cteq 2006 heavy ion collisions david hofman uic. cteq 2006 setting the stage
TRANSCRIPT
CTEQ 2006
Heavy Ion Collisions
David HofmanUIC
CTEQ 2006
Setting the Stage
CTEQ 2006
The “First” Heavy-Ion Experiment (circa 1909)
Rutherford: “It was quite the most incredible event that ever happened to me in my life. It was almost as incredible as if you had fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”
On a Diffuse Reflection of the a-ParticlesProceedings of the Royal Society A vol. 82, p. 495-500 1909
By H. GEIGER, Ph.D., John Harling Fellow, and E. MARSDEN, Hatfield Scholar, University of Manchester.
(Communicated by Prof. E. Rutherford, F.R.S. Received May 19, -- Read June 17, 1909.)
BEAM: Ra source
Detector: zinc sulfide screen
Results
Readout: Human eye (rate~1Hz & “new” eye every 60s)
Experiment
TARGET: Gold Foils
Different Reflectors:
62 scintillations/min for Lead67 “ “ Gold63 “ “ Platinum34 “ “ Tin27 “ “ Silver14.5 “ “ Copper10.2 “ “ Iron3.4 “ “ Aluminum
Thin Au foils
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Structure of an Atomic Nucleus
Can ‘see’ the smaller protons moving about inside the nucleus.
Helium Nucleus From D.H. Perkins, Intro. to High Energy Physics
Scale~ 2 fmelectron
Final Energy, E’
Final Electron Energy, E’ (GeV)
p
p
nn
Yie
ld o
f E
lect
rons
(cr
oss
sect
ion)
Elastic Scattering of Electron off the Nucleus
0.25 0.30 0.35 0.40
Method: Scattering of Electrons off Helium Nucleus
Initial Energy E = 0.4 GeV
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Let’s Free the Nucleons from He
• Mass of 2 protons + 2 neutrons = 4.0329812u• Mass of 4He = 4.0026033u
• Mass Difference m = 0.0303779u
E = mc2
0.9315 GeV = 1 u (atomic mass unit) x c2
• Energy Difference E=mc2 = 0.0283 GeV
• What does it mean? If you add 0.0283 GeV of energy to a Helium atom
– You can ‘take it apart’ and study the bits assembled and disassembled.– Its inner parts are protons and neutrons.– The protons, neutrons and electrons are stable and exist ‘on their own’.– Mass of the bits is more than the object together! → Makes sense.
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Structure of a Proton
Scale~ 1.3 fm
Method: Deep Inelastic Scattering of Electrons off Protons
electron
proton
uu
d
~Pquark/Pnucleon
~
From D.H. Perkins, Intro. to High Energy Physics
M
Qx
2
2
3/1 1
Increasing Energy Transfer ...
Peak at x = 1/3 if the beam scatters elastically with x = 1 from a quasi-free object of
mass m = M/3
Can ‘see’ the quarks & they are moving about inside in the proton.
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Breaking the Proton Apart
1. If you try to break a proton apart, you just get a second particle made up of 2 quarks!
e-p graphics: http://www.theorie.physik.uni-wuppertal.de/~wwwkroll/frames/main.eng.html
M. McDaniel, Copyright 1998
2. If you measure the mass of the quarks inside the proton, you only account for a fraction of the nucleon mass.
We can see the quarks inside the nucleus. Lets free them!
Two immediate problems:
… something very interesting is going on!
