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High p T -h Correlations Using the PHENIX Detector Matthew Nguyen, Stony Brook University

High p T g -h Correlations Using the PHENIX Detector

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High p T g -h Correlations Using the PHENIX Detector. Matthew Nguyen, Stony Brook University. Why Direct Photon Correlations?. “Leading Order” Picture Exact Momentum Balance w/ Away-Side Jet Compton Dominance p+p : Measure Gluon Distribution Function A+A: - PowerPoint PPT Presentation

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Page 1: High  p T g -h Correlations Using the PHENIX Detector

High pT -h Correlations Using the PHENIX Detector

Matthew Nguyen, Stony Brook University

Page 2: High  p T g -h Correlations Using the PHENIX Detector

IAA

2/8/2008Quark Matter 20082

Why Direct Photon Correlations? “Leading Order” Picture

Exact Momentum Balance w/ Away-Side Jet

Compton Dominance p+p: Measure Gluon Distribution

Function A+A:

Calibrated Probe of Energy Loss More Sensitive Probe than single particle

spectra, Di-Hadron Correlations The Golden Channel for Jet Tomography?

the fine print Fragmentation photons Initial state effects (Shadowing , kT) Still sensitive to geometry / space-time

evolution Quark vs. Gluon Energy Loss

q

qg

γ q

q g

γ

Compton AnnihilationDirect Photon Processes at LO

X.N. Wang, Z. Huang PRC55 (1997) 3047-3061

Page 3: High  p T g -h Correlations Using the PHENIX Detector

3

-h Correlations in PHENIX

Direct photon cross section in p+p

PbSc

ElectromagneticCalorimeters

PbGl

2/8/2008Quark Matter 2008

Drift Chamber

h-h Correlations in Au+Au

Page 4: High  p T g -h Correlations Using the PHENIX Detector

2/8/2008Quark Matter 20084

PYTHIA 6.1

Statistical Subtraction Method Large background from meson decay Direct S/B increased by jet

suppression in central Au+Au collisions

0-h decayed via MC to get decay -h -h measured in p+p R = N(inclusive) / N(decay) Can perform a statistical

subtraction of per-trigger yields:

Method well-suited for high multiplicity environment (Au+Au)

11 1

direct inclusive decayRY Y Y

R R

Where Y = # hadrons per photon

pT [GeV]

Photon Sources in PYTHIA

R

R measurement in Au+Au 200 GeV

Page 5: High  p T g -h Correlations Using the PHENIX Detector

QM2006 Direct Photon-Hadron Results

2/8/2008Quark Matter 20085

At QM2006 PHENIX showed “proof of principle” level -h results Run 5 p+p @ 200 GeV

Subtraction method is robustNear-side disappearance consistent with +jet expectationsAway-side comparable to hadron triggered case

Away-side yields in Au+Au are suppressed compared to p+p-h measurement is statistics limited

Run 4/5 p+p/Au+Au @ 200 GeV

Page 6: High  p T g -h Correlations Using the PHENIX Detector

New Results Increased Precision

2/8/2008Quark Matter 20086

*Note: Run 6, 7 Absolute Efficiencies not finalized – In Arbitrary Units

1/N

trig

dN

/d

(A.

U.)

Systematic error dominated by uncertainty in Rand -h contribution

Page 7: High  p T g -h Correlations Using the PHENIX Detector

Subtraction technique works over wide range of pT!

Direct Photon-Hadron Correlations in p+p

2/8/2008Quark Matter 20087

[rad]

1/N

trig

dN

/d

(A.

U.)

p T, h

adro

n

pT, photon

Page 8: High  p T g -h Correlations Using the PHENIX Detector

Photon Recoil Jets

2/8/2008Quark Matter 20088

1st approximation -- recoil jets similar to hadron triggered jets in p+p <Q2> of hard scattering should be lower due to z bias in hadron-triggered correlations kT effect need not be the same – needs to be measured triggered yields sensitive to the FF

-h measurement

h-h measurementpT, photon

Per-

Trig

ger

Yiel

d (A

.U.) Run 6 p+p @ 200 GeV

Page 9: High  p T g -h Correlations Using the PHENIX Detector

– DELPHI, Eur. Phys. J. C13,543, (1996)-- OPAL Z.Phys. C 69, 543 (1996)

Run 3 -h

– Quark FF--Gluon FF

PRD 74 (2006) 072002

Vacuum Fragmentation Function

Run 5 Direct -h

Preliminary

1/Nt

rig

dN/d

x E( A

.U.)

