Experiments at RHIC:Exciting Discoveries & Future Plans

outline

introductionplasmas and strong coupling

collective effectshydrodynamics and viscosity

transmission of probes by the quark-gluon plasma heavy quark probes

diffusion

color screening Color Glass Condensate (discussed by Dima) Plasma Physics of the Quark Gluon Plasma at RHIC II

required conditions (per lattice)

T/Tc

Karsch, Laermann, Peikert ‘99

/T4

Tc ~ 170 ± 10 MeV (1012 °K)

~ 3 GeV/fm3

~15% from ideal gas of weakly interacting quarks & gluons

We now know this leaves room for a big deviation from weak coupling

plasma

ionized gas which is macroscopically neutralexhibits collective effects

interactions among charges of multiple particlesspreads charge out into characteristic (Debye) length, D

multiple particles inside this lengththey screen each other

plasma size > D

“normal” plasmas are electromagnetic (e + ions)quark-gluon plasma interacts via strong interaction

color forces rather than EMexchanged particles: g instead of

Screening: Debye Length

distance over which the influence of an individual charged particle is felt by the other particles in the plasma

charged particles arrange themselves so as to effectively shield any electrostatic fields within a distance D

D = 0kT

-------

nee2

Debye sphere = sphere with radius D

number electrons inside Debye sphere is typically largeND= N/VD= VD VD= 4/3 D

3

1/2

in strongly coupled plasmas it’s 1

Debye screening in QCD: a tricky concept

in leading order QCD (O. Philipsen, hep-ph/0010327)

vv

don’t give up! ask lattice QCD

run

nin

g co

up

ling

coupling drops off for r > 0.3 fm

Karsch, et al.

Implications of D ~ 0.3 fm

can use to estimate Coupling parameter, = <PE>/<KE> but also = 1/ND

for D = 0.3fm and = 15 GeV/fm3

VD = 4/3 D3 = 0.113 fm3

ED = 1.7 GeVto convert to number of particles, use gT or g2T

for T ~ 2Tc and g2 = 4

get ND = 1.2 – 2.5 ~ 1

NB: for ~ 1plasma is NOT fully screened – it’s strongly coupled!other strongly coupled plasmas behave as liquids, even

crystals for ≥ 150dusty plasmas, cold atoms+ions , warm dense matter

to study experimentally:look at radiated & “probe” particles

as a function of transverse momentumpT = p sin with respect to beam direction)

90° is where the action is (max T, )midway between the two beams!

pT < 1.5 GeV/c

“thermal” particles radiated from bulk of the mediuminternal plasma probes

pT > 3 GeV/c

jets (hard scattered q or g)heavy quarks, direct photons produced early→“external” probe

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

collective effects

a basic feature distinguishing plasmas from ordinary matter

simultaneous interaction of each charged particle with a considerable number of others

due to long range of (electromagnetic) forces

magnetic fields generated by moving charges give rise to magnetic interactions

search for collectivity in QGPuse “internal” probes – emitted particles

dN/d ~ 1 + 2 v2(pT) cos (2) + …

“elliptic flow”

Almond shape overlap region in coordinate space

x

yz

momentum space

v2 is large & reproduced by hydrodynamics

• large pressure buildup • anisotropy happens fast • fast equilibration!

Kolb, et al

Hydrodynamics reproduces elliptic flow of q-q and 3q states Mass dependence requires softer than hadronic EOS!!

NB: these calculations have viscosity ~ 0“perfect” liquid (D. Teaney, PRC68, 2003)

Elliptic flow scales with number of quarks

implication: quarks are the relevant degrees of freedom when the pressure is built up.Hadronization: quark coalescence

Greco, Ko, Levai: PRC 68 (2003)034904

D. Morrison, SQM’06

at high pT v2 reflects opacity of medium

approximately expected level from jet quenching

hadrons

q

q

hadronsleadingparticle

leading particle

schematic view of jet production

.

