Hot QCD Matter: An Experimenter’s Dream and Nightmare

Hot QCD Matter: An Experimenter’s Dream and Nightmare

B. Jacak

Stony Brook

October 25, 2009

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Hot QCD Matter

Exciting and surprising results from RHICWhat IS the coupling in the plasma?What are the degrees of freedom - point particles? pure

fields? composite quasiparticles?

What are the physical properties of the plasma?Thermal: T,, EOS opacity, fluidityDynamic: viscosity, diffusion, energy transport color screening, correlations inside

Measure the above in a system lasting <10 fm/c!Nature does the time integral, whether we like it or not

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Today (results from PHENIX)

Exciting and surprising results from RHICWhat IS the coupling in the plasma?What are the degrees of freedom - point particles? pure

fields? composite quasiparticles?

What are the physical properties of the plasma?Thermal: TT,, EOS opacityopacity, fluidityDynamic: viscosity, diffusion, energy transportenergy transport color screening, correlations inside

Measure the above in a system lasting <10 fm/c!Nature does the time integral, whether we like it or not

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4

• Exponential fit in pT:Tavg = 221 ±23 ±18 MeV• Multiple hydro models reproduce data •Tinit ≥ 300 MeV

arXiv:0804.4168v1 [nucl-ex]

Initial State Temperature: direct photons

Low mass, high pT e+e-

nearly real photons

Large enhancement above p+p in the thermal region

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Lepton pair emission EM correlator

Emission rate of dilepton per volume

Boltzmann factortemperature

EM correlatorMedium property

ee decay

From emission rate of dilepton, the medium effect on the EM correlator as well as temperature of the medium can be decoded.

e.g. Rapp, Wambach Adv.Nucl.Phys 25 (2000)

Hadronic contributionVector Meson Dominance

qq annihilation

Medium modification of mesonChiral restoration

q

q

Thermal radiation frompartonic phase (QGP)

Yasuyuki Akiba - PHENIX QM09

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Dilepton emission

Vacuum EM correlatorHadronic Many Body theoryDropping Mass Scenarioq+q annihilation (HTL improved)(q+gq+qee not shown)

Calculation: R. Rapp

dMdydpp

dN

tt

eey=0, pt=1.025 GeV/c

Normally: dilepton emission as spectrum dN/dpTdM.

Mass spectrum at low pT is distorted by virtual photonee decay factor 1/M: steep rise as M0

qq annihilation contribution negligible at low mass due to m**2 factor of the EM correlator

NB: calculation omits partonic photon emission processq+gq+q+e+e-

Dilepton

virtual photon

Prob. *l+l-

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Relation of dileptons and virtual photons

Emission rate of dilepton per volume

Emission rate of (virtual) photon per volume

Relation between them

Virtual photon emission rate can be determined from dilepton emission rate

For M0, n* n(real) so real photon emission rate can also be determined

M x dNee/dM givesVirtual photon yield

Dilepton virtual photon

Prob. *l+l-

This relation holds for the yield after space-time integral


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Virtual photon emission rate

dydpp

dN

dMdydpp

dNM

tttt

ee*∝× at y=0, pt=1.025 GeV/c

dydpp

dN

tt

Vaccuum EM correlatorHadronic Many Body theoryDropping Mass Scenarioq+q annihilaiton (HTL improved)(q+gq+qee not shown)

Same calculation shown as virtual photon emission rate.

Note: steep rise at M=0 is gone, and the virtual photon emission rate is more directly related to the underlying EM correlator.

For M0, n* n(real)

q+gq+* is not shown; is similar to HMBT at this pT

Dilepton

virtual photon

Prob. *l+l-

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Excess of virtual photon

Excess over cocktail ~ constant with mass at high pT.

Convert to virtual photon yield by 1/M factor from the virtual photon decay. distribution is ~flat over 0.5 GeV/c2

Extrapolation to M=0 should give the real photon emission rate.

No indication of strong modification of EM correlator at high pT !

presumably the virtual photon emission is dominated by processes e.g. ++* or q+gq+*

Exc

ess

*M (

A.U

).


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How about low pT ?

0 < pT < 8 GeV/c 0 < pT < 0.7 GeV/c

0.7 < pT < 1.5 GeV/c 1.5 < pT < 8 GeV/c

Low pT shape incompatible with constant virtual photon emission rate…

Enhancement of EM correlator at low mass, low pT? NEED HELP FROM THEORY!!

