1. Collisional energy loss becomes probable André Peshier SUBATECH, Université de Nantes - Praha, 20 April 2007 -

2. Andre.Peshier@subatech.in2p3.fr 2 Phases of matter

3. Andre.Peshier@subatech.in2p3.fr 3 Relativistic heavy-ion collisions initial state pre-equilibrium QGP and hydrodynamic expansion hadronization hadronic phase and freeze-out What happens???

4. Andre.Peshier@subatech.in2p3.fr 4 A paradigm in trouble distinguished signal of QGP: jet quenching partonic energy loss: radiative  collisional transp. coeff. factor 10 too large!! Collisional energy loss would help. estimate of collisional contribution based on Bjorken, Gyulassy,... What is α ?

5. Andre.Peshier@subatech.in2p3.fr 5 How to fix α ? consider elementary quantity: Debye screening fundamental in plasma physics: describes polarization of medium by test charge, IR cut-off for long-range interaction hot QCD: Debye mass from self-energy

6. Andre.Peshier@subatech.in2p3.fr 6 How to fix α ? common folklore: GUESS 50% deviation (usually interpreted as higher order effects)

7. Andre.Peshier@subatech.in2p3.fr 7 Back to the roots Calculate  (instead of guess) running coupling from renormalized loop corrections, at running coupling from renormalized loop corrections, at appropriate momentum scale Which loop corrections? recall: Debye mass is property of POTENTIAL NO...

8. Andre.Peshier@subatech.in2p3.fr 8 Heavy quark potential (T=0) pQCD “confinement” ~ string potential

9. Andre.Peshier@subatech.in2p3.fr 9 Heavy quark potential (T=0) define coupling from force string parametrization: string parametrization inadequate: NO asymptotic freedom!

10. Andre.Peshier@subatech.in2p3.fr 10 Heavy quark potential (T=0) perturbation theory for small r (large momenta) running coupling from renormalized loop corrections +++... = running coupling bare coupling

11. Andre.Peshier@subatech.in2p3.fr 11 Heavy quark potential (T=0) legitimate question: Where does pQCD fail? single parameter: Λ = 0.2GeV QCD pQCD good for α ~1 asympt. freedom

12. Andre.Peshier@subatech.in2p3.fr 12 QCD Debye mass mended in-medium pQCD potential + ++... = α (t) T-part of selfenergy T self-consistent definition

13. Andre.Peshier@subatech.in2p3.fr 13 QCD Debye mass parameter-free “prediction”! [AP, hep-ph/060119] pQCD works near T c

14. Andre.Peshier@subatech.in2p3.fr 14 Didn't he want to talk energy loss? YES... it's coming NOW

15. Andre.Peshier@subatech.in2p3.fr 15 QCD collisional e-loss, textbook version consider mean energy loss [Bjorken'82] IR cut-off “by hand” Gyulassy, Braaten, Thoma calculate with hard thermal loop formalism Conceptional inconsistency: BGBT resum thermal fluctuations, but “forget” vacuum contributions ► value of coupling unspecified in

16. Andre.Peshier@subatech.in2p3.fr 16 QCD collisional e-loss mended the connection to the potential for s  t resummation renormalization  ► consequential modification of AP, hep-ph/0605294

17. Andre.Peshier@subatech.in2p3.fr 17 QCD collisional e-loss mended Theory changed! instead of theory now predictive, 1 parameter: 

18. Andre.Peshier@subatech.in2p3.fr 18 Collisional quenching weights consider probability for energy transfer  AP, hep-ph/0607299

19. Andre.Peshier@subatech.in2p3.fr 19 Collisional quenching weights mean free path length implicit definition mean free path ~ particle distance strongly coupled QGP

20. Andre.Peshier@subatech.in2p3.fr 20 Probabilistic quenching initialize jets - r φ ► “near-side” & “far-side” +

21. Andre.Peshier@subatech.in2p3.fr 21 Probabilistic quenching Monte-Carlo dynamics: Bjorken boost local T-dependent quenching weights

22. Andre.Peshier@subatech.in2p3.fr 22 Probabilistic quenching

23. Andre.Peshier@subatech.in2p3.fr 23 Probabilistic quenching AP, hep-ph/0607299 for reasonable geometry/dynamics: sizable quenching from collisions (parameter-free)

24. Andre.Peshier@subatech.in2p3.fr 24 Summary predictions require thorough renormalization 1 parameter  pQCD “applicable” in large-coupling regime  =  0.2GeV adjusted to lattice QCD correct theory of collisional energy loss now with asymptotic freedom changed paradigm collisions important for quenching collisions important for jet quenching

25. Andre.Peshier@subatech.in2p3.fr 25 Physics of the QGP Length scales : particle distance, thermodynamics : particle distance, thermodynamics : quasi-particle masses, Debye screening : quasi-particle masses, Debye screening : small angle scattering, interaction rates : small angle scattering, interaction rates : large angle scattering, transport coefficients : large angle scattering, transport coefficients for  1, clear hierarchy: