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Comparing energy loss phenomenology

Comparing energy loss phenomenology. Marco van Leeuwen Utrecht University. Energy loss in QCD matter. radiated gluon. propagating parton. m 2. QCD bremsstrahlung (+ LPM coherence effects). Transport coefficient. l. Energy loss. Energy loss probes:. Density of scattering centers:.

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Comparing energy loss phenomenology

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  1. Comparing energy loss phenomenology Marco van Leeuwen Utrecht University

  2. Energy loss in QCD matter radiated gluon propagating parton m2 QCD bremsstrahlung(+ LPM coherence effects) Transport coefficient l Energy loss Energy loss probes: Density of scattering centers: Nature of scattering centers, e.g. mass: radiative vs elastic loss Or no scattering centers, but fields  synchrotron radiation?

  3. Determining the medium density • For each model: • Vary parameter and predict RAA • Minimize 2 wrt data • Models have different but ~equivalent parameters: • Transport coeff. • Gluon density dNg/dy • Typical energy loss per L: e0 • Coupling constant aS PHENIX, arXiv:0801.1665,J. Nagle WWND08 PQM (Loizides, Dainese, Paic),Multiple soft-scattering approx (Armesto, Salgado, Wiedemann)Realistic geometry GLV (Gyulassy, Levai, Vitev), Opacity expansion (L/l), Average path length WHDG (Wicks, Horowitz, Djordjevic, Gyulassy)GLV + realistic geometry ZOWW (Zhang, Owens, Wang, Wang) Medium-enhanced power corrections (higher twist) Hard sphere geometry AMY (Arnold, Moore, Yaffe) Finite temperature effective field theory (Hard Thermal Loops)

  4. Medium density from RAA +2.1 - 3.2 ^ PQM <q> = 13.2 GeV2/fm +0.2 - 0.5 +270 - 150 ZOWW e0 = 1.9 GeV/fm GLV dNg/dy = 1400 +0.016 - 0.012 +200 - 375 AMY as = 0.280 WHDG dNg/dy = 1400 Method extracts medium density given the model/calculation Theory uncertainties need to be further evaluated e.g. comparing different formalisms, varying geometry Data constrain model parameters to 10-20% Different medium density parameters are used Each model ‘lives in its own world’ Side-by-side comparison needed to progress

  5. Some pocket formula results GLV/WHDG: dNg/dy = 1400 T(t0) = 366 MeV PQM: (parton average) T = 1016 MeV AMY: T fixed by hydro (~400 MeV), as = 0.297 Large difference between models ?

  6. TECHQM Brick problem Theory-Experiment Collaboration on Hot Quark Matter • Use simple geometry: • Brick of QGP: L = 2 fm, L = 5 fm • Various densities • Plot P(DE) for quark of 10, 100 GeV Goal: apples-to-apples comparison of energy loss formalisms Some models do not calculate P(DE) use fragmentation function instead Next slides: brick results (disregard nuclear geometry) https://wiki.bnl.gov/TECHQM/index.php/Partonic_Energy_Loss

  7. Back to data: oversimplified approach p0 spectra Nuclear modification factor PHENIX, PRD 76, 051106, arXiv:0801.4020 This is a cartoon! Hadronic, not partonic energy loss No quark-gluon difference Energy loss not probabilistic P(DE) Ball-park numbers: DE/E ≈ 0.2, or DE ≈ 2 GeVfor central collisions at RHIC Note: slope of ‘input’ spectrum changes with pT: use experimental reach to exploit this

  8. Energy distribution from theory TECHQM ‘brick problem’ L = 2 fm, DE/E = 0.2 E = 10 GeV ‘Typical for RHIC’ ASW: Armesto, Salgado, Wiedemann WHDG: Wicks, Horowitz, Dordjevic, Gyulassy • Not a narrow distribution: • Significant probability for DE ~ E • Conceptually/theoretically difficult Significant probability to lose no energy P(0) = 0.5 – 0.6

  9. RAA with DE/E= 0.2 Quarks only Spread in DE reduces suppression (RAA~0.6 instead of 0.2) 〈DE/E〉not very relevant for RAA at RHIC Large impact of P(0)?

