Richard SetoUniversity of California, Riverside
RHIC/STAR WorkshopBejing, PRC
August 29-31, 2002
WHY?
Where Does Mass come from?
Massive quarks in lite QCD? (u,d)
Chiral (R-L) Symmetry
Massless quarks! So Where does mass
come from?Massive quark?
Massless quarks
The Vacuum: Source of Mass
Start at high Temperature with massless quarks
Massless quarks
T>Tc
The Vacuum: Source of Mass
Start at high Temperature with massless quarks
Assume a background field = - goo of quarks and gluons
Similar to the higgs field for E-W theory
Couples to quarks(massless for now) and gluons
Potential term for has special Temperature Dependence
T>Tc
T<Tc
T~Tc
V()
LowTemperatureHigh
Massless quarks
T>Tc
The Vacuum: Source of Mass
T~Tc
As Temperature Cools past Tc
T>Tc
T<Tc
T~Tc
V()
LowTemperatureHigh
The Vacuum: Source of Mass As Temperature Cools
past Tc
Spontaneous symmetry breaking (I.e. chiral)
quark condensate at low Temperature
generates hadron masses
T>Tc
T<Tc
T~Tc
V()
LowTemperatureHighT~TcT~Tc
T<Tc
Condensate
Weird!
The idea that empty space should be full of complicated material is wilder than many crackpot theories, and more imaginative than most science fiction…
F. Wilczeck in Physics Today (April 1998)
The HOTHOT QCD vacuum
Can you create it? YES! AT RHIC RHI collision leaves
a region of excited qq and gluons – ie hot vacuum
What is the hot hot vacuum like? How hot is it? (Temperature) How sticky is it? (Energy Loss – aka Jet
quenching) How much energy can it store? (Latent
heat) What is its equation of state? What is (are) the phase transition(s) to a
cold vacuum like? 1st, 2nd order, cross over?
How does it generate mass? How/why does it confine? What interesting properties does it exhibit? …
Why it is timely
Theory + Experiment = Theory + Experiment = Understanding Understanding Theoretical Calculations Theoretical Calculations in regions
probed by experimentexperiment Experiments Experiments in regions calculable by
theorytheory New era of Precision (almost)
Precision CalculationsCalculations Precision Measurements Measurements
Precision Detectors Redundancy of measurements (4 detectors!) AA, pA (dA), pp, eA
Phases of Nuclear Matter
TWO phase transitions! The deconfinement
transition - particles are roam freely over large volume
The chiral transition - masses change
All indications are that these two are at or are very nearly at the same TC
T
Tc
Lattice Calculations
T
Tc
(F. Karsch, hep-lat/9909006)
/T4
T/Tc
Lattice Results Tc(Nf=2)=1738 MeVTc(Nf=3)=1548 MeV
0.5 4.5 15 35 GeV/fm375
• Transition – Sharp Crossover at RHIC
• That’s OK – 1st order for all practical purposes
Lattice Calculations:Tc = 170 15% MeV critical ~ 0.6 GeV/fm3
Critical point
1st order
Sharp Crossover
Stages of the Collision
Various stages Must be described using different physics
Hard Soft
Detectors see sum of all phenomena Importance of hard probes Keep an open mind –no single idea (or theorist) can
explain everything
Data
4 detectors STAR – Large acceptance PHENIX – photons, leptons PHOBOS – small, low-pt BRAHMS – small, high y
Runs 130 GeV run 200 GeV run – results from recent QM
Is it like the Vacuum?
Quantum Numbers of the Vacuum?
Baryon number = zero?
0.8pp
~YES
AGS
SPS
√s [GeV]
PHENIX preliminary
STAR prelim 1.0
0.1
p/p ratio
~0.002
~0.05
STAR 200prelim
Note: Thermal fitB~30 MeV
Worlds dependence
How Hot is it? Is it Hot enough?
dET/dy ~ The Initial Energy Density
PHENIX: Central 200 GeV Au Au
T
=0
dE=573±2GeV
d
Thermalization tim
e ?
High Initial energy High Initial energy density-density-Its “HOT “enough!Its “HOT “enough!
Bj~ 5.2 GeV/fm3
Bj~ 26.0 GeV/fm3
Latticec
R2
c
20
1 1~T
Bjorken
dE E
dy VR
~6.5 fm
Remember, from the Lattice T = 170 MeV ~ 0.6 GeV/fm3
You said theory was getting better. Can you make reliable calculations of the initial conditions?