Al

D2

time (ns)

shock front

Al pusher

dista

nce (µ

m)

0.0 5.01.0 2.0 3.0 4.0 6.0 7.0 8.0

0

100

200

300

x

L

for QGP: fast g and quarks probes must carry color charge

transmission of probes which interact with plasma

EM plasma: x-ray transmission

nuclear modification factor

photons escape plasma pions and other hadrons: strong interaction, absorbed

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

flat RAA via radiative energy loss only

(Quark Matter 05)

Dainese, talk at PANIC05AMY

A, Majumder

RAA wrt reaction plane – more discriminating

Energy loss depends on the path-length, expansion, collisions(?)

dihadrons: away side suppressed (low pT)

Pedestal&flow subtracted

some away side particles “reappear” at higher pT

STAR nucl-ex/0604018

pT trigger > 8 GeV/c

away side yield: some jets escape, some eatenSTAR nucl-ex/0604018

Note similarity ofaway side jetfragmentation.Only yield changes

how does plasma respond to deposited energy?

M.Miller, QM04

(1/N

trig)d

N/d

()

STAR Preliminary

cGeVp

cGevpassocT

trigT

/42.0

/64

CAN WE DO THIS????? +/-1.23=1.91,4.37 → cs ~ 0.33 (√0.33 in QGP, 0.2 in hadron gas)

PHENIX

dN

/d()

E. Shuryak: g radiates energykick particles in the plasma, acceleratethem in jet direction: a sound wave

not an experi-mental

artefact!

PHENIX preliminary

PHENIX preliminary

J. Jia

generallya phenomenonin crystals butnot liquids

3 particle correlations support cone-like structure

Au+Au Central 0-12% Triggered

Δ1

Δ2

d+Au

Δ1

J. Ulery, HP06

to further test interaction: heavy quarks

~ same E loss as u,d quarks energy loss not all radiativeneed collisions!

charm also flows

thermalization with the light quarks?not so easy!

RAA of e± from heavy flavors was a shock

Inclusion of collisional energy loss leads to better agreement with single electron data, even

for dNg/dy=1000.

Wicks, Horowitz, Djordjevic, & Gyulassy, nucl-th/0512076

NB: effect of collisional energyloss for light quarks…

diffusion = transport of particles by collisions

PHENIX preliminary

Moore & TeaneyPRC71, 064904, ‘05

D ~ 3/(2T) is small! → strong interaction of c quarks

larger D →less charm e loss fewer collisions, smaller v2

D = 1/3 <v> mfp = <v>/ 3D collision time → relaxation time

aim to measure the screening length

J/bound state of c and cbar quarks)

Tests screening & confinement: do bound c + c survive the medium?

or does QGP screening kill them?

Look at RAA for J/

different bound states probe different lengths

At RHIC:

CuCu

200 GeV/c

AuAu

200 GeV/c

dAu

200 GeV/c

J/ muon arm

1.2 < |y| < 2.2

mea

sure

d/e

xpec

ted

At RHIC:

CuCu

200 GeV/c

AuAu

200 GeV/c

dAu

200 GeV/c

AuAuee

200 GeV/c

CuCuee

200 GeV/c

J/ muon arm

1.2 < |y| < 2.2

J/ eeCentral arm

-0.35 < y < 0.35

At RHIC:

CuCu

200 GeV/c

AuAu

200 GeV/c

dAu

200 GeV/c

AuAuee

200 GeV/c

CuCu

62 GeV/c

J/ muon arm

1.2 < |y| < 2.2

J/ eeCentral arm

-0.35 < y < 0.35

Factor ~3suppression

in central events

CuCuee

200 GeV/c

RAA

vs Npart

: PHENIX and NA50

NA50 data normalized at NA50 p+p point.

Suppression similar in the two experiments, although the collision energy is 10 times higher (200GeV in PHENIX & 17GeV in NA50)

What suppression should we expect?

Models that were successful in describing SPS datafail to describe data at RHIC

- but lattice QCD says bound states until ~2Tc -

regeneratio

n

dire

ct

Rec

ombi

ned

only

Regeneration Narrowing of pT and y?

pT broadening in between Thews direct & in-medium formation: some regeneration

Recombination → narrower rapidity distribution with increasing Npart

BUT: From p+p to central Au+Au : no significant change in y distribution.

