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Results from the PHOBOS experiment at RHIC

Results from the PHOBOS experiment at RHIC. Christof Roland (MIT) for the PHOBOS Collaboration. Year 1: The Big Picture. Au+Au Collisions @  s = 130 GeV. Q: Entropy Production Hadro-Chemistry Thermal Equilibration. Multiplicity

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Results from the PHOBOS experiment at RHIC

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  1. Results from the PHOBOS experiment at RHIC Christof Roland (MIT) for the PHOBOS Collaboration

  2. Year 1: The Big Picture Au+Au Collisions @ s = 130 GeV Q: Entropy Production Hadro-Chemistry Thermal Equilibration • Multiplicity • Charged Particle Density • Particle Ratios • Event Anisotropy • Flow

  3. PHOBOS Collaboration ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ROCHESTER UNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLAND Birger Back, Nigel George, Alan Wuosmaa Mark Baker, Donald Barton, Alan Carroll, Stephen Gushue, George Heintzelman, Robert Pak, Louis Remsberg, Peter Steinberg, Andrei Sukhanov Andrzej Budzanowski, Roman Holynski, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki , Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Wozniak Wit Busza (Spokesperson), 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 Willis Lin, Jaw-Luen Tang Joshua Hamblen , Erik Johnson, Nazim Khan, Steven Manly, Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs Russell Betts, Clive Halliwell, David Hofman, Burt Holzman, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter Richard Bindel, Edmundo Garcia, Alice Mignerey

  4. PHOBOS Detector Paddle Trigger Counter TOF Spectrometer Octagon+Vertex Ring Counters • 96000 Silicon Pad channels • 4p Multiplicity Array • Mid-rapidity Spectrometer • Scintillator Paddles + Zero Degree Calorimeter for triggering • TOF wall for high-momentum PID

  5. Multiplicity at h=0 vs Energy First RHIC physics result: Back et al.,PRL 85 (2000) 3100 RESULT sNpart 56 GeV 330 +/-4 +10/-15 130 GeV 343 +/- 4 +7/-14 sdN/d h 56 GeV 408 +/-12 +/-30 130 GeV 555 +/- 12 +/-35 s2dN/d h/Npart 56 GeV 2.47 +/-.10 +/-.25 130 GeV 3.24 +/-.10 +/-.25 Ratio: 1.31 +/-.04 +/-.05 6% most central Au+Au @ 130 GeV: • 40% increase from p+p to central Au+Au • 70% increase from CERN-SPS

  6. Multiplicity at h=0 vs Npart Yellow band: Systematic uncertainty Preliminary Npart Q: How does dNch/dh@h=0 evolve from 2.3 (p+p) to 3.25 (Au+Au) per participant pair? Physics run July-Sept 2000 10 centrality bins for upper 45% of cross section dNch/dh/(0.5*Npart) EKRT Saturation disfavored Good agreement with previous PHOBOS point Neither HIJING nor EKRT describe data well

  7. Multiplicity in 4p (Hit counting) Occupancy correction (assuming Poisson statistics) O(h,b) ×fB(h,b) dNch Shits = dh A(ZVTX) Rings Octagon Rings f h h Background correction Acceptance Factor

  8. dNch/dhvs Centrality Preliminary Statistical errors only - 10-20% systematical uncertainty

  9. PHOBOS Prelim. Evolution of dNch/dh vs Npart Preliminary Statistical errors only Data Npart=356 HIJING Nch(|h|<5.4) Npart=215 (dNch/dh)/(½Npart) Npart=103 ±10% Systematic Uncertainty h Npart HIJING <Nch> = 4100 +/- 410 for 3% most central Additional particle production near h=0 Wider + more particles relative to HIJING (dNch/dh)/(½Npart) h

  10. Collective Effects: Elliptic Flow Q: Does the initial space anisotropy translate into final state momentum space anisotropy? b (reaction plane) dN/d(f -YR ) = N0 (1 + 2V1cos (f-YR) + 2V2cos (2(f-YR ) ) + ... )

  11. Elliptic Flow Results PHOBOS V2 STAR (PRL) h Preliminary Averaged over centrality |h| < 1.0 V2 Hydro. model SPS AGS Normalized Paddle Signal Systematic error ~ 0.007 Large V2 signal compared to lower energy Centrality Dependence close to Hydro. V2 drops for |h| > 1.5

  12. Hadro Chemistry: Particle Ratios p- Q: Baryo-Chemical Potential, Baryon Stopping Preliminary Centrality =12 % <Npart> ~ 310 - p = ± ± . . ( stat .) . ( syst .) 1 01 0 01 0 05 + p - K = ± ± . . ( stat .) . ( syst .) 0 91 0 09 0 1 + K p = ± ± . . ( stat .) . ( syst .) 0 54 0 05 0 1 p • Thermal Model Estimte : mB ~ 50 MeV • Central region not net baryon-free!

  13. Summary • dNch/dh @h=0 per participant • 70% higher than SPS for central Au+Au • 40% higher than p+p at RHIC energy • Npart evolution between HIJING and EKRT • dNch/dh in 4-p • <Nch> = 4100 +/- 410 (|h|< 5.4) for 3% central • Additional particle production near h=0 for central events • Wider than HIJING • Elliptic flow • V2 up to 0.06 – close to hydrodynamic limit • larger than SPS • V2 drops for |h| > 1.5 • Particle ratios • p/p ratio 0.54 +/- 0.1 • Central region not baryon free

  14. Outlook I: 2001 • >100x statistics • Physics: • low-pT physics • Spectra • HBT • Resonances (f at low pT) • Event-by-Event physics • Both arms completed • Energy systematics • Species systematics

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