Big Bang in the Big Bang in the Laboratory?Laboratory?A droplet of Quark Gluon A droplet of Quark Gluon PlasmaPlasmaBarbara JacakStony Brook University
outline
Energy densities characteristic of the early universeWhat is quark gluon plasma & why do we expect it?Nuclear Physics at very high energy
Experiments at the Relativistic Heavy Ion ColliderHow we probe the hot, dense matter
First glimpse of the matter’s properties
Relation to other plasmas
Conclusions & (some interesting) open questions
Evolution of the Universe
Nucleosynthesis builds nuclei up to HeNuclear Force…Nuclear Physics
Universe too hot for electrons to bindE-M…Atomic (Plasma) Physics
E/M Plasma
Too hot for quarks to bind!!!Too hot for quarks to bind!!!Standard Model (N/P) Physics
Quark-Gluon
Plasma??
Too hot for nuclei to bindNuclear/Particle (N/P) Physics Hadron
Gas
SolidLiquidGas
Today’s Cold UniverseGravity…Newtonian/General
Relativity
Quarks, gluons and hadrons
6 quarks: 2 light (up,down), 1 sort of light (strange), 2 heavy (charm,bottom), 1very heavy (top)Besides flavor, also have color quantum number
In normal life:
quarks are bound into hadrons
Baryons (e.g. n, p) have 3
Mesons (e.g. ) have 2
(1 quark + 1 anti-quark)• Plasma:
Ionized gas, but dense enoughthat the charges of nearbyneighbors shield one another
(the quarks & gluons aren’t bound
but do interfere with one another)
Energy Density in the Universe
high energy density: > 1011 J/m3
P > 1 MbarI > 3 X 1015W/cm2 Fields > 500 Tesla
QGP energy density > 1 GeV/fm3
i.e. > 1030 J/cm3
+ +…
Short distance: asymptotic freedom
phase transition to quark gluon plasma
Color charge of gluons gluons interact among themselves theory is non-abelian curious properties at large distance: confinement of quarks in hadrons
Colored quarks interact by exchange of gluons (also have color) Quantum Chromo Dynamics (QCD)
Field theory of the strong interaction Parallels Quantum Electrodynamics QED(EM interactions: exchanged photons electrically uncharged)
QCD – lattice gauge theory
T/Tc
Karsch, Laermann, Peikert ‘99
/T4
Tc ~ 170 ± 10 MeV (1012 °K)
~ 3 GeV/fm3
Solve problem of summing over all gluon interactions by calculating on a (big) lattice
Explore in the lab: collide BIG ions at v ~ c
Aim for T 170 MeV; > 3 GeV/fm3
Characterize the hot, dense mediumWhat’s the density, temperature, radiation rate,
collision frequency, screening length, conductivity?Evidence for phase transition to quark gluon plasma?does medium behave as a plasma? pressure vs. energy?
Probespassive (radiation) those created in the collision (“external”)
RHIC at Brookhaven National Laboratory
Collide Au + Au ions for maximum volumes = 200 GeV/nucleon pair, p+p and d+A to compare
4 complementary experiments
STAR
The Scope of the Tools (!)
STARspecialty: large acceptancemeasurement of hadrons
PHENIXspecialty: rare probes, leptons,
and photons
Uncovering nature’s secrets is not easy!
Large collaborationsPHENIX has ~500 peoplemany countries!“small” experimentshave > 50 people!
Write ~ 100 Mb/sec to tape
Use connected computing all around the world! transfer data over the internet, tape centrally located software libraries meetings span 3 continents
everyone phones in, post slides on the webcirculate agendas, questions by email
Use Grid computing
pressure builds up
probing early stage of heavy ion collision
PCM & clust. hadronization
NFD
NFD & hadronic TM
PCM & hadronic TM
CYM & LGT
string & hadronic TM
Kpnd,
Hadrons reflect (thermal) properties when inelastic collisions stop
, e+e-, +
Real and virtual photon radiation
total lifetime of the system ~ 10 fm/c or ~ 3 x 10-23 seconds
Hard scattered q,g(short wavelength) probes of plasmaformed
So what happens?
