Jet Quenching Status and Perspectives

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Jet Quenching Status and Perspectives
Urs Achim Wiedemann CERN TH and SUNY Stony Brook
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Jet Quenching AuAu vs. dAu

• Initial state enhancement

• Final state suppression

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The RHICness of Hard Probes

• Jets
• identified hadron specta
• D-,B-mesons
• Quarkonia
• Photons
• Z-boson tagged jets

The range
,x, luminosity
Basic strategy
Abundant yield at collider energies (allows
differential study of exp. signal) robust
large signal (medium effect larger than TH
uncertainty) Basis for controlled
experimentation controlled TH interpretation.
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Time scales hadronization vs.thermalization
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Parton Propagation in Dense Matter
Solve Dirac equation for partonic projectile in
external color field of the medium

• Leading order O(E0) scattering determined by
  eikonal Wilson line

During scattering, transverse coordinates are
frozen, color rotates
2. Leading energy correction transverse
Brownian motion
Furry approximation
Wiedemann, NPB582 (2000) 409
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Example gluon production in qA
Kovner Wiedemann, PRD 64 (2001) 114002
Kovchegov Mueller 1998
Target average
Bertsch Gunion spectrum Brownian
Motion
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The medium-modified Final State Parton Shower
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The medium-modified Final State Parton Shower
Baier, Dokshitzer, Mueller, Peigne, Schiff
(1996) Zakharov (1997) Wiedemann (2000)
Gyulassy, Levai, Vitev (2000) Wang ...
Medium characterized by transport coefficient

• pt-broadening of shower

• energy loss of leading parton

Salgado,Wiedemann PRD68014008 (2003)
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Energy Loss in a Strongly Expanding Medium

• In A-A collisions, the density of scattering
  centers is time-dependent

Salgado, Wiedemann PRL 89, 092303 (2002)

• Dynamical Scaling Law
• same spectrum obtained for
• equivalent static transport coefficient

• Calculations for a static medium
• apply to expanding systems

Rescaled spectrum
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Quenching Weights probability of energy loss
BDMS (2001)
Quenching weight defines medium-modified
fragmentation.
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The fragility of leading hadrons

• Why is RAA pT-independent?
• Trigger bias more severe for large pT

Eskola, Honkanen, Salgado, Wiedemann NPA747
(2005) 511, hep-ph/0406319
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The produced matter is opaque - why?
R. Baier, NPA 715 (2003) 209
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(No Transcript)
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How can we better gauge hard probes?
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Parton energy loss depends on parton identity
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Disentangling Color Charge vs. Mass Dependence at
the LHC
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Tracing heavy quarks with electrons at RHIC
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Jets in Heavy Ion Collisions at the LHC
A. Accardi et al., hep-ph/0310274 CERN TH
Yellow Report

• Experiments will detect jets above background
• How can we characterize the medium-modification
  of these jets
• above background ?

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Transverse Jet Heating
Salgado, Wiedemann, Phys. Rev. Lett. 93 042301
(2004)

• Energy fraction in fixed jet cone

• Multiplicity within small jet cone
• broadens strongly

. kt
weakly dependent on medium
vacuum
medium
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Longitudinal Jet Heating
Borghini,Wiedemann, hep-ph/0506218

• Medium expected to soften
• and increase the longitudinal
• multiplicity of true jets.

• Softening in qualitative agreement
• with triggered particle correlations.

• Awaits detailed test at the LHC.

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Jets in pionic winds and partonic storms
If medium shows strong collective flow, what are
additional measurable consequences?
Armesto, Salgado, Wiedemann, Phys. Rev. Lett.
93 (2004) 242301
Hard partons are not producedin the rest frame
comoving withthe medium
Flow effect
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Instead of a Summarysome directions, which
motivate the next exp. and th. steps

• WHY study the microscopic mechanism of high-pt
  hadron suppression?
• to characterize properties of dense QCD matter
• to understand onset of parton thermalization in
  a particularly
• well-controlled EXP TH setting
• to get novel access to the dynamics of
  hadronization by using the
• medium as tool to test it

• HOW study parton propagation and energy loss in
  the medium?
• improve theory (recoil, finite energy
  corrections, connection of BDMPS
• transport parameter to fundamental QCD
  predictions, )
• extend range of applicability (sensitivity to
  parton identity, to
• multiplicity distributions, to high-pt particle
  correlations )

• Connect study of medium-modified parton
  propagation to other collective phenomena in
  heavy ion collisions?
• independent test of collective flow?
• hadrochemical composition of jet remnants?