high p t hadron correlation

1

High pT Hadron Correlation

Rudolph C. HwaUniversity of Oregon

Hard Probes 2006

Asilomar, CA, June 10, 2006

and No Correlation

2

A. Conventional scenario

Hard scattering high pT jet

hadron correlation

(usual conductor has resistance)

(superconductor has no resistance)

High pT hadrons high pT jet

correlation

B. Unconventional scenario

3

B. No Jet Correlation

1. and production up to pT ~ 6 GeV/c

2. Forward production at any pT

3. Large pT at LHC

A. Jet Correlation

pT1-pT2 1-2 1-2

near sideaway sideauto-correl

1

4

same sideSTAR

4 < pTtrig < 6GeV / c

pTassoc < 4GeV / c

5

Associated particle pT distribution

dNπp2dp2

trig =dp1p1

dNππp1dp1p2dp24

6

∫dp1p1

dNπp1dp14

6

∫p1 -- trigger

p2 -- associated

F4 =(TT+ST+SS)13(TT+ST+SS)24

k

q3

q

1

q4

q2

dNππp1dp1p2dp2

=1

(p1p2)2

dqiqii

∏⎡

⎣ ⎢ ⎤

⎦ ⎥ ∫ F4(q1,q2,q3,q4)R(q1,q3,p1)R(q2,q4,p2)

In the recombination model

6

Associated particle distribution in the recombination model

-- for only

Hwa & Tan, PRC 72, 057902 (2005)

STAR

4 < pTtrig < 6

7

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

in white paper

Remember p/ ratioAll in recombination/ coalescence model

Medium modified dihadron fragmentation function -- more relevant at higher pT.

Majumder, Wang, Wang nucl-th/0412061

S S -- fragmentation

T S

Jet tomography CGC forward production

All use fragmentation for hadronization -- but not reliable at intermediate pT

If proton production cannot be described by fragmentation at intermediate pT, how much trust can be placed on pion production by fragmentation?

Dp / D

TTT TT

8

A. Jet Correlation

pT1-pT2 1-2 1-2


1

2

9

Away side

4 < pTtrig < 6

suppression

enhancement

medium effect on away-side jet

Jet quenching

10

4 < pTtrig < 6

suppression

enhancement

Dijet fragmentation STAR, nucl-ex/0604018

8 < pTtrig <15

11

production in AuAu central collision at 200 GeV



Hwa & CB Yang, PRC70, 024905 (2004)

fragmentation

recombination

12

STAR dijet

4 8 12 16

4

8

12

0

pT(a

ssoc)

pT(trig)

dN

dΔφ0.2

0.1

13

Trigger-normalized fragmentation functionD(zT )

Trigger-normalized momentum fraction

zT =pT (assoc)pT (trig)

D(zT ) is measurable without direct knowledge of the parton energy.

X.-N. Wang, Phys. Lett. B 595, 165 (2004)

J. Adams et al., nucl-ex/0604018

14

STAR, nucl-ex/0604018



15

4 8 12 16

4

8

12

0

pT(a

ssoc)

pT(trig)

STAR dijet

zT=0.5-0.6

zT=0.8-0.9

Bielcikova PANIC 05

16

STAR claims universal behavior in D(zT)

fragmentation

violation of universal behavior due to medium effect ---- thermal-shower recombinationSuggestion: look for p/ ratio in this

region. Large if dominated by recombination.

17

A. Jet Correlation

pT1-pT2 1-2 1-2


1

2

3

18

Correlation on the near side

Δ and Δ distributions

STAR, PRL 95, 152301 (2005)

peaks

19

Chiu & Hwa, PRC 72, 034903 (2005)

hard partonshower

parton, leads to the trigger particle

energy loss converts to soft particles

At higher trigger momentum, the hard parton originate closer to the surface, so less energy is lost. Hence no pedestal.

hard parton

trigger hadron

At low trigger momentum, hard partons can originate farther in.

Δ

Those soft particles form the pedestal.

pedestal ΔT=15 MeV

20

A. Jet Correlation

pT1-pT2 1-2 1-2


1

2

3

4

21

Casalderrey-Solana, Shuryak, Teaney Mach cone

Dremin Cherenkov gluons

Ruppert, Muller color wake

Koch, Majumder, Wang Cherenkov radiation

Vitev jet quenching+fragm

.

.

Chiu, Hwa parton multiple scattering

Away-side distribution

22

Parton multiple-scattering model

Sample trajectories for 2.5<p(trig)<4, 1<p(assoc)<2.5

exit tracksabsorbed (thermalized) tracks

high pT parton

23

Away-side Δ distribution

-

PHENIX 2.5<p(trig)<4 parton

p=4.5

energy loss thermalized

Event averaged, background subtracted.