Lots of information collected over past 4 years
I’ll establish it’s fair to look for new physics, and report only a few important results
Focus on “external” probesNo laser with sufficiently short wavelength!Use probes made in the first step of the collisionRate and spectrum calculable with (perturbative) QCD look for effects of the mediumStart by benchmarking the probe!
Start simple p+p collisions
p-p PRL 91 (2003) 241803
Good agreementwith NLO pQCD
QCD works for high p transfer processes!
Have a handle on initial NN interactions by scattering of q, g inside N
We also need:2
/( , )
a Nf x Q
2
/( , )ch a
D z Q
Parton distribution functions
Fragmentation functions
0
These are measured, so known
Now ask: is energy density high enough?
We measure the particles coming out, so add up their energy
energy density = E/volume
5.5 GeV/fm3 (200 GeV Au+Au) well above predicted transition!
R2
2c
Colliding system expands:
dy
dE
cRT
Bj 22
11
02
Energy tobeam direction
per unitvelocity || to beam
value is lower limit: longitudinal expansion rate, formation time overestimated
E
“external” probes of the medium
hadrons
q
q
hadronsleadingparticle
leading particle
schematic view of jet productionHard scattering of q,g early.Observe fast leading particles,back-back correlations Before creating hadron jets, scattered quarks induced to lose energy (~ GeV/fm) by the colored medium-> jet quenching
AA
AA
AA
ddpdT
ddpNdpR
TNN
AA
TAA
TAA /
/)(
2
2
nucleon-nucleon cross section<Nbinary>/inel
p+p
pp
AuAubinaryAuAuAA Yield
NYieldR
/
Au-Au s = 200 GeV: high pT suppressed!
PRL91, 072301(2003)
look for the jet on the other sideSTAR PRL 90, 082302 (2003)
Central Au + Au
Peripheral Au + Au
near side
away side
peripheral central
22 2 2( ) ( ) (1 cos(2 ))D Au Au D p p B v
Medium is opaque!
STAR
Suppression: a final state effect?
1AuAuR
Such a medium is absent in d+Au collisions!But Au provides all initial state effects of q, g
wavefunction inside a Au nucleus
d+Au is the “control” experiment
Hot, dense medium causes
Centrality Dependence
Dramatically different and opposite centrality evolution of AuAu experiment from dAu control.
Jet Suppression is clearly a final state effect.
Au + Au Experiment d + Au Control
PHENIX preliminary
Are back-to-back jets there in d+Au?
Pedestal&flow subtracted
Yes!
hadronsleadingparticle suppressed
q
q
?
So this is the rightpicture for Au+Au
Collective motion? Pressure: a barometer called “elliptic flow”
Origin: spatial anisotropy of the system when created, followed by multiple scattering of particles in the evolving system spatial anisotropy momentum anisotropy
v2: 2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane
Almond shape overlap region in coordinate space 2cos2 v
x
y
p
patan
y2 x2 y2 x2
The data show
Particle emission really is azimuthally anisotropic
Magnitude of the anisotropy grows with beam energy, then flattens
c.m. beam energy
Hydro. CalculationsHuovinen, P. Kolb,U. Heinz
v2 reproduced by hydrodynamics
PRL 86 (2001) 402
• see a large pressure buildup • anisotropy happens fast while system is deformed• success of hydrodynamics early equilibration !
~ 0.6 fm/c
central
STAR
Collective effect probes equation of state
Hydrodynamics can reproduce magnitudeof elliptic flow for , p. BUT correct mass dependence requiressofter than hadronic EOS!!