QuickTime™ and a decompressor

are needed to see this picture.



Exc

ess

*M (

A.U

).

NEW DATA COMING IN 2010

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Interactions within the plasma

Experimentalist’s simple minded picture

Strong coupling = interactions among multiple neighbors

Of course this must cause correlations within plasmaalso increases opacity

how is the energy loss mechanism affected? is the quark gluon plasma “black”?

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Iconic jet quenching (opacity) result



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Insights somewhat unsatisfying





S. Bass, et al.Phys.Rev.C79:024901,2009

Put 3 different energy loss schemes into common, realistichydrodynamic calculation

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We can do better!

Extend the pT range

Difficult for 0 because decay ’s merge in the

calorimeter Measuring instead of

0 is the solution

RAA remains flat to at least 22 GeV/c!

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Next step: constrain geometry: high-pT v2

arXiv:0903.4886 (Run-4

data)

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pT

NPart

RA

A

• Out-of plane RAA nearly flat with centrality at low pT

• In- and out-of-plane converge at high-pT (~10GeV/c)

Out-of-plane vs. in-plane

in-plane

intermediate

out-of-

plane

Carla Vale - PHENIX QM09

Run-7

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Calculations by S.Bass et al in arXiv:0808.0908

Differentiate among energy loss models!

Carla Vale - PHENIX QM09

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More differential yet: dijet reaction plane dependence

in-plane

out-plane

AwayPTY

0 πφs

π

π

PTY

= p

er-

trig

ger

yie

ld

Penetrating production in-plane

out-plane

π

π

AwayPTY

0 πφs

Tangential production

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Away side yield

Away side yields drop from in-plane to out-of-plane: jets do penetrate medium

Medium is not totally opaque

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Shocks? Medium spectrum

p+p

centralAu+Au

3<pt,trigger<4 GeV

pt,assoc.>2 GeV

Au+Au 0-10%

preliminary

STAR

Harder than inclusive, softer than jet

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Jet-medium interaction

jet

Jet suppressedmedium

medium

Centrality:40-45%

Central:5-10%

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-jet (-h) correlation: calibrated probe

p+p slope:

6.89 0.64

Au+Au slope:

9.49 1.37

fragmentation of tagged jets in/out of medium

Challenge: understand energy transfer to/from the medium! Coupling properties…

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Next step: full jet reconstruction



Gaussian filter algorithm optimize signal/background by focusing on jet core stabilizes jet axis in presence of background



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In ion collisions life is tougher



signalbackground

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In Cu+Cu


are needed to see this picture.QuickTime™ and a

decompressorare needed to see this picture.

Yikes! RAA flat to > 30 GeV/c pT



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Heavy quark energy loss (large!)

PRELIM.Run-4

Run-7

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

minimum-bias

Non photonic electrons

0,

Who ordered that?Mix of radiation + collisions (diffusion)

but collisions with what?AdS/CFT provides an answer, but…

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Not all energy loss is created equal!

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High meff large collisional energy loss

R. Kolevatov &

U.A. Wiedemann

arXiV:0812.0270

The “clumps”?b/c separation allows to test!

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Upgrades over next ~3 years

PHENIX Upgrades

Forward Calorimeter at = 1-3Correlate with mid-y h±

Silicon VTX, FVTX Tag displaced vertex for heavy quark decaysTrack charged hadrons in large acceptance

*In addition to RHIC-II luminosity upgrade x8

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Over next decade: entirely new questions

Precision jet probes of energy transport in medium What degrees of freedom?Heavy quark fragmentation modified?Theory + dynamics: qualitative quantitative

What is the screening length in strongly coupled QCD matter?Experiment: onium spectroscopy in pp, dAu, AuAuTheory: understand production & cold matter effects

Supplement silicon tracker to enhance momentum resolutionEnhance electron ID capabilities inner barrel compact calorimeter?

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Conclusion:

It could be that theorists’ dreams make for the experimenters’ nightmares…The really interesting stuff is hard to measure

Experimenters’ dream results are definitely the stuff of the theorists’ nightmaresWe really want to pin you downExtract properties of hot QCD matter by constraining

theory + phenomenology with data!

