Helen Caines Yale University Yale Colloquium – April 2006 Sampling the flavor of the Quark-Gluon Plasma. QGP – Phase of matter where quark and gluons are

Helen CainesYale University

Yale Colloquium – April 2006

Sampling the flavor of the Quark-Gluon Plasma.

QGP – Phase of matter where quark and gluons are the relevant degrees of freedom

Outline• Motivation: What is the QGP?• Understanding its properties• The future

Sampling the flavour of the Quark-Gluon Plasma.

Helen Caines

Yale Colloquium - April 2006 2

Have we created a system that is not hadronic?

Have we created a weakly interacting gas of quarks and gluons (the Quark-Gluon Plasma)?

What have we created then?

The Relativistic Heavy Ion Collider has been operationalsince 2000 to study matter at extreme temperatures.

Have the accelerator and experiments been successfully commissioned and operated?

Yes

Yes

No

That’s the rest of this talk

The bottom line

Helen Caines


Strong color fieldForce grows with separation !!!

Confinement - QCD

“white” proton

quark

quark-antiquark paircreated from vacuum

“white” proton(confined quarks)

“white” 0

(confined quarks)

Confinement: fundamental & crucial (but not understood!) feature of strong force - colored objects (quarks) have energy in normal

vacuum

To understand the strong force and confinement: Create and study a system of deconfined colored quarks and gluons

Helen Caines


/T4 ~ # degrees of freedom

confined:few d.o.f.

deconfined:many d.o.f.

TC ≈ 173 MeV ≈ 21012 K C 0.7 GeV/fm3 (~6x normal nuclear densities)

QGP expectation came from Lattice calculations

Helen Caines


RHIC BRAHMSPHOBOS

PHENIXSTAR

AGS

TANDEMS

1 km

v = 0.99995c

Au+Au @ sNN=200 GeV

Relativistic Heavy-Ion Collider (RHIC)

Helen Caines


“A first-order QCD phase transition that occurred in the early universe would lead to a surprisingly rich cosmological scenario.” Ed Witten, Phys. Rev. D (1984)

The order of the phase transition

Apparently it did not !Thus we suspect a smooth cross over or

a weak first order transition

NASA/WMAP

Helen Caines


3. Properties of the Plasma

Medium’s effect on partons/hadrons

Outline of the rest of the talk

How we use the different quark flavors to:

1. Final State

Chemical and Thermal equilibrium

(Yields of particles)

2. Initial State

A perfect fluid?

(flow)

Helen Caines


Heavy-ion collision terminology

Number of participants (Npart): number of incoming nucleons (participants) in the overlap regionNumber of binary collisions (Nbin): number of equivalent inelastic nucleon-nucleon collisions

Reaction plane

x

z

y

Non-central collision

“peripheral” collision (b ~ bmax)“central” collision (b ~ 0)

Nbin Npart

Helen Caines


Head-on Au+Au collision in STAR TPC

~1500 charged hadrons and leptons

39.4 TeV in a central Au-Au collision

26 TeV is removed from the colliding beams.

Helen Caines


R2

Energy density in central Au-Au collisions

BJ 5.0 GeV/fm3

~30 times normal nuclear density ~ 5 times above critical from lattice QCD

Bjorken-Formula for Energy Density:

Time it takes to thermalize system (t0 ~ 1 fm/c)

R~6.5 fm

dy

dE

RV

E TTBj

02

11

dydz 0

Helen Caines


5 GeV/fm3. Is that a lot?

Last year, the U.S. used ~100 quadrillion BTUs of energy:

At 5 GeV/fm3, this would fit into a volume of:

In other words, in a box of the following dimensions:

mfm 5105 9

Helen Caines


Helen Caines


Chemical equilibrium after hadronization?

• Statistical Thermal Models:– Assume a system that is thermally (constant Tch) and

chemically (constant ni) equilibrated

– System composed of non-interacting hadrons and resonances

– Obey conservation laws: Baryon Number, Strangeness, Isospin

• Given Tch and 's (+ system size), ni's can be calculated in a grand canonical ensemble

22

0/))((

2

2 ,12

iiTpEi mpEe

dppgn

ii

Helen Caines


Chemical equilibration of hadrons

Au-Au √sNN = 200 GeVSTAR Preliminary

• Data are very well described.

• Tch ~ Tc

• Disagreement of resonances hints at significant lifetime of the hadronic phase.

Tch = 168 ± 6 MeV

Strange particles also in chemical equilibrium

Helen Caines


Initial state

What state is the system in before hadronization?