Kolb, et al
NB: these calculations have viscosity = 0medium behaves as an ideal liquid
STAR
Elliptic flow scales as number of quarks
v2 scales ~ with # of quarks! evidence that quarks are the particles when the pressure is built up
equilibrated final state, including s quarks
Hadron yields in agreement with Grand Canonical ensembleT(chemical freeze-out) ~ 175 MeV (~ Tc)(multi)strange hadrons enhanced over p+p, but QGP
hypothesis not unique explanation
So, what do E loss & collectivity tell us?
Medium is “sticky” or opaque to colored probes Thermalization must be very fast (< 1fm/c) Constrain hydrodynamic, energy loss models with data:
Energy loss <dE/dz> (GeV/fm) 7-10 0.5 in cold matter
Energy density (GeV/fm3) 14-20 >5.5 from ET data
dN(gluon)/dy ~1000 200-300 at SPS
T (MeV) 380-400 Experimentally unknown as yet
Equilibration time0 (fm/c) 0.6 Parton cascade agrees
Opacity (L/mean free path) 3.5
Is enough for fast equilibration & large v2 ?
Parton cascade using free q,g scattering cross sections underpredicts pressure must increase x50
Lattice QCD shows qqresonant states at T > Tc, also implying high interaction cross sections
What is going on?
The objects colliding are not baryons and mesons
The objects colliding also do not seem to be quarks and gluons totally free of the influence of their neighbors
Quarks and gluons are interacting, but are not locally neutral like the baryons & mesons
Plasma coupling parameter?
Very high gluon density!estimate = <PE>/<KE>
using QCD coupling strength<PE>=g2/d d ~1/(41/3T)
<KE> ~ 3Tg2 ~ 4-6 (value runs with T) ~ g2 (41/3T) / 3T so plasma parameter NB: such plasmas known to behave as a liquid!
May have bound q,g states, but not color neutral So the quark gluon plasma is a strongly coupled plasma
As in warm, dense plasma at lower (but still high) TBut strong interaction rather than electromagnetic
Other strongly coupled plasmas
Inside white dwarf and neutron stars (n star core may even contain QGP)
In ionized gases subjected to very high pressures or magnetic fields
Dusty plasmas in interplanetary space & planetary rings Solids blasted by a laser We would like to know:
How do these plasmas transport energy?How quickly can they equilibrate?What is their viscosity? >10 can even be crystalline! How much are the charges screened? Is there evidence of plasma instabilities at RHIC? Can we detect waves in this new kind of plasma?
nove
l pla
sma
of
str
ong
inte
ract
ion
E. Shuryak
How about the screening length?
J/Test confinement:
do bound c + c survive? or does QGP screening kill them?Suppression was reported in lower energy heavy ion collisions at CERN
Need (a lot) more statistics (currently being analyzed)
But can take a first look…
Color screening?
Lattice predictions for heavy quarks 40-90%most central Ncoll=45
0-20%most central Ncoll=779
20-40%most central Ncoll=296
These data still inconclusive
Evidence that RHIC creates a strongly coupled, opaque plasma energy density & equation of state not hadronic!still is debate in community about the standard of proof
With aid of hydrodynamics, l-QCD and p-QCD models: ~ 15 GeV/fm3
dNgluon/dy ~ 1000
int large for T < 2-3 Tc Are poised to characterize this new kind of plasma
T, radiation rate, conductivity, collision frequency More interdisciplinary than we first thought!
will have a workshop with Plasma community in Decemberalso close to Particle & Condensed Matter Physics, Astrophysics, Mathematical modeling, Large-scale computing…
conclusions
Saturation of gluons in initial state(colored glass condensate)
Wavefunction of low x (very soft) gluons overlap and the self-coupling gluons fuse.
Saturation at higher x at RHIC vs. HERA due to nuclear size
suppressed jet cross section; no back-back pairsr/ggg
Mueller, McLerran, Kharzeev, …
d + Au collisionscent/periph. (~RAA)
PHENIX PRELIMINARY
Open charm: baseline is p+p collisions
fit p+p data to get the baseline for d+Au and Au+Au.
Measure charm via semi-leptonic decay to e+ & e-
, photon conversions are measured and subtracted
The yellow band represents the set of alpha values consistent with the data at the 90% Confidence Level.