Cannot distinguish between 1-jet and 2-jet contributions (e.g., Mach cone)

A new measure proposed that suppresses statistical background event-by-event

Chiu & Hwa, nucl-th/0605054

Chiu’s talk in parallel session on Monday

24

A. Jet Correlation

pT1-pT2 1-2 1-2


1

2

3

4

5

25

Autocorrelation

Trainor (STAR) Jamaica workshop (2004)

QuickTime™ and a

TIFF (LZW) decompressorare needed to see this picture.

Consider an example in time series analysis

26

Correlation function C2 (1,2) =ρ2 (1,2)−ρ1(1)ρ1(2)

Treat 1,2 on equal footing --- no trigger

The only non-trivial contribution to near , would come from jets

θ− : 0 φ− : 0

A(θ−,φ−)

Define

θ−=θ2 −θ1φ−=φ2 −φ1

C2(1,2)

Fix and , and integrate over all other variables in

θ− φ−

A(θ−,φ−) =1

Rθ+

dθ+Rθ+

∫ C2 (θ+,θ−,φ−)Autocorrelation

No ambiguous subtraction procedure; only do as defined.

27

hard parton momentum k

Radiated gluon momentum q

two shower partons with angular difference

(a much larger set)

jet axis

q2

q1

x

yz

2

1

k

thermal partons

p2

p1

x

yz

θ1θ2

pion momenta (observable)

-

28

STAR data on Autocorrelation for central Au+Au at 130 GeV for ||<1.3, 0.15<pT<2 GeV/c

nucl-ex/0605021

NO trigger, no subtraction



Chiu & Hwa, PRC 73, 014903 (2006)

TS recombination in a jet with pT>3 GeV/c

dominated by soft partons

Δρρref

=C2 (

rp1,

rp2 )

ρ ref (rp1,

rp2 )

29

A. Jet Correlation

pT1-pT2 1-2 1-2


1

2

3

4

5




3. Large pT at LHC

30

and production at intermediate pT

For

strange-quark shower is very suppressed.

pT distribution of by recombination

31





s

hard parton scattering

fragmentation

If they are produced by hard scattering followed by fragmentation, one expects jets of particles.

There are other particles associated withφ and

Hwa & CB Yang, nucl-th/0602024

recombination s s φ0

sss −recombination

32





Select events with or in the 3<pT<6 region, and treat them as trigger particles.

Predict: no associated particles giving rise to peaks in Δ,

near-side or away-side.

We claim that no shower partons are involved in production, so no jets are involved.

33

Δ

(1/N

trig)

dN

/d(Δ)

background

SignalAu+Au top 5%

trigger (pT>3 GeV/c) in Au+Au

?

charged hadrons

34

A. Jet Correlation

pT1-pT2 1-2 1-2


1

2

3

4

5




3. Large pT at LHC

35

Forward production of hadrons

PHOBOS, nucl-ex/0509034

Without knowing pT, it is not possible to determine xF

Back et al, PRL 91, 052303 (2003)

' = η − ybeam

36

Theoretically, can hadrons be produced at xF > 1?It seems to violate momentum conservation, pL > √s/2.

In pB collision the partons that recombine must satisfy

xii∑ <1

p

B

But in AB collision the partons can come from different nucleons

BA

xii∑ >1

(TFR)

In the recombination model the produced p and can have smooth distributions across the xF = 1 boundary.

37proton-to-pion ratio is very large.





proton

pionHwa & Yang, PRC 73,044913 (2006)

: momentum degradation factor

38

BRAHMS, nucl-ex/0602018

39

TT

TS

TTT

xF = 0.9

xF = 0.8 TFR

xF = 1.0

40

no shower partons involved no jets involved

no jet structure no associated particles

Hwa & Yang, nucl-th/0605037

Thermal distribution fits well

41

A. Jet Correlation

pT1-pT2 1-2 1-2


1

2

3

4

5




3. Large pT at LHC

42

and p production at high pT at LHC

New feature at LHC: density of hard partons is high.

High pT jets may be so dense that neighboring jet cones may overlap.

If so, then the shower partons in two nearby jets may recombine.

2 hard partons

1 shower parton from each

p

43

The particle detected has some associated partners.

There should be no observable jet structure distinguishable from the

background.

10 < pT < 20 GeV/c

That is very different from a super-high pT jet.

But they are part of the background of an ocean of hadrons from other jets.

A jet at 30-40 GeV/c would have lots of observable associated

particles.

44

Proton-to-pion ratio at LHC -- probability of overlap of 2 jet cones

single jet

Rp / : 50

Hwa & Yang nucl-th/0603053

45

We predict for 10<pT<20 Gev/c at LHC

• Large p/ ratio

• NO associated particles above the

background

46

Summary




3. Large pT at LHC

A. Jet Correlation

pT1-pT2 1-2 1-2


Jet fragmentation at high andpTtrig pT

assoc

Recombination at pTtrig , pT

assoc < 6GeV / c

No trigger bias, need more data at high pT

There’s jet quenching, but not necessarily fragmentation

?

?

?When recombination dominates over fragmentation, B/M ratio can be very large, and there would be no jets, no jet structure and no correlation above background.

high p t hadron correlation

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