Poking at the Quark Gluon Plasma with Jets and Heavy Quarks

Scattered partons propagate:fast quarks & gluons traverse

the interesting stuffradiate gluonsinteract with QGP partons

Fragment into jets - usually described by

phenomenological fragmentation function

- in/outside the medium

coneRFragmentation:

z hadron

parton

p

p

What’s this stuff? let’s poke it with a stick!

follow in the footsteps of Rutherford and friends experimenting with radioactivity…

lattice QCD F. Karsch

properties of matter

thermodynamic (equilibrium)T, P, EOS (relate T,P,V, )vsound, static screening length

transport properties*particle number, energy, momentum, charge diffusion sound viscosity conductivity

* measuring these is new for nuclear/particle physics!

^ QCD

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 gluons self-interacting, number (not fixed) T

typical plasma diagnostics

X-ray tomography: to get temporal and spatial evolution of plasma mode activity, use 10 soft X-ray cameras with 20 channels each, at 70 kHz max. 

heavy ion collision diagnostics

PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TM

Kpnd,

Hadrons reflect (thermal) properties when inelastic collisions stop (chemical freeze-out).

not possible to measure as a function of time nature integrates over the entire collision history

thermal radiation

(, e+e-,

+

color-screened QGP

pressure builds up

Hard scattered q,g(short wavelength) probes of plasmaformed

time

study plasma by radiated & “probe” particles

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

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

midrapidity pT < 1.5 GeV/c

“thermal” particles radiated from bulk of the medium

pT > 3 GeV/c

jets (hard scattered q or g)heavy quarks, direct photonsdescribe by perturbative QCDproduced early→“external” probe

PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TM

RHIC at Brookhaven National Laboratory

Collide Au + Au ions for maximum volumes = 200 GeV/nucleon pair, p+p and d+A to compare

STAR

Experimenter’s Tools

STARspecialty: large acceptancemeasurement of hadrons

PHENIXspecialty: rare probes, leptons,

and photons

a bit of geometry, terminology

baseline for heavy ion collisions: p+p collisions peripheral collisions (large impact parameter) are like

a handful of p+p collisions central (small impact parameter) collisions produce

largest plasma volume, temperature, lifetime report centrality as fraction of total A+A cross section

» 0-5% = very central

peripheral:few participant nucleons (small Npart)few NN collisions (Ncoll)

central:large Npart & Ncoll

Ncoll near 1000 in ~ head-on Au+Au

The matter is opaque! jets are quenched

p-p PRL 91 (2003) 241803

Good agreementwith pQCD

head-on Au+AuN

coll = 975 94

colored objects lose energy, photons don’t

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

how opaque is hot QCD matter?

interaction of radiated gluons with gluons in

the plasma greatlyenhances the amount

of radiation

energy loss by induced gluon radiation

opacity expansion analysis shows <medium length traversed>/mean free path ~ 3.5 → ~ 1400 gluons/unit rapidity

I. Vitev

d+Au

Au+Au

energy transport

constrain with data

extract transport parameter q from data, get ~ 13 GeV2/fm

but pQCD favors ~1 (Baier, et al)

^

PQM model: C. LoizidesEur.Phys.J. C49 (2007) 339

data & fit: arXiv:0801.1665

momentum exchange: complicated process

The medium is dense and opaque!Quantifying energy deposit ..ongoingDifferent models include radiation, w/ or w/o collisions some/no transfer medium→probe different level of detail describing collision geometry different handling of fluctuations different description of the expansion dynamics

medium transport of deposited energy?

study using hadron pairs high pT trigger to tag hard

scattering second particle to probe the

medium

Central Au + Au

opposing jet

collective flowin underlying event

same jet

at high momentum, jets punch through

STAR

centralcollisions

on away side:same distribution ofparticles as in p+pbut ~5 times fewer!expected for opaque medium

X

Phys.Rev.Lett. 97 (2006) 162301

2/8/2008Quark Matter 2008

Direct Photon-Hadron Correlations in p+p

2/8/2008Quark Matter 200819

[rad]

1/N

trig

dN

/d

(A

.U.)

