, the Early Years

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, the Early Years
Presented in the spirit(s) of Charles Dickens

• The Ghost of Past
• What was built and why
• The Ghost of Present
• What has been accomplished
• The Ghost of Future
• What is still to come

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Collaboration (Jan 2002)
ARGONNE NATIONAL LABORATORY Birger Back, Alan
Wuosmaa BROOKHAVEN NATIONAL LABORATORY Mark
Baker, Donald Barton, Alan Carroll, Joel Corbo,
Nigel George, Stephen Gushue, Dale Hicks, Burt
Holzman, Robert Pak, Marc Rafelski, 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 Wit Busza (Spokesperson), Patrick
Decowski, Kristjan Gulbrandsen, Conor Henderson,
Jay Kane, Judith Katzy, Piotr Kulinich, Johannes
Muelmenstaedt, Heinz Pernegger, Michel Rbeiz,
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 NATIONAL CENTRAL
UNIVERSITY, TAIWAN Chia Ming Kuo, Willis Lin,
Jaw-Luen Tang UNIVERSITY OF ROCHESTER Joshua
Hamblen , Erik Johnson, Nazim Khan, Steven
Manly,Inkyu Park, Wojtek Skulski, Ray Teng, Frank
Wolfs UNIVERSITY OF ILLINOIS AT CHICAGO Russell
Betts, Edmundo Garcia, Clive Halliwell, David
Hofman, Richard Hollis, Aneta Iordanova, Wojtek
Kucewicz, Don McLeod, Rachid Nouicer, Michael
Reuter, Joe Sagerer UNIVERSITY OF
MARYLAND Abigail Bickley, Richard Bindel, Alice
Mignerey
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Goals of ,

• Measure numerous observables quickly accurately
• Perform several unique measurements
• Large multiplicity phase space coverage
• Particle measurements extended to low p
• Large event sample
• Eliminate the word preliminary from
  relativistic heavy ion vocabulary
• Good (to be)published data Thanks to the
  collaboration
• Wild physics speculation Blame GSFS

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Detectors used by ,

• Multiplicity array (Si sensors)
• Almost 4p coverage and high granularity
• 2 Arm Spectrometer (Si sensors)
• 2 Tesla magnetic field
• PID using dE/dx
• Time-of-Flight wall for extended PID
• Trigger counters (Scintillator Paddles
  Cherenkov T0)
• ZDCs common to all RHIC experiments

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Frodo (to scale)
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Trigger paddles
All held together by excellent engineering!
4p Multiplicity array
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Detector Performance I
Detectors signals stable and well understood
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Detector Performance II
137,000 total Si channels
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Excellent signal/noise
Before RHIC blasts
Very few dead channels (even after RHIC assault)
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Triggering on Interactions
Positive Paddles
Negative Paddles
ZDC N
ZDC P
Au
Au
PN
PP
Valid Collision
3 10
Determining Centrality of Interaction
For more discussion, see later talk by Andrzej
Olszewski
Data
HIJING GEANT Glauber calculation Model of
paddle trigger
Paddle signal
DataMC
Nparticipants
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Multiplicity Measurements

• Unrivaled phase space coverage
• High granularity in f and h
• Low mass detectors situated very close to the
  beam pipe
• Multiple detectors and/or independent analysis
  methods for the same observable
• MC and data combined for a very detailed
  understanding of systematics

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OctagonRing hits
-5.4
5.4
Single-event display
Vertex tracklets
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Energy Dependence of Central Multiplicity
h1 6 most central AA collisions
Phys Rev Lett 85, 3100 (2000) 88, 22302 (2002)
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Centrality Dependence I
dNch/dh //2
h1 AuAu
Kharzeev/Nardi
HIJING PRL 86, 3496 (2001) EKRT
hep-ph/0106330 KN scaling PLB 507,121 (2001)
nucl-ex/0105011 Accepted Phys Rev C
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Centrality Dependence II
h1 AuAu
See Kharzeev and Levin, Phys. Lett. B523, 79
(2001)
To be submitted to PRL
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Two Component Parameterization
soft hard
x is the fraction of particles produced by hard
scattering
At RHIC npp2.3, x10
Hard Scattering
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Two Component Parameterization
For Symmetric systems, colliding pairs
From geometry, the number of collisions
where n is the average number of binary
collisions
In old language

• Ratio to pp is a mix
• of nuclear geometry and the fraction of
• hard scattering

Note Asymmetric systems (pAu, SiAu, etc.) will
have different ratios between NColl and NPart
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Model Comments

• Fit of AuAu centrality data to two component
  parameterization extrapolates very close to pp
  data.
• Underlying physics of two-component model and
  saturation model are very different!
• Hopefully, further study (as well as other
  systems including pA) will help to differentiate
  the two.
• Note Several different saturation calculations
  agree that gluon densities are large on the
  QCD scale.