Baseline for modified FF in Au+Au

0-h xE distributions were shown to poorly discriminate between quark (– ) and gluon

(--) fragmentation due to 0 trigger bias (z<1)

2/8/2008Quark Matter 20089

p+p @ 200 GeV

2triggerT

triggerT

partnerT

Ep

ppx

)(zDdxdNppE

jetT

triggerT

In “leading order” picture:

Direct photon xE distributions should be sensitive to underlying(quark) fragmentation functionUse Run 6 data to reduce errors

Page 10: High  p T g -h Correlations Using the PHENIX Detector

Au+Au Run 7 Direct Photon-Hadron Correlations (7 < pT, < 9)

2/8/200810 Quark Matter 2008

Little or no near-side production associated with direct photon triggers Away-side yields indicate large jet suppression in +jet channelWorking to reduce systematics and more data to analyze (~2X)

0

Au+Au analysis is challenging: Additional sources of uncertainty from underlying event subtraction (ZYAM), elliptic flow subtraction and 0 combinatoric background

Page 11: High  p T g -h Correlations Using the PHENIX Detector

The pT Landscape

2/8/2008Quark Matter 200811

Direct Photon S/B (R)0 Combinatoric S/BpQCD Accuracy

pT, hadron

pT, photon

Run7 Au+Au 200 GeV

Jet S/B

Rate

Near/Away-Side > 1

Run7 Au+Au 200 GeV

Near/Away-Side ≈ 1

12-15 X 3-5 GeV7-9 X 3-5 GeV

Page 12: High  p T g -h Correlations Using the PHENIX Detector

Near-Side Fragmentation

2/8/2008Quark Matter 200812

Near-Side yield small but non-zero for z 0Expect near-side contribution from photon fragmentationSystematic errors for -h correlations large on the near-side

-h (h-)measurement

h-h measurement Per-

Trig

ger

Yiel

d (A

.U.)

z0.10.3 0.25 0.2

Run 6 p+p @ 200 GeV

pT, photon

Page 13: High  p T g -h Correlations Using the PHENIX Detector

Fragmentation Photons

2/8/2008Quark Matter 200813

q

qg

γ

Bremsstrahlung diagrams

q

qgγ

gFragmentation diagrams must be included at NLO to cancel divergences |z| < 1 for fragmentation photons, but how much less?Dparton/photon(z) not well constrainedMay oppose either quark or gluon jetsImportant for LHCSuppressed by E-loss

I. Vitev, 2007 RHIC-AGS Meeting

Rate of fragmentation photons may be increased by presence of medium partons

InducedBremstrahlung

--RHIC– LHC

Page 14: High  p T g -h Correlations Using the PHENIX Detector

h- Correlations

2/8/2008Quark Matter 200814

10-

6

X10-6

X10-3

X10-3

h-inclusive

h-decay

h-direct

Idea: By triggering on a hadron and looking for near-side direct photon partners one can measure the fragmentation photon yield directly

Measure hadron - inclusive and hadron - decay correlations

Decay corr’s are made by tagging0 and by invariant mass

Must know tagging efficiency and false tagging rate precisely dominant source of systematic uncertainty