M.A. Nguyen

toward jet tomography: Compton scattering

q+g → q+ tags q energy12-15 GeV “monoenergetic jet”

0 - h dir - h right mechanism same jet partners are absentaway jet shows similar modificationnext step: quantify energy/momentum flow

Where we need to go

tags q energy >12 GeV

“monoenergetic” jets

all we need is:more eventsbigger detector coverage

all those near-by curvesvery different

with no mediumALL use weak coupling!

RHIC II AuAu 20 nb-1

-jet

lower pT partners look funny! medium responds to the “lost” energy

3<pt,trigger<4 GeV

pt,assoc.>2 GeV

Au+Au 0-10%

preliminary

STAR

1 < pT,a < 2.5 < pT,t <4 GeV/c

peripheralcentral

jets shock the medium

p+p

centralAu+Au

lost energy excites a sound (density) wave?

if shoulder is sound wave… LOCATION at +/-1.23=1.91,4.37 → speed of sound cosm=cs~0.35-0.4 (cs

2=0.33 in QGP,~0.19 in hadron gas)

relative excitation of sound and diffusion wake in intense studydata →sound mode large

Gubser,Pufu,Yarom PRL100, 012301’08

Chesler & Yaffe, 0706.0368(hep-th)

strong coupling: ask AdS/CFT answer: yes it does!

machcone

wake

Diffusion of heavy quarks traversing QGP

How do they interact? Prediction: lower energy loss than light quarks

large quark mass reduces phase space for radiated gluons

Measure via semi-leptonic decaysof mesons containing charm or bottom quarks

D Au

AuD

X e±

K

c,b decays via single electron spectrum

compare data to “cocktail” of hadronic decays

sufficient interaction to equilibrate??

Measure correlation of e± with the light hadrons Ask whether they flow along.

NB: rate of equilibration gives

information on the viscosity

of the liquid!PRELIMINARY

Run-4

Run-7

Rapp & van Hees, PRC 71, 034907 (2005)

minimum-bias

Heavy quarks do flow!!Use to probe transportproperties of QGP!

heavy quarks lose energy too

cannot be dominantly by bremsstrahlung (gluon radiation)

plasmas have collisions among constituents! including it helps

larger than expected scattering → stronger coupling

e± from heavy quark decayWicks et al., NPA 784(2007)426

heavy quark transport: diffusion & viscosity

diffusion = brownian motion of particles

definition: flux density of particles J = -D grad n integrating over forward hemisphere:

D = diffusivity = 1/3 <v>

so D = <v>/ 3nD collision time, determines relaxation time

Langevin: equation of motion for diffusion thru a medium

drag force random force <pT2>/unit time D*

particle concentration

= mean free path

note: viscosity is ability to transport momentum = 1/3 <v> so D = S → measure D get !

* G. Moore and D. Teaney, hep-ph/0412346

confronting mechanisms with dataPRL98, 172301 (2007)

Radiative energy loss alone: fails to reproduce v2

Heavy quark transport model (i.e. diffusion) shows better agreement with RAA and v2

Though agreement with data is so-so, slow relaxation ruled out by v2

D ~ 4-6/(2T) for charm /S = (1.3 – 2.0)/ 4

4/)8.30.1(/ s

S. Gavin and M. Abdel-Aziz: PRL 97:162302, 2006

pTfluctuations STAR

Comparison with other estimates

4/)2.12.01.1(/ sR. Lacey et al.: PRL 98:092301, 2007

v2 PHENIX & STAR

4/)4.24.1(/ s

H.-J. Drescher et al.: arXiv:0704.3553

v2 PHOBOS

conjectured quantum limit

estimates of /s based on flow and fluctuation dataindicate small value as wellclose to conjectured limitsignificantly below /s of

helium (s ~ 9)

What about b quarks?

PRL 98, 172301 (2007)

e± from heavy flavor

b quark contribution tosingle electrons becomessignificant. do they alsolose energy?

Hard probes tell us:

Energy loss in the plasma is large.

and/or s ~ 0.27. What quantity DO we measure? Eloss mechanism?

Deposited energy shocks the medium. Mach cones?cs ~ (0.35 – 0.4) c (closer to hadron gas than QGP)expected diffusion wake AWOL (baryon enhancement?)

