Results from the PHOBOS experiment at RHIC Birger

Results from the PHOBOS experiment at RHIC Birger Back Argonne National Laboratory for the PHOBOS Collaboration Winter Workshop on Nuclear Dynamics, 2001 1 Birger Back/ANL

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 NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ROCHESTER UNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLAND Winter Workshop on Nuclear Dynamics, 2001 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 Mc. Leod, Rachid Nouicer, Michael Reuter Richard Bindel, Edmundo Garcia, Alice Mignerey 2 Birger Back/ANL

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 Winter Workshop on Nuclear Dynamics, 2001 3 Birger Back/ANL

PHOBOS Detector Paddle Trigger Counter TOF Spectrometer Octagon+Vertex Ring Counters • 96000 Silicon Pad channels • 4 p Multiplicity Array • Mid-rapidity Spectrometer • Scintillator Paddles + Zero Degree Calorimeter for triggering • TOF wall for high-momentum PID Winter Workshop on Nuclear Dynamics, 2001 4 Birger Back/ANL

Year 2000 running • Commissioning run: (May-July) • Sacrificial detectors installed • 56 Ge. V: 6352 collisions • 130 Ge. V: 12074 collisions • Physics run: (July-August) • Full complement of detectors • 130 Ge. V: ~3. 5 M collisions • Well over 1 TB of data written to tape • Essentially flawless performance of PHOBOS detector Winter Workshop on Nuclear Dynamics, 2001 5 Birger Back/ANL

Results from 2000 run MEASUREMENT Charged Particle Density Event Anisotropy - Flow Particle Ratios CONTEXT • Energy Dependence (vs. AGS/SPS Data) • System Size (p+p, Npart Dependence ) Winter Workshop on Nuclear Dynamics, 2001 6 Birger Back/ANL

Selecting Collisions Positive Paddles Negative Paddles ZDC N Au Au PN x ZDC P z PP • Coincidence between Paddle counters • Paddle + ZDC timing reject background • Sensitive to 97% of inelastic cross-section for Au+Au at Ss. NN = 130 Ge. V Winter Workshop on Nuclear Dynamics, 2001 7 Birger Back/ANL

Multiplicity of charged particles • Physics motivation • Time integral of particle production during the collision • Total entropy production • Lots of existing data for pp, p. A, AB, AA • How do RHIC data fit into this picture? • Methods of analysis • 2 Si layers: • 1 Si layer: • Winter Workshop on Nuclear Dynamics, 2001 Tracklet counting Hit counting – Poisson statistics Check with energy deposition 8 Birger Back/ANL

Multiplicity from tracklet counting • • Commissioning run May-July 2000 Ss = 56 and 130 Ge. V Select 6% most central events Count Tracklets near h = 0 Vertex Double Si layer Spectrometer Winter Workshop on Nuclear Dynamics, 2001 9 Birger Back/ANL

Multiplicity at h=0 vs Energy RESULT Ss d. N/dh 56 Ge. V 408612630 130 Ge. V 555612635 p+p Ss Phobos 2 d. N/dh/Npart 56 Ge. V 2. 476. 106. 25 130 Ge. V 3. 246. 106. 25 SPS Ratio: 1. 316. 046. 05 @ 130 Ge. V 30% higher than p+p 70% higher than SPS First RHIC physics result: Back et al. , PRL 85 (2000) 3100 About 20 theoretical papers (Feb 15, 2001) Winter Workshop on Nuclear Dynamics, 2001 10 Birger Back/ANL

Some model comparisons EKRT (saturation model) HIJING • 40% increase from p+p to central Au+Au • Data constrain model parameter space • Further insight from centrality dependence Winter Workshop on Nuclear Dynamics, 2001 11 Birger Back/ANL

Multiplicity at h=0 vs Centrality (130 Ge. V) Physics run July-Sept 2000 Complete year 1 setup Tracklets in spectrometer and vertex 12 centrality bins for upper 55% of cross section Winter Workshop on Nuclear Dynamics, 2001 12 Birger Back/ANL

d. Nch/dh/(0. 5*Npart) Multiplicity at h=0 vs Npart Preliminary Yellow band: Systematic uncertainty Npart • Good agreement with previous PHOBOS point • Good agreement with recent PHENIX data • Neither HIJING nor EKRT describe data well Winter Workshop on Nuclear Dynamics, 2001 13 Birger Back/ANL

