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Heavy quark energy loss: radiative v.s. collisional Magdalena Djordjevic

Heavy quark energy loss: radiative v.s. collisional Magdalena Djordjevic The Ohio State University. Quark Gluon Plasma. High Energy Heavy Ion Physics. Form, observe and understand Quark-Gluon Plasma (QGP).

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Heavy quark energy loss: radiative v.s. collisional Magdalena Djordjevic

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  1. Heavy quark energy loss: radiative v.s. collisional Magdalena Djordjevic The Ohio State University

  2. Quark Gluon Plasma High Energy Heavy Ion Physics Form, observe and understand Quark-Gluon Plasma (QGP). Heavy quarks (charm and beauty, M>1 GeV) are widely recognized as the cleanest probes of QGP. N. Brambilla et al., e-Print hep-ph/0412158 (2004). Heavy mesons not yet available, but they are expected soon!

  3. Indirect probe- single electron suppression – is available V. Greene, S. Butsyk, QM2005 talks J. Dunlop, J. Bielcik; QM05 talks Significant reduction at high pT suggests sizeable heavy quark energy loss! Can this be explained by the energy loss in QGP?

  4. Outline Discuss the heavy quark energy loss mechanisms: • Radiative energy loss. • Collisional energy loss. • Single electron suppression results that come from the above mechanisms.

  5. c c L • Radiative heavy quark energy loss • Three important medium effects control the radiative energy loss: • Ter-Mikayelian effect (M.L.Ter-Mikayelian (1954); Kampfer-Pavlenko (2000); Djordjevic-Gyulassy (2003)) • Transition radiation (Zakharov (2002); Djordjevic (2006)). • Medium induced radiative energy loss (Djordjevic-Gyulassy (2003); Zhang-Wang-Wang (2004); Armesto-Salgado-Wiedemann (2004)) 1) 2) 3)

  6. Transition & Ter-Mikayelian effects on 0th order radiative energy loss M.D., Phys.Rev.C73:044912,2006 CHARM BOTTOM Transition & Ter-Mikayelian effects approximately cancel each other for heavy quarks.

  7. c c L Medium induced radiative energy loss Caused by the multiple interactions of partons in the medium. To compute medium induced radiative energy loss for heavy quarks we generalize GLV method, by introducing both quark M and gluon mass mg. Neglected in further computations.

  8. + + This leads to the computation of the fallowing types of diagrams: Final Result to Arbitrary Order in Opacity (L/l) with MQ and mg> 0 M. D. and M. Gyulassy, Phys. Lett. B 560, 37 (2003); Nucl. Phys. A 733, 265 (2004)

  9. Numerical results for 1st order in opacity induced radiative energy loss RHIC, dNg/dy=1000 LHC, dNg/dy=3000

  10. Can single electron suppression be explained by the radiative energy loss in QGP? M. D., M. Gyulassy, R. Vogt and S. Wicks, Phys. Lett. B 632, 81 (2006) Radiative energy loss predictions with dNg/dy=1000 Disagreement! Radiative energy loss alone is not able to explain the single electron data as long as realistic parameter values are taken into account!

  11. Is collisional energy loss also important? Early work: Recent work: E. Braaten and M. H. Thoma, Phys. Rev. D 44, 2625 (1991). M. H. Thoma and M. Gyulassy, Nucl. Phys. B 351, 491 (1991). Collisional energy loss is negligible! Conclusion was based on inaccurate assumptions (i.e. they used α=0.2), and assumed that dE/dL<0.5 GeV/fm is negligible. Collisional and radiative energy losses are comparable! M.G.Mustafa,Phys.Rev.C72:014905,2005 A. K. Dutt-Mazumder et al.,Phys.Rev.D71:094016,2005 Will collisional energy loss still be important once finite size effects are included? Above computations are done in an ideal infinite QCD medium.

  12. Radiative energy loss Collisional energy loss Radiative energy loss comes from the processes which there are more outgoing than incoming particles: Collisional energy loss comes from the processes which have the same number of incoming and outgoing particles: 0th order 0th order 1st order

  13. L The effective gluon propagator: Collisional energy loss in a finite size QCD medium M.D., nucl-th/0603066 Consider a medium of size L in thermal equilibrium at temperature T. The 0th order collisional energy loss is determined from:

  14. Comparison between computations of collisional energy loss in finite and infinite QCD medium M.D., nucl-th/0603066 Finite size effects are not significant, except for very small path-lengths.

  15. Comparison between charm and bottom collisional energy loss Bottom quark collisional energy loss is significantly smaller than charm energy loss. M.D., nucl-th/0603066

  16. Collisional and radiative energy losses are comparable! Collisional v.s. medium induced radiative energy loss M.D., nucl-th/0603066 Complementary approach by A. Adil et al., nucl-th/0606010: consistent results obtained.

