Birger Back/ANLDOE visit, February, 2001 -1-

Results from the PHOBOS experiment at RHIC

Birger Back Argonne National Laboratory

for the PHOBOS Collaboration

Birger Back/ANLDOE visit, February, 2001 -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

Birger Back/ANLDOE visit, February, 2001 -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)

Birger Back/ANLDOE visit, February, 2001 -4-

PHOBOS Detector

Ring Counters

Paddle Trigger Counter

Spectrometer

TOF

Octagon+Vertex

• 96000 Silicon Pad channels

• 4 Multiplicity Array • Mid-rapidity Spectrometer• Scintillator Paddles + Zero Degree Calorimeter for triggering• TOF wall for high-momentum PID

Birger Back/ANLDOE visit, February, 2001 -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

Birger Back/ANLDOE visit, February, 2001 -6-

Multiplicity of charged particles / tracklets

Tracklet counting in double Si layers

Spectrometer

Vertex

Birger Back/ANLDOE visit, February, 2001 -7-

First RHIC physics result: Back et al., PRL 85 (2000) 3100About 20 theoretical papers (Feb 15, 2001)

Multiplicity at =0 vs Energy

RESULTSs dN/dh56 GeV 4081230130 GeV 5551235

Ss 2dN/dh/Npart

56 GeV 2.47.10.25130 GeV 3.24.10.25

Ratio: 1.31.04.05

@ 130 GeV 30% higher than p+p70% higher than SPS

SPS

Phobos

p+p

Birger Back/ANLDOE visit, February, 2001 -8-

Multiplicity at =0 vs Npart

Npart

•Good agreement with recent PHENIX data•Good agreement with previous PHOBOS point•Neither HIJING nor EKRT describe data well

Yellow band: Systematic uncertainty

PreliminarydN

ch/d/

(0.5

*Npa

rt) HIJING

KharzeevNardi

EKRT

Birger Back/ANLDOE visit, February, 2001 -9-

Multiplicity in 4(Hit counting)

• Determine dNch/d for –5.4 < < 5.4• Shape• Total multiplicity• Evolution vs Npart

• Hit counting • Poisson occupancy corrections

Octagon

Rings

Single Si layer

Birger Back/ANLDOE visit, February, 2001 -10-

dNch/d vs Centrality Preliminary

Statistical errors only - 10-20% systematical uncertainty

Birger Back/ANLDOE visit, February, 2001 -11-

Centrality Dependence of Nch(||<5.4)

Npart

PHOBOS Prelim.

±10% Systematic Uncertainty±10% Systematic Uncertainty

HIJING

Nch

(||

<5.

4)

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Centrality dependence of dN/dh

Phobos HIJING

CentralMid centralPeripheral

•Increased particle production at mid-rapidity•Differences in shapes

Birger Back/ANLDOE visit, February, 2001 -13-

Elliptic Flow

dN/d(R ) = N0 (1 + 2V1cos (R) + 2V2cos (2(R) + ... )

Octagon Ring

V2

PHOBOS

STAR

Reaction plane

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Anti-particle / particle ratios

•Tracking in the spectrometer•Alternate 2T magnetic fields•Energy loss and momentum

+-

Central region not baryon-free

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• dNch/d @=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/d in 4• <Nch> = 4100 +/- 410 (||< 5.4) for 3% central

• Additional particle production near =0 for central events

• Wider than HIJING

• Elliptic flow• V2 up to 0.06 – close to hydrodynamic limit

• larger than SPS

• V2 drops for || > 1.5

• Particle ratios• p/p ratio 0.55 +/- 0.1

• Central region not yet baryon free – maybe at 200 GeV

Summary

Birger Back/ANLDOE visit, February, 2001 -16-

Outlook I: 2001

• 100x statistics• Both arms completed• Physics:

• low-pT physics

• Spectra• HBT

• Resonances (at low pT

• Event-by-Event physics

• Energy systematics• Species systematics

Birger Back/ANLDOE visit, February, 2001 -17-

Outlook II: 2003 + beyond

Micro-Vertex

Transition Radiation Detector

EM-Calorimeter

• Existing Spectrometer• High rate (> 0.5 kHz)• High Resolution

• Add

• Micro-vertex Detector• Narrow beam-pipe• ALICE prototype TRD

Electron ID• EM-Calorimeter

•Charm Production at RHIC•Measure single electrons from displaced vertices