11/1/06william horowitz 1 jet quenching at rhic and the lhc william horowitz columbia university...
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11/1/06 William Horowitz
Jet Quenching at RHIC and the LHC
William HorowitzColumbia UniversityNovember 1, 2006
With many thanks to Simon Wicks, Azfar Adil, Magdalena Djordjevic, and Miklos
Gyulassy.
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11/1/06 William Horowitz
Outline
• What a difference the LHC makes!– HUGE disagreement over LHC
predictions– Why there’s a difference– Why we’re right (hopefully robustly)
• P0, P0, P0…
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11/1/06 William Horowitz
LHC Predictions
WH, S. Wicks, M. Gyulassy, M. Djordjevic, in preparation
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11/1/06 William Horowitz
K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. A747:511:529 (2005)
A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38:461-474 (2005)
BDMPS-Based Predictions
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11/1/06 William Horowitz
Suppression of BDMPS– LHC predictions require an extrapolation from
RHIC• Their pQCD-based controlling parameter qhat must
be nonperturbatively large to fit RHIC data-pQCD gives qhat = c 3/4, where c ~ 2; they require c ~ 8-20 for RHIC
-Needed because radiative only energy loss (and Pg0 > 1?); R = (1/2) qhat L3
K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. A747:511:529 (2005)
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11/1/06 William Horowitz
BDMPS Extrapolation to the LHC
• Importance of medium density– qhat ~ scatterers
– EKRT used => LHC ~ 7 RHIC
– qhat goes from 14 at RHIC to 100 at the LHC!
– Almost all the energy loss is in (-1) part of P()
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11/1/06 William HorowitzWH, S. Wicks, M. Gyulassy, M. Djordjevic, in preparation
Asymptopia at the LHCAsymptotic pocket formulae:Erad/E 3 Log(E/2L)/EEel/E 2 Log((E T)1/2/mg)/E
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11/1/06 William Horowitz
LHC Production Spectra
• Much flatter power law and asymptotic jet energies allows for easy interpretation of LHC predictions
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11/1/06 William Horowitz
LHC Conclusions• LHC appears to reach jet
asymptopia where pocket formulae hold
• Lack of fragility means pions will make a good, independent probe of the density
• With current predictions, the momentum dependence of RAA at LHC should distinguish between BDMPS and GLV type loss models
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11/1/06 William Horowitz
A Quick Update on Fragility
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11/1/06 William Horowitz
Jets as a Tomographic Probe
• Requires:– Theoretical understanding of
underlying physics (esp. quenching mechanisms)
– Mapping from the controlling parameter of the theory to the medium density
– Sensitivity in the model + data for the measurement used (FRAGILITY???)
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11/1/06 William Horowitz
Recall the BDMPS-based Plots
K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. A747:511:529 (2005)
A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38:461-474 (2005)
The lack of sensitivity needs to be more closely examined because (a) unrealistic geometry (hard cylinders) and no expansion and (b) no expansion shown against older data (whose error bars have subsequently shrunk
(a) (b)
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11/1/06 William Horowitz
Our Jets Probe the Volume and are Sensitive to the Medium
WH, S. Wicks, M. Gyulassy, M. Djordjevic, in preparation
S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076
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11/1/06 William Horowitz
BDMPS with Realistic Geometryis Not Fragile!
T. Renk and K. J. Eskola, hep-ph/0610059
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11/1/06 William Horowitz
Heavy Quark Puzzle
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11/1/06 William Horowitz
Before the e- RAA, the picture looked pretty good:
– Null Control: RAA()~1
– Consistency: RAA()~RAA()
– GLV Prediction: Theory~Data for reasonable fixed L~5 fm and dNg/dy~dN/dy
Y. Akiba for the PHENIX collaboration, hep-ex/0510008
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11/1/06 William Horowitz
But with Hints of Trouble:
• Theory v2 too small
• Fragile Probe?
A. Drees, H. Feng, and J. Jia, Phys. Rev. C71:034909 (2005)(first by E. Shuryak, Phys. Rev. C66:027902 (2002))
K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. A747:511:529 (2005)
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11/1/06 William Horowitz
What Can Heavies Teach Us?