No Recombination

Thews et al.

slide from T. Ullrich, HP06

Karsch, Kharzeev, Satz, hep-ph/0512239

Probe experimentally: onium spectroscopy

40% of J/ from and ’ decays

they are screened but direct J/ not?

moments of the distribution function of particles f(x,v)0th moment → particle density (n)higher moments are <velocity> & temperature,

pressure tensor, heat flux tensoropacity/transmission is a probe of choice

Transport properties (e.g. diffusion, viscosity) Screening Collective Effects

hydrodynamic expansion, shock propagation, plasma waves→ density correlations inside plasma

Radiationbremsstrahlung, blackbody, collisional and recombination

Plasma oscillations, instabilities

Plasma Physics of the QGP with RHIC IIplasma diagnostics:

moments of the distribution function of particles f(x,v)0th moment → particle density (n)higher moments are <velocity> & temperature,

pressure tensor, heat flux tensoropacity/transmission is the first probe

Transport properties (e.g. diffusion, viscosity) Screening Collective Effects

hydrodynamic expansion velocity, shock propagation→ density correlations inside plasma

Radiationbremsstrahlung, blackbody, collisional and recombination

Plasma oscillations, instabilities

Plasma properties & “diagnostics”

next step in transmission study: jet tomography

jet quenching vs. system size, energy→ parton & energy density for EOS→ vary pT to probe medium coupling,

early development of system golden channel: -jet correlations fixes jet energy

flavor-tagged jets to sort out g vs. q energy loss

need detector upgrades (calorimeter coverage, DAQ) must have RHIC II’s increased luminosity x10 for:

statistics for clean -jet & multi-hadron correlationssystem scan in a finite time

tool of choice to study medium response/conductivity

small , low rate

measure D & B decays; onium spectroscopy

inner trackers for PHENIX and STAR

STAR

PHENIX

+ RHIC II luminosity!

need high luminosity to scan energy & system

pin down viscosity (and the collision dynamics)sort out via 3D hydro +measure v2 vs. v3, v4c, flows to separate late stage dissipation

from early viscous effects thermalization

plasma temperature via radiated *c, flows can we identify signals of early plasma instability?

probe 2q correlations via baryon production?direct search for density correlations poses a

challenge to experiment & theory both!

conclusion - discoveries

The matter created shows collective flowsdeveloped early, with quarks/gluons the likely d.o.f.magnitude implies very low viscosityQGP behaves as a liquid

similar to other strongly coupled plasmas! Very opaque to color charged probes

even charm quarks lose energy and flow!another result of strong coupling

J/ suppressed, but only partiallyperhaps screening + recombination from thermal bath?or sequential melting of and `

Evidence of CGC initial state The matter behaves as expected for a plasma!

conclusion – future plans

figure out the plasma physics of this new kind of matter:temperaturetransport propertiescollective excitations

expansion dynamicsdensity wavesinstabilities?

screening length

needdetector upgrades (planning, construction underway)high luminosity of RHIC II (x10 via electron cooling)

low probes, scan properties with system & energy

Energy density of matter

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

backup slides

conclusions

the matter formed at RHIC is a “perfect” fluidshows collective flows with small viscosityhuge interaction cross sections, very opaque multiple collisions affect even heavy charm quarks

color is partially, but not completely, screened this is like other strongly coupled plasmas

as it should be → it is a plasma!neutrality scale > interparticle distance

How does this super high energy density plasma work?□ map properties of the new stuff at RHIC

how does the plasma transport the “lost” energy? radiation rate? initial temperature achieved? (theory says ~380 MeV)

□ collide Pb+Pb at the LHC for higher Tinitial reach ~ 800 MeV: is coupling strong or weak?

collective effects

a basic feature distinguishing plasmas from ordinary matter

simultaneous interaction of each charged particle with a considerable number of others

due to long range of the forcesEM plasma: charge-charge & charge-neutral interactions

charge-neutral dominates in weakly ionized plasmasneutrals interact via distortion of e cloud by charges

very sensitive to coupling, viscosity…

magnetic fields generated by moving charges give rise to magnetic interactions

not an experi-mental

artefact,part I

PHENIX preliminary

PHENIX preliminary

J. Jia

the ridge

Au+Au 0-10%preliminary

3<pt,trigger<4 GeV

pt,assoc.>2 GeV

J. Putschke

preliminary“jet” sloperidge slopeinclusive slope

STAR preliminary

Jet + Ridge

STAR preliminary

Jethadrochemistry of jet-associated particles

jet & ridge similar but not identical for Npart<50K trigger typical meson??

