, the Early Years
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Transcript of , the Early Years
4-Jan-2002G.S.F.Stephans Epiphany 2002
, the Early Years
The Ghost of PastWhat was built and why
The Ghost of PresentWhat has been accomplished
The Ghost of FutureWhat is still to come
Presented in the spirit(s) of Charles Dickens:
4-Jan-2002G.S.F.Stephans Epiphany 2002
Collaboration (Jan 2002)
ARGONNE NATIONAL LABORATORYBirger 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, KRAKOWAndrzej Budzanowski, Roman Holynski, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki , Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Wozniak
MASSACHUSETTS INSTITUTE OF TECHNOLOGYWit 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, TAIWANChia Ming Kuo, Willis Lin, Jaw-Luen Tang
UNIVERSITY OF ROCHESTERJoshua Hamblen , Erik Johnson, Nazim Khan, Steven Manly,Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs
UNIVERSITY OF ILLINOIS AT CHICAGORussell Betts, Edmundo Garcia, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer
UNIVERSITY OF MARYLANDAbigail Bickley, Richard Bindel, Alice Mignerey
4-Jan-2002G.S.F.Stephans Epiphany 2002
Goals of ,
Measure numerous observables quickly & accurately
Perform several unique measurementsLarge 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
4-Jan-2002G.S.F.Stephans Epiphany 2002
Detectors used by ,
Multiplicity array (Si sensors)Almost 4 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
4-Jan-2002G.S.F.Stephans Epiphany 2002
Frodo (to scale)
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~4 Multiplicity array
Trigger paddles Spectrometer
The 42-ton monster
All held together by excellent engineering!
Spectrometer module
4-Jan-2002G.S.F.Stephans Epiphany 2002
Detector Performance IDetectors signals stable and well understood
4-Jan-2002G.S.F.Stephans Epiphany 2002
Excellent signal/noise
Very few dead channels (even after RHIC assault)
Detector Performance II
Before RHIC blasts
10%
15~137,000 total Si channels
4-Jan-2002G.S.F.Stephans Epiphany 2002
Triggering on Interactions
t (ns)
Eve
nts
Negative
Paddles
Positive Paddles
ZDC N
ZDC PAu Au
x
z
PPPN
3<||<4.5
ValidCollision
4-Jan-2002G.S.F.Stephans Epiphany 2002
For more discussion, see later talk by
Andrzej Olszewski…
Determining Centrality of Interaction
Data
Paddle signal
Nparticipants
Data+MC
HIJING +GEANT Glauber calculation Model of paddle trigger
4-Jan-2002G.S.F.Stephans Epiphany 2002
Multiplicity Measurements
Unrivaled phase space coverage
High granularity in and 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
4-Jan-2002G.S.F.Stephans Epiphany 2002
-5.4 +5.4
Single-event display
Octagon&Ring hits
Vertextracklets
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Energy Dependence of Central Multiplicity
||1 6% most central AA collisions
Phys Rev Lett 85, 3100 (2000) & 88, 22302 (2002)
4-Jan-2002G.S.F.Stephans Epiphany 2002
nucl-ex/0105011Accepted: Phys Rev C
Kharzeev/Nardi
Centrality Dependence I
HIJING: PRL 86, 3496 (2001)EKRT: hep-ph/0106330KN scaling PLB 507,121 (2001)
||1 AuAu
dN
ch/d
/<
Np
art>
/2
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Centrality Dependence II
To be submitted to PRLSee: Kharzeev and Levin, Phys. Lett. B523, 79 (2001)
||1 AuAu
4-Jan-2002G.S.F.Stephans Epiphany 2002
“soft” “hard”
Two Component Parameterization
collpppart
pp NxnN
nxddN
2)1(
(mini)jet
(mini)jet
Hard ScatteringSoft Scattering
x is the fraction of particles produced by hard scatteringAt RHIC: npp~2.3, x~10%
4-Jan-2002G.S.F.Stephans Epiphany 2002
Two Component Parameterization
4.13.1~ PairColl NN
In old language:PairColl NN
From geometry, the number of collisions:
For Symmetric systems, colliding pairs:
where is the average number of binary collisions
4.03.0 PairN
11
xnNddN
ppPair Ratio to pp is a mix
of nuclear geometry and the fraction of hard scatteringNote: Asymmetric systems (pAu,
SiAu, etc.) will have different ratiosbetween NColl and NPart
2Part
PairNN
4-Jan-2002G.S.F.Stephans Epiphany 2002
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.
4-Jan-2002G.S.F.Stephans Epiphany 2002
2-Component Energy Prediction
37.0
291.0 25.0 0078.0 PairCollNN
NNsx
~20 at LHCdN/d~3500
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PRL 87, 102303 (2001)
Shapes I
Distributions get narrower for more central collisions.
