jet probes at rhic

1/13/06 Frif Power Corr. Wkshop – Justin Frantz

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Jet Probes at RHIC

Justin FrantzStony Brook University

FRIF Workshop on QCD Power CorrectionsJanuary 13, 2006


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The Heavy Ion/QGP Mission• …in the context of this workshop…• See q’s/g’s outside of pQCD• (Often delicate) NP effects in

pQCD jet event shape… • Lattice QCD predicts

deconfinement phase change → a Quark Gluon Plasma

• Specifically, observe collective behavior of many q/g‘s in this plasma?

• “Larger Scale” observables– Temperature, Pressure, Density…

• Also how does it modify particle physics?– Chiral symmetry restoration?– Color screening melts J/Psi? – S modified @ finite Temp.

pion gas

Energy Density / T4

Lattice Calculation

T/TC

TC estimates ~ 170 MeV


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RHIC• The Relativistic Heavy Ion Collider: QGP Search

• Collides AuAu, pp, dAu, CuCu, … at energies √s = , 20, 62, 130, 200, 400, 500 GeV

• Polarized proton beams, Spin program → probe gluon spin structure

NYCRHIC

STAR


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Highlights of Basic Results• Runs 1/yr 2001-2006… interesting yield of results: • Requisite Densities • Thermalization: success of statistical models w/ T

in the critical range• Hydrodynamic Flow: Too large for ideal QGP but

evidence against hadron gas– Baryon/Meson flow vs pT follows (common!) quark

number scaling instead of mass scaling– Hydro-models with only hadrons fail to reproduce– Hadron cross sections (esp. strange) too small to

build it up • Large Baryon Excess at soft-hard transition

energies (p/ ≈ 1)– Recombination of quarks promising way to explain

• “Strongly interacting QGP” (sQGP)– perfect liquid

Jargon:

CentralPeripheral

Npart participating nucleons

(%)


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Hard Scattering Probes

• Hard scattering in Au+Au → pQCD (works well in p+p)• Insert into HI medium, observe differences• E.g. high pT hadron and direct photon production• High pT spectral shapes clearly power law as expected

for all centralities • And same shape— & ~ same as p+p

Au+Au → direct + X Au+Au → + X p+p → + X


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RAA

• = Ratio of A+A/ scaled p+p• Scaling factor: number of equiv

N+N crossings (Ncoll)• FLAT• Prediction: jet energy loss leads

to suppression effect for fragmentation products

• But not for EM direct photons• Energy loss models depend on

dN/dygluons

– Many models: LPM effect, Modified D(z)

• → Density!• E ~ E was surprise (just E

shift - like NP?)


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Elliptic Flow (v2)Transverse Plane

dN/d

pT 3-4 GeV/c

PHENIX

Incl. Hadrons

• In semi-central events initial state spacial anisotropy → momentum space

• v2 – second Fourier harmonic w/ w.r.t the (measured) global reaction plane

• 2 Kinds:– At low pT (soft), hydrodynamic (of

quarks we believe)– At high pT, energy loss of jet partons

traversing the matter


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Di-Jet Di-Hadron Correlations

Nearside Awayside

P(A,B)P(A)P(B)=

STAR

PHENIX

200 GeV pT

trig 5-10, pT

assoc 1-2 GeV/c

p+pAu+Au

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5

4

3

2

1

• Huge Soft background (dN/d ~ 1000) • Jet Finding difficult (Impossible?) in HI environment• Rely on 2-particle opening angle (azimuthal)

correlations

• 2 categories in pT: “Trigger” (high pT) & “Assoc”

h-h


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Experimental Method: Flow Subtraction

• Assume 2-source correlation Flow + Jet

• Main source of systematic error• b0 determined by “Zero Yield At Minimum” (ZYAM),

other methods

Note scale

PHENIX 0–h pTtrig 5-10 GeV/c pT

assoc 3-5 GeV/c


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First Results (High x Low pT)

• Jet suppression of awayside shape

• Nearside per trigger yield same

• Absolute NS yield suppressed

• At low pT, “recovered”

w/ pT,assoc 0.2 GeV/c

4-6 x 2-4 GeV/c

0

0

0.0

0.1

0.2


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High x High “Re-emergence”

• Low/No Background (Flow Sub. Unimportant)

• Clear emergence of jet structure at the away-side

• Away side width consistent with constant

• Away side yield suppressed

8 < pT(trig) < 15 GeV/cpT(assoc)>6 GeV/c

STAR Preliminary


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Really Weird! Low x Low

• Large modication on the awayside!

