1. Elastic, Inelastic and Path Length Fluctuations in Jet Tomography Simon Wicks Hard 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

2. Slide 212 th June Hard Probes 2006 Introduction – The single electron puzzle Pion suppression predictions seem to work well … DGLV predictions: Djordjevic, Gyulassy, Vogt, Wicks Phys Lett B 632:81-86 (2006) GLV predictions for pions compared to PHENIX data Vitev prediction – plot from T. Isobe nucl-ex/0605016 … but (entropy constrained) pQCD radiative only FALSIFIED by e - data.

3. Slide 312 th June Hard Probes 2006 Possible Solutions I. 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?

4. Slide 412 th June Hard Probes 2006 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

5. Slide 512 th June Hard Probes 2006 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 p t for bottom in BT)

6. Slide 612 th June Hard Probes 2006 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.

7. Slide 712 th June Hard Probes 2006 WHDG extended theory ~IdealOur 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 ~ T AA Propagate through Bjorken expanding ρ part αsαs Running Fixed α s =0.3 (large uncertainty as energy loss strongly dependent on α s ) Energy loss mechanism Collisional and radiative in same theoretical framework Incoherent addition of DGLV radiative and leading log TG / BT collisional NOTE: Using realistic dN g /dy=1000

8. Slide 812 th June Hard Probes 2006 Results RHIC RHIC theoretical uncertainties LHC

9. Slide 912 th June Hard Probes 2006 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.

10. Slide 1012 th June Hard Probes 2006 Results – RHIC - Uncertainty Sources of uncertainty:  Fixed α s =0.3 approximation  Shape of spectra, fragmentation … (does not affect R AA significantly)  Magnitude of spectra: ie c / b ratio in contribution to e-

11. Slide 1112 th June Hard Probes 2006 Results – RHIC – Uncertainty in α s α s =0.4 improves e - fit, over predicts pion quenching … need a fully running coupling calculation to reduce theoretical uncertainty.

12. Slide 1212 th June Hard Probes 2006 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

13. Slide 1312 th June Hard Probes 2006 Results – LHC (1) Energy loss for high p T jets at LHC ‘dominated’ by radiative … … but collisional energy loss is still a ~25% effect.

14. Slide 1412 th June Hard Probes 2006 Results – LHC (2) Partonic R Q (p T ) (for one sample value of dN g /dy = 2900):

15. Slide 1512 th June Hard Probes 2006 Results – LHC (3) Pion R AA (p T ) (for two sample values of dN g /dy = 1750, 2900):

16. Slide 1612 th June Hard Probes 2006 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: V 2 Multi-particle correlations More LHC work

17. Slide 1712 th June Hard Probes 2006 (end of talk) (go England!!)