Medium is also opaque to charm quarks

Heavy quark diffusion, hadron flow & fluctuations →viscosity: S = (1 – 3)/ 4 close to conjectured bound

First hint of b decay contributions bottom quarks maybe not gobbled up by medium?

for further (experimental) progress

STAR HFT

PHENIX VTX

Si vertex detectors separate c from b

-3 -2 -1 0 1 2 3 rapidity

NCCNCCM

PC

MP

C

VTX & FVTX

HBD

EM

CA

LE

MC

AL

RHIC II AuAu 20 nb-1

-jetacceptance and ∫L mechanism of eloss

and do it again at higher T at the LHC!

backup slides

long standing baryon puzzle…

baryons enhanced for 1.5 < pT < 5 GeV/c

coalescence of thermal quarks from an expanding quark gluon plasma.

STAR

baryons come from jets – enhanced by wake?

●the “extra” baryons have jet-like partners●only in central collisions do we see a dilution from thermal baryons

meson-meson

baryon-meson

Near side

●collectively flowing medium boosts quarks to higher pT

●wake of fast quark builds particle density to coalesce●baryon enhancement reflects dynamics…?!

speculate:

Gubser, Pufu, Yarom 0706.4307(hep-th)

sound wave (shoulder) vs. jet remnant

shoulder (medium response)

jet remnant

away-side total

pp collisions

peripheral central

sum associated pT observed in charged particles

punch-through decreases vs. p+pshoulder grows with centralitynear & far totals both increase

(line: expected in PHENIX acceptance according to PYTHIA generator)

ratio near/far:nearly constant with centrality! at p+p value!near side increase tracks away sideloss of pT in punch-through balanced by shoulder growth

Ratio of Away pTasso / near pT

asso

Ratio constant with centrality Consistent with p+p value, also with PYTHIA Even though the total vector sum of nearside/awayside both increase, the ratio

of the two still hold constant , i. e. the total contribution from “head” and “shoulder” part is hold, but the portion between the two is changing.

head

shoulder

Head+shoulder

PYTHIA

LPM effect up to O(gs) + (3+1)d hydro + collisions

Qin, Ruppert, Gale, Jeon, Moore and Mustafa, 0710.0605

Fix initial state by constraining hydro with particle spectra Reproduce observed energy loss vs. centrality using s = 0.27

Three particle correlations

Two Analysis Approaches:• Cumulant Method

Unambiguous evidence for true three particle correlations.

• Two-component Jet+Flow-Modulated Background Model

Within a model dependent analysis, evidence for conical emission in central Au+Au collisions

pTtrig=3-4 GeV/c

pTassoc=1-2 GeV/c

off-

diag

onal

pro

ject

ion

d+Au

0-12% Au+Au

=(12)/2

Δ2

Δ1 Δ1

0-12% Au+Au: jet v2=0

Δ2

From J. Dunlop, Montreal Workshop ‘07C. Pruneau, QM2006J. Ulery, HP2006 and poster, QM2006

more complex jet fragment measurements

3 – particle correlationsconsistent with Mach-cone shoulder

sum of jet fragment momentum▪ increases together on trigger and away sides▪ momentum loss in punch-thru jet balanced by momentum in the shoulder peak▪ evidence for wakes?

d+Au 0-12% Au+AuΔ2

Δ1

suppression at RHIC very similar to that at SPS!why??more suppressed at y 0

PHENIX PRL98 (2007) 232301

J/

screening length: onium spectroscopy

40% of J/ from and ’ decays they are screened but direct J/ not?

Karsch, Kharzeev, Satz, hep-ph/0512239

y=0

y~1.7

what does non-perturbative QCD say?

Lattice QCD shows heavyqq correlations at T > Tc, also implying that interactions are not zero

Big debate ongoing whether these are resonant states, or “merely” some interactions

Color screening – yes!but not fully…Some J/ may emerge intact

Hatsuda, et al.

J/ is a mystery at the moment!

