1 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Results from the PHOBOS experiment at RHIC Steve Manly (Univ. of Rochester) for the PHOBOS Collaboration

2 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 PHOBOS Collaboration ARGONNE NATIONAL LABORATORY Birger Back, Nigel George, Alan Wuosmaa BROOKHAVEN NATIONAL LABORATORY Mark Baker, Donald Barton, Alan Carroll, Stephen Gushue, George Heintzelman, Robert Pak, Louis Remsberg, Peter Steinberg, Andrei Sukhanov INSTITUTE OF NUCLEAR PHYSICS, KRAKOW Andrzej Budzanowski, Roman Holynski, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki, Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Wozniak MASSACHUSETTS INSTITUTE OF TECHNOLOGY Wit Busza, Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane, Judith Katzy, Piotr Kulinich, Johannes Muelmenstaedt, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Leslie Rosenberg, Pradeep Sarin, Stephen Steadman, George Stephans, Gerrit van Nieuwenhuizen, Carla Vale, Robin Verdier, Bernard Wadsworth, Bolek Wyslouch NATIONAL CENTRAL UNIVERSITY, TAIWAN Willis Lin, JawLuen Tang UNIVERSITY OF ROCHESTER Joshua Hamblen, Erik Johnson, Nazim Khan, Steven Manly, Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs UNIVERSITY OF ILLINOIS AT CHICAGO Russell Betts, Clive Halliwell, David Hofman, Burt Holzman, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter UNIVERSITY OF MARYLAND Richard Bindel, Edmundo Garcia-Solis, Alice Mignerey April 2001

3 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 PHOBOS Detector Ring Counters Paddle Trigger Counter Spectrometer TOF Octagon+Vertex Silicon Pad channels 4-  Multiplicity Array Mid-rapidity Spectrometer Scintillator Paddles + Zero Degree Calorimeter for triggering TOF wall for high-momentum PID

4 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001

5 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001

6 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 The first look run Energy dependence (vs. AGS/SPS data) System size (p+p, N part dependence ) Angular dependence (  and  ) Energy density and Entropy Production Thermal Equilibration Hadro-Chemistry Charged Particle Density Event Anisotropy - Flow Particle Ratios

7 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Results to date - I dN/d  Versus energy Central,  =0,  s NN = 56 and 130 GeV PRL 85 (2000) 3100 Versus centrality Varying centrality,  =0,  s NN = 130 GeV QM2001, to be submitted soon Versus angle (and centrality) Varying centrality, |  |<5.4,  s NN = 130 GeV QM2001, to be submitted soon

8 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Results to date - II p/p, K - /K +,  - /  + ratios, central,  s NN = 130 GeV QM2001, Submitted to PRL hep-ex/ Elliptic flow,  s NN = 130 GeV, as function of centrality and |  |<5.3 QM2001, to be submitted soon

9 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Selecting Collisions Coincidence between Paddle counters Paddle + ZDC timing reject background Sensitive to 97% of inelastic cross-section for Au+Au at  s NN = 130 GeV Negative Paddles Positive Paddles ZDC NZDC P Au x z PP PN

10 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 HIJING +GEANT Glauber Calculation Model of Paddle trigger Paddle signal (a.u.) Determination of N part N part MC Data

11 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Vertex Determination with vertex detector cm counts +z Si Tracklets

12 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Vertex determination with spectrometer arms form 3D vertex z tracklets 100 MeV/c ++  - --

13 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001  s NN = 56 GeV  s NN = 130 GeV dN ch /d  measurements What is the density of particles near  =0? How does it compare to p+p and SPS? How does it vary with centrality? How does the density of particles vary with angle? Total multiplicity Energy density Entropy production Relative importance of hard and soft production processes

14 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Tracklets and dN ch /d  =0 Hundreds of tracklets per central event Corrections –Background subtraction –Uncertainty due to model differences –Feed-down from strange decays See talk by Mike Reuter in Session J12 (Sunday 15:18)

15 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 PRL 85 (2000) 3100 dN ch /d  =0 vs Energy

16 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 dN ch /d  =0 vs N part N part Good agreement with previous PHOBOS point Good agreement with recent PHENIX data Neither HIJING nor EKRT describe data well Yellow band: Systematic uncertainty Preliminary dN ch /d  /(0.5*N part )

17 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 octagon Ring counter -1.1 m 1.1 m 2.3 m -2.3 m 5.0 m - 5.0m |  | < 5.3 ( , 0  (  Interaction Point dN ch /d  for |  |<5.4

18 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Count hits –remove much background by demanding energy deposition consistency with angle –Occupancy per hit pad determined as fn of  via number of empty and hit pads Corrections –residual background corrected via MC simulations   RingsN Octagon RingsP “Unroll” the octagon and rings See talk by Carla Vale in Session J12 (14:30, Sunday afternoon