QCD - Notoriously hard to calculate Regime where QCD simplifies:
High Gluon Densities at low-x gluons ~ x- ,i.e. there are more of
them as you go to lower x They begin to overlap Gluons saturate
Classical Approx (McLerran, Venogopolan etc)
Robust calculations in QCD using “renormalization group” methods
Depends on a single scale
The Colored Glass CondensateA layman’s view
xG(x)
x
High x
low x
QS2=(1/R2)(dNgluon/dy) ~ 2-D gluon density
At RHIC, QS~1-2 GeV
The Approximation
The Approx Non-perturbative (high
density) Small coupling
Requires S(QS) to be “small”
Expected to fail for QS small
Low energy Peripheral High y
Qs
S RHIC 130central
At RHIC, QS~1-2 GeVS(QS)~0.3 –0.4
Running of S
Calculations dN/dy for s, centrality, y, A energy in terms of
one variable: QS. Set QS at a single point
Predict dN/dy for all other s, centrality, y QS larger – more central, higher energy, mid-rapidity
A constant C=CLCMult must be set CL is gluon liberation coefficient – probability that a virtual
gluon becomes “real” upon collision (can be calculated on the Lattice)
Cmult is the gluon multiplication coefficient from final state interactions
We would like this to be >1, otherwise thermalization produces no new particles
One to one correspondence between gluons and final state particles (I.e. entropy conserved)
Does it work? (post-diction)Saturation models can predict the scaling with centrality and rapidity!
Kharzeev & Levin, nucl-th/0108006Schaffner-Bielich et al, nucl-th/0108048
Np
dN
ch/d
/(0
.5N
p)
Kharzeev/Levin
energy density
~18GeV/fm3
Does this explain why dN/dy is less
than we might have thought?
QS depends on Npart,
S, y If S did not run,
there would be no dependence!
Dependence on NpartS, y
/ Constant0.5* ( )
gluon
part sS
dN dy
N Q
Prediction at 200 GeV
Not bad!
0-6%
15-25%
35-45%
Kharzeev/Levin
Prediction at 22 GeV Do we expect it to work?
At low energy QS becomes small S large
Expected to fail first for Peripheral High y
Np100
1
0200 400300
20-6%
15-25%
35-45%
Fails (worst for peripheral, high y)
All data PHOBOS Preliminary
0-6%
35-45%
15-25%
Is it thermalized? When?… it better be early, before hadronization,
if you are interested in a QGP…
Azimuthal anisotropy: v2 “Elliptic flow”
Late equilibration i.e. free streaming in early stages causes almond shape to become spherical
Strong elliptic flow Early thermalization
2 2
2 2 2cos 2x y
x y
p pv
p p
Momentum space: final asymmetry
multiple collisions (pressure)
py
px
x
y
Coordinate space: initial asymmetry
Elliptic Flow
Hydrodynamical model (Kolb et al)Good pt<2, more centralRapid thermalization
0 ~ 0.6 fm/c~20 GeV/fm3
(possibly later if some comes from CGC?)
RHIC: Very strong elliptic flow
What about Chemical and Thermal Equilibrium? (at freezout)
Thermal model fit-Chemical Freezout
Model assuming Chemical Equilibration describes yields Pretty well s ~ 1
From yields, 130 GeVTch freezeout=177 MeVBaryon=36 MeV
Particle Ratios
Central events
Thermal Model fit - Kinetic Freezout
Tthermal freezout ~ 130 GEV ~AGS/SPS
radial increases to ~ 0.5
From inverse slopes
As at SPS Strange particlesFreeze out earlierOmegas freeze-out differently? Explosive radial expansion
high pressure
130 GeV
K*
STAR 200
You’ve talked about the initial state, and the final state. What about the stuff in the Middle? Do you have a QGP?
ColorlessHadrons
ColoredQGP
Beams of colored quarks
Hard Probes, aka Jet quenching
Deep Inelastic Scattering of the QGP?
“hard” probes Formed in initial
collision penetrating sensitive to state
dE/dx by strong interaction
jet quenching
Jets by Jets by leading particles Look forLook for a a
suppression of high suppression of high pT hadron production.pT hadron production.
Scaling from pp to AA
Low pT
•Thermal •Hydro(Flow)•Exponential in MT
Npart
Scaling
High pT
•Jetlike•Jet frag (No flow)•Pwr law in pT
Nbin Scaling
Transition ~ 2 –4 GeV?
Nbinary at high pT
Npart at low pT
pp effects Intrinsic kT
pp to pA effects “Cronin effect”, initial state quark
scatteringi.e. pT broadening
Enhances higher pT
Nuclear shadowing Gluon shadowing
is not measured large role at RHIC
Models – scaling pp to AA
Measure pA at RHIC!
pp 0 spectrum
Peripheral:
Consistent with Nbin scaling
0-10% CENTRAL
Nbin
=975±94
Consistent with Nbin scaling?
