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Results from the PHOBOS experiment at RHIC

Results from the PHOBOS experiment at RHIC. Birger Back Argonne National Laboratory for the PHOBOS Collaboration. PHOBOS Collaboration. ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY

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Results from the PHOBOS experiment at RHIC

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  1. Results from the PHOBOS experiment at RHIC Birger Back Argonne National Laboratory for the PHOBOS Collaboration

  2. 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

  3. Outline • Apparatus • 2000 run statistics • Physics results • Charged particle multiplicity • Energy dependence at h=0 • Centrality dependence at h=0 • Pseudo-rapidity distributions • Total charged particle multiplicity • Flow of charged particles • Antiparticle / particle ratios • Summary • 2001 run plan • Future upgrade plans

  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. Year 2000 running • Commissioning run: (May-July) • Sacrificial detectors installed • 56 GeV: 6352 collisions • 130 GeV: 12074 collisions • Physics run: (July-August) • Full complement of detectors • 130 GeV: ~3.5 M collisions • Well over 1 TB of data written to tape • Essentially flawless performance of PHOBOS detector

  6. Results from 2000 run Energy Dependence (vs. AGS/SPS Data) System Size (p+p, Npart Dependence ) MEASUREMENT Charged Particle Density Event Anisotropy - Flow Particle Ratios CONTEXT

  7. Selecting Collisions Positive Paddles Negative Paddles ZDC N ZDC P Au Au PN PP x z • Coincidence between Paddle counters • Paddle + ZDC timing reject background • Sensitive to 97% of inelastic cross-section for Au+Au at SsNN = 130 GeV

  8. Multiplicity of charged particles • Physics motivation • Time integral of particle production during the collision • Total entropy production • Lots of existing data for pp, pA, AB,AA • How do RHIC data fit into this picture? • Methods of analysis • 2 Si layers: Tracklet counting • 1 Si layer: Hit counting – Poisson statistics • Check with energy deposition

  9. Multiplicity from tracklet counting Commissioning run May-July 2000 Ss = 56 and 130 GeV • Select 6% most central events • Count Tracklets near h = 0 Vertex Double Si layer Spectrometer

  10. Multiplicity at h=0 vs Energy RESULT SsdN/dh 56 GeV 408612630 130 GeV 555612635 Ss2dN/dh/Npart 56 GeV 2.476.106.25 130 GeV 3.246.106.25 Ratio: 1.316.046.05 @ 130 GeV 30% higher than p+p 70% higher than SPS p+p Phobos SPS First RHIC physics result: Back et al.,PRL 85 (2000) 3100 About 20 theoretical papers (Feb 15, 2001)

  11. Some model comparisons HIJING EKRT (saturation model) 40% increase from p+p to central Au+Au Data constrain model parameter space Further insight from centrality dependence

  12. Multiplicity at h=0 vs Centrality (130 GeV) Physics run July-Sept 2000 Complete year 1 setup Tracklets in spectrometer and vertex 12 centrality bins for upper 55% of cross section

  13. Multiplicity at h=0 vs Npart Preliminary Yellow band: Systematic uncertainty dNch/dh/(0.5*Npart) Npart Good agreement with previous PHOBOS point Good agreement with recent PHENIX data Neither HIJING nor EKRT describe data well

  14. Multiplicity in 4p (Hit counting) Single Si layer Rings • Determine dNch/dh for –5.4 < h < 5.4 • Shape • Total multiplicity • Evolution vs Npart • Hit counting Octagon

  15. PHOBOS Multiplicity detectors Octagon 1 of 6 Rings

  16. Count hits binned in h, centrality (b) Calculate acceptance A(ZVTX)for that event Find occupancy in hit pads O(h,b)by counting empty to hit channels assuming Poisson statistics Fold in a background correction factor fB(h,b) Rings Octagon Rings DE deposition in multiplicity detectors for one event. f h O(h,b) ×fB(h,b) dNch Shits = dh A(ZVTX)

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

  18. Centrality dependence of dN/dh Phobos HIJING Central Mid central Peripheral Increased particle production at mid-rapidity Differences in shapes

  19. Centrality Dependence of Nch(|h|<5.4) PHOBOS Prelim. HIJING Nch(|h|<5.4) ±10% Systematic Uncertainty Npart

  20. Elliptic Flow Octagon Ring b (reaction plane) |h| < 1.0 dN/d(f -YR ) = N0 (1 + 2V1cos (f-YR) + 2V2cos (2(f-YR) + ... )

  21. Centrality Dependence Preliminary |h| < 1.0 V2 Hydrodynamic model Preliminary SPS AGS Systematic error ~ 0.007 Normalized Paddle Signal Large V2 signal compared to lower energy

  22. Elliptical flow vs h PHOBOS V2 STAR (PRL) h Preliminary Systematic error ~ 0.007 Averaged over centrality V2 drops for |h| > 1.5

  23. Anti-particle / particle ratios + p K+ p+ p K- Tracking in the spectrometer Alternate 2T magnetic fields Energy loss and momentum p-

  24. Particle Ratios Preliminary Centrality =12 % <Npart> ~ 310 Central region not baryon-free

  25. 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 4p • <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 • between HIJING and RQMD • Central region not yet baryon free – maybe at 200 GeV

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

  27. Outlook II: 2003 + beyond Charm Production at RHIC Measure single electrons from displaced vertices EM-Calorimeter Transition Radiation Detector • Existing Spectrometer • High rate (> 0.5 kHz) • High Resolution • Add • Micro-vertex Detector • Narrow beam-pipe • ALICE prototype TRD Electron ID • EM-Calorimeter Micro-Vertex

  28. The End

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