Understanding jet quenching and medium response via dihadron correlations

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Understanding jet quenching and medium response
via dihadron correlations
Jiangyong Jia Stony Brook University BNL

• Interplay between jet quenching medium
  response
• The origin of triggers/pairs contributing to the
  medium response
• Connection between near- and away-side medium
  response

Tamura Symposium on Heavy Ion Physics Nov. 20-22
UT at Austin
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Using single jets and dijets as probe

pp
Jet1
??
Jet2
??

• Single hadron yield vary pT
• Correlated hadron pairs shape and yield
• vary Df, Dh, pT1, pT2.

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Using single jets and dijets as probe

pp
?
Jet1
?
?
??
Jet2
??
AuAu
??
??
away
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Four components

• Near-side surface jet medium (ridge)
• Away-side suppressed jet medium (the cone)

• Jet fragmentation dominates high pT
• Medium response dominates low pT (lt4 GeV/c)

Low pT
High pT
Competition of jet quenching and medium response
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pT Scan evolution of jet quenching and medium
response
Phys. Rev. C 78, 014901 (2008)
Result of the variation of the four components
with pT
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pT Scan jet quenching and medium response

Head region (suppressed jet) Shoulder region
(Cone)
Near region (jetridge) project in Dh
Study the pTa , pTb dependence of the four
components

• RHS(pTa,pTb), D(pTa,pTb), s(pTa,pTb)
• Yield(pTa,pTb), IAA(pTa,pTb) in
• three regions

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Yield(pTa,pTb) in three Df regions
Near
Shoulder
Head
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IAA(pTa,pTb) in three Df regions

• High pT jet like.
• Low pT enhancements are due to ridge and cone.

Detailed interplay between jet and medium
Near-side
Away-side
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Jet and medium
Jet strength depends on both hadron pT,
pTapTb Transition region pTapTb6-8 GeV/c
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Compare ridge and cone

• Ridge and cone important to pTa,pTb4 GeV/c.

Near-side
Away-side
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Away-side shoulder spectra slope

• Shoulder slope 0.45 GeV/c, independent of
  trigger pT and centrality, and harder than
  inclusive.

Mean-pT at intermediate pT (1ltpTblt 5)
4ltpTalt5
3ltpTalt4
2ltpTalt3
arxiv0705.3238 nucl-ex Phys.Rev.C77011901,2008
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Near-side ridge spectra slope
J. Putschke QM06
Ridge

• Ridge slope is universal and slightly harder than
  the shoulder

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PID composition of ridge and cone
Near-side
Away-side

• Their particle compositions are similar to bulk.

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Compare ridge cone

• Ridge and cone important up to pTa,pTb4 GeV/c
• They have similar slope (ridge is slightly
  harder)
• Their particle compositions are similar to bulk.

Are ridge and shoulder related?
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What constitutes the triggers? PP

• Jet fragmentation is important to rather low pT
• pQCD calculation describe hadrons spectra done to
  2 GeV
• Large fraction of soft pairs show jet-like
  correlation.

2-3 x 2-3 GeV/c
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What constitutes the triggers? AuAu

• Intermediate pT particles are not jet-like.
• Less suppression and large v2.
• Strong dependence on flavor

Not simple jet fragmentation Soft hadrons, jet
medium response etc
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Per-trigger yield

• Per-trigger yield is useful if triggers comes
  fragmentation,
• But origins of triggers are complicated at pT lt 4
  GeV/c.
• Per-trigger yield cant be compared with pp
  directly.

Low pT triggers may originate from the whole
overlap
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Dilution by soft triggers
High pT trigger
Low pT trigger
Near side
IAA
5-10 x 2-3 GeV/c IAA1 2-3 x 5-10 GeV/c IAAlt1
Non-jet triggers dilute the high pT per-trigger
yield
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Dilution Reaction Plane dependence

• We often plot per-trigger yield as a function of
  angle between trigger and RP.
• These triggers may not come from jet
  fragmentation
• They have their own large v2 (gtgt jet quenching
  limit), thus per-trigger yield may not be good
  for jet tomography.

