Using RHIC to figure out nature’s first liquid

outline

what we know about the quark gluon plasma at RHIC

how to experimentally extract QGP propertiesespecially from particle jets arising from

quarks/gluons traversing the plasma

the fate of the away side jetwhere does the energy go?tools to extract the jet contribution (<1%) from the

complex underlying eventthe speed of sound in the quark gluon plasma

Quarks, gluons, hadrons

6 quarks: 2 light (u,d), 1 sort of light (s)2 heavy (c,b), 1very heavy (t)flavor & color quantum numbers

Quarks are bound into hadronsBaryons (e.g. n, p) have 3Mesons (e.g. ): 2 (q + anti-q)

Colored quarks interact by exchange of gluons Quantum Chromo Dynamics (QCD)

Field theory of the strong interaction parallels Quantum Electrodynamics (QED)

EM interactions: exchanged photons electrically unchargedgluons carry color charge

QCD phase transition

Color charge of gluons gluons interact among themselves theory is non-abelian

curious properties at large distance: confinement of quarks in hadrons

+ +…

At high temperature and density: force is screened by produced color-chargesexpect transition to free gas of quarks and gluons

non-perturbative QCD – lattice gauge theory

T/Tc

Karsch, Laermann, Peikert ‘99

/T4

Tc ~ 170 ± 10 MeV (1012 °K)

~ 3 GeV/fm3

required conditions to study quark gluon plasma

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

42

30Tg

RHIC is the tool

Collide Au + Au for maximum volume & temperatures = 200 GeV/nucleon pair, p+p and d+A to compare

What we’ve learned at RHIC so far

PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TM

time0 10-22 sec

the initial state:gluon interactionlimits max. density“color glass condensate”?

quarks andgluonsinteract

nearly instantthermalization

quark gluonplasma : “perfect”liquid, veryopaque

final state hadrons freeze out

final state hadrons retain memory of conditions at freezeout→ analogous to CMB

thermalization and liquid properties

experimental observablesuse final state distributions

to probe dynamics at freezeout

hydrodynamicsconstrained by datayields information on properties

collective effects are a basic feature of plasmas!

search for particle final state patterns indicative of early dynamics – “elliptic flow”

dN/d ~ 1 + 2 v2(pT) cos (2) + …

“elliptic flow”

Almond shape overlap region in coordinate space

x

yz

momentum space

Hydro. CalculationsHuovinen, P. Kolb,U. Heinz

v2 reproduced by hydrodynamics

STARPRL 86 (2001) 402

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

central

Hydrodynamics solves eqn. of motionEquation of state from lattice QCD

data say: Ti ~ 400 MeV, i ~ 15 GeV/fm ~ 0, i ~ 0.6 fm/c

Collective effect probes early phase

correct dependence of flow on mass requiressofter than hadronic EOS!!

Kolb, et al

magnitude scales with thenumber of quarksimplication: quarks are the relevant degrees of freedom when the pressure is built up.

measure transmission of colored probes

hadrons

q

q

hadronsleadingparticle

leading particle

schematic view of jet productionfirst chance hard scattering of q,g

QGP induces scattered quarks to radiate energy -> jet quenching

AA

AA

AA

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

nucleon-nucleon cross section<Nbinary>/inel

p+p

QGP very opaque to quarks & gluons

hadrons suppressedby factor of 5photons have no colorcharge no suppressionmechanism: gluon radiation

Pedestal&flow subtracted

test role of collisions using heavier charm quarks

electrons (0.5 MeV/c2 mass) stop in matter (bremsstrahlung) radiation dominant process

muons (mass = 106 MeV/c2) have long range radiation is suppressed by the large massdominant energy loss mechanism is via collisions

use heavy quarks as second kind of probe collisions should be important for c, b quarks masses are > 1, 4 GeV/c2

heavy quarks lose energy and flow too!

~ same E loss as u,d quarks energy loss not purely

radiativeneed collisions!

charm also flows thermalization with the light quarks??

what is the collision ?must exceed that for free qthermalization needs same!

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

should expect screening and bound states should melt

lattice QCD can sort out

run

nin

g co

up

ling

coupling drops off for r > 0.3 fmso large bound states should melt

Karsch, et al.

Karsch, Kharzeev, Satz, hep-ph/0512239

so the larger bound states should melt

40% of J/ from and ’ decays

they are screened but direct J/ not?

obse

rved

/exp

ecte

d J

/

lattice says: larger than for free quarks

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

have multiple kinds of evidence for increased scatteringcross section & correlations which survive in QGPnatural to expect behavior as in other strongly coupled plasmas

generallya phenomenonin crystals butnot liquids

how does QGP transport energy from a jet?

g radiates energy, which gives akick totheQGP

1) can we detect evidence of asound (density) wave afterpassage of a jet?

