The Landscape of the Strong Interaction: Results from .

1
The Landscape ofthe Strong InteractionResults
from .
ee-
RHIC
pp
SPS
AGS

• Peter Steinberg
• Brookhaven National Laboratory
• Nuclear/Particle Physics SeminarYale University
  Physics Department19 February 2004

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What we do _at_ RHIC
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National Attention
New York Times coverage of
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Lattice QCD calculations
Teraflop-scale computers are used to study
equilibrium QCD on a space-time
lattice Calculations predictphase transition
at Tc hadrons ? quarks gluons New degrees of
freedom!
cf. T0 170 MeV,e(proton) .5
GeV/fm3 e(nucleus) .17 GeV/fm3
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Proposed QCD Phase Diagram
Temperature(AverageKinetic Energyper Particle)
QuarkGluonPlasma
T170 MeV(2?1012 oK!)
Phase Transition?
Tgt0 Hadron Gas
NeutronStars?
Nuclei
T0
Nuclear Density
r0
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QGP Search _at_ RHIC
Tandem
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PHOBOS 2003
C
B
A

1. Spectrometer
2. Vertex detector
3. Octagon
4. Rings A,B,C

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PHOBOS Collaboration 2004
Birger Back, Mark Baker, Maarten Ballintijn,
Donald Barton, Russell Betts, Abigail Bickley,
Richard Bindel, Wit Busza (Spokesperson), Alan
Carroll, Zhengwei Chai, 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, Willis Lin, Steven Manly, Alice
Mignerey, Gerrit van Nieuwenhuizen, Rachid
Nouicer, Andrzej Olszewski, Robert Pak, Inkyu
Park, Heinz Pernegger, Corey Reed, Michael Ricci,
Christof Roland, Gunther Roland, Joe Sagerer,
Iouri Sedykh, Wojtek Skulski, Chadd Smith, Peter
Steinberg, George Stephans, Andrei Sukhanov,
Marguerite Belt Tonjes, Adam Trzupek, Carla
Vale, Siarhei Vaurynovich, Robin Verdier, Gábor
Veres, Edward Wenger, Frank Wolfs, Barbara
Wosiek, Krzysztof Wozniak, Alan Wuosmaa, Bolek
Wyslouch, Jinlong Zhang ARGONNE NATIONAL
LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITU
TE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS
INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL
UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT
CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF
ROCHESTER
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PHOBOS Physics Program

• Broad range of control variables (landscape)
• Beam Energy
• System size
• Impact parameter
• Pseudorapidity
• Research program
• Particle multiplicities
• Identified particle ratios
• Spectra at high pT
• Focus on Multiplicity
• Analog to entropy

pp
dAu
AuAu
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Multiplicity as a QGP Signal

• 1st-order phase transition
• Jump in entropy density (s)
• hadrons ? QGP
• Jet quenching energy loss of jets leads to
  additional gluons
• Clear effect in models (HIJING)