Helen Caines


Tampa press release, April 2005

•“The truly stunning finding at RHIC that the new state of matter created in the collisions of gold ions is more like a liquid than a gas gives us a profound insight into the earliest moments of the universe. … It may well have a profound impact on the physics of the twenty-first century.” Dr. Raymond L. Orbach, Director of the DOE

Helen Caines


Applicability of hydrodynamics at RHIC• Assumes local thermal equilibrium (zero mean-free-path limit) and solves

equations of motion for fluid elements (not particles)

• Equations given by continuity, conservation laws, and Equation of State (EOS)

• EOS relates quantities like pressure, temperature, chemical potential, volume• Most hydro calculation no viscosity

• Fluid elements system will flow

Helen Caines


Strong collective radial expansion

• Different spectral shapes for particles of differing mass strong collective radial flow

mT1/m

T d

N/d

mT

light

heavyT

purely thermalsourceexplosive

source

T,

mT1/m

T d

N/d

mT light

heavy

mT = (pT2 + m2)½

Au+Au central , √s = 200 GeV

Hydro pQCD

Good agreement with hydrodynamicprediction for soft EOS (QGP+HG)

Tfo~ 100 MeV T ~ 0.55 c

Helen Caines


Aniotropic/Elliptic flow

Almond shape overlap region in coordinate space

Anisotropy in momentum space

Interactions/ Rescattering

dN/d ~ 1+2 v2(pT)cos(2) + …. =atan(py/px) v2 =cos2

v2: 2nd harmonic Fourier coefficient in dN/d with respect to the reaction plane

Elliptic flow observable sensitive to early evolution of system

Mechanism is self-quenching

Large v2 is an indication of early thermalization

Time –M. Gehm, S. Granade, S. Hemmer, K, O’Hara, J. Thomas - Science 298 2179 (2002)

Helen Caines


Strong elliptic flow observed

Compatible with early equilibration

200 GeV Au+AuSTAR preliminary

v2(p

T)

pT (Gev/c)

0

0.1

0.2v2(K) > v2() > v2()

Hydrodynamical models with soft Equation-of-State describe data well for pT (< 2.5 GeV/c)

Although poor statistics even flows - low hadronic cross-section.

Evidence v2 built up in partonic phase

Helen Caines


Hydro: small mean free path,lots of interactions NOT plasma-like

The perfect fluidFirst time: hydrodynamics quantitatively describes heavy ion reactions at low pT.

Prefers a QGP EOS

Hydro without any viscosity.An ideal (perfect) fluid

Thermalization time t=0.6 fm/c and =20 GeV/fm3

Helen Caines


What interactions can lead to equilibration in < 1 fm/c?Need to be REALLY strong

Microscopic picture

R. Baier, A.H. Mueller, D. Schiff, D. Son, Phys. Lett. B539, 46 (2002).MPC 1.6.0, D. Molnar, M. Gyulassy, Nucl. Phys. A 697 (2002).

Perturbative calculations of gluon scattering lead to long equilibration times (> 2.6 fm/c) and small v2.

v2

pT (GeV/c)

2-2 processes with pQCD = 3 mb

Clearly this is not the weakly coupled perturbative QGP we started looking for.

s(trong)QGP

Helen Caines


Perfect fluid - caveats

Hydrodynamic calculations only just gone “3D” and don’t yet fully describe the longitudinal motion.

Calculations of two particle correlations are not properly described. “A theory that agrees with all available data must be wrong, since some data is always wrong.” - Sir Arthur

Eddington

Helen Caines


Probes of the Plasma State

Looking at plasma properties using “auto-generated” probes

3. Properties of the Plasma

Medium’s effect on partons/hadrons

Helen Caines


Produced photonsProduced photons

High energy probes are well described NLO perturbative QCD.

pQCD calculations work in p-p

Helen Caines


Schematically partons (quarks and gluons)

Scattered partons on the “near side” lose energy, but emerge;

those on the “far side” are totally absorbed

Helen Caines


Schematically photons

Scattered partons on the “near side” lose energy, but emerge;

the direct photon always emerges

Helen Caines


pQCD in Au-Au?

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

<Nbinary>/sinelp+p

p+p cross section

Compare Au+Au with p+p Collisions RAA

NuclearModification Factor:

R < 1 at small momentaR = 1 baseline expectation for hard processesR > 1 “Cronin” enhancements

(as in pA)R < 1: Suppression

A+A yield

Helen Caines


Photons

0, from quark and gluon jets

RAA Au-Au central events

0 = 0.43 (vacuum fragmentation ratio)partonic level absorption

~ 15 GeV/fm3

Helen Caines


Au-Au

d-Au

The control experiment – d-Au

Suppression not caused by initial state effects

• d-Au - no medium - no suppression

Initial state effects:

- Intrinsic KT

- Cronin

Charge particles

STAR

Helen Caines


Species dependence of RAA

• Use peripheral Au-Au data since lack of available p-p

• All particles suppressed

Au-Au0-5%/40-60%

Baryon/meson splitting at intermediate pT

Helen Caines


Parton recombination at medium pT

• Parton pT distribution is

~exponential+power-law

•7 GeV particle via :