• Cone/ Volcano shape• Medium response to the

jets?• Explained by:

– Mach cone sound wave– Color cerenkov cone– Bending jets

• If Mach Cone, size → vsound → direct measure of matter property

0

STAR

PHENIX

2.5-4 GeV/c trig

1-2.5 GeV/c assoc


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How Robust is The Volcano?

In plane

• Still questions about robustness (oversubtraction in v2?)

• Look @ trigger w.r.t. RP• Over subtraction→ opposite

effect


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IAA etc.

• Looking for best way to analyze extracted jet (-integrated) yields

• Good parameter – pT, zT,xE ? • IAA : ratio of integrated per-trigger yield in

A+A/p+p• How does it fit together with RAA? Better

quantity? Still open

STAR Awayside

IAA (≈ RAA !)

An Eloss model: Wang et. al.Phys. Lett. B579 (2004) 299–308.


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Direct -Jet

• In central Au+Au high suppression effect → higher purity of direct

• Complement of jet-jet Eloss

• Probes interior of collision volume

• E proxy for Ejet • Extraction of direct-jet from

inclusive correlations underway

S/B

Measured Direct Signal/Bkg(Decay bkg)

Central Au+Au 200 GeV

__ pQCD w/ had. suppression

≈p+p 200 GeV

dir-jetjet-jet


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Jet Event Shapes @ RHIC• Good things @ RHIC

– Not just A+A: p+p, p+A, polarized p+p (& lots!)– Dectectors optimized for soft physics (Good E,p resolution/ PID above 50

MeV…) in addition to hard• Bad things

– As h+h, central rapidity restriction– Ambiguity of Q/√s12 – In Au+Au…well… e.g. no jet finding (jets modified!)…etc…

• From your standpoint– For p+p, best source of low Q? (mid- x ranges like Tevatron/LHC, but

lower s) – Au+Au Interesting modification to hadronization – could Power Correction

frameworks say anything sensible? How about in d+Au ?• From HI experimentalist standpoint

– Want to use jets to probe medium: event shapes are a natural goal

What am I doing @ this workshop?


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Energy Energy Correlations

• Instead of muliplicity correlations, energy flow, correlations (“combining” info in all pT bins)

• No jet finding neccesary• auto-convolution of JCEF →other shape observable as

correlations?• Sensitive to S , NP effects (plasma?)

–


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EEC in h+h?

• EEC never measured in h+h?• Structure Fn complication x1x2 distribution of Q• But theory work says it should be possible

– Basham, Et al: Use Tranverse EEC()– Gale et. al. QGP multiple scatt. → large effects to

TEEC (hep-ph/9406208)• Measured and used in DIS

@ HERA (1 S.F.)


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EEC in A+A

• 2 EEC’s in A+A? sQGP has its own? (beyond flow?…)

• Large flow harmonic contribution

• Extract Jet EEC– Large underlying ET

(shape distorting) – Combinatoric pair subtraction– PHENIX ½ solid ang. → missed ET even p+p

Lokhtin et al., hep-ph/0402108


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Effect of Inaccurate ET

• Pythia study of EEC (200 GeV p+p)

ET (GeV)

Q (GeV)Q (GeV)

In PHENIX

EE

C(

)

A.U

. Ratio to Blue (Arbitrary Norm)

EEC w/ ET in Denom

EEC w/ true Q in Denom

EEC w/ real Phx Acc

EEC w/ Phenix ET Denom

Q = 10-15 GeV/c


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Idea: EEC Direct-Gamma Events

• Similar to the DIS t-channel

• Does it probe the same properties? (g/q jet)

• Ever done before?• Two varieties

– only charged particles-E only – Including neutral (w/ direct )– Is one better?

PYTHIA direct events E 10-15 GeV

2E TRIG

(GeV)

Q (GeV)

EEC() A.U.

PYTHIA direct events


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Conclusions

• Interesting time at RHIC• Jet/Hard observables continue to provide key

information• We see jet modification!• Can we use “traditional” event shape?• …& same perturbative inspired frameworks? • Need help from theorists

– What can be calculated?– What can be learned?


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Flat RAA? (Energy Loss)

• Example of using hard scattering probes


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Understanding RAA(Npart, )– Can we find a consistent description of centrality and dependence of RAA?

– Define with

– Perform survival-weighted average over all production points, emission directions.

– Survival weighting:

ldlLeff )( 0

0)(

21 neffsurv Lkp


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Energy Loss Calculations

jet probes at rhic

Documents

high pt hadron

believeat high pt

recoveredw pt

low pt soft

high pt assocnearside

x au au p0 x p p p0

jet energy loss

jet probes