Electron
Electron
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1. QCD: Confinement (& asymptotic freedom)
Visualization of QCD by Derek Leinweber Centre for the Subatomic Structure of
Matter (CSSM) and Department of Physics, University of Adelaide, 5005
Australia
Separation of quarks varies from 0.125 fm to 2.25 fm (~1.3x diameter of proton)
distance
energy density, temperature
rela
tive
stre
ngth
asymptotic freedom
http://www.physics.adelaide.edu.au/theory/staff/leinweber/VisualQCD/ImprovedOperators/index.html
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Running Coupling Constant
M. Schmelling hep-ex/9701002
experimental data and perturbative QCD (pQCD) calculation
Distance
Energy Density, Temperature
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2. QCD: The Properties of our Vacuum
Visualization of QCD: by Derek Leinweber
Volume2.4x2.4x3.6 fm3
Action Density (~Energy Density)
(same references as earlier slide)
Topological Charge Density (measure of winding of gluon field lines)
(Can hold a couple of protons)
“Contrary to the concept of an empty vacuum, QCD induces chromo-electric and chromo-magnetic fields throughout space-time in its lowest energy state.” - D. Leinweber
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QCD Vacuum is a Condensate!
→ The reason why hadrons are so heavy.
uu
dd
uu
dd
uu
dd
T = 0 T > 0 (but < Tc)
T > Tc
Diagrams & discussion from
Krishna Rajagopal
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QCD and The Masses of Particles
Comparison of the “hadronic spectrum” with first-principles calculations from QCD, using techniques of lattice guage theory.
“…confinement and chiral symmetry breaking [i.e. the QCD condensate] are simply true facts about the solution of QCD, that emerge by direct calculation” – F. Wilczek
R. Burkhalter,hep-lat/9810043
Mas
s (G
eV/c2
)
Nucleons (protons +neutrons)Measured Mass ~0.9 GeV/c2
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Back to Einstein…
2mcE
2c
Em
“Does the Inertia of a Body Depend Upon its Energy Content?”By A. Einstein
September 27, 1905
Idea From: F. Wilczek’s Nobel Prize Lecture
“The mass of a body is a measure of its energy-content;… It is not impossible that with bodies whose energy-content is variable to a high degree … the theory may be successfully put to the test. “ – A. Einstein (translated from the German of his 1905 paper).
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Forward to Today…
Figure and quote From B. Muller; nucl-th/0404015
“Because of the energy scales involved, only the QCD Vacuum is amenable to modification at energies accessible with present technologies.”
Current (or ‘naked’) Quarks
Mass u,d = 5-10 MeV generated by Higgs condensate.
Constituent Quarks
Mass u,d ~ 300 MeV generated by QCD condensate.
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Melting the QCD Vacuum
Temperature
Con
dens
ate
Temperature
Ene
rgy
Den
sity pion gas
quark-gluon plasma
Critical “melting” temperature, Tc
The condensate “melts” (Chiral Symmetry is ≈ restored)
Deconfinement
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Lattice QCD at Finite Temperature
B=0)
F. Karsch, hep-ph/010314
Critical Temperature, TC ~ 170 MeV Critical Energy Density,C ~ 1 GeV/fm3
A new form of matter (Quark Gluon Plasma)
Normal “cold” vacuum
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How Much “Heat” is Needed?
Quark-Gluon plasma:Need ~2 trillion degrees K
2 x 1012 K (or oC)
Too much “heat” to think about creating in a traditional sense.
TC ~ 170 MeV
1eV corresponds to an energy kT (where T~11,600 K) . Assume transition at about 170 MeV (~1.2 x pion mass), 170E6*11600 = 1.7E8*1.16E4 ~2E12
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Big quark-gluon p + n low mass nuclei neutral atom star dispersion of TODAYBang plasma formation formation formation formation heavy elements
time 10-6s 10-4s 3 min 400,000 yr 109 yr >109yr 15x109yr
Copyright 1998 Contemporary Physics Education Project (CPEP)
...so much “heat” that we are actuallyforming a window back in time
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Collide heavy nuclei at relativistic speeds (e.g. 0.99996c at sNN = 200 GeV)
We believe these conditions will reach the necessary temperature and pressures (energy-density) to create conditions in which the QGP could exist.
How to Get this Much “Heat”?
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Heavy Nuclei in Collision
Collision
?Mixed Phase?
Freeze-out
Hard partons
Dense partons
QGP ?