3ltpTtriglt4GeV/c 1.0ltpTassolt1.5GeV/c 20-60
STAR
Should study the pair yield vs. angle
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Pair yield modification

• Pair yield in AuAu normalized by Ncoll scaled
  pp pair yield.

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Pair yield modification

• Energy scale is controlled by pTsumpTapTb
• Low pT pair yield is not suppressed!
• Pair yield scale faster than Ncoll at low pTapTb
• Medium response important up to pTsum7 GeV/c

Near-side
Away-side
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Source of pairs at intermediate pT

jet-jet
medium-medium
jet-medium
nucl-ex/0806.1225

• Most models include only jet-jet and jet-medium
  contribution.
• The medium-medium contribution (triggering on the
  medium) could be large, in the limit of RAA ? 0,
  it dominates.

We investigate the role of medium-medium pairs
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Simulation set up
nucl-th/0310044

• Jet absorption picture loose all energy in a
  single interaction

• Glauber modeling of AuAu (Woods-Saxon). Generate
  dijets according to rNcoll (x,y) with random
  direction, then swim the dijet through a medium
  with density ? rNpart (x,y)

• Chose k0.7 to reproduce ltfgt RAA 0.22 in 0-5
  AuAu collisions.

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Reproduce the centrality dependence
nucl-th/0310044

• Can reproduce the centrality dependence of RAA
  and IAA

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Simulation setup

• The quenched jets are converted into jet-induced
  medium particles.

Surviving jet
Medium response to quenched jet

• We consider 1ltpTlt4 GeV/c as a single bin and
  choose
• Jet multiplicity ltNjgt 1 (roughly
  corresponds to 6 GeV/c jet).
• Medium multiplicity ltNmgt2 (account for
  enhancement)

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Centrality dependence

• Jet-Jet decreases with Npart
• Medium-medium increases with Npart
• Jet-medium first increase then decrease with
  Npart.

Geometry determines the relative contributions of
three types of pairs jet-jet lt jet-med lt med-med
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Jet-Jet and Jet-Medium term

• Jet Kinematics are chosen to qualitatively match
  the data.
• Jet fragmentation width 0.3 rad, kT smearing
  width 0.4 rad, accept 30 away-side jet pairs in
  Dh.
• Medium response hadrons appear at D 1.1, with a
  width of 0.3 rad.
• Concentrated at 0, p, p?D.

This step is trivial, but what does it imply for
medium-medium contribution?
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Medium-Medium term

• Both jets are converted into hadrons emitted at
  angle D from original jet direction. Pairs peaks
  at 0, p, ?2D, p ? 2D.

And they come from the Mach cone of the same
jet!!!
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Connection between ridge and cone

• If only consider jet-medium contribution, pairs
  at the near-side and away-side are different.
• But medium-medium pairs are symmetric between the
  two sides.
• Near- and away-side pairs will have identical
  properties.
• If medium-medium pairs are elongated
  longitudinally, they will end up as ridge (but
  they are really the pairs from Mach cone).

medium-medium
jet-medium
Mach cone
ridge
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How about 3-p correlation?
jet-med-medjet-jet-med appears in off-diagonal
and along-diagonal But med-med-med triplets do
not show a clear off-diagonal component. (kinemati
cs are different from jet-med-med)
The interpretation of 3-p is complicated when
triggering on the medium response!
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Pair v2

• Quenched jets should have negative v2.
• But large emission angle w.r.t the jet direction
  smears and changes the sign of v2.

V2quen - v2surv
Jetall JetsurvJetquen
0v2all v2survv2quen
No jet tomography when triggering on medium
response?
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Conclusion

• Correlation patterns are consistent with
  competition between jet fragmentation and medium
  response.
• Similarity between the near-side ridge and the
  away-side cone.
• Understanding the medium response requires
  knowledge of the origins of the particles
  involved in the pair.
• Both the spectra and correlation results suggest
  we are triggering on medium response at
  intermediate pT.
• The correlation among medium response particles
  may dominate the pair yield at intermediate pT.
• They may naturally explains the similarity
  between ridge and cone
• Triggering on medium may complicate the
  interpretation of 2 3 particle correlation and
  jet tomography study