• Provide a unique test of our understanding of energy loss– Mass => Dead Cone => Reduction in E
loss
Bottom Quark =
(Gratuitous Pop Culture Reference)
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11/1/06 William Horowitz
Entropy-constrained radiative-dominated loss FALSIFIED by e- RAA
Problem: Qualitatively, RAA~ e- RAA
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11/1/06 William Horowitz
Inherent Uncertainties in Production Spectra
M. Djordjevic, M. Gyulassy, R. Vogt, S. Wicks, Phys. Lett. B632:81-86 (2006)
How large is bottom’s role?
– Vertex detectors could de-convolute the e- contributions
N. Armesto, M. Cacciari, A. Dainese, C. A. Salgado, U. A. Wiedemann, hep-ph-0511257
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11/1/06 William Horowitz
The BDMPS-Z-WS Approach
• Increase to 14 to push curve down
• Fragility in the model allows for consistency with pions
N. Armesto, M. Cacciari, A. Dainese, C. A. Salgado, U. A. Wiedemann, hep-ph-0511257
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11/1/06 William Horowitz
What Does Mean?
We believe it’s nonperturbative:– = .5 => dNg/dy ~ 13,000
R. Baier, Nucl. Phys. A715:209-218 (2003)
“Proportionality constant ~ 4-5 times larger than perturbative estimate”
K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. A747:511:529 (2005)
“Large numerical value of not yet understood”
U. A. Wiedemann, SQM 2006
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11/1/06 William Horowitz
Is this Plausible?Renk says No
T. Renk and K. J. Eskola, hep-ph/0610059
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11/1/06 William Horowitz
Our Results
• Inclusion of elastic decreases the discrepancy
• Direct c and b measurements required to truly rule out approaches
S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076
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11/1/06 William Horowitz
LHC Predictions for Heavies
WH, S. Wicks, M. Gyulassy, M. Djordjevic, in preparation
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11/1/06 William Horowitz
Conclusions III
– Elastic loss cannot be neglected when considering pQCD jet quenching• Coherence and correlation effects between elastic
and inelastic processes that occur in a finite time over multiple collisions must be sorted out
• Fixed must be allowed to run; the size of the irreducible error due to integration over low, nonperturbative momenta, where > .5, needs to be determined
– Large uncertainties in ratio of charm to bottom contribution to non-photonic electrons• Direct measurement of D spectra would help
separate the different charm and bottom jet dynamics
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11/1/06 William Horowitz
Backup Slides
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11/1/06 William Horowitz
Our Extended Theory
• Convolve Elastic with Inelastic energy loss fluctuations
• Include path length fluctuations in diffuse nuclear geometry with 1+1D Bjorken expansion
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11/1/06 William Horowitz
Significance of Nuclear Profile
• Simpler densities create a surface biasHard Cylinder Hard Sphere Woods-Saxon
Illustrative Only! Toy model for purely geometric radiative loss from Drees, Feng, Jia, Phys. Rev. C.71:034909
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11/1/06 William Horowitz
– Null Control: RAA()~1
– Consistency: RAA()~RAA()
Y. Akiba for the PHENIX collaboration, hep-ex/0510008
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11/1/06 William Horowitz
Elastic Can’t be Neglected!
M. Mustafa, Phys. Rev. C72:014905 (2005) S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076
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11/1/06 William Horowitz
Length Definitions– Define a mapping from the line integral
through the realistic medium to the theoretical block
– where
– Then
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11/1/06 William Horowitz
Geometry Can’t be Neglected!
• P(L) is a wide distribution– Flavor
independent
• Flavor dependent fixed length approximations LQ’s not a priori obvious
S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076
11/1/06 William Horowitz
Comparison to Vitev
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11/1/06 William Horowitz
Increasing dNg/dy
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11/1/06 William Horowitz
Our Extended Theory
• Convolve Elastic with Inelastic energy loss fluctuations
• Include path length fluctuations in diffuse nuclear geometry with 1+1D Bjorken expansion
• Separate calculations with BT and TG collisional formulae provide a measure of the elastic theoretical uncertainty
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11/1/06 William Horowitz
• Qhat = c eps^3/4 \propto rho (density of scattering centers)
• pQCD=> c~=2• To fit RHIC, c ~ 8-20• Extend to LHC, everything crushed
to nothing
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11/1/06 William Horowitz
BDMPS RHIC ’s
K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. A747:511:529 (2005)
A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38:461-474 (2005)
Huge qhat needed!
(a) (b)
Note: fragility due to lack of Bjorken expansion
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