Time
Space
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Heavy-Ion Collisions
The Latest ExperimentsSelected DataWhat We Have LearnedWhere We Are Going From Here
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History of Heavy Ion Experiments
BNL AGS (1986)
sNN 5 GeV/u
O+O, Si+Si, Au+Au
CERN SPS (1986)
sNN 20 GeV/u
O+A, Pb+Pb
BNL RHIC (2000)
sNN 200 GeV/u
Au+Au, d+Au, Cu+Cu Figs. from R.Betts
LBL Bevatron/Bevelac and GSI SIS (1970’s)
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Relativistic Heavy Ion Collider
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Important Features of a Heavy Ion Collision
x
z
y
Npart Participantsthat undergoNcoll Collisions
A-0.5Npart
Spectators
A-0.5Npart
Spectators
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Npart Participants
Ncoll Binary Collisions
Npart/2 ~ A
L~A1/3
Ncoll ~ A4/3
b
Participants (Npart) and Collisions (Ncoll)
In pp collisions: Npart/2 = Ncoll = 1
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Measuring Collision Centrality
Data
Trigger signal
Peripheral Collision:
Small number of participating nucleons
Central Collision
Large Npart
HIJING +GEANT Get Npart
Glauber calculation Model of trigger signal
Data+MC
NpartNOTE: Also use Zero Degree Calorimetry to measure the spectator fragments
Denote Centrality by Percentage of inelastic cross-section. 0-5% is the top 5% most central and/or
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Number of Binary Collisions vs. Centrality and Energy
inel=42 mb(RHIC)
inel=33 mb (SPS)
inel=21 mb (AGS)
Glauber Monte Carlo Calculation for Au + Au Collisions
Au+Au
=
Nc
oll/(
Np
art/2
) max~ 6 (√s=200 GeV)
max~ 5 (√s= 17 GeV)
max = 1 (p+p)
max~ 3 (√s= 4.8 GeV)
Peripheralcollisions
Centralcollisions
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One Central Au+Au Collision
Beamline
= 0
+1
+2
+3
-1
-2
-3
“Midrapidity”
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Charged Particle Production
Total # of charged particles (central collision):
5060±250 @ 200 GeV
4170±210 @ 130 GeV
1680±100 @ 19.6 GeV
=-ln tan /2
dN
ch/d
PHOBOS: Phys. Rev. Lett. 91, 052303 (2003)
At 200 GeV:
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Energy Density Estimates
Phenix: ET measurement at 130 GeV
0 = 4.6 [GeV/fm3] PRL 87, 052301 (2001)
c0
R ~ r0A1/3
Energy density reached 0 > 4 GeV/fm3
Above the critical value c ~ 1 GeV/fm3
Bjorken
From: B.B. Back – Lake Lousie 2006
Central (head-on) Collision(for 200 GeV Au+Au)
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What State of Matter are we Producing?
1. Almost baryon-free with thermalization and expansion
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Matters of Matter and Anti-Matter
• Tracking in the spectrometer• Alternate 2T magnetic fields• Energy loss and momentum
+
Matter
Anti-MatterK-
p
-
K+
p
+
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Anti-Particle/Particle Ratios
p/p
K–/K+
Approaching equal production of matter and anti-matter as the collision energy increases. (i.e. “Baryon-Free”)
PHOBOS: Nucl. Phys. A 757, 28 (2005)
AGSSPS
RHIC
A+A central collisions
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Statistical/Thermal Description of Ratios
Braun-Munzinger, Redlich, Stachel - nucl-th/0304013
Have a chemical potential for every conserved quantum number
Constrain parameters with conservation laws
Only B and T are free parameters if look at production in 4. (Fix volume for smaller rapidity slices.)
Grand Canonical Ensemble
Make the assumption that the initial state has time to thermalize and this “chemical” thermal nature is preserved during hadronization.