Charm production scales as Ncoll!
Curves are the p+p fit, scaled by the number of binary collisions
No large suppression as for light quarks!
PHENIX PRELIMINARY
Simple quark counting:K-/K+
= exp(2s/T)exp(-2q/T)
= exp(2s/T)(pbar/p)1/3
= (pbar/p)1/3
local strangeness conservation K-/K+=(pbar/p)
= 0.24±0.02 BRAHMS = 0.20±0.01 for SPS
Good agreement with statistical-thermal model of Beccatini et al. (PRC64 2001) w/T=170 MeV
At y=0
From y=0 to 3
PRL 90 102301 Mar. 2003
Evidence for equilibrated final hadronic stateBRAHMS
Implications of the results for QGP
Ample evidence for equilibration initial dN(gluon)/dy ~ 1000, energy density ~ 15
GeV/fm3, energy loss ~ 7-10 GeV/fm
Very rapid, large pressure build up requiresparton interaction cross sections 50x perturbative
How to get 50 times pQCD ?
• Lattice indicates that hadrons don’t all melt at Tc!c bound at 1.5 Tc Asakawa &
Hatsuda, PRL92, 012001 (2004)
charmonium bound states up to ~ 1.7 Tc Karsch; Asakawa&Hatsuda
, survive as resonances Schaefer & Shuryak, PLB 356 , 147(1995)
q,g have thermal masses at high T. s runs up at T>Tc? (Shuryak and Zahed)would cause strong rescattering
qq meson
spectral function
Implications of the results for QGP
Ample evidence for equilibration v2 & jet quenching measurements constrain initial gluon
density, energy density, and energy loss parton interaction cross sections 50x perturbative
parton correlations at T>Tccomplicates cc bound states as deconfinement probes!
Hadronization by coalescence of thermal,flowing quarksv2 & baryon abundances point to quark recombination
as hadronization mechanismJet data imply must also include recombination between
quarks fromjets and the thermalized medium medium modifies jet fragmentation!
Locate RHIC on phase diagram
Baryonic Potential B [MeV]
0
200
250
150
100
50
0 200 400 600 800 1000 1200
AGS
SIS
SPS
RHIC
quark-gluon plasma
hadron gas
neutron stars
early universe
thermal freeze-out
deconfinementchiral restauration
Lattice QCD
atomic nuclei
From fit of yields vs. mass (grand canonical ensemble):
Tch = 176 MeV B = 41 MeV
These are the conditions when hadrons stop interacting
T
Observed particles “freeze out” at/near the deconfinement boundary!
Do see Cronin effect!
“Cronin” enhancement more pronounced in the charged hadron measurement
Possibly larger effect in protons at mid pT
Implication of RdAu? RHIC at too high x for gluon saturation…
(h++h-)/2
0
How about Color Glass Condensate?
Pt (GeV/c) Pt (GeV/c)
Rda
Rda
Peripheral d+Au (like p+p)
Central: Enhancednot suppressed PHENIX preliminary
y=0
Xc(A)
pQCD
BFKL, DGLAP
G-sat.
>2
RHIC
Log Q2
No CGC signalat mid-rapiditySo, perhaps
But at forward rapidity reach smaller x
y = 3.2 in deuteron direction x 10-3 in Au nucleus
Strong shadowing, maybe even saturation?
d Au
Phenix Preliminary
Why no energy loss for charm quarks?
“dead cone” predicted by Kharzeev and Dokshitzer, Phys. Lett. B519, 199 (1991)
Gluon bremsstrahlung:kT
2 = 2 tform/transverse momentum of radiated gluon
pT in single scatt. mean free path
~ kT / gluon energy But radiation is suppressed below angles 0= Mq/Eq
soft gluon distribution is
dP = sCF/ d/ kT2 dkT
2/(kT2+ 2 0
2) 2not small forheavy quarks!causes a dead cone
Look at “transverse mass” mT2 = pT
2 + m02
— is distribution e-E/T?i.e. Boltzmann distribution from thermalized gas?