NO Central:
Consistent with Nbin scaling
Scale up with Nbin=12.3
70-80% PERIPHERAL
Nbin
=12.3 ±4.0
Consistent with Nbin scaling
PHENIX P
relim
inar
y
NO!
Scaled pp
AuAu
RHIC – Run 2 200 GeV) 5!
Nuclear Modification Factor
Effect of nuclear medium on yieldsRun 2 Data Shows a manySigma Effect!
SPS – shows Cronin Effect
RHIC – Run 1 (130 GeV)
0-10%
(dE/dx)initial~7 GeV/fm15x Cold matter (Hermes)
PHENIX Preliminary
binary scaling
0-10%
70-80%
central binary centralAA T
pp
Yield NR (p )
Yield
/
RHIC central -Suppressionperipheral – Nbin scaling
PHENIX P
relim
inar
y
Centrality Dependence of RAA
Smoothly varies with centrality
PHENIX P
relim
inar
y
Smoothly varies with centrality
Dependence changes with pt?peripheral central
How does Jet energy loss depend on energy, path length etc?
What can we learn? Types of energy loss
Constant (probably not physical)
QCD motivated Bethe-Heitler (BH) type
dE/dx~E LPM type
dE/dx~ L ~E gluon coherence>MFP or Egluon> Ecr~pT,gluon
2 MFP 5 GeV at RHIC (?)
Static and Expanding plasma considered
Can learn about Energy loss mechanism Density of gluons ~ gluon
L dependence …
BH MFP
LPM
coh
01 expansion static
2D
A
E ER
Phase transition from quench?
Calculate qhat from QGP, pion gas
Jet quenching sensitive to energy
density NOT phase
transition? But this calculation
does not have confinement, chiral symmetry restoration…
2ˆSE qL
Massless pion gas
Ideal QGP
Nuclear Matter
Phase Transition?
Energy Density (GeV/fm3)En
erg
y L
oss
Coeffi
cien
t (G
eV
2/f
m)
BDMS
Vitev: GLV, nucl-th/0204019, PRC 65 (2002) 041902Comparing to 130 GeV theoryLPM type, Static Source
Theory Comparisons for RAA – GLV
Theory Comparisons for RAA –BH type
Compare to B-H type loss (dE/dx~E)
Static source RAu/ ~6
Assumes independent scattering
dE/dx ~ 6%E
dE/dx~0.03E GeV/fm (BH)
dE/dx~0.06E GeV/fm (BH)
dE/dx~0.10E GeV/fm (BH)
dE/dx~L (LPM)
dE/dx~0.3 GeV/fmConstant
Jeon, Jalilian-Marian, Sarcevic nucl-th/0208012
Phenix Preliminary
What about charged particles?
Charged particles: Central to Peripheral Ratio
peripheralbinaryperipheral
centralbinarycentral
NYield
NYield
//
Suppression seen in 3 independent measurements
Difference in 0/charged h ratio particle composition
(A variation on RAA)
Single Particle Spectra (0-5 %) Jet Fragmentation?
PHENIX Preliminary
Au+Au at sqrt(sNN) =200GeV
proton/antiproton contribution above pT > 2 GeV dominates charged spectra !
Particle Composition at high pT
0/(h++h-)/2 ratio ~ 0.5 up to 9 GeV/c do protons
continue to make up a large fraction of the charged hadron yield?How far in pt is hydrodynamics (flow) applicable?Is some other physics responsible?
Are there other ways to Look at “jet quenching”?
v2 “Elliptic flow” from jets energy loss?
2 2
2 2 2cos 2x y
x y
p pv
p p
Momentum space: final asymmetry
multiple collisions (pressure)
py
px
x
y
Coordinate space: initial asymmetry
distance of fast parton propagation
(energy loss)
Jet 1
Jet 2
V2 Non-flow component?
Methods of extracting v2
Momentum vs Event plane
Correlations 4th order cumulant
Sensitive only to flow
~20% of v2 from non-flow components Jets?
Azimuthal Asymmetries - Elliptic Flow
saturation of v2 observed hydrodynamic flow
increase with pT
non-equilibrium contribution jets (unquenched) decrease with pT
asymmetric energy loss
increase of v2 saturation from interplay models necessary
to disentangle effects
Adler et al., nucl-ex/0206006
Can you look at Di-jets?
2-Jet-Events in pp in the STAR TPC
p+p dijet from 200 GeV run
D. Hardtke, STAR
Two-particle azimuthal correlations
Identify jets on a statistical basis
Trigger particle with pT>pT(trigger)
associate particles with pT>pT(associated)
C2 is probability to find another particle at (,)
pT(associated)>2 GeV/c pT(trigger): 4-6 GeV/c,
3-4 GeV/c, 6-8 GeV/c ||<0.7 ||<1.4
2
1 1( , ) ( , )
Trig
C NN Eff
Jet
Away side Jet
Trigger jet shows little centrality dependence
Away side-Jet Suppression
Away side-jet strong suppression
with centrality jet quenching?