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Results At RHIC Energies
Phys Lett. B. 518, 41 (2001); J. Phys G28, 1745 (2002)
Can fit each energy with a common chemical “freeze-out” temperature, Tch, and baryon chemical potential B. Suggests a high degree of chemical equilibrium (and thermalization) at the point where particles are “frozen-out” (created).
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Results at SPS and AGS Energies
Phys. Lett. B465, 5 (1999) & nucl-th/0304013
Tch=125 MeV, B = 540 MeV @ AGS (√sNN~ 4 GeV)
Tch=148 MeV, B = 400 MeV @ SPS (√sNN~ 9 GeV)
Tch=170 MeV, B = 255 MeV @ SPS (√sNN~18 GeV)
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Phase Diagram of Nuclear Matter
Figure modified from Stachel – Trento 2004
Quark Gluon Plasma
Hadronic Matter
The calculated freeze-out points approach (or even exceed) the Lattice QCD Tc values.
CTEQ 2006
Identified Particle Spectra
PHENIX - Phys. Rev. C 69, 034909 (2004)
Observation only to motivate next slide
p = mv
Common Expansion Velocity?
CTEQ 2006
Detailed Analysis of Particle Spectra
Retiere and Lisa – nucl-th/0312024
This velocity is large <T>~0.5c
Central
Can describe the data with a common transverse “flow” velocity.
Mid-central PeripheralFit with hydro-dynamically motivated “blast waves” to gain insight into the dynamics of the collision.
* Assumptions include particle freeze-out at a common temperature.
* Seven fit parameters.
Note: Other analyses show a centrality dependence of <BT>
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What State of Matter are we Producing?
1. Almost baryon-free with thermalization and expansion
2. A “Liquid” with Quark DoF
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Particle Emission Patterns
Peripheral Collisions: Overlap “hot spot” looks like an almond.
The degree that they do (or do not) tells us about the properties of the medium created (liquid or gas-like) and the equilibration timescales.
Do the particle emission patterns reflect this initial shape?
Reaction plane
x
z
y
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b (reaction plane)
View along beamline
Emission patterns follow the shape of the overlap region.
More particles are emitted along the reaction plane.
PHOBOS – S. Manly
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Fourier Analysis of Emission Patterns
n
RnR
nvd
dN)(cos21
)(
Extract n=2, elliptic flow
Study v2
Increasing Collision Centrality
Find significant values of v2 for non-central collisions Collective Behavior Reaches Hydro Limit (first time seen in HI collisions) Fast Equilibration Timescales
PHOBOS: Phys. Rev. C72, 051901(R) (2005)
CTEQ 2006
Momentum and Species Dependence of v2
v2(pt) is different for different particles Similar effect of mass-splitting as in spectra Even the mass splitting can be described in full hydro models (with, e.g., the additional collective transverse flow velocity from spectra fits)
200 GeV Au+Aumin-bias
STAR PRC 72 (05) 014904
Lower Momentum Higher Momentum
STAR PRC 72 (05) 014904
CTEQ 2006
v2 Evidence of Constituent Quark Scaling!
v2(particle) converges when scaled by the number of quarks in each particle
F. Wang – STAR - Quark Matter 2005
time
A Possible Scenario
Start with a thermalized “liquid” QGP with quark
degrees of freedom
At particle “freeze out” these quarks coalesce out
of the QGP quark coalescence (or recombination)
CTEQ 2006
Recombination and Fragmentation
Figs from B. Muller: nucl-th/0404015, R. Fries: QM 2004, PRL 90 202303 (2003)
fragmenting parton:ph = z p, z<1
recombining partons:p1+p2=ph
DATA and FITS
Should have a strong effect on Baryon to Meson ratios
Thermal Exponential
pQCD power-law
THE IDEA
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Quark Recombination (or Coalescence)
STAR; nucl-ex/0606003
Gluon Jets?
Experiment sees ratios ~ 1 at lower pT for central AuAu!
Bary
on
/Meson
Rati
os
e+e- (proton/pion)
Transverse Momentum (MeV/c)
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What State of Matter are we Producing?