Multiplicity in 4 p (Hit counting) Single Si layer Rings Octagon • Determine d. Nch/dh for – 5. 4 < h < 5. 4 • Shape • Total multiplicity • Evolution vs Npart • Hit counting Winter Workshop on Nuclear Dynamics, 2001 14 Birger Back/ANL

PHOBOS Multiplicity detectors Octagon Winter Workshop on Nuclear Dynamics, 2001 1 of 6 Rings 15 Birger Back/ANL

Rings Octagon Rings f DE deposition in multiplicity detectors for one event. h 1 Count hits binned in h, centrality (b) 2 Calculate acceptance A(ZVTX) for that event 3 Find occupancy in hit pads O(h, b) by counting empty to hit channels assuming Poisson statistics 4 Fold in a background correction factor f. B(h, b) O(h, b) ×f. B(h, b) A(ZVTX) d. Nch =S hits dh Winter Workshop on Nuclear Dynamics, 2001 16 Birger Back/ANL

d. Nch/dh vs Centrality Preliminary Statistical errors only - 10 -20% systematical uncertainty Winter Workshop on Nuclear Dynamics, 2001 17 Birger Back/ANL

Centrality dependence of d. N/dh Phobos HIJING Central Mid central Peripheral • Increased particle production at mid-rapidity • Differences in shapes Winter Workshop on Nuclear Dynamics, 2001 18 Birger Back/ANL

Centrality Dependence of Nch(|h|<5. 4) PHOBOS Prelim. HIJING ± 10% Systematic Uncertainty Npart Winter Workshop on Nuclear Dynamics, 2001 19 Birger Back/ANL

Elliptic Flow Octagon Ring b (reaction plane) |h| < 1. 0 d. N/d(f -YR ) = N 0 (1 + 2 V 1 cos (f-YR) + 2 V 2 cos (2(f-YR) +. . . ) Winter Workshop on Nuclear Dynamics, 2001 20 Birger Back/ANL

Centrality Dependence Preliminary Hydrodynamic model V 2 |h| < 1. 0 Preliminary SPS AGS Systematic error ~ 0. 007 Normalized Paddle Signal Large V 2 signal compared to lower energy Winter Workshop on Nuclear Dynamics, 2001 21 Birger Back/ANL

Elliptical flow vs h Preliminary PHOBOS V 2 STAR (PRL) Systematic error ~ 0. 007 h • Averaged over centrality • V 2 drops for |h| > 1. 5 Winter Workshop on Nuclear Dynamics, 2001 22 Birger Back/ANL

Anti-particle / particle ratios p + K+ p+ p K- • Tracking in the spectrometer • Alternate 2 T magnetic fields • Energy loss and momentum Winter Workshop on Nuclear Dynamics, 2001 p- 23 Birger Back/ANL

Particle Ratios Preliminary Centrality =12 % <Npart> ~ 310 Central region not baryon-free Winter Workshop on Nuclear Dynamics, 2001 24 Birger Back/ANL

Summary • d. Nch/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 • d. Nch/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 • V 2 up to 0. 06 – close to hydrodynamic limit • larger than SPS • V 2 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 Ge. V Winter Workshop on Nuclear Dynamics, 2001 25 Birger Back/ANL

Outlook I: 2001 • 100 x statistics • Both arms completed • Physics: • • • low-p. T physics Spectra HBT Resonances (f at low p. T) Event-by-Event physics • Energy systematics • Species systematics Winter Workshop on Nuclear Dynamics, 2001 26 Birger Back/ANL

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 k. Hz) • High Resolution • Add • Micro-vertex Detector • Narrow beam-pipe • ALICE prototype TRD Electron ID • EM-Calorimeter Micro-Vertex Winter Workshop on Nuclear Dynamics, 2001 27 Birger Back/ANL

The End Winter Workshop on Nuclear Dynamics, 2001 28 Birger Back/ANL