  17. Most up to date single electron prediction (collisional + radiative) See talk by S. Wicks, parallel session I Radiative energy loss alone is not able to explain the single electron data, as long as realistic gluon rapidity density dNg/dy=1000 is considered. Inclusion of collisional energy loss leads to better agreement with single electron data, even for dNg/dy=1000. (S. Wicks, W. Horowitz, M.D. and M. Gyulassy, nucl-th/0512076)

  18. Conclusions Radiative energy loss mechanisms alone are not able to explain the recent single electron data. Collisional and radiative energy losses are comparable, and both contributions are important in the computations of jet quenching. Inclusion of the collisional energy loss lead to better agreement with the experimental results.

  19. Acknowledgements: Miklos Gyulassy (Columbia University) Simon Wicks (Columbia University) Ramona Vogt (LBNL, Berkeley and University of California, Davis) William Horowitz (Columbia University)

  20. Ter-Mikayelian effect This is the non-abelian analog of the well known dielectric plasmon effectw(k) >wpl~ gT. In pQCDvacuumgluons are massless andtransversely polarized. However, in a medium the gluon propagator has bothtransverse(T)and longitudinal(L)polarization parts. T vacuum L

  21. In order to compute the main order radiative energy loss we calculated |Mrad|2, where Mradis given by Feynman diagram: We used the optical theorem, i.e.: Where M is the amplitude of the following diagram: Dielectric Effect

  22. To compute the effect we start from work byB.G. Zakharov,JETP Lett.76:201-205,2002. This computation was performed assuming a static medium.

  23. D, B e- c, b 1) production 2) medium energy loss 3) fragmentation 4) decay Single electron suppression 1) Initial heavy quark pt distributions 2) Heavy quark energy loss 3) c and b fragmentation functions into D, B mesons 4) Decay of heavy mesons to single e-.

  24. A D mesons B , Y’, c Initial heavy quark pt distributions M. Cacciari, P. Nason and R.Vogt, Phys.Rev.Lett.95:122001,2005; MNR code(M. L. Mangano, P.Nason and G. Ridolfi, Nucl.Phys.B373,295(1992)). R.Vogt, Int.J.Mod.Phys.E 12,211(2003). High quark mass, i.e. M»ΛQCD Perturbative calculations of heavy quark production possible.

  25. Before quenching After quenching Pt distributions of charm and bottom before and after quenching at RHIC M. Gyulassy, P. Levai and I. Vitev, Phys.Lett.B538:282-288 (2002). M. D., M. Gyulassy and S. Wicks, Phys. Rev. Lett. 94, 112301 (2005).

  26. Single electrons pt distributions Panels show single e- from FONLL M. Cacciari, P. Nason and R. Vogt, Phys.Rev.Lett.95:122001,2005 M. D., M. Gyulassy, R. Vogt and S. Wicks, Phys.Lett.B632:81-86,2006 Before quenching After quenching Bottom dominate the single e-spectrum above 4.5 GeV!

  27. Single electron suppression as a function of pt At pt~5GeV, RAA(e-) 0.7±0.1at RHIC.

  28. Are there other energy loss mechanisms? Finite size effects significantly lower collisional energy loss S. Peigne, P.-B. Gossiaux, T. Gousset, hep-ph/0509185 Collisional and radiative energy losses are comparable! M.G.Mustafa,Phys.Rev.C72:014905,2005 The paper, however, did not make separation between elastic and part of radiative energy loss effects.

  29. b+ce- b 0 g Why, according to pQCD, pions have to be at least two times more suppressed than single electrons? Suppose that pions come from light quarks only and single e-from charm only. Pion and single e- suppression would really be the same. • However, • Gluon contribution to pions increases the pion suppression, while 2) Bottom contribution to single e- decreases the single e- suppression leading to at least factor of 2 difference between pion and single e- RAA.

  30. Comparison with other models Ideal infinite QCD medium case: • Thoma-Gyulassy (1990) (linear response approach). • Braaten-Thoma (1991) (quantum-mechanical approach). • Romatasche-Strickland (2003) (anisotropic medium). Finite QCD medium case: • Peigne-Gossiaux-Gousset (hep-ph/0509185, 2005) (linear response approach): Finite size effects significantly reduce the collisional energy loss. • Wang (nucl-th/0604040, 2006) (quantum-mechanical approach): interference effects exist at 0th order energy loss level. • Adil-Gyulassy-Horowitz-Wicks (nucl-th/0606010, 2006) (linear response approach): obtained consistent results.

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