?
trigger-jet
Away side -jet
Centrality dependence similar to quenching of neutral pion spectrum!
Stages of the CollisionWhat can we say?
0.1 1
0.1Energ
y
Densi
ty
(GeV
/fm
3)
10Time (fm)
10
100
Stages of the Collision
Simulation and model byK. Geiger, …. From L. McLerran
modified by R.Seto
0.1 1
0.1
En
erg
y
Den
sity
(G
eV
/fm
3)
10Time (fm)
10
100
Stages of the Collision
t~0 Nuclei are Lorenz
contracted White – quarks Green – gluons
large number of (low x) gluons in the center of the nuclei
Stages of the Collision
0.1 1
0.1
En
erg
y
Den
sity
(G
eV
/fm
3)
10Time (fm)
10
100
Initial State t~0.1-0.6 fm ~20-30 GeV/fm3
Hard processes – PQCD Soft Processes – CGC(?) Early Thermalization(?) Flow (elliptic) starts to
develop
0.1 1
0.1
En
erg
y
Den
sity
(G
eV
/fm
3)
10Time (fm)
10
100
Stages of the Collision
QGP??? t~0.6-2.0 fm ~2-3 GeV/fm3
Q#’s of vacuum Parton energy loss
~10 GeV/fm Chiral Symmetry?
Stages of the Collision
0.1 1
0.1
En
erg
y
Den
sity
(G
eV
/fm
3)
10Time (fm)
10
100
Mixed Phase? t~2-5 fm Phase Transition? Latent Heat? Chiral Condensate
Develops? Mass develops?
Confinement sets in?
0.1 1
0.1
En
erg
y
Den
sity
(G
eV
/fm
3)
10Time (fm)
10
100
Stages of the Collision
Freezeout Chemical
T~175 MeV B~30 MeV S~1
Thermal T~130 MeV ~0.5
Finally – What do we know? Have we created a very high energy density – greater than
needed for a QGP “yes” Does it have the Quantum numbers of the vacuum? “yes” Initially what is it? “gluons-Very strongly Interacting
Init cond-Colored Glass Condensate? “tentatively” (dA, eA, theory)
Does it thermalize? “tentatively” (theory needed?) When? “ tentatively early t=0.6 fm/c”
Is there jet quenching? “probably(almost certainly)” (dA needed)
Do quarks thermalize? “probably – final hadrons seem thermalized”
Is the system in equilibrium at freezout “yes” Have we got it? (the QGP) … “maybe” Is there deconfinement?, chiral symmetry restoration?….WE HAVE COME A LONG WAYS,
BUT THERE IS STILL A LOT OF WORK TO DO!
pT (GeV/c)
v2
Negativespi-&K-,pbar
PHENIX Preliminary
hydro model including the1st order phase transition with Tf=120MeV (*)
pion proton
v2
Au+Au at sqrt(sNN)=200GeVr.p. ||=3~4min. bias
(*) P.Huovinen, P.F.Kolb, U.W.Heinz, P.V.Ruuskanen and S.A.Voloshin, Phys. Lett. B503, 58 (2001)
v2(pt) of identified hadronsproposed scenario: flavor dependence
Baryon production by a non-perturbative mechanism (junctions or hydro)
M. Gyulassy, I. Vitev, X.N. Wang and P. Huovinen, Phys. Lett. B 526 (2002) 301-308
pions
protons
RHIC – Run 2 200 GeV) 5!
Nuclear Modification Factor
central binary centralAA T
pp
Yield NR (p )
Yield
/
Effect of nuclear medium on yieldsRun 2 Data Shows a manySigma Effect!
SPS – shows Cronin Effect
RHIC – Run 1 (130 GeV)
0-10%
(dE/dx)initial~7 GeV/fm15x Cold matter (Hermes)
Nuclear Modification Factor
RHIC central -Suppressionperipheral – Nbin scaling
PHENIX Preliminary
binary scaling
central binary centralAA T
pp
Yield NR (p )
Yield
/
Effect of nuclear medium on yields• Comparison of peripheral to central
0-10%
70-80%
Hidden slides
Connections…
“The experimental method to alter the properties of the vacuum may be called vacuum engineering. An effective way may well be to to use Relativistic Heavy Ions… If indeed we are able to alter the vacuum, then because the vacuum is ever present and everywhere, our microscopic world of elementary particles would become inextricably connected to the macroscopic world of the cosmos.”
T. D. Lee in Particle Physics and Introduction to Field Theory
(1981)