Elastic, Inelastic and Path Length Fluctuations in Jet Tomography

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Elastic, Inelastic and Path Length Fluctuations
inJet Tomography
Re The single electron puzzle at RHIC

• Simon Wicks
• Hard Probes 2006
• Work done with William Horowitz, Magdalena
  Djordjevic and Miklos Gyulassy
• arXiv nucl-th/0512076 and in preparation

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Introduction The single electron puzzle

• Pion suppression predictions seem to work well

DGLV predictions Djordjevic, Gyulassy, Vogt,
Wicks Phys Lett B 63281-86 (2006)
but (entropy constrained) pQCD radiative only
FALSIFIED by e- data.
GLV predictions for pions compared to PHENIX
data Vitev prediction plot from T. Isobe
nucl-ex/0605016
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Possible Solutions

• Fit the data with free parameters, explain the
  magnitudes later
• Improve understanding of pQCD production spectra
  (but still cannot match data with entropy
  bounded radiative energy loss alone)
• Use novel non-perturbative techniques to explain
  extra charm / bottom quenching
• Fully explore all perturbative energy loss
  techniques.
• Q Can pQCD explain the pion and electron
  suppressions at RHIC, or do we have to resort to
  solution III above?

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What have we swept under the rug?

• Elastic energy loss
• - Same order of magnitude as radiative energy
  loss for the kinematic region of interest.

M. Mustafa, Phys. Rev. C72014905 (2005)
SW, W. Horowitz, M. Djordjevic M.
Gyulassy, nucl-th/0512076
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Elastic energy loss

• Thoma-Gyulassy (TG) vs Braaten-Thoma (BT) as
  estimate of uncertainty of leading log
  approximation
• Romatschke-Strickland infinite time / Djordjevic
  finite time calculations lie TG for bottom, BT
  for charm (note unphysical energy gain at low pt
  for bottom in BT)

• Finite time effects on elastic energy loss SMALL
• (see poster by A.Adil, nucl-th/0606010, talk and
  nucl-th/0603066 by M.Djordjevic, nucl-th/0604040
  by X-N Wang)
• Interference between collisional and radiative
  energy losses left as open question. See later

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Path length fluctuations

• Our model NOT fragile, NOT surface emission (nor
  is DGLV radiative alone).
• See parallel talk by W. Horowitz on Wednesday.
• Various uses of fixed lengths L5-6fm.
• We find a hierarchy of fixed lengths fit the
  full geometrical calculations.

• No a priori justification for any fixed length
  without doing the full numerically intensive
  calculation.
• (if a fixed length can fit the full geometry at
  all)
• V important for gluons and consistency of
  electron and pion predictions.

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WHDG extended theory
Ideal Our model
Production All orders pQCD NLO pQCD (FONLL for LHC spectra) (large uncertainty in magnitude, small uncertainty in the power law of the tail)
Geometry Propagate through evolving hydro simulation Realistic Woods-Saxon nuclear density Jets produced TAA Propagate through Bjorken expanding ?part
as Running Fixed as0.3 (large uncertainty as energy loss strongly dependent on as)
Energy loss mechanism Collisional and radiative in same theoretical framework Incoherent addition of DGLV radiative and leading log TG / BT collisional
NOTE Using realistic dNg/dy1000
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Results

• RHIC
• RHIC theoretical uncertainties
• LHC

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Results RHIC
Charm, bottom -gtElectrons
Gluons, u,d -gtPions
Note kt smearing, EMC neglected here.
Good agreement with pions, improved agreement
with e- than for (entropy constrained) radiative
only.
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Results RHIC - Uncertainty

• Sources of uncertainty
• Fixed as0.3 approximation
• Shape of spectra, fragmentation (does not
  affect RAA significantly)
• Magnitude of spectraie c / b ratio in
  contribution to e-

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Results RHIC Uncertainty in as

• as 0.4 improves e- fit, over predicts pion
  quenching

need a fully running coupling calculation to
reduce theoretical uncertainty.
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Results RHIC uncertainty in c/b ratio

• Uncertainty in charm spectrum and c / b
  contribution to e-
• A quick estimate of uncertainty shift entire
  charm cross-section up / down.

Armesto, Cacciari, Dainese, Salgado,
Wiedermann hep-ph/0511257
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Results LHC (1)

• Energy loss for high pT jets at LHC dominated
  by radiative

but collisional energy loss is still a 25
effect.
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Results LHC (2)
Partonic RQ(pT) (for one sample value of dNg/dy
2900)
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Results LHC (3)
Pion RAA(pT) (for two sample values of dNg/dy
1750, 2900)
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Conclusion

• Important effects to include
• Elastic energy loss
• Path length fluctuations Geometry
• For stronger conclusions, we need
• Theory
• Elastic and inelastic in the same theoretical
  framework
• Include effect of fully running coupling
• Theory or experiment
• Better understanding of charm and bottom
  productioneg measure D mesons directly
• Further applications
• V2
• Multi-particle correlations
• More LHC work

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(end of talk)(go England!!)