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Counting Particles in PHOBOS
f
Signals in the Si for a single RHIC event!
z
Rings
Octagon
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Angular Distributions in pp
PHOBOS pp Preliminary
UA1 900 GeV
q
h1
h0
h is an approximation torapidity (y)
Longitudinal distribution
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Centrality Dependence of dAu
b
We slice our datausing signals in rings
Shape Changes!Lets integrate over4p!
Data vs. AMPT
PHOBOS Preliminary
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Total Multiplicity vs. Npart
b
dAu scaled by Nppvs. wounded nucleons(2 in
pp)
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Can we build dAu with pp?
PHOBOS 200 GeV
Yes
dAu pp preliminary
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Is Npart Fundamental?
Expectations in dAustopping in d
directioncascading in Au direction Why do
they add up toNpart scaling so
robustly? Long-range correlation?
nucl-ex/0311009
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Geometry of AuAu Collisions
Do we have thebuilding blocks forAuAu
collisions?
b
Impact parameter controlsNumber of participants
Binary Collisions per participant (some
dependence on sNN)
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Estimating Centrality in AuAu
PHOBOS Data
We only assume signalis monotonic with Npart
Top 6 in signalcorrespond totop 6 in Npart
HIJING MC
Use full MC calculationsto account for
fluctuations
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dN/dh in AuAu
PHOBOS PRL91 (2003)
130 GeV
200 GeV
19.6 GeV
dN/dh
Most Central
h
h
h
Extensive data set3 CMS Energies, Npart from 65
340, hlt5.4 Once again, we just integrate
over 4p!
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Participant Scaling in AuAu
Extrapolatedto 4p
PHOBOS AuAu nucl-ex/0301017
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Can we build AuAu with pp/dAu?
PHOBOS 200 GeV
Fundamental differencebetween pp / dAu AuAu?
No!
AuAu nucl-ex/0301017dAu pp preliminary
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Nch vs. ?s in pp and AA
Central AA
PHOBOS nucl-ex/0301017
Particle Data Book (2000)
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Comparisons with ee-
Multiparticle hadronic final statesHow do they
compare?
q
q
UA1 900 GeV
DELPHI 209 GeV
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A New Wrinkle
Central AA
PHOBOS nucl-ex/0301017
Particle Data Book (2000)
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A New Wrinkle
(MLLA pQCD, Mueller 1983)
Central AA
PHOBOS nucl-ex/0301017
Particle Data Book (2000)
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AuAu approaches ee-
Central AA
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Angular Distributions
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Energy Dependence near h0
(dN/dyT )
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More Questions than Answers

• Why is Npart appropriate?
• How many participants in ee-?
• Why does AuAu agree with ee- at high energies?
• How does pp fit in?
• Why do AA and ee- disagree at lower energies?

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1. Is Npart/2 Appropriate?
So, by transitivity
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2. What about pp?

• In pp collisions, have leading particles
• Flat distribution of
• independent of energy
• Only ½ of energy available for particle production

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Three Behaviors
Correct for leading particles
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Down to Two
Universality of particle production?
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Historical Note
Leading particle effectstudied at ISR ppby
comparison to ee-(Basile et al, 1981-1984)
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Why is AA already like ee- ?

• Leading particle effect is reduced
• Presumably by multiple collisions
• In PHOBOS result, at least 3 per participant

dAu dominated bysingly-struck nucleons
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3. Why does AA approach ee-
AA pp ee-
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Thermal-Statistical Model
Pioneered by R. Hagedorn, 1963
Grand Canonical Relativistic Gas
HadronMass Spectrum
RHICappears to bein chemicalequilibriumat
T170 MeV mB 41 MeV!
Figure from P. Braun-Munziger, D. Magestro, J.
Stachel
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Phase Diagram
Kaneta Xu
High energy
Low energy
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Statistical Models and ee-/pp
F. Becattini, hep-ph/9701275

• Statistical models also describe ee- and pp
• Temperature constant vs. ?s
• Typically mB assumed to be 0

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Relating AA and ee-
ThermalModelscancalculateentropydensity
Experimental
Theoretical
Assumption!
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Entropy Density vs. Beam Energy
J. Cleymans M. StankiewiczUniversity of Cape
Town
Evaluated alongfreezeout contour
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Comparison with Data
Qualititative agreement
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Universality of Strong Interaction

• So it seems as if
• Separating wounded baryons (participants)
• Produce same number of particles (and dN/dh) as
  separating quarks with same available energy
• Unless there are initial baryons to conserve!

y
Not a new concept,even in gauge theories Brodsky
Gunion (1976)
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What Now?

• Interesting phenomenology ? will it work _at_ LHC?