  10. How to summarize E-loss? (Suggested by B. Mueller) n: power law indexn ~ 8 at RHIC  R8 ~ RAA Use Rn to characterise P(DE)

  11. T-dependence ASW vs WHDG ASW: Armesto, Salgado, Wiedemann WHDG: Wicks, Horowitz, Dordjevic, Gyulassy WHDG (GLV) and ASW (BDMPS) give similar suppression, but DT~200 MeV With L = 2 fm, RAA >> 0.2

  12. T-dependence ASW vs WHDG (L=5 fm) ASW: Armesto, Salgado, Wiedemann WHDG: Wicks, Horowitz, Dordjevic, Gyulassy L=5 fm: Reach RAA ~ 0.2 at T = 370 MeV (WHDG) and T = 500 MeV (ASW) So, why ~ 14 GeV2/fm, T~1000 MeV in PQM? Geometry

  13. Typical P(DE) at RHIC x → 1 important for phenomenology at RHIC Not well controlled in theory

  14. Note on geometry WHDG PQM (BDMPS) rcoll more sharply peaked rpart gives longer ‘typical’ pathlengths

  15. Geometry II rpart: larger ‹Leff › rpart: qhat more sharply peaked Changing rcoll to rpart may reduce needed to reproduce data (Note: distributions only for illustration, need to tune rpart to reproduce data)

  16. More differential measurements • Di-hadron correlations • RAA vs reaction plane (elliptic flow) • g-jet • Jet reconstruction RAA integrates out parton kinematics, energy loss distribution Energy loss distribution P(DE) integrates out geometry More differential measurements help probe P(DE), geometry:

  17. Di­hadron correlations Combinatorialbackground 8 < pT,trig < 15 GeV associated  trigger 8 < pTtrig < 15 GeV pTassoc > 3 GeV STAR PRL 95, 152301 Near side Away side No zT-dependence of away-side suppression  indicates importance of P(0) ?

  18. Medium density from di-hadron measurement associated  trigger J. Nagle, WWND2008 8 < pT,trig < 15 GeV d-Au IAA constraint DAA constraint DAA + scale uncertainty Au-Au Higher twist: Medium density fromaway-side suppression and RAA Theory: ZOWW, PRL98, 212301 e0=1.9 GeV/fm single hadrons Caveats: • Theory curve does not match d+Au: need to evaluate systematics • pT relatively low (recombination?) Data: STAR PRL 95, 152301 Would like to see other models! zT=pT,assoc/pT,trig

  19. Model predictions for RAA(f) Bass et al. arXiv:0808.0908 ASW shows larger variation vs f Geometry is additional handle on/for models

  20. Parton energy from g-jet and jet reconstruction  second-generation measurements at RHIC Qualitatively: known pQCDxPDF extract `known’ from e+e- Full deconvolution large uncertainties (+ not transparent) Fix/measure Ejet to take one factor out • Two approaches: • g-jet • Jet reconstruction See talks by Putschke, Hamed (and others) for results and more discussion

  21. Towards LHC RHIC: n = 8 LHC: n = 6 L = 5 fm E = 10 GeV pT-6 instead of pT-8 spectrum has only small effect on RAA R8≈ R6

  22. LHC: DE vs E L = 5 fm E = 10 GeV L = 5 fm E = 100 GeV Dependence of R6 on E,T different in ASW, WHDG Due to added log(√(ET)) in WHDG (trivial) or more fundamental?

  23. RAA at LHC GLV BDMPS T. Renk, QM2006 RHIC RHIC S. Wicks, W. Horowitz, QM2006 Dependence of R6 on E,T different in ASW, WHDG Due to added log(√(ET)) in WHDG (trivial) or more fundamental? ... or even something else? Should clarify before first data at LHC Predictions, not postdictions

  24. Conclusion • Nuclear suppression data (RAA, IAA) are becoming accurate – Need accurate theory • Side-by-side comparison: TECHQM brick problem makes a clean start • BDMPS-ASW and GLV-WHDG give DT~200 MeV(results for Higher Twist and AMY still need to be put on same scale –expected soon) • Next step: uniform treatment of geometry, time evolution Beware of P(0) and P(DE = E): both are important for phenomenology Are they under control? Thanks to: W. Horowitz, C. Salgado, N. Armesto, U. Wiedemann, A. Majumder

  25. Thank you for your attention

  26. Fragmentation functions Include some FF plots?

  27. Direct-g recoil suppression Expected recoil for various P(DE) T. Renk  Measurement sensitive to energy loss distribution P(DE) Need precision to distinguish scenarios 8 < ET,g < 16 GeV 2 < pTassoc < 10 GeV J. Frantz, Hard Probes 2008 A. Hamed, Hard Probes 2008 STAR Preliminary ET,g DAA(zT) IAA(zT) = Dpp(zT) Large suppression for away-side: factor 3-5 Results agree with model predictions Uncertainties still sizable Some improvements expected for final resultsFuture improvements with increased RHIC luminosity

  28. Energy loss in QCD matter : no interactions RAA = 1 Hadrons: energy loss RAA < 1 Yield per collision Nuclear modification factor : RAA = 1 C. Vale, K. Okada, Hard Probes 2008 0: RAA≈ 0.2 D. d’Enterria Hard partons lose energy in the hot matter

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