC QM’06PHOBOS 41 Future of PHOBOS Physics Rare events, multiplicity fluctuations and cluster model – poster K. Wozniak Continue studies of dynamical flow fluctuations Two-particle correlations with high-p T trigger in spectrometer. Identified particles at low p T in 200 GeV Au+Au as detailed function of centrality Spectator breakup in the fragmentation region Charged particle yields in 200,410 p+p Phi-meson production TALKS: Rachid Nouicer - v 1 and v 2 flow (Saturday, 2:40pm, Parallel 2.4) Constantin Loizides - v 2 and  part fluctuations (Saturday, 4:20pm, Parallel 2.4) Wei Li - Two-particle correlations (Sunday, 5:00pm, Parallel 3.2) Gabor Veres - Identified particle spectra and ratios (Sunday, 5:00pm, Parallel 3.4) POSTERS: Burak Alver – Elliptic flow fluctuations (Wednesday, 5:20pm, poster 14) Krzysztof Wozniak - Multiplicity fluctuations (Wednesday, 5:20pm, poster 82) Total Number of Hits

42. Backups

43. Shanghai David Hofman - UIC QM’06PHOBOS 43 Summary of Backup Slides From R. Nouicer’s talk (Flow) –44 Measuring flow in PHOBOS –45 Track-based method details –46 Moments of  part From C. Loizides’ talk (v 2 fluct.) –47 Overview e-by-e v 2 meas. –48 Methodology –49 Glauber overview –50 Glauber Robustness From W. Li’s talk (2-part. corr.)From W. Li’s talk (2-part. corr.) –51 Methodology –52 Cluster size parameterization From G. Veres’ talk (ident. part.) –53 PHOBOS PID capability –54 Particle ratios measurement

44. 44 Rachid Nouicer - BNL PHOBOS QM2006 44 Measuring Flow in PHOBOS Hit-based method Ring counter Vertex detector Large coverage: |  | < 5.4 Ring counters Octagon Spectrometer Track-based method PHOBOS: PRC C72, 051901R (2005) PHOBOS: PRL 89, 222301 (2002)

45. 45 Rachid Nouicer - BNL PHOBOS QM2006 45 Track-based method: Robustness of Measurements of v 2 vs. p T The large separation on  between the reaction plane subevents and the measured region reduces the non-flow correlations in track-based (hit-based) method. Octagon and Rings Rings Only Octagon Only 1) 2.0 < |  |< 3.2 2) 3.0 < |  |< 5.43) 2.0 < |  |< 5.4 Reaction plane subevents v 2 (p T ) measured in 0 <  < 1.6 Statistical errors only Spectrometer Cu+Cu at 200 GeV PHOBOS Preliminary Track-based method

46. 46 Rachid Nouicer - BNL PHOBOS QM2006 46 It has been suggested that v 2 may scale as instead of - Bhalerao, Ollitrault – PLB 641, 260 (2006) - Ollitrault – private communications (2006) Theorists & PHOBOS since QM2005 In Collaboration with Ulrich Heinz 2 part ε ε PHOBOS MC

47. Shanghai David Hofman - UIC QM’06PHOBOS 47

48. Shanghai David Hofman - UIC QM’06PHOBOS 48

49. Shanghai David Hofman - UIC QM’06PHOBOS 49

50. Shanghai David Hofman - UIC QM’06PHOBOS 50

51. Methodology Two-particle correlation function: Background: Foreground: Event 1 Event 2 ~ ~ Wei Li, MIT QM2006, Shanghai

52. Parameterize cluster size (multiplicity) K eff : effective cluster size Decay width:  : background distribution Quantitatively understand cluster phenomena Two-particle rapidity correlation function: correlations between particles from one cluster k: cluster size K. Eggert et al., Nucl. Phys. B 86:201, 1975 Wei Li, MIT QM2006, Shanghai

53. 53 p T (GeV/c) 0.03 0.3 3.0 Stopping particles dE/dxTOF Particle ID from low to high p T E loss (MeV) PHOBOS PID Capabilities 1 23 4 50 p (GeV/c) 30 40 50 60 70 1/v (ps/cm) p+p K +K + - ++-++- p (GeV/c) Gábor I. VeresQuark Matter 2006, Shanghai, November 14-20, 2006

54. 54 Controlling systematic uncertainties Geometrical a cceptance drops out of the ratios: Ratios measured independently for different: bending directions spectrometer arms Z Z B+B+ B–B– h+h+ h–h– h+h+ h+h+ h+h+ h–h– h–h– h–h– by changing the polarity of the magnetic field Gábor I. VeresQuark Matter 2006, Shanghai, November 14-20, 2006