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Elastic , Inelastic and Path Length Fluctuations in Jet Tomography

Re: The single electron puzzle at RHIC. 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.

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Elastic , Inelastic and Path Length Fluctuations in Jet Tomography

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  1. Re: The single electron puzzle at RHIC Elastic, Inelastic and Path Length Fluctuations inJet Tomography Simon Wicks Hard Probes 2006 Work done with William Horowitz, Magdalena Djordjevic and Miklos Gyulassy arXiv: nucl-th/0512076 and in preparation

  2. 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) … 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 Hard Probes 2006

  3. 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? Hard Probes 2006

  4. 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

  5. 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 … Hard Probes 2006

  6. 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

  7. WHDG extended theory NOTE: Using realistic dNg/dy=1000 Hard Probes 2006

  8. Results • RHIC • RHIC theoretical uncertainties • LHC Hard Probes 2006

  9. Results – RHIC Charm, bottom ->Electrons Gluons, u,d ->Pions Note: kt smearing, EMC … neglected here. Good agreement with pions, improved agreement with e- than for (entropy constrained) radiative only. Hard Probes 2006

  10. 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

  11. 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

  12. 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 Hard Probes 2006

  13. 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

  14. Results – LHC (2) Partonic RQ(pT) (for one sample value of dNg/dy = 2900): Hard Probes 2006

  15. Results – LHC (3) Pion RAA(pT) (for two sample values of dNg/dy = 1750, 2900): Hard Probes 2006

  16. 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 Hard Probes 2006

  17. (end of talk)(go England!!) Hard Probes 2006

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