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)