2.5 < pT, < 3.5

Page 15: High  p T g -h Correlations Using the PHENIX Detector

h- Correlations II

2/8/2008Quark Matter 200815

Page 16: High  p T g -h Correlations Using the PHENIX Detector

Outlook

2/8/2008Quark Matter 200816

Direct photon-hadron correlations are moving from the proof of principle stage towards the precision measurement stage Finalizing Run 6 p+p for increased precision and broader

kinematic range compared to previous results Analyzing Run 7 Au+Au data set and working to reduce

systematic uncertainties Baseline measurements of -h and h- correlations are

being made to ensure that theory is well under control Fragmentation component measured – Nfrag ≈ 0.1 Ninc Away-side jet suppression in the +jet channel appear

strong PHENIX is currently working on Run 6 and Run 7 p+p and

Au+Au -h correlations at high pT

Page 17: High  p T g -h Correlations Using the PHENIX Detector

Backup Slides

2/8/200817 Quark Matter 2008

Page 18: High  p T g -h Correlations Using the PHENIX Detector

2/8/2008Quark Matter 200818

Constructing the Decay Background To start: Construct (0) - h

from 0-h Problem is that tagging the

0’s introduces a bias <pT> tagged = <pT>

true Developed a pair-by-pair

correction procedure

Per-Trigger Yield from 0):

07

5

( , )T T TP p p dp

Correction Procedure:

Decay kinematics reproduced by Monte Carlo include energy resolution effects and acceptance (P)This is just for 0’s, What about contributions from other mesons? This approach implicitly assumes they have the same associated yield

00 0

00

0

( )d, , ,T

hhTT T TT TT p YPY pp p p ppp

000( ) (( )TrueTagged )

TT T

d dNdNdp

Nd dpp

– Analytic Form – w/ Detector Response

Sample MC weight function:

Page 19: High  p T g -h Correlations Using the PHENIX Detector

2/8/2008Quark Matter 200819

-h CorrelationsRun 5 p+p @ 200 GeV

Parent-h

PRC 75, 024909 (2007)

First measurement of -h correlations at RHIC!

()-h Yields generated by same procedure as (0)-h

Combinatorial background under h peak subtracted using a sideband procedure

•-h•(h)-h

Page 20: High  p T g -h Correlations Using the PHENIX Detector

Zharkarov –JETP Lett. 80 (2004)

Turbide et al., Phys. Rev. C72 (2005)

2/8/2008Quark Matter 200820

QGP Induced Photon Production

InducedBremstrahlung

Jet Conversion– Hard partons re-scatter off medium partons via Compton process

Induced Bremsstrahlung – Rate of fragmentation photons increased by presence of medium partons

Both effects still speculative Are there experimental signatures? pT, v2 dependence (see other talks in session) h- correlations

Jet Conversion

Page 21: High  p T g -h Correlations Using the PHENIX Detector

Prompt Photon Spectrum

2/8/2008Quark Matter 200821

Page 22: High  p T g -h Correlations Using the PHENIX Detector

p+p Integrated Yields

2/8/2008Quark Matter 200822

Page 23: High  p T g -h Correlations Using the PHENIX Detector

kT Effect

2/8/2008Quark Matter 200823

kT measurement for 0-h

• kT = 2.5 GeV• kT = 0

kT Effect: Net momentum of di-jets(and -jets) due to initial state radiation

xE slopes for -h from PYTHIA

kT measurements the di-jet channelshow a large effect -- 2.5 – 3.0 GeV

PYTHIA shows that kT changes the xE distribution significantlykT measurement in -h is needed

PRD 74 (2006) 072002

Page 24: High  p T g -h Correlations Using the PHENIX Detector

Gluon Fragmentation Functions

2/8/200824 Quark Matter 2008

Compilation by Hirai et al.Phys Rev D75 (2007) 94009

Gluons contribute significantly to single inclusive measurements at RHIC However different parameterizations give divergent estimations of gluon contribution e.g., AKK FF’s indicate much higher gluon contribution than previous fits

Inclusive production from AKK FF

Page 25: High  p T g -h Correlations Using the PHENIX Detector

Rg from Run 4 Au+Au 200 GeV

2/8/2008Quark Matter 200825

Page 26: High  p T g -h Correlations Using the PHENIX Detector

2/8/2008Quark Matter 200826

Using p+p data in FF‘sSTAR, Phys Lett B, 637 (2006) 161

200 GeVs

STAR identified hadron spectra constrain the gluon FF at large zUse twoparticle correlations to constrain g p at all z?

