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Results from the PHOBOS experiment at RHIC

This article presents the results and findings from the PHOBOS Experiment conducted at the RHIC. It covers various aspects such as charged particle multiplicity, energy and centrality dependence, pseudo-rapidity distributions, antiparticle/particle ratios, and more. The PHOBOS detector, apparatus, and running statistics are also discussed.

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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. Multiplicity of charged particles / tracklets Vertex Tracklet counting in double Si layers Spectrometer

  7. 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)

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

  9. 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 • Poisson occupancy corrections Octagon

  10. dNch/dh vs Centrality Preliminary Statistical errors only - 10-20% systematical uncertainty

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

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

  13. Elliptic Flow Octagon Ring Reaction plane PHOBOS STAR V2 h dN/d(f -YR ) = N0 (1 + 2V1cos (f-YR) + 2V2cos (2(f-YR) + ... )

  14. Anti-particle / particle ratios + Tracking in the spectrometer Alternate 2T magnetic fields Energy loss and momentum - Central region not baryon-free

  15. 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 0.55 +/- 0.1 • Central region not yet baryon free – maybe at 200 GeV

  16. 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

  17. 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

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