J. Bielcikova

jet core yields unchangedchemistry constant

jet + (less) ridgev. central: baryon+meson drops toward reco expectation

A. Sickles

meson-meson

baryon-meson

plasma properties known, so far

Extract from models, constrained by 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

above hadronic E density!

dN(gluon)/dy ~1000 From energy loss, hydro huge!

T (MeV) 380-400

Experimentally unknown as yet

Equilibration time0 (fm/c) 0.6 From hydro initial condition; cascade agrees very fast!

NB: plasma folks have same problem & use same technique

Opacity (L/mean free path) 3.5 Based on energy loss theory

can get better agreement with data

if add formation of “extra” J/ by coalescence of c and anti-c from the plasma

caveat: not necessarily unique or correct explanation!

baryon puzzle…

baryons enhanced for pT < 5 GeV/c

RAA

NA50 and NA60 show suppression in Pb+Pb & In+In

suppression follows system size

Normal nuclear absorption from p+A data: = 4.18±0.35 mb

At CERN (√s = 17 GeV):

Is the energy density high enough?

5.5 GeV/fm3 (200 GeV Au+Au) well above predicted transition!

PRL87, 052301 (2001)

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

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)

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

FONLL Predictions

Mateo Cacciari provided a prediction using the Fixed Order Next Leading Logarithm pQCD approach

His calculation agrees perfectly with our “poor man’s” HVQLIB+PYTHIA predictions

Data exceed the central theory curve by a factor of 2-3

Possible explanations:NNLO contribution Fragmentation mechanisms

need to be studied in more details

use this technique to measure viscosity

melt crystal with laser lightinduce a shear flow (laminar)image the dust to get velocitystudy: spatial profiles vx(y) moments, fluctuations → T(x,y) curvature of velocity profile → drag forces viscous transport of drag in direction from lasercompare to viscous hydro. extract shear viscosity/mass densityPE vs. KE competition governs coupling & phase of matterCsernai,Kapusta,McLerran nucl-th/0604032

can get better agreement with data

if add formation of “extra” J/ by coalescence of c and anti-c from the plasma

caveat: not necessarily unique or correct explanation!

screening and thermal masses

Screening mass, mD, defines inverse length scaleInside this distance, an equilibrated plasma is sensitive to

insertion of a static sourceOutside it’s not.

T dependence of electric &magnetic screening massesQuenched lattice studyof gluon propagator

figure shows: mD,m= 3Tc, mD,e= 6Tc at 2Tc D ~ 0.4 & 0.2 fm

magnetic screening mass significantnot very gauge-dependent, but DOESgrow w/ lattice size (long range is important)

Nakamura, Saito & Sakai, hep-lat/0311024

use to get & compare to molecular dynamics

B. Liu and J. Goree, cond-mat/0502009

minimum arises because kinetic part of decreases with & potential part increases

MD: solve theequations of motionfor massive particlessubject to (screened)interaction potential

follow evolution ofparticle distributionfunction (&correlations)

solve coupled diff.eq’sover nearby space

density-densitycorrelations →

RHIC’s “perfect fluid”

one that exhibits ideal, non-dissipative hydrodynamics“not-quite-ideal” = can support a shear stress, ≠ 0Viscosity is

~ <v>/ ~ √kT/so viscosity increases with T

decreases with

yv

AF xx

Ideal hydrodynamics ( ~ 0) reproduces data at RHICdoes this make sense to QCD? → ≥h S : conjectured quantum mechanical limit

“A Viscosity Bound Conjecture”, P. Kovtun, D.T. Son, A.O. Starinets, hep-th/0405231 entropy density

mesons show common pT dependence

Fast equilibration, high opacity (even for charm): how?

multiple collisions using free q,g scattering cross sections doesn’t work! need x50 in the medium

Molnar

Lattice QCD shows qqresonant states at T > Tc, also implying high interaction cross sections

Hatsuda, et al.

Color glass condensate?

Hadron Punch Through

Better agreement with BRAHMS data“normal” shadowing cannot explain (R. Vogt hep-ph/0405060)

…sign of CGC?

Kharzeev, hep-ph/0405045

Centrality, pT

dependence

~ correct

Compare with BRAHMS

Overall consistent.

nucl-ex/0411054

deposited energy doesn’t thermalize so fast

T. Renk

distribution +longitudinal expansion depopulate region & shift Mach peak