Fragmentation from high pT

Meson - 2 quarks at ~4 GeV

Baryon - 3 quarks at ~2.5 GeV

Recombination - more baryons than mesons at medium pT

Helen Caines


Recombination and v2

Works for p, , K0s, ,

v2s ~ v2

u,d ~ 7%

The complicated observed flow pattern in v2(pT) for hadrons

is predicted to be simple at the quark level pT → pT /n

v2 → v2 / n ,

n = (2, 3) for (meson, baryon)

)2cos( )( 21 2

2

T

T

pvddp

Nd

Helen Caines


Suppression unique to RHIC?√sNN=200 GeV

√sNN=62 GeV 0-5%

40-60%

0-5%

40-60%

NA57, PLB in print, nucl-ex/0507012

√sNN=17.3 GeV

See Baryon/Meson splitting even at SPS

Helen Caines


STAR Preliminary

NA57: G. Bruno, A. Dainese: nucl-ex/0511020

Baryon/meson splitting at SPS and RHIC is the

same

Plasma present in all systems?

The Rcp double ratio

Helen Caines


The heavy quark sector

c, b D, B

1)

production

2)

medium energy loss

3)

fragmentation

light

M.Djordjevic PRL 94 (2004)

ENERGY LOSS

Energy loss a) depends on properties of medium (gluon densities, size) b) depends on properties of “probe” (color charge, mass)

Gluon radiation suppressed for

< m/E “Dead cone effect”

Y. Dokshitzer & D. Kharzeev PLB 519(2001)199Expectation: Little suppression for heavy flavor particles

Helen Caines


Detecting charm/beauty via semileptonic decaysHadronic decay channels: Only small B.R. very hard Non-photonic electrons:

Semileptonic channels: c e+ + anything (B.R.: 9.6%)

– D0 e+ + anything (B.R.: 6.87%) – D e + anything (B.R.: 17.2%)

b e+ + anything (B.R.: 10.9%)– B e + anything (B.R.: 10.2%)

Drell-Yan (small contribution for pT < 10 GeV/c)

Photonic electron background: conversions (0 ; e+e- ) 0, ’ Dalitz decays , … decays (small) Ke3 decays (small)

Helen Caines


Non-photonic e- RAA in central Au-Au

Very strong suppression at high pT

•Theory agrees only when: ignore b e contributions very high gluon density

– Is our understanding of c and b production correct?

– Is our understanding of partonic energy loss correct?

– How strong are the in-medium interactions?

– How dense is the medium?

Helen Caines


Heavy quarks also flow

• PHENIX also measures non-photonic electron v2

nucl-ex/0502009

Greco,Ko,Rapp.

PLB595, 202 (2004)

Another puzzle!

Time for charm 7 larger than for light quarks

(t > 10 fm/c)

Need large cross-sections - Further evidence of strong coupling

Helen Caines


We have successfully createdthe Quark Gluon Plasma!

- but its not what we expected when we started out

Now we have many exciting properties to understand...

• what causes the strong coupling?• what is the exact viscosity?• rapid equilibration?• novel hadron formation mechanisms?• what is the exact energy loss mechanism?• initial temperature determination?

Conclusions

Helen Caines


What about the future

The Large Hadron Collider (LHC) at CERN will be commissioned in 2008 with over an order of magnitude higher energy than at RHIC.

3 experiments with dedicated heavy-ion experiments

ALICE ATLASCMS

Instead of 40 TeV, 1000 TeV !

Can make more detailed measurements at the LHC

Helen Caines


Preliminary

Prediction from statistical model

Tpart

B

B

BeN

nBV

VnB

/

/

part

partT

Tpart

TT

N

Ne

eNee

Vn

S

BSB

/

/// )(

partT

partTT

Tpart

TT

Ne

Nee

eNee

Vn

B

SB

BSB

/2

//2

/// )(

Behavior as expected

Helen Caines


Su

ppre

ssio

n F

acto

rJ/cc) yields are suppressed

Heavy quarks produced in initial violent collisions.

Expect:

YieldAuAu/(Nbin*Yieldpp) = 1

Significant suppression of J/ in central events

|y|<0.35

Helen Caines


Quarkonia suppression

0.8 Tc 2 Tc 2.5 Tc

” ’J/’

Tdis(’) < Tdis(”) < Tdis(J/) < Tdis(’) < Tdis()

Color Screening

cc

Measurement of initial temperature

Matsui & Satz (1986):

Heavy quark bound states suppressed due to color screening in the QGP.

T < 3 Tc or new regeneration mechanisms?

Documents

Helen Caines Yale University Yale Colloquium – April 2006 Sampling the flavor of the Quark-Gluon Plasma. QGP – Phase of matter where quark and gluons are