2) does the induced correlationin q density distributionmanifest itself in particle production somehow?

experimental tool : 2 particle correlations

hadrons

q

q

hadronsleadingparticle

leading particle

schematic view of jet production

jet formation process in e+e- collisions :correlated hadrons

coneR

azimuth angle

Jet physics in PHENIX

Trigger:hadron with pT > 2.5 GeV/c

Count associated particles for each trigger at lower pT

(> 1 GeV/c) “conditional yield”

Near side yield: number of jet associated particles from same jet in specified pT bin

Away side yield: jet fragments from opposing jet

trigger“near side” < 90° jet partner

“away side” > 90° opposing jet

do a statistical analysis

CARTOON

flow

flow+jet dN

Ntrig d

includes ALL triggers(even those with no

associated particles inthe event)

jet Combinatorialbackground;collective flow causes additional correlation :

B(1+2v2(pTtrig)v2(pT

assoc)cos(2))

associated particles with non-flow angular

correlations -> jets!

1

combinatorial background large in Au+Au!

Detector acceptance induces correlations too

sources of uninteresting correlations: detector acceptance (square of singles acceptance), performance “holes”/dead channels

folding two 90° angular bites → pair acceptance

0 π

Acc

(Δφ

)

ΔΦ

Area = π

small probability tocatch pair of particleswith 90° opening angle

within each arm of PHENIXacceptance is nonuniformdetails vary slowly with time

complicated to correct analyticallypainful Monte Carlo simulation

MEASURE the acceptance correction from data

technique: “event mixing”select class of events with correlated pairspick one particle (trigger) from one event, partner

from a different eventensures no physics correlation

make exactly the same kinematic cuts on “fake” pairs from mixed eventsbin real and mixed events in the same way

collision location in detectorcollision impact parameter (centrality)

divide real by mixed event distribution

treat mixed events as “background”

divide foreground by this

to correct for acceptance

(mixed events)

dN

/d

resulting correlation function

normalize correction tofull acceptance

allows absolute count ofnumber of partners pertrigger

ncomb = <Ntrig/event><Npartner/event>

also remove the 3rd undesirable correlation

yesterday’s signal is today’s background!

ncomb counts probability of trigger-partner pairs in

underlying event (non-jet source) yet, we know these are not flat in !

elliptic flow → cos modulation

amplitude is measuredso we modulate ncomb by

1+2v2trigv2

partcos(2)

alas, we’re not done yet!

time dependent efficiency variationsonly mix events similar in time

or performancenormalize absolutely

for each group → residual multiplicity correlation

2 remaining non-jet correlations

real & mixed events differ in centralitymixed events sample this distribution twice, real once mixed have lower multiplicitycorrection depends on centrality bin width, mean & resolutiondetermined by simulating measured

probability distributions# NN collisions

N p

artn

er

Au+Au shows a sound-wave like pattern

peripheralcollisions(normal jet)

centralcollisions

system (in)dependence → medium property

g radiates energy, which gives akick totheQGP

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

How about the mysterious baryon excess?

Radiated gluons are collinear (inside jet cone)

Can also expect a jet “wake” effect,medium particles“kicked” alongside the jet by energy they absorb

And expect hard-soft combinations too C.M. Ko et al, Hwa & YangPRC68, 034904, 2003PRC67, 034902, 2003nucl-th/0401001 & 0403072

Fries, Bass & Muellernucl-th/0407102

Both increase probability of finding quarks near each other

again use 2 particle correlations

Select particles with pT= 2.5-4.0GeV/c

Identify them as mesons or baryons viatime-of-flight

Find second particle with pT = 1.7-2.5GeV/c

Plot distribution of the pair opening angles;integrate over 55°

Jet partner ~ equally likely for trigger baryons & mesons! Same side: slight decrease with centrality for baryonsDilution by combinations of 3 soft quarks

intermediate pT baryons ARE from jets

thermal quark combination

Dilutes jet partner yield

Conclusions

RHIC makes amazing new/old stuff behaves not like a weakly coupled gas, but like a strongly

coupled plasma we see structures in 2 particle correlations

away side like a sound wave in a shocked mediumnear side shows extra baryons compared to p+p

as expected if jet creates a bow wave have developed techniques to study < 1% level signals

on top of complex not-quite statistical backgroundsuse 2 particle correlationsmeasure the background in real datafold to determine “boring” correlationssuch techniques critical to extracting plasma properties

A word about the data handling

yearly raw data set size ~0.4 PB

large dataset size drives some limitations

cannot all be disk residentnot even post reconstructing detector info → particle tracks

insufficient server, disk, tape bandwidth for random access by ~200 analyzers

we run an “Analysis Train”single orderly pass over all data, utilizing many CPU’scopy a file from mass store to each CPUrun analysis modules from many users (current pass has 41)store histograms, small ntuples to diskcopy results onto shared diskaggregate multiple files per “run”

script driven by a single “conductor”

