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Simon Wicks, QM2006 Work done with Miklos Gyulassy, William Horowitz, Magdalena Djordjevic

Jet energy loss at RHIC and LHC including collisional and radiative and geometric fluctuations. Simon Wicks, QM2006 Work done with Miklos Gyulassy, William Horowitz, Magdalena Djordjevic. Institut für Theoretische Physik. pQCD and energy loss.

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Simon Wicks, QM2006 Work done with Miklos Gyulassy, William Horowitz, Magdalena Djordjevic

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  1. Jet energy loss at RHIC and LHCincluding collisional and radiativeand geometric fluctuations Simon Wicks, QM2006 Work done with Miklos Gyulassy, William Horowitz, Magdalena Djordjevic Institut für Theoretische Physik

  2. pQCD and energy loss • At RHIC and LHC:Radiative mechanisms are important, but not ‘dominant’ M. Mustafa, Phys. Rev. C72:014905 (2005) SW, W. Horowitz, M. Djordjevic M. Gyulassy (WHDG) nucl-th/0512076 Simon Wicks

  3. Integration over production positions • Integrals over the initial geometry just have to be done. Simon Wicks

  4. WHDG extended theory NOTE however: we use physical dNg/dy~1000 Simon Wicks

  5. The results – RHIC • Important consistency check: Compare predictions to both pion and electron data (WHDG = nucl-th/0512076v3) STAR: nucl-ex/0607012, PHENIX (QM2006): nucl-ex/0611018 Result: inclusion of collisional+geometry ~fits pion data, and improves the heavy quark quenching, but still underpredicts pT~4-8 data with FONLL b/c ratio. (B/D ratio or direct D measurement very important to reduce uncertainties) Simon Wicks

  6. The results – More RHIC Integrated RAA v2 Simon Wicks

  7. The results - LHC • See William Horowitz’s poster for more details about LHC and comparison to other predictions. • Here: estimate dNg/dy=2900 via CGC Light jets Heavy jets Pions • Note the slope of our pion predictions. Simon Wicks

  8. Improving the model • 1) Toward a better description of collisional fluctuations. • 2) Effects of running QCD coupling. Simon Wicks

  9. Collisional fluctuations in WHDG (Fokker-Planck-like) • Fokker-Planck:Characterised by 2 numbers / functions: (drag, diffusion) • Small ε approx (used in WHDG):Gaussian, centered at average energy loss (given by BT or TG), width (in WHDG) given by fluctuation-dissipation theorem, σ2 = 2T<ε> (Green curve = collisional fluctuations in WHDG) Simon Wicks

  10. A model of elastic energy loss E,M Use this model in order to study fluctuations: • Jet interacts with a medium modified HTL propagator with initially static medium particles which recoil. • Mass of medium particle tuned to give ΔE~ ΔETG or BT • Gives mean free path of quark jet ~ 2.5fm meff ~0.3 GeV Simon Wicks

  11. Bottom jets – extreme 10 collisions (L~25fm) • Multiple collisions:Poisson weighted convolution of single collision distribution(ie independent collisions) Bottom, for 10 collisions: • Full distribution (red) is wider than the Gaussian (black). • Full distribution is still slightly skew even at 10 collisions. • Gaussian gives RAA=0.19 vs 0.20 • FP good in this case Simon Wicks

  12. Bottom jets – typical 2 collisions (L~5fm) • Multiple collisions:Poisson weighted convolution of single collision distribution(ie independent collisions) Bottom, for 2 collisions: • Full distribution (red) is wider than the Gaussian (black). • Full distribution is very skewed for 2 collisions. • Gaussian (FP) approx misses the physics, BUT gets RAA close! Simon Wicks

  13. Light jets – 2 and 5 collisions For small numbers of collisions, the Gaussian / FP-like approximation over predicts the quenching by ~0.1 (similar result for charm quarks) Simon Wicks

  14. Elastic fluctuations: Summary After all the elastic+geometric fluctuations, we expect: • All RAA predictions move up, charm, light quarks, gluons (by ~0.1). • Bottom quarks stay ~ same place. At DRAA~0.1 level there are other effects that need to be taken into account: • Large theory uncertainty in electron prediction is bottom/charm ratio. • … (next slide) Simon Wicks

  15. Effect of running the QCD couplinga(Q2) Simon Wicks

  16. Running the QCD coupling I • Peshier hep-ph/0607275 Braun & Pirner hep-ph/0610331 Simon Wicks

  17. Running the QCD coupling II Model: Bjorken estimate, 1/t2, cutoff at t=μ2 1-loop running α, ΛQCD = 0.2GeV. Result: • Running alpha results similar to fixed alpha For T< 1GeV except in unphysical E=Infty limit Further investigation needed to determine: RAA prediction including full geometry and elastic fluctuations (in progress) Peshier = Running α, infinite energy jet (black dashed) Running α = finite energy jet “Fixed α (1)”= α at t=(2πT)2 “Fixed α (2)”= α fixed at 0.3 Simon Wicks

  18. Extended WHDG Theory Status • 1) WHDG shows that elastic energy loss cannot be neglected in jet tomography. • 2) Full geometry path fluctuations must be included. • 3) Our extended theory with collisional + radiative +geom comes close to a consistent explanation of both pion and electron data at RHIC.4) Large uncertainty from bottom/charm ratio, DRAA~0.2-0.3. • 5) Fokker-Planck formalism misses the physics of small collision number distributions. • 6) For light quarks and gluons, WHDG with FP elastic fluctuations probably overestimates the influence of collisional by DRAA~0.1. However: for bottom quarks, the WHDG result for RAA is insensitive to (5)).(=> Bottom quark RAA moves closer to light quark RAA) • 7) Running alpha increases the collisional quenching. • Resulting RAA predictions: calculation in progress. Simon Wicks

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