19 - S. Manly, Univ. of Rochester APS - Washington D.C. - April %35-45% 25-35% 15-25% 6-15% 0-6%  dN ch /d  dN ch /d  vs Centrality Preliminary The width of the distribution changes with centrality Statistical errors only - 10% systematical uncertainty

20 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Evolution of dN ch /d  vs N part   (dN ch /d  )/(½N part ) Data HIJING N part =356 N part =215 N part =103 (dN ch /d  )/(½N part ) = /- 410 for 3% most central Additional particle production near  =0 Wider + more particles relative to HIJING Preliminary Statistical errors only

21 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Baryo-Chemical Potential Baryon Stopping Determine ratio of  - /  +, K - /K +, p/p Compare to AGS/SPS results Particle ratios: Hadro-chemistry See talk by Conor Henderson - session Q12 (11 am Monday)

22 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Tracking and Particle ID Particle ID –dE/dx in silicon Two B-field polarities –Many systematic effects cancel in the ratio

23 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Results for ratios Higher values of K - /K + and p/p than at lower energies Results consistent with  B =45±5 MeV, which is much lower that that observed at SPS (~ MeV) Assumes freezeout temp ~170 MeV in statistical model of Redlich (QM01)

24 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Elliptic flow dN/d(  R ) = N 0 (1 + 2V 1 cos (  R ) + 2V 2 cos (2(  R ) +... ) Determine to what extent is the initial state spatial/momentum anisotropy preserved in the final state. b (reaction plane) Sensitive to the initial equation of state and the degree of thermalization. Affects other variables, such as HBT and spectra.

25 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Elliptic Flow -2.0 <  < -0.1 RingPRingN SubE (a)SubE (b) nana nbnb 0.1 <  < 2.0 Subevent technique: correlate reaction plane in one part of detector to  asymmetry in hit pattern in other part of detector Correct for imperfect reaction plane resolution and hit saturation (formalism given in A. M. Poskanzer,S. A. Voloshin Phys. Rev. C 58, 1671)

26 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Centrality Dependence Hydrodynamic model V2V2 Normalized Paddle Signal Systematic error ~ |  | < 1.0 SPS AGS Preliminary Large V 2 Signal compared to lower energy, closer to hydrodynamic limit implying substantial thermalization Preliminary

27 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001  V2V2 PHOBOS STAR (PRL) V 2 vs  Averaged over centrality V 2 drops for |  | > 1.5 Preliminary Systematic error ~ 0.007

28 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Conclusions from year 1 dN ch /d  =0 per participant –Substantially higher than SPS (Pb-Pb) and p+p –N part evolution between HIJING and EKRT dN ch /d  in 4-  –Additional particle production near  =0 for central events –Distribution wider than HIJING Elliptic flow –V 2 – large, close to hydrodynamic limit –drops for |  | > 1.5 Particle ratios   ~ 45 MeV vs 270 MeV at SPS

29 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Expectations for year 2 (starts mid-June!) 100x statistics Both arms completed Physics: –low-p T physics –Spectra –HBT –Resonances (  at low p T  –Event-by-Event physics Energy systematics [Species systematics if enough running time]

30 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 BACKUP SLIDES FOLLOW

31 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001

32 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Comparison to SPS General features (rapid rise/flat top) similar Note that WA98 dN ch /d  measured in lab frame WA98 Pb+Pb PHOBOS Au+Au` N part dN ch /d  /(0.5*N part ) p+p

33 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Spectrometer : Vertex Reconstruction form 3D vertex z

34 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Event Selection vertex available Rings P Rings N To cover pseudo-rapidity -2.0 to 2.0, only events with vertex -38cm to -30 cm are used Rings will cover 3.0 < |  | < K events are used finally for the analysis -56cm-14cm Octagon  z

35 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 If we know the reaction plane perfectly: V n = Flow Analysis* (Subevent correlation) In real experiment,  R is unknown: use  n V n obs = ) 1/2 Finally, correct for event plane resolution V n = V n obs / * Phys. Rev. C 58, 1671 A. M. Poskanzer, S. A. Voloshin -2.0 <  < -0.1 RingPRingN SubE (a)SubE (b) nana nbnb 0.1 <  < 2.0

36 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Subevent Plane Correlation Normalized Paddle Signal

37 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Kinematic Coverage Acceptance near y=0.5 Identical for positive particles in BPLUS/negative particles in BMINUS P K 

38 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Discriminating background with  E  E (“MIP”)  E (“MIP”) Data Monte Carlo Si  E vs.  in the Octagon From vertex Not from vertex  

39 - S. Manly, Univ. of Rochester APS - Washington D.C. - April 2001 Future plans: beyond Micro-Vertex Transition Radiation Detector EM-Calorimeter Existing Spectrometer High rate (> 0.5 kHz) High Resolution Add Micro-Vertex Detector ALICE prototype TRD Electron-ID EM-Calorimeter Discussing upgrade to focus on charm production at RHIC. Measure single electrons from displaced vertices