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Single electron puzzle at RHIC Magdalena Djordjevic Columbia University

Single electron puzzle at RHIC Magdalena Djordjevic Columbia University. Heavy ion physics has a goal to form and observe a QGP. Is the QGP already discovered at RHIC?. Jet Quenching of light partons strongly suggest that QGP is discovered .

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Single electron puzzle at RHIC Magdalena Djordjevic Columbia University

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  1. Single electron puzzle at RHIC Magdalena Djordjevic Columbia University

  2. Heavy ion physics has a goal to form and observe a QGP. Is the QGP already discovered at RHIC? • Jet Quenching of light partons strongly suggest that QGP is discovered. • Further tests of jet tomography using heavy quarks could be decisive as a complementary test of the theory. Heavy mesons not yet measured at RHIC. However, single electron measurements are available.

  3. Single electron suppression measurements from PHENIX 0 V. Greene, S. Butsyk, QM2005 talks Significant reduction at high pT suggest sizable energy loss!

  4. Single electron suppression from STAR Charged Hadron RAA 0.2 J. Dunlop, J. Bielcik; QM05 talks “Suppression is approximately the same as for hadrons.” Can this be explained by the radiative energy loss in QGP?

  5. Outline To apply the radiative heavy quark energy loss that we developed to compute the heavy quark (c and b) suppression.(M. D., M. Gyulassy and S. Wicks, Phys. Rev. Lett. 94, 112301 (2005); Euro Phys. J C, in press) Decay heavy quarks into single electrons and compute single electron suppression. (M. Djordjevic, M. Gyulassy, R. Vogt and S. Wicks, nucl-th/0507019, submitted to Phys. Lett. B (2005)) Answer:Can pQCD theory explain similar pion and single electron suppression?

  6. e- c, b 1) production 2) medium energy loss 3) fragmentation Single electron suppression To make theoretical predictions for heavy meson and single electron suppression we generalized the GLV method described inPLB538:282-288,2002. To apply this method we need to know: 1) Initial heavy quark pt distribution 2) Radiative heavy quark energy loss 3) c and b fragmentation functions into D, B mesons and how they decay to single e-.

  7. Initial heavy quark pt distributions To compute the initial charm and beauty pt distributions we applied the MNR code (Mangano et al.Nucl.Phys.B373,295(1992)). Parameters values from R.Vogt, Int.J.Mod.Phys.E 12,211(2003).

  8. c c L • Radiative heavy quark energy loss • Three important medium effects control the radiative energy loss: • Ter-Mikayelian effect (M. D. and M. Gyulassy, Phys. Rev. C 68, 034914 (2003)) • Transition radiation (M. D. and M. Gyulassy, in preparation). • Energy loss due to the interaction with the medium (M. D. and M. Gyulassy, Phys. Lett. B 560, 37 (2003); Nucl. Phys. A 733, 265 (2004)) 1) 2) 3)

  9. u,d u,d 0 g 0 g The heavy quark radiative energy loss depends on the gluon rapidity density, which we can determine from 0 RAA.

  10. Numerical results for induced radiative energy loss are shown for first order in opacity, with assumed Rx=Ry=6 fm. Mc=1.2 GeV, Mb=4.75 GeV. Due to its high mass, bottom looses less than half of charm quark energy loss.

  11. M. D., M. Gyulassy and S. Wicks, Phys. Rev. Lett. 94, 112301 (2005); Euro Phys. J C, in press (2005). After quenching Before quenching

  12. Single electrons at RHIC Panels show single e- from FONLL(M. Djordjevic, M. Gyulassy, R. Vogt and S. Wicks, nucl-th/0507019, submitted to Phys. Lett. B (2005)) Beauty dominate the single e-spectrum after 4.5 GeV!

  13. At pt~5GeV, RAA(e-)> 0.5±0.1at RHIC. Single electron suppression as a function of pt red curves: be;blue curves: ce; black curves: b+c  e;green curves: Pions

  14. RAA(e-) / RAA(0)> 2

  15. 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.

  16. Parton Level RAA(pT) B B Parton Level RAA(pT) u,d u,d D D 0 g g pT [GeV] pT [GeV] Heavy quark suppression as a function of pt red curve: B mesons; blue curve: D mesons; green curve: Pions Moderate D mesonsuppression ~ 0.3-0.5at RHIC. (M. D., M. Gyulassy and S. Wicks, Phys. Rev. Lett. 94, 112301 (2005);Euro Phys. J C, press)

  17. Conclusions We here applied the theory of heavy quark radiative energy loss to compute single electron suppression. We obtained that at pT~5GeV, RAA(e-)> 0.5±0.1at RHIC. Theoretically, single electron suppression has to be at leasttwo times smallerthan pion suppression. If STAR RAA(e-) RAA(0)is confirmed, it will be a theoretical challenge to devise novel energy loss mechanisms able to explain these data.

  18. Acknowledgements: Miklos Gyulassy Ramona Vogt Simon Wicks

  19. Backup slides

  20. RAA pT [GeV/c] Comparison with results by Armesto et al. Single electrons from Charm only reproduce Armesto et al. plots M. Djordjevic et al., hep-ph/0410372 N. Armesto et al. hep-ph/0501225

  21. 0 0 be dNg/dy=1000 dNg/dy=3500 be b+ce b+ce Single Electron RAA(pT) Single Electron RAA(pT) ce ce pT [GeV] pT [GeV] dNg/dy=1000 dNg/dy=3500

  22. The ratio of charm to bottom decays to electrons obtained by varying the quark mass and scale factors. The effect of changing the Peterson function parameters from c = 0.06, b = 0.006 (lower band) to c = b = 10−5 (upper band) is also illustrated.

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