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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. F. Scardina INFN-LNS Catania, University of Messina V. Greco, M. Di Toro. [ Phys . Rev. C 82:054901, 2010]. International School on “ Quark-Gluon Plasma and Heavy Ion Collisions :

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F. Scardina INFN-LNS Catania, University of Messina V. Greco, M. Di Toro

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  1. Sensitivityof the jet quenching observablesto the temperature dependenceof the energy loss F. Scardina INFN-LNS Catania, Universityof Messina V. Greco, M. Di Toro [Phys. Rev. C 82:054901, 2010] International School on “Quark-Gluon Plasma and HeavyIonCollisions: past, present, future” Torino 08/03/2011

  2. Outline z y x • Our simple model • Quenching observables : • Nuclear modification factor • RAA(quarks)/RAA(gluons) • linked to the flavour dependence of ΔE • Open question • Simultaneous description of both RAA and V2 • is still a theoretical challenge – “azimuthal puzzle” • High PT protons less suppressed than pions- flavor puzzle • First results for LHC • Conclusion and future developments • Elliptic flow

  3. Modelling jet quenching Ourmodelisbased on the approximationbywhichjetsloseenergy in a bulk medium thatisexpanding and coolingindependentlyfrom the jetsenergy loss. a) Initialcondition transverseplane • Density profiler(t, r, f) for the • Bulk medium in the transverse • plane (GlauberModel) • Hard partonsdistributions • - spacecoordinates (GlauberModelNcoll) • - momentacoordinates (pQCD)

  4. b) Eloss on particlespropagatinginstraightlines(path-length) Ex. GLV Constant with c) Hadronizationby AKK fragmentationfunction z=ph/pf

  5. Applicationof the modeltoevaluate RAA π0 Au+Au at 200 AGeV RAAIntegratedforpT> 6 GeV • For pT<5 GeV there are non-perturbative mechanisms (coalescence) • RAA(pT), RAA(Npart) does not allow discrimination of Eloss(T)

  6. Open issues RAAAu+Aucentral 0-12% • Flavor puzzle But protons should be more suppressed High PT protons less suppressed than pions because they come more from gluons… protons …and gluons are more suppressed than quarks ΔE for gluons=9/4* ΔE forquarks pions Doesitmean? RAA(q)/RAA(g)≤1 RAA(q)/RAA(g)=9/4 • Azimuthal puzzle • Simultaneous description of both RAA and V2 is still a theoretical challenge The experimental data show V2 above theoretical prediction

  7. One solution to azimuthal puzzle: Eloss near Tc Predominantenergy loss at low T [Liao, Shuryak Phys. Rev. Lett. 102 (2009)] Solution of azimuthal puzzle? We analyze relation between T dependence of quenching and v2, with RAA fixed on data 20-30% they are strongly correlated

  8. RAA (quark)/RAA(gluon) and T dependenceofenergy loss RAA fixed on experimental data for pions (RAA=0.2) ΔEgluon =9/4*ΔEquark 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 Tc

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

  10. The sensitivityto the amountofElossisdampedalready bya smallpercentageofpartonsthat don’t loseenergy Ifenergy loss occurs at low T allparticleslose a largeamountofenergy Ifenergy loss ispredominant at high T particlesnear the surfacelose a smallamountenergy

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

  12. Correlation RAA (quark)/RAA (gluon) - V2 (Wood-Saxon) RAA (PT) fixed on experimental data for pions Togetclosetoexperimental data: • DE strongerclosetophasetransitionisneeded Eloss athigh T GLVc GLV α(T) Eloss at low T • flavorconversionbecomesmore necessary Eloss at low T EoS lattice QCD without conversion ButIfDE isstrongerclosetoTcdeviationsofr(T) from the free gas approximationbecomeimportant -> uselQCDEoS with conversion Exp FittoLattice QCD Lattice QCD EoS state moves V2 and RAA(q)/RAA(g) to the right a= 0.15; n=1.89

  13. First results for LHC We use less extreme T dependencies of the energy loss V2 for RHIC and LHC

  14. First results for LHC RAA(gluon)/RAA(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 RAA(q)/RAA (g) and v2 • Observed v2 and RAA(q)/RAA(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 [Catania] [Greiner Group]

  16. Initialcondition • Density profilefor the bulk In longitudinal direction evolvesaccordingto the Bjorkenexpansion at the velocityof light The initialtransverse density profile can bemodelled in twodifferent way GlauberModelpartecipantdistribution Sharp ellipticshape Ideal gas Dal profilo di densita otteniamo il profilo di T • High PTpartonsdistribution • Momentaspace The spectra are calculated in the NLO pQCDscheme The valueof the parametersAf ,Bfand nf are takenfromRef. [Ko, Liu, Zhang Phys. Rev C 75][Liu, Fries Phys. Rev C 77] • Coordinatesspace(Ncoll)

  17. GlauberModel Proiezione lungo l’asse x Density profilefor the bulk Density profilefor the jet • The trasverse density profilefor the bulk isproportionalto the partecipantdistribution • The hard partondistribution in spacecoordinatesscaleswith the numberofbinaryNucleoncollision

  18. Hadronization The partondistributionafter the quenching are employedtoevaluate the hadronspectrumbyindipendent jet fragmentationusing the AKK fragmentationfunction z=ph/pp [S. Albino, B. A. Kniehl, and G. Kramer, Nucl. Phys B597]

  19. Ratio RAA(q)/RAA(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+De*η where η=1 for quarks and 9/4 for gluons There is no reason why this ratio must be 9/4

  20. RAA (quark)/RAA(gluon): profile and T dependenceofenergy loss Over simplified case: all quark lose the the same amount of energy and all gluons lose ΔEg =9/4*ΔEquark Minimal realistic case: 2 classes of quarks undergoing different quenching, always with ΔEg =9/4*ΔEq The ratio is dominated by the way the energy loss is distributed among partons Sharp Ellipse: direct relation T<->τ Wood Saxon: No direct relation T<->τ (Surface -> low T also at early times) • 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 ≠ • 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); particlesin the surface escape almostwithout Eloss ≠

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