, K, p, pbar spectra indicate pressure
yes !
Protons are flatter velocity boost to beamResult of pressure built up
QCD Phase Transition
Basic (i.e. hard) questionshow does process of quark confinement work?how nature breaks symmetries massive particles from ~
massless quarks transition affects evolution of early universe
latent heat & surface tension matter inhomogeneity in evolving universeequation of state compression in stellar explosions
Study simple complex systems: p+p, “p”+A, A+A collisions
did something new happen at RHIC?
Study collision dynamics (via final state)
Probe the early (hot) phase
Equilibrium?hadron spectra, yields
Collective behavior?i.e. pressure and expansionelliptic, radial flow
vacuum
QGP
Must create probes in the collision itself: predictable quantity, interact differently in QGP vs. hadron matter
fast quarks/gluons, J/fast quarks/gluons, J/, D mesons, D mesonsthermal radiation
we look for physics beyond simple superposition of NNat low momentum/large distance scales:
J/ suppression was observed at CERN at s=18 GeV/A
Fewer J/ in Pb+Pb than expected!Interpret as color screening of c-cbar
by the mediumInitial state processes affect J/ tooso interpretation heavily debated...
collaboration
J/yield
The Physics of Heavy Ion Collisions
Create very high temperature and density mattersimilar to that existing ~1 sec after the Big Bangdistance between hadrons comparable to that in neutron starsstudy only in the lab – relics from Big Bang inaccessible
Goal is to characterize the hot, dense mediumexpect QCD phase transition to quark gluon plasmadoes medium behave as a plasma?find density, temperature, radiation rate, collision frequency,
conductivity, opacity, Debye screening length?probes: passive (radiation) and those created in the collision
Collide Au + Au ions for maximum volumes = 200 GeV/nucleon pair, p+p and d+A to compare
Predicted signatures of QGP
Debye screening of color charges (Matsui & Satz)Suppresses rate of c-c bound state (J/
Strangeness enhancement (Rafelski & Mueller)Tplasma ~ masss-quark
Enhances strange hadron yields (e.g. K/ increased)
Jet quenching (Gyulassy & Wang)Dense medium induces coherent gluon radiationDecreased yield of jets of hadrons from hard scattered
quarks or gluons
Where does the lost energy go?
Away side jet is significantly broadened
preliminary
• recover the energy in hadrons ~ 500 MeV• comparable to <pT> of the bulk medium• lost energy is thermalized
Au+Au 0-5%
pT > 200 MeV
STAR Preliminary
Suppression: an initial state effect?
Gluon Saturation (color glass condensate)
Wavefunction of low x gluons overlap; the self-coupling gluons fuse, saturating the density of
gluons in the initial state. (gets Nch right!)
• Multiple elastic scatterings (Cronin effect) Wang, Kopeliovich, Levai, Accardi
Levin, Ryshkin, Mueller, Qiu, Kharzeev, McLerran, Venugopalan,
Balitsky, Kovchegov, Kovner, Iancu …
probe rest frame
r/ggg
dAu AuAuR R RdAu~ 0.5D.Kharzeev et al., hep-ph/0210033
1dAuR Broaden pT :
Property probed: density
Au-Au
d-AudAu
Induced gluon brehmsstrahlung pQCD calculationdepends on number of scatterings
Agreement with data:initial gluon density
dNg/dy ~ 1100
~ 15 GeV/fm3
hydro initial state same
Lowest energy radiation sensitive to infrared cutoff.
pQCD in Au+Au? direct photons
[w/ the real suppression]
( pQCD x Ncoll) / background Vogelsang/CTEQ6
[if there were no suppression]
( pQCD x Ncoll) / ( background x Ncoll)
Au+Au 200 GeV/A: 10% most central collisions
[]measured / []background = measured/background
Preliminary
g+q +q
TOT
pT (GeV/c)