Others may form in final state if c and cbar find each other

are J/’s regenerated late in the collision?

c + c coalesce at freezeout → J/

R. Rapp et al.PRL 92, 212301 (2004) R. Thews et al, Eur. Phys. J C43, 97 (2005)

Yan, Zhuang, Xu, PRL97, 232301 (2006) Bratkovskaya et al., PRC 69, 054903 (2004)

A. Andronic et al., NPA789, 334 (2007)

R. Rapp et al.PRL 92, 212301 (2004) R. Thews et al, Eur. Phys. J C43, 97 (2005)

Yan, Zhuang, Xu, PRL97, 232301 (2006) Bratkovskaya et al., PRC 69, 054903 (2004)

A. Andronic et al., NPA789, 334 (2007)

should narrow rapidity dist. … does it?

central

peripheral

J/ is a mystery at the moment!

plasma basics – Debye screening

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 of order D

D = 0kT

-------

nee2

Debye sphere = sphere with radius D

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

3

1/2 ne = number densitye = charge

plasma frequency and oscillations

instantaneous disturbance of a plasma → collective motionsplasma wants to restore the original charge neutralityelectrons oscillate collectively around the (heavy) ionscharacterized by natural oscillation frequency

plasma frequencyit’s typically high

restoring force: ion-electron coulomb attraction

damping happens via collisionsif e-ion collision frequency < electron plasma frequency pe/2 then oscillations are only slightly dampeda plasma condition: electron collision time large vs. oscillation

nee2

p = ------me0

1/2

For all distributions described by temperature T and (baryon) chemical potential :

dn ~ e -(E-)/T d3p

Does experiment indicate thermalization?

Tf ~ 175 MeV

minimum at phase boundary?

Csernai, Kapusta & McLerran PRL97, 152303 (2006)

quark gluon plasma

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

minimum observed in other strongly coupled systems –kinetic part of decreases with while potential part increases

strongly coupled dusty plasma

Elliptic flow scales with number of quarks

transverse KE

implication: valence quarks, not hadrons, are relevant pressure field builds early → dressed quarks born of flowing field (as strongly interacting liquids

lack well-defined, long-lived quasi-particles)

The acid test for quark scaling

meson (bound state of s+sbar) mass ~ mproton but flows like the mesons

PHENIX

dielectron spectrum vs. hadronic cocktail

R.Rapp, Phys.Lett. B 473 (2000)R.Rapp, Phys.Rev.C 63 (2001)R.Rapp, nucl/th/0204003

low mass enhancement at 150 < mee < 750 MeV3.4±0.2(stat.) ±1.3(syst.)±0.7(model)

Comparison with conventional theory

calculations: min bias Au+Authey include:QGP thermal radiation chiral symmetry restoration

Direct photon v2

1

* _2

.2.

2

R

vvRv

photonBGphotonincphotondir

transport in QGP (theoretical approach)

weak coupling limit strong coupling limit

perturbative QCD not so easy!

kinetic theory, cascades gravity supersym 4-d

QCD-like theory resummation of hard thermal loops

Collectivity: measuring elliptic flow (v2)

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

must begin hydro in < 1 fm/cviscosity must be ~ 0 - 0.1 i.e. “perfect” liquid viscosity decreases longitud. pdV work → higher transverse velocity

First indication of small /S

data constrains hydro: as in plasma physics

D. Teaney, PRC68, 034913 (2003)

Michael P. McCumber for PHENIX Quark Matter – 5 February 2008

Away-side CompositionarXiv:0712.3033

arXiv:0712.3033

Shapes: - Similar shape in away-side mesons and baryons

Ratios: - Away-side baryon/meson ratios approach inclusive values

- Incompatible with in-vacuum fragmentation

Michael P. McCumber for PHENIX Quark Matter – 5 February 2008

Connections - Centrality

PHENIX poster (Chin-Hao Chen)

- Away-side shoulder and near-side ridge share a common centrality dependence

- Scale similarity here is largely a factor of pT

selection

Michael P. McCumber for PHENIX Quark Matter – 5 February 2008

Connections - Balance

0.0 < |Δη| < 0.1 0.5 < |Δη| < 0.7

- Jet & Ridge balances Shoulder & Head

- Ridge & Shoulder balance seperately!