But for Al - we wish very sweet dreams!We’ll work hard for those sugarplums

HAPPY BIRTHDAYHAPPY BIRTHDAY

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backup slides

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Tag jet energy with direct photon

M. McCumber WWND ‘09

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Local Slopes of Inclusive mT Spectra

Data have soft mT component not expected from hadron decays

Note: Local slope of all sources!need more detailed analysis

Axel Drees34

Soft component below mT ~ 500 MeV:

Teff < 120MeV independent of mass

more than 50% of yield

Tdata ~ 120 MeV

Tdata ~ 240 MeV

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Mike Leitch - PHENIX QM09

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determined three different ways:• single electron spectra methods:

• cocktail subtraction• converter

• di-electrons

Muon measurement at forward rapidity is consistent

cc

bb

d h

eavy/d

y (

mb

)

Open Heavy Flavor

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b quarks and medium effects…

B meson spectra

e-h correlations totag D vs. B decays

b + c !

Oh oh!

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04/02/2009 Quark Matter '09 Y. Yamaguchi

Should modify low pT direct yield→ Evaluate using d+Au data.

Systematic errors on Run3 d+Au results are still large.At 2-3 GeV/c, data looks in agreement with pQCD calculation.

→ No modification of direct yield by nuclear effects?

Run 8 analysis underway: x30 statistics

37/12Nuclear Effects

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Both ridge & shoulder yields grow



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Away/near to ~ cancel acceptance



Shoulder and ridge have the same physics!See also Rudy Hwa, Jiangyong Jia recent talks

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From the bulk or jet-like?

arXiv:0712.3033

arXiv:0712.3033

Answer:it’s more like the bulk! QGP-like

PHENIX PRL 101, 082301 (2008)

pT spectra

Particle content

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(shear generallya phenomenonin crystals butnot liquids)

Are shocks in strongly coupled EM plasma.So sQGP could also support shockwaves

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In the most central collisions

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Quantifying the viscosity

Need:3-d viscous hydro calculationsPrecision dataMass dependence of v2

+ other observables for pT transport

pT (GeV/c)

v2/s ~ 0 - 0.8Recall: in ideal hydro mfp=0Conjectured /s bound: 1/4

Work is underway to control: initial state geometry gluon distribution

€

~ n p λ mfp

Romatschke & Romatschke, arXiv:0706.1522

PHENIX Preliminary

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p+p Au+Au (MB)Gluon Compton

q

g q

e+

e-

Dileptons at low mass and high pT

•m<2 only Dalitz contributions•p+p: no enhancement •Au+Au: large enhancement at low pT

•A real source virtual with v. low mass•We assume internal conversion of direct photon extract the fraction of direct photon

PHENIX Preliminary PHENIX Preliminary

1 < pT < 2 GeV2 < pT < 3 GeV3 < pT < 4 GeV4 < pT < 5 GeV

r : direct */inclusive *

Direct */Inclusive * determined by fitting each pT bin

( ) ( ) ( ) ( )eedirecteecocktaileedata MfrMfrMf ⋅+⋅−= 1

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direct photons via e+e-

for low mass, pT > 1 GeV/c

direct * fraction of inclusive *

(mostly , ) is real fraction

of (mostly , )

low mass and pT >> mee

dominated by decay of *

mee

hadron cocktail

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Virtual Photon Measurement

Case of Hadrons

Obviously S = 0 at Mee > Mhadron

Case of direct *

– If pT2>>Mee

2

Possible to separate hadron decay components from real signal in the proper mass window.

Any source of real can emit * with very low mass. Relation between the * yield and real photon yield is known.

α

SdNMM

m

M

m

dM

Nd

eeee

e

ee

e

ee

121

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3

22

2

2

22

⎟⎟⎠

⎞⎜⎜⎝

⎛+−=

S : Process dependent factor

( )3

2

222 1 ⎟⎟

⎠

⎞⎜⎜⎝

⎛−=

hadron

eeee M

MMFS

1=S

Eq. (1)

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Where does the lost energy go?

Radiated particles still correlated with the jet

Completely absorbed by plasmaThermalized?Collective conservation of momentum?

Excites collective response in plasmaShocks or sound waves?Wakes in the plasma?

Documents

Hot QCD Matter: An Experimenter’s Dream and Nightmare