1. F. Scardina INFN-LNS Catania, University of Messina V. Greco, M. Di Toro Sensitivity of the jet quenching observables to the temperature dependence of the energy loss [Phys. Rev. C 82:054901, 2010] International School on “Quark-Gluon Plasma and Heavy Ion Collisions: past, present, future” Torino 08/03/2011

2. Outline  Our simple model Our simple model  Quenching observables : Quenching observables : Nuclear modification factor R AA (quarks)/R AA (gluons) linked to the flavour dependence of ΔE linked to the flavour dependence of ΔE  Open question Open question Simultaneous description of both R AA and V 2 is still a theoretical challenge – “azimuthal puzzle” High P T protons less suppressed than pions - flavor puzzle High P T protons less suppressed than pions - flavor puzzle  First results for LHC  Conclusion and future developments Conclusion and future developments x y z Elliptic flow

3. Modelling jet quenching Our model is based on the approximation by which jets lose energy in a bulk medium that is expanding and cooling independently from the jets energy loss.  Density profile  r  for the Bulk medium in the transverse plane (Glauber Model) a) Initial condition  Hard partons distributions - space coordinates (Glauber Model N coll ) - momenta coordinates (pQCD) transverse plane

4. Constant with b) E loss on particles propagating in straight lines b) E loss on particles propagating in straight lines (path-length) Ex. GLV c) Hadronization by AKK fragmentation function z=p h /p f

5. Application of the model to evaluate R AA R AA Integrated for p T > 6 GeV π0π0 Au+Au at 200 AGeV  For p T <5 GeV there are non-perturbative mechanisms (coalescence)  R AA (p T ), R AA (N part ) does not allow discrimination of E loss (T)

6. Open issues  Azimuthal puzzle Simultaneous description of both R AA and V 2 is still a theoretical challenge The experimental data show V 2 above theoretical prediction High P T protons less suppressed than pions R AA Au+Au central 0-12% protons pions because they come more from gluons… …and gluons are more suppressed than quarks ΔE for gluons=9/4* ΔE for quarks But protons should be more suppressed R AA (q)/R AA (g)≤1 Flavor puzzle  Flavor puzzle R AA (q)/R AA (g)=9/4 Does it mean?

7. they are strongly correlated 20-30% One solution to azimuthal puzzle: E loss near T c Predominant energy loss at low T [Liao, Shuryak Phys. Rev. Lett. 102 (2009)] Solution of azimuthal puzzle? We analyze relation between T dependence of quenching and v 2, with R AA fixed on data

8. R AA (quark)/ R AA (gluon) and T dependence of energy loss R AA fixed on experimental data for pions (R AA =0.2) ΔE gluon =9/4*ΔE quark The ratio is related to T dependence of energy loss, it is not necessarily 9/4 The ratio is lower if quenching mainly occur close to T c

9. Energy Loss The sensitivity to the amount of E loss is damped already by a small percentage of partons that don’t lose energy initial

10. The sensitivity to the amount of E loss is damped already by a small percentage of partons that don’t lose energy If energy loss is predominant at high T particles near the surface lose a small amount energy If energy loss occurs at low T all particles lose a large amount of energy

11. A solution to flavor puzzle: Jet q  g conversion [Ko, Liu, Zhang Phys. Rev C 75] [Liu, Fries Phys. Rev C 77] We also have introduced this mechanism in our code: results confirmed conversion rate is given by the collisional width R AA (q)/R AA (g) Inelastic collisions cause a change in the flavor q g

12. without conversion with conversion E loss at high T GLVc GLV α(T) E loss at low T Exp Correlation R AA (quark)/R AA (gluon) - V 2 (Wood-Saxon) R AA (P T ) fixed on experimental data for pions Lattice QCD EoS state moves V 2 and R AA (q)/R AA (g) to the right To get close to experimental data:   E stronger close to phase transition is needed But If  E is stronger close to T c deviations of  (T) from the free gas approximation become important -> use lQCD EoS a= 0.15; n=1.89  flavor conversion becomes more necessary E loss at low T EoS lattice QCD Fit to Lattice QCD

13. First results for LHC We use less extreme T dependencies of the energy loss V 2 for RHIC and LHC

14. First results for LHC R AA (gluon)/R AA (quark) The rises are due to the changes in the slope of the partons spectra

15. Conclusions and Perspective  Different ΔE(T) generate very different R AA (q)/R AA (g) and v 2  Observed v 2 and R AA (q)/R AA (g) seem to suggest a ΔE stronger near Tc and a strong flavor conversion  Sensitive to deviation from the free gas expansion (EoS) for Eloss (T~Tc)  Our first results for LHC seem to confirm these indications. Future Developments  transport code takes into account collisional and radiative energy loss joined to a dynamics consistent with the used EoS [Greiner Group][Catania]

17. Initial condition  Density profile for the bulk In longitudinal direction evolves according to the Bjorken expansion at the velocity of light 1.Glauber Model partecipant distribution 2.Sharp elliptic shape  Momenta space  High P T partons distribution  Coordinates space (N coll ) Dal profilo di densita otteniamo il profilo di T Ideal gas The initial transverse density profile can be modelled in two different way The spectra are calculated in the NLO pQCD scheme [Ko, Liu, Zhang Phys. Rev C 75][Liu, Fries Phys. Rev C 77] The value of the parameters A f,B f and n f are taken from Ref.

18. Glauber Model  The trasverse density profile for the bulk is proportional to the partecipant distribution  The hard parton distribution in space coordinates scales with the number of binary Nucleon collision Proiezione lungo l’asse x Density profile for the bulk Density profile for the jet

19. Hadronization z=p h /p p [S. Albino, B. A. Kniehl, and G. Kramer, Nucl. Phys B597] The parton distribution after the quenching are employed to evaluate the hadron spectrum by indipendent jet fragmentation using the AKK fragmentation function

21. Ratio R AA (q)/R AA (g) We consider a simplified case in which all quarks lose the the same amount of energy DE and all gluons lose their energy according to DE=9/4*DE Spectra are shifted by a quantity equal to the energy lost Partons that finally emerge with an energy pT Are those which before quenching had an energy pT+  e*η where η=1 for quarks and 9/4 for gluons There is no reason why this ratio must be 9/4

22. Over simplified case: all quark lose the the same amount of energy and all gluons lose ΔE g =9/4*ΔE quark Minimal realistic case: 2 classes of quarks undergoing different quenching, always with ΔE g =9/4*ΔE q The ratio is dominated by the way the energy loss is distributed among partons Sharp Ellipse: direct relation T τWood Saxon: No direct relation T τ (Surface -> low T also at early times) quenching at high T particles lose energy early; all particle lose energy (dotted line) quenching at high T No DE at the surface but only in the inner part of the fireball (strong DE); particles in the surface escape almost without Eloss quenching at low T ( later tau) Many particles escape without Eloss; those in the inner part must be strongly quenched  blue thin line) quenching at low T DE is strong in a layer on the surface -> all particles across this layer so all particles lose energy ≠ R AA (quark)/R AA (gluon): profile and T dependence of energy loss ≠