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Photon-Jet Correlations at RHIC. Saskia Mioduszewski Texas A&M University. 18 July, 2007. Outline. What can be learned from g -jet measurements? How to measure? Current Status of Measurement at RHIC. Dominant. g. q. γ. q. g. γ. q. g. q. Bremsstrahlung. Why g -jet?. q.

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Photon-Jet Correlations at RHIC


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photon jet correlations at rhic

Photon-Jet Correlations at RHIC

Saskia Mioduszewski

Texas A&M University

18 July, 2007

outline
Outline
  • What can be learned from g-jet measurements?
  • How to measure?
  • Current Status of Measurement at RHIC
why g jet

Dominant

g

q

γ

q

g

γ

q

g

q

Bremsstrahlung

Why g-jet?

q

γ

γ

q

“Golden Probe” of energy loss - calibrated probe of jet energy - X.-N. Wang et al.

Gluon jet vs. quark jet energy loss – compare g-jet to p0-jet (in g-jet, the jet will mostly be from quarks) - need to understand the surface bias to interpret data !

g

q

g

q

Compton

Annihilation

what can be learned
What can be learned?
  • Ultimate goal is to understand energy loss mechanism
  • Complementary to single particle spectra and di-jets
  • No surface bias for trigger particle, different surface bias for g-jet coincidence
single particle spectra what have we learned
Single-Particle Spectra – What have we learned?

Hadrons are suppressed by factor ~5, Photons are not

single particle spectra what have we learned1

PHENIX p0 Spectrum

PHENIX preliminary

Fractional “effective” energy loss Sloss ~ 20% in most central Au+Au collisions

Single-Particle Spectra – What have we learned?

Hadrons are suppressed by factor ~5, Photons are not

PHENIX, Phys. Rev. Lett. 96, 202301 (2006)

di jets through hadron hadron correlations

Escaping Jet

“Near Side”

Lost Jet

“Far Side”

pedestal and flow subtracted

Di-Jets through Hadron-Hadron Correlations

“Disappearance of away-side jet” in central Au+Au collisions

4 < pT,trig< 6 GeV/c, 2< pT,assoc< pT,trig

0-5%

STAR, PRL 90 (2003) 082302

reappearance of away side jet
“Reappearance of away-side jet”

With increasing trigger pT, away-side jet correlation reappears

STAR, Phys. Rev. Lett. 97 (2006) 162301

Higher pT Jet

“Near Side”

“Punch-through” Jet?

reappearance of away side jet1
“Reappearance of away-side jet”

With increasing trigger pT, away-side jet correlation reappears

STAR, Phys. Rev. Lett. 97 (2006) 162301

Tangential emission?

surface bias of di jets

Renk and Eskola, hep-ph/0610059

BDMPS-style energy loss + evolving bulk system

Surface Bias of Di-Jets?

STAR, Phys. Rev. Lett. 97 (2006) 162301

8 < pT,trig< 15 GeV/c

8 < pT,trig< 15 , 4< pT,assoc< 6 GeV/c

what can be learned1

q

g

What can be learned?
  • Di-jets suffer surface bias of trigger jet, punch-through of away-side (or only tangential emission)
  • g-Jet  trigger photon has no bias, but existence of away-side jet creates a (different) bias

 Measurement of % transmission as a function of true jet energy

challenging measurement
Challenging Measurement
  • Trigger photon measured with electro-magnetic calorimeter
  • Large background from hadronic decays (p0, h)

PHENIX, Phys. Rev. Lett. 94, 232301 (2005)

  • Background sources of photons (hadronic decays) suppressed in central Au+Au collisions
g jet analysis in au au collisions
g-jet Analysis in Au+Au collisions

Thomas Dietel, Quark Matter 2005

challenging measurement1
Challenging Measurement
  • Trigger photon measured with electro-magnetic calorimeter
  • Large background from hadronic decays (p0, h)
  • Background signal is di-jet (p0-jet)
  • Subtract from inclusive signal
  • Need large-statistics data set for g-jet measurement
statistical measurement of g jet yields
Statistical measurement of g-jet yields
  • Measure inclusive g-jet correlation function
  • Measure p0-jet (h-jet) correlation function
  • Construct resulting gdecay-jet correlation taking into account decay kinematics
  • Subtract gdecay-jet from ginclusive-jet

 Result is gdirect-jet

phenix g jet in p p
PHENIX g-jet in p+p

J.Jin, QM 2006

PHENIX Preliminary

PHENIX Preliminary

Comparison to PYTHIA – verification of method

direct g h yields
Direct g-h Yields

Run 5 p+p @ 200 GeV

M. Nguyen, APS 07

  • Signature small near-side correlation signal apparent
  • Yield sensitive to h contribution at the near-side
  • New h corrected results consistent with QM result within systematic error
  • Still room for some fragmentation contribution

9-12 X 1-2 GeV/c

5-7 X 1-2 GeV/c

7-9 X 1-2 GeV/c

9-12 X 2-5 GeV/c

5-7 X 2-5 GeV/c

7-9 X 2-5 GeV/c

phenix g jet in au au collisions

1/NtrigdN/dDf

Df(rad)

PHENIX g-jet in Au+Au collisions

Black: Au+Au Red: p+p

J.Jin, QM 2006

cu cu g direct h vs p 0 h jet yields
Cu+Cu gdirect-h+/- vs. p0-h+/- jet yields

A. Adare, WWND 2007

per-trigger jet pair yields:

systematic from Rg

systematic from subtraction method

distinguishing direct photons from p 0

Opening angle (radians)

pT (GeV/c)

Distinguishing direct photons from p0
  • Segmentation of calorimeter towers in STAR (Dj,Dh) = (0.05,0.05)  2 decay photons hit same tower starting pT ~ 5 or 6 GeV/c
  • Segmentation in PHENIX ~ 0.01 radians

Opening angle of p0 as a function of pT

distinguishing direct photons from p 01
Distinguishing direct photons from p0
  • Reject clusters that look like 2 close photons (from p0 decay) from shower shape
  • Retain sample of correlations that are gdirect-jet “rich”
  • Estimate remaining contamination from p0-jet
  • Measure and subtract p0-jet away-side yield
distinguishing single photons from 2 decay photons in star
Distinguishing single photons from 2 decay photons in STAR

Shower-max detector

(Dh,DF)~(0.007,0.007)

  • Hamed, Collective Dynamics 2007
star g jet in p p

p0

g

p0 bin

mixed bin

photon bin

STAR g-jet in p+p

Subhasis Chattopadhyay, QM 2006

-- Improved p0/g separation using shower profile in SMD

star g jet in p p1
STAR g-jet in p+p

Comparison to HIJING p+p –

verification of method

Ettrigger from 8.5GeV/c to 10.5 GeV

Subhasis Chattopadhyay, QM 2006

next steps
Next Steps
  • Do similar analysis for Au+Au collisions as was done in p+p and d+Au
  • Challenge within large-multiplicity background
  • Run-7 results coming soon
  • Results must be interpreted together with di-jet results and/or within model to take surface bias into account
summary
Summary
  • Di-Jets’ surface bias  results indicate jets are either transmitted with negligible energy loss or absorbed completely
  • Photon-Jet Measurement will complement the di-jet for more complete probe
  • A significant (statistically and systematically) g-jet Measurement in Au+Au is needed
  • Need a great deal of statistics!
  • Stay tuned for the results from Run-7…. Increase in statistics over Run-4 Au+Au > factor of 10