Updated Status and Plansof the

PHOBOS Experiment

Gunther Roland/MIT

Presentations to RHIC Planning Group and PAC

12/03 and 12/05 2003

Collaboration (Dec 2003)

Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Bruce Becker, Russell Betts,

Abigail Bickley, Richard Bindel, Andrzej Budzanowski, Wit Busza (Spokesperson), Alan Carroll,

Patrick Decowski, Edmundo Garcia, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen,

Stephen Gushue, Clive Halliwell, Joshua Hamblen, Adam Harrington, Conor Henderson,

David Hofman, Richard Hollis, Roman Holynski, Burt Holzman, Aneta Iordanova, Erik Johnson,

Jay Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo, Jang Woo Lee, Willis Lin, Steven Manly,

Alice Mignerey, Gerrit van Nieuwenhuizen, Aaron Noell, Rachid Nouicer, Andrzej Olszewski,

Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Louis Remsberg, Christof Roland,

Gunther Roland, Joe Sagerer, Pradeep Sarin, Pawel Sawicki, Iouri Sedykh, Wojtek Skulski,

Chadd Smith, Peter Steinberg, George Stephans, Andrei Sukhanov, Ray Teng,

Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Robin Verdier, Gábor Veres, Bernard

Wadsworth, Frank Wolfs, Barbara Wosiek, Krzysztof Wozniak, Alan Wuosmaa, Bolek Wyslouch,

Jinlong Zhang

ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORYINSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGYNATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO

UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER

PHOBOS Future

• Complete Baseline Program in the next 3-4 Runs

• Essential Items– Long Au+Au Run – Energy Scan (63 GeV + 1 addt’l Energy)– Species Scan (Cu+Cu + 1 addt’l Species)– p+p Reference Data

• Budget constraints link near-term and long-term RHIC running considerations

PHOBOS Status

2000 2001 2002 2003

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15

~550 citations on SPIRES

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Exponential Growth

RHIC Status

• Unique State of Matter formed in Au+Au– Very High Density– Equilibrated Strangeness production– Collective Behavior in Early Stage– Opaque to fast partons

• What are the initial conditions that lead to these properties?

• Systematic Study vs – Energy Density– System Size

– Rapidity, xf

• Data continue to surprise us

PHOBOS Detector 2004 (+beyond)

T0

T0

• Final Configuration

• Compared to Au+Au Run II:– 15x faster DAQ – 2.5x higher PID reach– new forward Proton Calorimeters– p+p, d+Au Spectrometer Trigger– SpecCal for high pT trigger in Au+Au

SpecCal

PHOBOS Capabilities: Multiplicity Array

QM’04 Preview

PHOBOS preliminary

h+ + h- Au-Au data

Phys. Rev. Lett. 91, 052303 (2003)

130 GeV: PRL 89:222301, 2002

PHOBOS Capabilities: Spectrometer

pT (GeV/c)0.05 0.5 5.0

Stoppingparticles

dE/dx ToF

Continuous Particle ID from low to high pT

QM’04 Previewp

K

Eloss (MeV)

dE

/dx

p (GeV) p (GeV)

PHOBOS Capabilities: Spectrometer

Acceptance forward of mid-rapidity: 0 < < 2.5

Spectrometer Acceptance

PHOBOS Future

• Complete Baseline Program in the next 3-4 Runs

• Essential Items– Long Au+Au Run – Energy Scan (63 GeV + 1 addt’l Energy)– Species Scan (Cu+Cu + 1 addt’l Species)– p+p Reference Data

• Budget constraints link near-term and long-term RHIC running considerations

PHOBOS Future

• Complete Baseline Program in the next 3-4 Runs

• Essential Items– Long Au+Au Run (Run IV)– Energy Scan (63 GeV + 1 addt’l Energy)– Species Scan (Cu+Cu + 1 addt’l Species)– p+p Reference Data

• Budget constraints link near-term and long-term RHIC running considerations

Crucial Link to d+Au!

must-do itemsin white paper

Comparison to Parton Saturation and RQMD Models

Parton saturation model prediction D. Kharzeev et al., hep-ph/0212316

Charged Hadron dN/d Distribution in d+Au

First result on d+Au min bias multiplicity

Many features reminiscent of lower energy p+A data

Important lessons for Saturation Model

nucl-ex/0311009 (subm.to PRL)

Comparison to Parton Saturation and RQMD ModelsCharged Hadron dN/d Distribution in d+Au

AMPT/HIJING close to data (-5.4 < < 4)

nucl-ex/0311009 (subm.to PRL)

Particle Ratios in d+Au: p/p vs Centrality

First particle ratio data from d+AuConstant p/p ratio vs centrality

Disagreement with expectations/models

nucl-ex/0309013 - submitted to PRC

Au+Au Phys. Rev. C 67, 021901R (2003)

d+Au pT Spectra

Phys. Rev. Lett. 91, 072302 (2003)

Au+Au

d+Au

RHIC d+Au/Au+Au results conclusively show that high pT suppression

at mid-rapidity is unique to Au+Au

?

??Exciting hints in d+Au

Need p+p reference data to fully

exploit existing d+Au

BRAHMS DNP’03 PreliminaryVitev, CIPANP’03

Scheduling Considerations

We considered 27wk/yr, 37wk/yr, 32wk/yr, 37wk/1.5yr, 54wk/2yr scenarios

54wk/2yr scenario not workable

Scheduling of energy/species scan early on critical for PHOBOS

Species Scan

• For many observables– rapid change from p+p to peripheral Au+Au

– large uncertainty in <Npart> for peripheral events

• Fe+Fe overlaps with well-measured <Npart> range in Au+Au

• AGS/SPS results on Si+Si vs Pb+Pb show violations of <Npart> scaling

Au+Au

Energy Scan

2x increase in particle density: Change from high-pT enhancement to strong suppression

SPS

RHIC

[ ]

[ ] [ ]

Energy Scan

NA49

AGS

PHENIX

Shape of excitation function between SPS and RHIC?

NA49, SQM’03

Summary

• PHOBOS/RHIC Data Set is expanding rapidly• Exciting (and puzzling) results in Au+Au and d+Au• Further insight from

– Energy Scan– Species Scan– p+p reference data

• Unique contributions from PHOBOS– Multiplicity Array– Spectrometer

• Very difficult scheduling – Timing of species/energy scans is crucial to fully exploit

PHOBOS (and RHIC) capabilities