Identifying the underlying physics of the ridge via 3particle correlations in STAR

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Identifying the underlying physics of the ridge
via 3-particle ??-?? correlations in STAR

• Pawan Kumar Netrakanti (For STAR Collaboration)
• Purdue University

2
Outline

• Ridge phenomenon and theoretical models
• Motivation for 3-particle correlation in ?
• Analysis techniques
• Results
• Summary

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Ridge Phenomena
STAR, PRL 95 (2005) 152301
AuAu
dAu
4
Theoretical model interpretations
1)In medium radiation longitudinal flow
push N.Armesto et.al Phys.Rev.Lett. 93(2004)
242301
2) Transverse flow boost S.A.Voloshin,
Phys.Lett.B. 632(2006)490 E.Shuryak,
hep-ph0706.3531
4) Momentum Kick C.Y. Wong hep-ph0712.3282
3)Turbulent color fields A.Majumder et.al Phys.
Rev. Lett.99(2004)042301
5) Recombination between thermal and shower
partons R.C. Hwa C.B. Chiu Phys. Rev. C 72
(2005) 034903
Can we discriminate between these physics
interpretations? ? 3-particle Correlation in ?
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Motivation for 3-particle correlation in ?
T Trigger particle A1 First Associated
particle A2 Second Associated particle
STAR TPC acceptance for 3-particle correlation in
? (?lt1 and full azimuth)
Dh1 A1-T Dh2 A2-T
1) Jet fragmentation in vacuum

• In medium radiated gluons still collimated
• 4) Combination between jet fragmentation and
  diffused gluons

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Analysis techniques

• AuAu and dAu at ?sNN 200 GeV
• Trigger 3ltpTlt10 GeV/c, ?lt1
• Associated 1lt pTlt3 GeV/c, ?lt1
• Select both associated particles
• Near Side ?? lt0.7
• Away Side ?? - ?lt0.7
• Mixed events to obtain background
• (a) Min-bias events with same centrality
• (b) ?(primary vertex z) lt 1 cm
• (c) Same magnetic field configuration

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2-particle correlation
AuAu ZDC central (0-12) triggered data,
3ltpTTriglt10 GeV/c, 1ltpTAssolt3 GeV/c
Black Raw signal Pink Mixed-event
background Blue Scaled bkgd by ZYA1 Red
Raw signal bkgd
Dh acceptance corrected
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3-particle correlation background
correlated

• Raw ? Raw ?Raw signal
• Raw ? Bkg ?Hard-Soft
• Bkg1 ? Bkg1
• Bkg1 ? Bkg2

Soft-Soft
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3-particle correlation (??lt0.7)
3ltpTTriglt10 GeV/c 1ltpTAssolt3 GeV/c
Shaded sys. error. Line v2 uncer.
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Comparison (Projections)
3ltpTTriglt10 GeV/c 1ltpTAssolt3 GeV/c
?? lt0.7
STAR Preliminary
0.7ltRlt1.4
STAR Preliminary
AuAu 0-12 is higher than dAu and AuAu 40-80
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Comparison (in pT)
?? lt0.7
STAR Preliminary
Run 4 3ltpTTriglt10 GeV/c 1ltpTAssolt3 GeV/c
STAR Preliminary
Run 7 ETTriggt5.5 GeV 3ltpTAssolt5.5 GeV/c
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Summarizing.
3ltpTTriglt10 GeV/c, 1ltpTAssolt3 GeV/c, ??lt0.7

• The ridge is approximately uniform or broadly
  falling with ??.
• No significant structures along diagonals or axes.

Ridge is uniform event by event.
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Potential for away-side analysis
STAR Preliminary
3ltpTTriglt10 GeV/c 1ltpTAssolt3 GeV/c ??-? lt0.7
Another tool to study Ridge
3ltpTtriglt4GeV/c 1.0ltpTassolt1.5GeV/c
Study the ridge with the help of Di-hardon
correlation w.r.t. reaction plane. Aoqi Feng
(Parallel Talk QM08)
STAR Preliminary
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Summary

• Three-particle correlation in ??-?? can
  potentially identify the underlying physics of
  the ridge.
• Correlation peak at ????0, characteristic of
  jet fragmentation, is observed in dAu, AuAu
  40-80 and central AuAu 0-12.
• The peak sits atop of pedestal in central AuAu.
  This pedestal, composed of particle pairs in the
  ridge, is approximately uniform or broadly
  falling with ?? in the measured acceptance. No
  significant structures along diagonals or axes.
• Significant step forward in experimental study.
  Quantitative theoretical calculations are needed
  for further understanding.

Thank you
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Back Up
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Motivation for 3-particle correlation in ?
STAR TPC acceptance for 3-particle correlation in
? (?lt1 and full azimuth)
T Trigger particle A1 First Associated
particle A2 Second Associated particle
In medium radiation Longitudinal flow
Jet fragmentation in vacuum
N.Armesto et.al Phys.Rev.Lett. 93(2004) 242301
Transverse flow boost
Turbulent color field.
Momentum Kick C.Y. Wong hep-ph0712.3282
S.A.Voloshin, Phys.Lett.B. 632(2006)490 E.Shuryak,
hep-ph0706.3531
A.Majumder et.al Phys. Rev. Lett.99(2004)042301
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Comparison with pTTrig
1ltpTAssoclt3 GeV/c ?? lt 0.7
STAR Preliminary
3ltpTTriglt4 GeV/c
STAR Preliminary
4ltpTTriglt10 GeV/c
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Comparison with pTAssoc
3ltpTTriglt10 GeV/c ??lt0.7
1ltpTAssolt2 GeV/c
STAR Preliminary
2ltpTAssolt3 GeV/c
STAR Preliminary
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Soft-Soft and Hard-Soft terms
3ltpTTriglt10 GeV/c 1ltpTAssolt3 GeV/c ??lt0.7,
0-12 AuAu
Soft-Soft Term
STAR Preliminary
STAR Preliminary
STAR Preliminary
Hard-Soft Term
STAR Preliminary
STAR Preliminary
STAR Preliminary
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3-particle correlation
3ltpTTriglt10 GeV/c 1ltpTAssolt3 GeV/c
STAR Preliminary
dAu 0-100
AuAu 40-80
AuAu 0-12
STAR Preliminary
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Projections For all regions
3ltpTTriglt10 GeV/c 1ltpTAssolt3 GeV/c
STAR Preliminary
dAu 0-100
AuAu 40-80
STAR Preliminary
AuAu 0-12
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2-particle Correlation
3ltpTTriglt10 GeV/c 1ltpTAssolt3 GeV/c R1 ??lt0.7

STAR Preliminary
STAR Preliminary
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3-particle Signal and Background
3ltpTTriglt10 GeV/c 1ltpTAssolt3 GeV/c R1
??lt0.7
Raw?Raw
Jet?Jet
Soft?Soft
Hard-Soft
STAR Preliminary
STAR Preliminary
STAR Preliminary
Background
Raw Signal
Final Signal ?
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3-particle correlation (??lt0.7)
3ltpTTriglt10 GeV/c 1ltpTAssolt3 GeV/c
Shaded sys. error. Line v2 uncer.