Data Archiving Rates

ATLASCMS

LHCb

ALICE

CDF

~25 ~40

~100 ~100

All in MB/sall approximate

~100

~150

~1250

~600

PHENIX Run-2

PHENIX Run-3

PHENIX Run-4

PHENIX Run-5

auxilliary slides

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

Evolution of the Universe

Nucleosynthesis builds nuclei up to HeNuclear Force…Nuclear Physics

Universe too hot for electrons to bindE-M…Atomic (Plasma) Physics 104

K

E/M Plasma

Too hot for quarks to bind!!! Too hot for quarks to bind!!! 1012 KStandard Model (N/P) Physics

Quark-Gluon

Plasma??

Too hot for nuclei to bind 1010 KNuclear/Particle (N/P) Physics Hadron

Gas

SolidLiquidGas

Today’s Cold UniverseGravity…Newtonian/General

Relativity

Two Major Experiments to probe the Early Universe

With thanks to Tetsuo Hatsuda

WMAP

RHIC

4 complementary experiments

STAR

The Scope of the Tools (!)

STARspecialty: large acceptancemeasurement of hadrons

PHENIXspecialty: rare probes, leptons,

and photons

Benchmark the Probes in p+p collisions

calculable with perturbative QCD!

Produced photonsProduced photonsProduced pionsProduced pions

peripheralN

coll = 12.3 4.0

centralN

coll = 975 94

strongly interacting probe: a different story!

general explanation of jet quenching

Inelastic (radiative) energy loss in Au+Au

interaction of radiated gluons with gluons in

the plasma greatlyenhances the amount

of radiation

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

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!

Possibility of plasma instability → anisotropy

small deBroglie wavelength q,g point sources for g fieldsgluon fields obey Maxwell’s equationsadd initial anisotropy and you’d expect Weibel instability

moving charged particles induce B fieldsB field traps soft particles moving in A directiontrapped particle’s current reinforces trapping B fieldcan get exponential growth

(e.g. causes filamentation of beams)doesn’t require strong coupling

could also happen to gluon fields early in Au+Au collisiontimescale short compared to QGP lifetimebut gluon-gluon interactions may cause instability to

saturate → drives system to isotropy & thermalization

Transport properties

transport of particles → diffusion

transport of energy by particles → thermal conductivity

transport of momentum by particles → viscosity

transport of charge by particles → electrical conductivityis transport of color charge an analogous question for us?

transport in plasmas is driven by collisions

Other strongly coupled plasmas

Inside white dwarfs, giant planets, and neutron stars (n star core may even contain QGP)

In ionized gases subjected to very high pressures, magnetic fields, or particle interactions

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

Strategy for conditional yields

Quality cutspT selection(PID cuts)

(Seed)trigger partner list

Pair cutsRaw correlation

Pair cutsEnsure sameacceptance

background

subtract

Subtracted correlation

acceptancenormalizeto or 2

divide PartnerConditional yield

(uncorrected)

Conditional Yield (true)

Partner efficiency correction:track efficiency, quality, etc.

norm by events

Mixed events

nB

perP.S.

others say maybe collisions not needed

BUT v2 is small…

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

not an experimental artefact, part IIAu+Au Central 0-12% Triggered

Δ1

Δ2

d+Au

Δ1

J. Ulery

deposited energy doesn’t thermalize so fast

T. Renk

distribution +longitudinal expansion depopulate region & shift Mach peak

put together to get conditional Yields

Combinatoric background level determined by convolution of trigger and associated particle rate

v2 values taken from PRL 91 (2003) 182301 modulates combinatoric level by 1+2v2(pT

trig)v2(pTassoc)cos(2)

(solid lines in plot)

Trigger pT: 2.5-4.0GeV/c

Associated pT: 1.7-2.5GeV/c

QGP 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

viscosity ~0 hydro constrained by flow

Plasma properties we will measure at RHIC II

property measurement

T as fn. of

equation of state particle flows as fn. of critical point location

screening length onium spectroscopy

(x,v) jet tomography

diffusion open C, B spectra & flow

viscosity strange & charmed hadron flows

used to constrain 3d hydro

energy transport >2 particle correlations vs. T, pT

something new? follow up on surprises…

to explore at RHIC II ≥ 2014

property measurement challengequantify screening length

Y(2s), Y(3s)

c in Au+Au

statistics (acceptance) resolution? (~100 MeV)

S/B, granularity?

medium modified fragmentation fn.

-identified hadron correlations

>5 GeV/c h statistics (acc)

direct tag/decay subtract.

(granularity?? acceptance)

chiral symmetry chiral partners

(a1, )

? doable? granularity?

thermalization time flow of high pT non- 0

di-hadrons pT>20 GeV

acceptance, trigger, momentum resolution

plasma parton correlations

? something new?