Understanding Jet quenching and Mediumresponse via dihadron correlations

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Understanding Jet quenching and Medium-response
via dihadron correlations
Jiangyong Jia Stony Brook University BNL
Thanks Fuqiang Wang for inputs
Medium
Jet
?
Mostly based on PHENIX paper nucl-ex/0801.4545
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Deers antler
??? The four-unlikes Pere davids deer
Horses head
Donkeys tail
Cows hoof
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Jet quenching medium response

The mechanisms for single hadron production are
important for dihadron and vice versa
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pT Scan evolution of jet quenching and medium
response
Head region (suppressed jet) Shoulder region
(hump)
Near region (jetridge)
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pT Scan evolution of jet quenching and medium
response
Increase partner pT
Dip develops
Yield suppressed
Yield enhanced
Increase trigger pT
Jet reemerges
Can all the features fit in the four-components
picture?
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Away-side pT Scan
RHS Head_yield/shoulder_yield (area normalized)
RHSgt1
RHSlt1

• 1ltpTa,b lt 4 -gt RHSlt1 -gt Shoulder region
  dominant!
• pTa or b gt5 -gt RHSgt1 -gt Head region dominant!
• pTa or b lt 1 -gt RHS1

Competition between Head (Suppression) and
shoulder (enhancement) Shoulder is important up
to 4 GeV/c
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Near-side pT Scan

• For low pT region
• AuAu shape in Dh is broader than for pp
• AuAu yield is enhanced, especially at large Dh.
• For high pT region
• Dh shape/yield is similar between AuAu and pp

The ridge component is important to 4 GeV/c Jet
fragmentation takes over at higher pT.
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Spectra slope at shoulder region
arxiv0705.3238 nucl-ex Phys.Rev.C77011901,2008
Mean-pT at intermediate pT (1ltpTblt 5)
4ltpTalt5
3ltpTalt4
2ltpTalt3
Shoulder slope 0.45 GeV/c, independent of
trigger pT
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Near-side slope
John Chen poster
J. Putschke QM06
Jet Ridge
0.44 GeV/c
0.36 GeV/c

• Ridge slope is slightly harder than the shoulder

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Connection between ridge and shoulder

• Ridge and shoulder persist up to pTa,pTb4 GeV/c
• They have similar slope (ridge is slightly harder)

• Ridge Shoulder energies are roughly balanced in
  a given Dh slice.

0.5lt?????0.7
John Chen poster
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Energy dependence for shoulder ridge

Head200 GeV ? Head17.2 GeV Shoulder200
GeV ? 2x Shoulder17.2 GeV Near200 GeV ? 8
x Near17.2 GeV
At SPS Smaller jet quenchingStronger Cronin
-gt Less suppression in Head Smaller medium
component -gt Smaller ridge/ Shoulder
hlt0.35
0.1lth-hCMlt0.7
Df
RAA at SPS is totally different, dominated by
Cronin effect Ridge is almost gone at SPS
energy, the shoulder due to kT broadening?
Energy scan is important!
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Quantify the medium modifications

per-trig yield
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Iaa vs pT
High pT trigger
IAA1
Near side
IAA
IAA RAA
Away side
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Dilution of soft triggers
IAA not symmetric wrt trigger/partner pT
selection
Near-side
Since one particle is high pT, hadron pair come
from jets emitted near surface The second
particle in the pair also comes from surface.
But the low pT triggers in per-trigger yield
include all soft hadrons.
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Dilution to ridge

Scale up the AuAu by 1/IAA(pTa), then subtract pp
Near-side
consistent with pp jet roughly flat ridge
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Another example Dilution effect in dAu

Small x
Large x
Triggers h0, 3 GeV/c partners h3, 0.2 GeV/c
Fuqiang
CGC suppress num. of forward-scattering
Per-trigger yield p-p 1/2
Au-side 1/3 d-side 2/3
Df
Dilution effect due to trigger counting! Do not
need recombination
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Geometrical bias?