1. Almost baryon-free with thermalization and expansion
2. A “Liquid” with Quark DoFs3. Strongly Interacting Matter
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Study of High Momentum Particles
0.2<y<1.4
Transverse momentum
distributions of charged particles
PHOBOS: Phys. Lett. B578, 297 (2004)
CTEQ 2006
Comparing Au+Au Spectra to pp
Use The Nuclear Modification Factor
ddpd
ddpNdNpR
Tpp
TAAinelpp
collTAA 2
2
/1
1)(
The Heavy Ion data scaled by the avergae number of collisions <Ncoll> compared to the proton+proton baseline.
RAA = 1 if Au+Au is simply an incoherent sum of pp collisions
Looking for effects of the Extended Nuclear Volume.
CTEQ 2006
RAA(p
T)Peripheral Central Mid-Central
See a strong suppression of high pT yields in AuAu Central Collisions
Suppression of High Momentum Particles
Phenix: Phys.Rev. C69 (2004) 034910
(h++h-)/2
0
Binary collision expectation
CTEQ 2006
Suppression Holds to Very High pT
V. Greene – PHENIX – QM2005
0-10% Central Au+Au Collisions
PHENIX preliminary
0
RAA(p
T)
pT(GeV/c)
Binary collision expectation
CTEQ 2006
Initial vs. Final State Effect
Is it due to the hot-dense matter created or are we just making fewer to start with? Perform “control” experiment with d+Au
Central Au+Au suppressed relatve to p+p AND d+Au data. It appears to be a “final state” effect due to medium created
pT (GeV/c)
BRAHMS, PRL 91 (2003)
Au+Aucentral
d+AuRAA(p
T)
Binary collision expectation
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“Final State” Energy Loss in a Strongly Interacting Medium?
Energy loss models can account for suppression at pT>3 GeV/c
V. Greene – PHENIX – QM 2005
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Important Cross Check of Ncoll Expectation
PHENIX: Phys.Rev.Lett. 96 (2006) 202301
Binary collision expectation
Direct Photons
YES. Direct photons scale as Ncoll (and they don’t interact with the medium)
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Fast Probes of Dense Matter
a jet
a jet
First think about proton + proton collisions
Fig From: G. Roland
Can calculate with pQCD Unique dijet signature exists
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Use dijets to Probe the Created Matter
Animation by Jeffrey Mitchell (Brookhaven National Laboratory)
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The Challenge: Finding dijets at RHIC
p+p jet+jet Au+Au ???
nucleon nucleon
parton
jet
STARSTAR
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Azimuthal dijet Distributions
Au+Au Peripheral
Trigger “jet”
Opposite (away-side) “jet”
p+p
4 < pT(trig) < 6 GeV/cpT(assoc) > 2 GeV/c
STAR, PRL 91 (2003) 072304Bkg. subtracted
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Azimuthal dijet Distributions
Au+Au central
Trigger “jet”
Away-side “jet” is MISSING in central Au+Au collisions
p+p
4 < pT(trig) < 6 GeV/cpT(assoc) > 2 GeV/c
STAR, PRL 91 (2003) 072304Bkg. subtracted
CTEQ 2006
Check our d+Au Result
Away-side jet is suppressed ONLY in central Au+Au collisions. More evidence it is a “final state” effect – due to the created medium.