New set of fragmentation functions include p+p (and DIS) data and obtain very different parameterizations of the gluon FF’s

Phys. Rev. D75, 114010 (2007).

De Florian, Sassot, Stratmannhep-ph:0707.1506

Page 27: High  p T g -h Correlations Using the PHENIX Detector

recoil jets more likely to be a quark jet than 0 recoil jets Quark and gluon jets may have different particle content p/ on the away-side of vs. 0 recoil sensitive the FF’s

0

0

1/

/ ( recoil)/ ( re

2 + 1/ 2

coi

/ ( recoil)/ ( recoi

l)

l)

2 1

p pq q g g

pq

pq q

pg

q

g

D D D Dpp D D

D D DD pp

2/8/2008 Quark Matter 200827

Identified Hadron Correlations

For definiteness assume:

Quar

k/Gl

uon

Cont

ribut

ion

q

qg

γ

Double ratio gives partial cancellation of systematics due to particle identificationand direct photon subtraction

Kretzer Acta Phys. Polon. B36, 179 (2005)

qDD )recoil(

gq DDD 2/12/1)recoil ( 0 &

In this simplified picture particle ratios can be written in terms of FF’s:

pT()

Well constrained from e+e-Quark

Gluon

Page 28: High  p T g -h Correlations Using the PHENIX Detector

2/8/2008Quark Matter 200828

-Identified h Results (Under Construction)

PHENIX5 < pT

< 7 X 1 < pTh < 2

Hadron efficiencies not finalized Systematic errors are large but will most cancel in ratio So far run 5 only Run 5 + 6 should enable a significant measurement (integrated over away-side)

Arbi

trar

y N

orm

aliza

tion

- identified hadron correlations can be performed in the range 5 < pT

< 12 X 1 < pTh <2

This corresponds to about 0.1 < z < 0.2

Page 29: High  p T g -h Correlations Using the PHENIX Detector

2/8/2008Quark Matter 200829

R from p+p CollisionsIn p+p there is no published Rbut deriveable from 0 and spectraFor pure power law: N(0)/N() = (n-1)/2; n = 0 slope parameter

0

0total decay( ) /

1( /

1)2

T

T

dN dpRdN dp

n

Quoted from x-sec analysis

Page 30: High  p T g -h Correlations Using the PHENIX Detector

2/8/2008Quark Matter 200830

kT effect affects:–away-side jet width–Inclusive high pT x-sections–Recoil spectra (dN/dxE)

Trigger Biases and the kT effect

kT Effect: Acoplanarity of di-jets(and -jets) due to initial state radiation

Insensitivity of dN/dxE to true FF is the interplay of two trigger biases:

Trigger Bias #1: Trigger requirement

biases the near side FF to high z Does not affect away-side jet Absent in g-h

kT measurement for di-jets

Trigger Bias #2: Longitudinalcomponent of kT biases jet CM indirection of the trigger for pT,t >

pT,a Does affect the away-side jet Present in -h

kT described by NLO, Why do we need to measure it?

Page 31: High  p T g -h Correlations Using the PHENIX Detector

2/8/2008Quark Matter 200831

Gluon Fragmentation

The gluon fragmentation function has large uncertainties! Is there an independent test of gp?

Page 32: High  p T g -h Correlations Using the PHENIX Detector

2/8/2008Quark Matter 200832

pQCD Limitations

at 200 GeVp p s+ =

Data Fit

Auranche 2006

Agreement w/ data is remarkable!Better than jet cross-sections

Closer: Agreement only 20% Not good enough to constrain kT

Page 33: High  p T g -h Correlations Using the PHENIX Detector

2/8/2008Quark Matter 200833

kT in the -jet channel

M. Begel, Nucl. Phys. B 79, 244 1999;Ph.d thesis (1998)

Tk s Measurement for -0 at lower sIndependent of process

Page 34: High  p T g -h Correlations Using the PHENIX Detector

2/8/2008Quark Matter 200834

Page 35: High  p T g -h Correlations Using the PHENIX Detector

2/8/2008Quark Matter 200835