Elastic, Inelastic and Path Length Fluctuations in
Jet Tomography
Simon WicksHard Probes 2006
Work done with William Horowitz, Magdalena Djordjevic and Miklos Gyulassy
arXiv: nucl-th/0512076 and in preparation
Re: The single electron puzzle at RHIC
Hard Probes 2006 Slide 212th June
Introduction – The single electron puzzle
Pion suppression predictions seem to work well …
DGLV predictions: Djordjevic, Gyulassy, Vogt, WicksPhys Lett B 632:81-86 (2006)
GLV predictions for pions compared to PHENIX dataVitev prediction – plot from T. Isobe nucl-ex/0605016
… but (entropy constrained) pQCD radiative only FALSIFIED by e- data.
Hard Probes 2006 Slide 312th June
Possible SolutionsI. Fit the data with ‘free’ parameters, explain the
magnitudes later …II. Improve understanding of pQCD production
spectra (but still cannot match data with entropy bounded radiative energy loss alone)
III. Use novel non-perturbative techniques to explain extra charm / bottom quenching
IV. 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?
Hard Probes 2006 Slide 412th June
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. C72:014905 (2005) SW, W. Horowitz, M. Djordjevic M. Gyulassy, nucl-th/0512076
Hard Probes 2006 Slide 512th June
Elastic energy loss
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 …
•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)
Hard Probes 2006 Slide 612th June
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: L=5-6fm.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.
Hard Probes 2006 Slide 712th June
WHDG extended theory~Ideal Our model
ProductionAll orders
pQCDNLO pQCD (FONLL for LHC spectra)
(large uncertainty in magnitude, small uncertainty in the power law of the tail)
GeometryPropagate through
evolving hydro simulation
Realistic Woods-Saxon nuclear density Jets produced ~ TAA
Propagate through Bjorken expanding ρpart
αs Running Fixed αs=0.3(large uncertainty as energy loss strongly dependent on αs)
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/dy=1000
Hard Probes 2006 Slide 812th June
Results
RHICRHIC theoretical uncertaintiesLHC
Hard Probes 2006 Slide 912th June
Results – RHIC
Gluons, u,d ->Pions Charm, bottom ->Electrons
Note: kt smearing, EMC … neglected here.
Good agreement with pions, improved agreement with e - than for (entropy constrained) radiative only.
Hard Probes 2006 Slide 1012th June
Results – RHIC - Uncertainty
Sources of uncertainty:
Fixed αs=0.3 approximation Shape of spectra, fragmentation …
(does not affect RAA significantly)
Magnitude of spectra:ie c / b ratio in contribution to e-
Hard Probes 2006 Slide 1112th June
Results – RHIC – Uncertainty in αs
αs =0.4 improves e- fit, over predicts pion quenching
… need a fully running coupling calculation to reduce theoretical uncertainty.
Hard Probes 2006 Slide 1212th June
Results – RHIC – uncertainty in c/b ratioUncertainty 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
Hard Probes 2006 Slide 1312th June
Results – LHC (1)Energy loss for high pT jets at LHC ‘dominated’ by radiative …
… but collisional energy loss is still a ~25% effect.
Hard Probes 2006 Slide 1412th June
Results – LHC (2)Partonic RQ(pT) (for one sample value of dNg/dy = 2900):
Hard Probes 2006 Slide 1512th June
Results – LHC (3)Pion RAA(pT) (for two sample values of dNg/dy = 1750, 2900):
Hard Probes 2006 Slide 1612th June
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 production
eg measure D mesons directly
Further applications: V2 Multi-particle correlations More LHC work