130 GeV AuAu Data
Full dN/d distribution yields the total number of charged particles.
For 3% most central<Nch> = 4200 470
Peripheral
Central
4-Jan-2002G.S.F.Stephans Epiphany 2002
Shapes II
PRL 87,102303(2001)
130 GeV
Notecrossover
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beamy
FragmentationFragmentation
UA5: Alner et al., Z. Phys. C33,1 (1986) PHOBOS 2000/2001
7-10% syst error
Shapes III
200 GeV shape from Phys Rev Lett 88, 22302 (2002)
4-Jan-2002G.S.F.Stephans Epiphany 2002
Multiplicity Conclusions (so far)Whatever measure or model is used, systems
being created are dense & denser.
Extensive results on energy, centrality, andrapidity dependence
Data have significant impact on theoryInitial conditions and subsequent evolution
Global properties and fundamental interactions
Rules out or severely restricts many proposed exotic processes
Much more to come…
4-Jan-2002G.S.F.Stephans Epiphany 2002
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
4-Jan-2002G.S.F.Stephans Epiphany 2002
Observation: Centrality data at both beam energies rise for the most central events (systematics? physics? mean p?) ||1
AuAu
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Spectrometer
z
-x
10 cm
y
70 cm Magnetic Field
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dE/dx resolution 7%
Particle ID using dE/dx
Momentum resolution
Spectrometer Characteristics
2%
10 GeV
K
p d
4-Jan-2002G.S.F.Stephans Epiphany 2002
130 GeV Data Phys.Rev.Lett. 87, 102301 (2001)
06.004.060.0
06.007.091.0
02.001.000.1
p
p
K
K
Stat. Syst.
Spectrometer I: Chemistry
Using model of Redlich (QM ’01) T~165 implies B=45
4-Jan-2002G.S.F.Stephans Epiphany 2002
K-/K+ vs Energy
Particle Ratios @ 130 GeV
p/p vs Energy
Phys Rev Lett 87, 102301 (2001)
4-Jan-2002G.S.F.Stephans Epiphany 2002
Spectrometer II: Stopping ParticlesThe Ultimate in Low p
X[c
m] A
BC
D
E F
Z[cm]
Beam pipe
For tracks stopping in the 5th Si layer:
p 50 MeV/cpK 140 MeV/c pp 200 MeV/c
Note: At low p, particles are at y~0 for any angle
4-Jan-2002G.S.F.Stephans Epiphany 2002
High signals fromnuclear fragmentation
can identify -
dE/dx from in Individual Layers
0 2
0 20
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Eloss
Mp
K
P
Eloss = (ΣdEi )/nhits , i=A-E
Mi = (dE/dx)i * Ei
(~1/2) (m2)
MC Results
4-Jan-2002G.S.F.Stephans Epiphany 2002
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 at low p), and much more…
4-Jan-2002G.S.F.Stephans Epiphany 2002
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
4-Jan-2002G.S.F.Stephans Epiphany 2002
• Add
• ALICE prototype TRD Electron-ID
• EM-Calorimeter
• Micro-Vertex Detector
Micro-Vertex
Transition Radiation Detector
EM-Calorimeter
Use existing spectrometer
Discussing upgrade to focus on charm production at RHIC.
Measure single electrons from displaced vertices.
One Possible Charming Future…
4-Jan-2002G.S.F.Stephans Epiphany 2002
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!
G.S.F.Stephans Epiphany 2002 4-Jan-2002
PHOBOS web-site: www.phobos.bnl.gov Physics Results
Charged particle multiplicity near mid-rapidity in central Au+Au collisions at 56 and 130 GeV Phys. Rev. Lett. 85, 3100 (2000)
Ratios of charged antiparticles-to-particles near mid-rapidity in Au+Au collisions at 130 GeV Phys. Rev. Lett. 87, 102301 (2001)
Charged-particle pseudorapidity density distributions from Au+Au collisions at 130 GeV Phys. Rev. Lett. 87, 102303 (2001)
Energy dependence of particle multiplicities in central Au+Au collisions Phys. Rev. Lett. 88, 22302 (2002)
Centrality Dependence of Charged Particle Multiplicity at h=0 in Au+Au Collisions at 130 GeV Accepted to Phys. Rev. C (December 2001); nucl-ex/0105011
Technical Array of Scintillator Counters for PHOBOS at RHIC
Nucl. Instr. Meth. A474, 38-45 (2001) Silicon Pad Detectors for the PHOBOS Experiment at RHIC
Nucl. 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)
For More Information…