HIJING isx2 higher!
JETSET
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What About the QGP?
Was the QGPcreated at RHIC?
Constraint on entropy ? Constraint on Dynamics
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We need a physical scenario that builds
in Entropy creation conservation Thermal/Stat
istical Phenomenology
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Landau Hydrodynamics
UniversalEntropyper Npart/2 Ss1/4
Landau consideredstrong interactions ascomplete
stoppingof Lorentz-contractedpancakes in 1953
Landau, Carruthers, Cooper/Frye, P. Steinberg
(BNL), G. Roland (QM04)
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Conclusions

• PHOBOS is an excellent detector to survey the
  landscape of strong interactions
• pp, dAu, AuAu (energies, centralities)
• Energy and species scan still to come!
• Nch reveals connections between AuAu and
  elementary reactions (pp, ee-) in conjunction
  with thermal ( hydrodynamic) approaches
• Npart scaling, Universal multiplicity, mB effect
• Counterintuitive, but apparently useful
• Consolidates understanding of strong interaction
• A map for understanding nuclear dynamics from
  AGS through RHIC LHC!

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.
ee-
RHIC
pp
SPS
AGS
Birger Back, Mark Baker, Maarten Ballintijn,
Donald Barton, Russell Betts, Abigail Bickley,
Richard Bindel, Wit Busza (Spokesperson), Alan
Carroll, Zhengwei Chai, 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, Willis Lin, Steven Manly, Alice
Mignerey, Gerrit van Nieuwenhuizen, Rachid
Nouicer, Andrzej Olszewski, Robert Pak, Inkyu
Park, Heinz Pernegger, Corey Reed, Michael Ricci,
Christof Roland, Gunther Roland, Joe Sagerer,
Iouri Sedykh, Wojtek Skulski, Chadd Smith, Peter
Steinberg, George Stephans, Andrei Sukhanov,
Marguerite Belt Tonjes, Adam Trzupek, Carla Vale,
Siarhei Vaurynovich, Robin Verdier, Gábor Veres,
Edward Wenger, Frank Wolfs, Barbara Wosiek,
Krzysztof Wozniak, Alan Wuosmaa, Bolek Wyslouch,
Jinlong Zhang
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Gaussian Rapidity Distributions
Shown by G. Roland, QM04
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Jet Quenching Entropy
Suppression of high-pTparticles indicatesparton
energy loss
Npart scaling ?Surface emission
Absorbed jets mustradiate. Where isthis
extra entropy?
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Quarks Gluons
Gluons are like charged photons
Quarks are the matter in everyday matter
u up c charm t top
d down s strange b bottom
Non-Abelian Terms(ggg gggg)
QED (qqg)
u
QCD Quantum Chromodynamics Field theory
describinginteractions of quarks gluons
u
d
HARD (non-perturative)
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Bound States of QCD
Instead, we see colorlessbound states ?
hadrons
No-one has ever seen a quark.QCD is a
confining gauge theory,with an effective
potential
p
p
mp 135 MeV
mp 938 MeV
K
Coulomb
Confining
Coulomb
Confining
L
V(r)
Ss
mK 495 MeV
mL 1115 MeV
r
We do not yetunderstand thesemasses (or their
spins!)by using pQCD!
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Strong Thermodynamics
Figures fromW. Zajc, Columbia University
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The Bulk of Particles _at_ RHIC
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Strong Blackbody Radiation
PHOBOS Central (head-on) AuAu 200 GeV
(Transverse momentum)
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RHIC Experiments (to scale)
PHENIX
BRAHMS
STAR
PHOBOS
Two BIG Spectrometers100s-1000s particles
eventParticle ID, photons leptons
Two small detectorsForward particles,Particle
multiplicity
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2-jet Events in ee-
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What happened to leading particles?

• BRAHMS measured net protons vs. y _at_ 200 GeV
• Baryons not fully stopped at 200 GeV Ep/Ebeam
  286
• Why does AuAu seem to get the whole ?s?

nucl-ex/0312023
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Hint Leading Particles in ee-

• What fraction of beam energy does fastest
  particle in ee- get?
• BRAHMS estimates
• Neither ee- nor AAare fully stopped

PYTHIA 6.205/JETSET 7.3
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Non-Universality?
Details showdifferences betweenkinematic
quantitesvs. ?s Again, only claimis that
entropyis universal These differencesmay
illuminate theessential differences(e.g.
transverse size,fluctuations)
(h0)
(4p)
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Predictions at h0