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2-Component Energy Prediction
20 at LHC dN/dh3500
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Shapes I
130 GeV AuAu Data
PRL 87, 102303 (2001)
Distributions get narrower for more central
collisions.
Full dN/dh distribution yields the total number
of charged particles. For 3 most central
4200 ? 470
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Shapes II
130 GeV
PRL 87,102303 (2001)
Note crossover
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Shapes III
PHOBOS 2000/2001
UA5 Alner et al., Z. Phys. C33,1 (1986)
7-10 syst error
Fragmentation
Fragmentation
200 GeV shape from Phys Rev Lett 88, 22302 (2002)
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Multiplicity Conclusions (so far)

• Whatever measure or model is used, systems being
  created are dense denser.
• Extensive results on energy, centrality,
  and rapidity dependence
• Data have significant impact on theory
• Initial conditions and subsequent evolution
• Global properties and fundamental interactions
• Rules out or severely restricts many proposed
  exotic processes
• Much more to come

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Charged Multiplicity Future

• Soon 20 GeV AuAu (RHIC injection energy, run in
  November specifically for Phobos) and
• 200 GeV pp (currently running)
• Later More details, fluctuations, event shape
• Next Run More species and energies

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Observation Centrality data at both beam
energies rise for the most central events
(systematics? physics? mean p??)
h1 AuAu
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Spectrometer
Magnetic Field
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Spectrometer Characteristics
Momentum resolution
2
Particle ID using dE/dx
10 GeV
d
p
K
p
dE/dx resolution 7
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Spectrometer I Chemistry
130 GeV Data Phys.Rev.Lett. 87, 102301 (2001)
Stat. Syst.
Using model of Redlich (QM 01) T165 implies
mB455
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Particle Ratios _at_ 130 GeV
K-/K vs Energy
Phys Rev Lett 87, 102301 (2001)
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Spectrometer II Stopping ParticlesThe Ultimate
in Low p
For tracks stopping in the 5th Si layer pp
? 50 MeV/c pK ? 140 MeV/c pp ?
200 MeV/c Note At low p, particles are at y0
for any angle
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dE/dx from p in Individual Layers
0
2
High signals from nuclear fragmentation can
identify p-
20
0
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MC Results
Eloss (SdEi )/nhits , iA-E
Mi (dE/dx)i Ei (1/?2)
(?m?2)
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Spectrometer Future

• Soon Particle ratios from 200 GeV AuAu
• Later
• Spectra (with and without PID)
• Extended PID
• Low and high p
• HBT
• Beyond Reaction plane, resonances (especially f
  at low p), and much more

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Future for ,

• Eagerly awaiting more beam energies and beam
  species (including pA) for systematic study
• Continue the program discussed as well as many
  additional physics topics (flow)
• Far Future Considering addition of electron
  identification to study charm production

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One Possible Charming Future
Discussing upgrade to focus on charm production
at RHIC. Measure single electrons from displaced
vertices.
Use existing spectrometer

• Add
• ALICE prototype TRD Electron-ID
• EM-Calorimeter
• Micro-Vertex Detector

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Conclusion

• Early results have proven more robust and more
  interesting than (I) expected.
• Detector (and analysis teams) have performed
  spectacularly.
• Bright prospects for productive years ahead.
• An even Happier 2002!

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For More Information

• PHOBOS web-site www.phobos.bnl.gov
• Physics Results
• Charged particle multiplicity near mid-rapidity
  in central AuAu collisions at 56 and 130 GeV
  Phys. Rev. Lett. 85, 3100 (2000)
                    
• Ratios of charged antiparticles-to-particles near
  mid-rapidity in AuAu collisions at 130 GeV Phys.
  Rev. Lett. 87, 102301 (2001)
• Charged-particle pseudorapidity density
  distributions from AuAu collisions at 130 GeV
  Phys. Rev. Lett. 87, 102303 (2001)      
  
• Energy dependence of particle multiplicities in
  central AuAu collisions Phys. Rev. Lett. 88,
  22302 (2002)
• Centrality Dependence of Charged Particle
  Multiplicity at h0 in AuAu Collisions at 130
  GeV Accepted to Phys. Rev. C (December 2001)
  nucl-ex/0105011   
• Technical
• Array of Scintillator Counters for PHOBOS at
  RHICNucl. Instr. Meth. A474, 38-45 (2001)
• Silicon Pad Detectors for the PHOBOS Experiment
  at RHICNucl. Instr. Meth. A461, 143-149
  (2001)                                            
                         
• Development of a double metal, AC-coupled silicon
  pad detectorThe silicon detector for the PHOBOS
  experiment at RHICNucl. Instr. Meth. A389, 415
  (1997)