d+Au
STAR, PRL 91 (2003) 072304
4 < pT(trig) < 6 GeV/c pT(assoc) > 2 GeV/c
Trigger “jet” Away-side “jet”
CTEQ 2006
Dijets: lower pT(assoc)
STAR, PRL 91 (2003) 072304
Higher pT: Away-side suppression for pT(assoc)>2 GeV/c
STAR, Phys.Rev.Lett. 95 (2005) 152301
Lower pT: Away-side enhancement for pT(assoc) > 0.15 GeV/c
4 < pT(trig) < 6 GeV/c
Bkg. subtracted
Missing dijet yield seems to “reappear” at lower momentum
CTEQ 2006
Dijets: higher pT(trig)
D. Magestro – STAR – QM 2005
preliminary
Au+Au central
pT(assoc) > 2 GeV/c
PRELIMINARY: Background not subtracted
4 < pT(trig) < 6 GeV/c 6 < pT(trig) < 6 GeV/c 8 < pT(trig) < 15 GeV/c
CTEQ 2006
Dijets: higher pT(trig) and pT(assoc)
8 < pT(trig) < 15 GeV/cpT(assoc) > 2 GeV/cpT(assoc) > 3 GeV/cpT(assoc) > 4 GeV/cpT(assoc) > 5 GeV/cpT(assoc) > 6 GeV/cpT(assoc) > 7 GeV/cpT(assoc) > 8 GeV/c
D. Magestro – STAR – QM 2005
PRELIMINARYBackground not subtracted
pT(assoc)cut value
At higher pT , Missing away-side dijets Reappear
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Energy Loss in a Strongly Interacting Medium?
F. Wang – STAR – QM 2005
<pT> from away jets
<pT> from medium decay
Aw
ay s
ide <
pT>
(G
eV
/c)
STAR, nucl-ex/0501016.
Medium
Increasing Centrality
Leadinghadrons
away
trig
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Dijets: Collision Geometry Dependence
STAR, PRL 93 (2004) 252301
Suppression magnitude depends on collision geometry Path length dependence of energy loss.
b (reaction plane)
More absorption out of the reaction plane
Less absorption in the reaction plane
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Summary Slide for RHIC Results
• Evidence for:– A high-energy density matter above the critical value– which exists as a thermalized “fireball” – in an increasingly baryon-free state– that expands quickly and collectively (a “liquid”)– with quark degrees of freedom– and is extremely strongly interacting.
• I think it is highly likely we have created a strongly-interacting quark gluon plasma (sQGP).
• RHIC Work: more theory and more experiments (e.g. smaller systems, energy scans) to see what we can learn about the sQGP we have created.
CTEQ 2006
The Future of Heavy Ion Physics
K. Rajagopal, MIT – BNL Workshop 2006
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The Future of Heavy Ion Physics
B
RHIC (B = 30-40 MeV , √sNN~ 130-200 GeV)
SPS (B = 255-400 MeV , √sNN~ 9-18 GeV)
AGS (B = 540 MeV , √sNN~ 4 GeV)
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The Future I:
Possible connections with dramatic non-monotonic behavior seen at the lower-energy CERN-SPS experiments.
M. Gazdzicki- NA49 – QM 2004
EXPLORE FURTHER WITH: Low-energy Running at RHIC New Accelerator: FAIR @ GSI, Darmstadt
LOWER ENERGY
RH
IC
Search for the Critical Point
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The Future II:
HIGHER ENERGY R
HI
C
LHC (B =??, √sNN= 5.5 TeV)
EXPLORE FOR FIRST TIME WITH: Heavy-Ion Running at the LHC
Heavy-Ions at the LHC
Closer to our universe path.
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A New Viewpoint for QCD Matter at LHCA New Viewpoint for QCD Matter at LHC
• Factor 28 Higher sNN than RHIC
• Initial state dominated by low-x components (Gluons).
• Abundant production of variety of perturbatively produced high pT particles for detailed studies
• Higher initial energy density state with longer time in QGP phase
• Access to new regions of x Do we find the weakly interacting QGP?
J/
Z0
Detector Coverage
Colli
sion
Rate
, Tri
gg
eri
ng
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Final Thoughts
• In the brief moment of a relativistic heavy-ion collision, we have created a new state of matter with extremely interesting properties. – We think: At RHIC (& likely the SPS) sQGP– We wonder: At the LHC wQGP
• Work continues to understand exactly what the new state of matter is, and what it will teach us about the strong interaction.
• It is an extremely exciting time in our field.
• I want to Thank – the organizers for the opportunity to be here– the audience for listening
CTEQ 2006