Low pT correlated pairs Bulk emission
High pT correlated pairs Surface emission
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Geometrical bias?
Low pT correlated pairs Bulk emission
High pT correlated pairs Surface emission

• Low pT triggers may from cone/ridge surface bias
  reduced!
• Each side contain both ridge and cone
  contributions

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Jet contribution _at_ low pT

Quantify the jet contribution in two-particle
momentum space Help understand the particle
production mechanism
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Near side pair yield modification JAA
Reach same level (RAA) at High pTb

• Approximately scales with pTsumpTapTb (since
  coming from same jet)

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JAA _at_ away-side head region

• Low pT pair yield is not suppressed!
• Away-side JAA RAA2 at large pT.
• away-side jet IAA inclusive jets RAA

JAA(pTa,pTb)
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3-p correlation telling the same story?

D1.1
D1.36
Exclusive process selects very different
kinematical region and phase space
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RP dependence at low pT

• Rich dependence patterns of medium response on
  trigger orientation
• PHENIX show jet function, need to x
  (12v2trigcos2Df) to compare.
• V2/V4 systematics are clearly important!! (enter
  linearly)

M. McCumber, A.Feng, Session VIII, Feb. 5
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Models for medium response

• Production mechanisms of associated hadrons
• New particle creation feedback of shower gluons,
  cerenkov gluons
• Local heating bending jet, momentum kick, Mach
  cone, backsplash, Glasma bending, coupling to
  transverse or longitudinal flow etc.
• Residual correlations with geometry elliptic
  flow (subtracted), correlation between radial
  flow boosted beam and surfaced emitted transverse
  jet.
• Easier to generate large yield by pickup from the
  bulk (since no particle production is required)
• We know the pair yield is enhanced at low pt.
• Supported by the property of the ridge/cone (PID,
  slope etc)
• Mechanisms for ridge and shoulder may well be
  related.

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Final remarks Jet quenching medium response

• Jet _at_ High pT, surface biased, eloss mechanism is
  constrained indirectly from those with little
  eloss
• Medium response _at_ Low pT, no surface bias,
  directly sensitive to energy loss process.
• The energy loss mechanism affects characteristics
  of medium response, example
• collisional/radiative lt-gt momentum kick/gluon
  feedback.
• Different medium response mechanism may require
  different energy loss scenario.
• Energy loss and energy dissipation to the medium
  are modeled separately. But there shouldnt be a
  strict separation of scale, especially for
  intermediate pT.
• Need a unified framework that include both jet
  quenching medium response, and can describe
  correlation data at all pT.

More details M. McCumber, Session VIII, Feb.
5 H.Pei, A.Adare, SessionIX, Feb.8 Poster 23,24
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Backup
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Constraining the eloss dynamics
Case I
Case II
Shift to left
Absorption Downward shift

• Absorption
• Longer path for away-side jet, IAAltRAA
• Independent of spectra shape
• Left shift
• Stronger energy loss, IAAgtRAA
• Flatter away-side spectra IAAltRAA
• Data suggests IAA RAA
• Flatter spectra compensated by bigger energy loss
  
• By combing IAA and RAA, one gain some sensitivity
  on energy loss.

nucl-ex/0703047
dn/dpt (1/pt)9 for single spectra dn/dpt
(1/pt)5 for away-side spectra
50 bigger
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High pT jet fragmentation
H. Zhang, J.F. Owens, E. Wang and X.-N. Wang ,
PRL 98(2007)212301

• Observed jet are those do not suffer much
  energy loss.
• Near-side surface emission
• Away-side tangential/punch-through emission.
• IaaRaa, consistent with energy loss calculation

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Low pT medium response to jet

• Away-side strongly modified shape and yield
• Suppressed jet (head region) medium-induced
  component (Shoulder region)
• Near-side elongated structure in Dh,
  enhancement in yield.
• Surface Jet medium-induced component (ridge)

STAR