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Electron ion collisions and the Color Glass Condensate

Electron ion collisions and the Color Glass Condensate. F.S. Navarra. University of São Paulo. Introduction. Higher energy/resolution: proton has more gluons. Well understood with BFKL and DGLAP. Linear evolution: gluon splitting g -> g g. High densities: non-linear evolution.

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Electron ion collisions and the Color Glass Condensate

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  1. Electron ion collisions and the Color Glass Condensate F.S. Navarra University of São Paulo

  2. Introduction Higher energy/resolution: proton has more gluons Well understood with BFKL and DGLAP Linear evolution: gluon splitting g -> g g High densities: non-linear evolution gluon recombination g g -> g Gribov, Levin, Ryskin (1983) Saturation: Color Glass Condensate McLerran, Venugopalan, Iancu, Al Müller, Levin, Kharzeev, Balitsky, Kovchegov,... ( 1994 -> ) Non-linear evolution equations: JIMWLK and BK “Laws of motion” in the x-Q plane

  3. Evidence at RHIC: suppression of the Cronin peak in the forward region BRAHMS High energy hadronic collisions: LHC Confirmation of CGC High energy e-nucleus collisions: eRHIC Deshpande, Milner,Venugopalan,Vogelsang, hep-ph/0506148 eRHIC: electron-ion collider at RHIC

  4. CGC visible when is large ! Saturation scale Saturation condition: target area completely filled by gluons QS : saturation scale dilute (linear) dense (saturation) LHC : x may be small eRHIC : A may be large

  5. proton quark b antiquark to fit data and understand the physics ! Analytical form for Color dipole approach Nikolaev, Zakharov (1991), A. Müller (1994) from the numerical solution of the BK equation (Study of parton distributions in DIS --> study of dipole cross sections)

  6. Testing dipole cross sections

  7. Dipole cross sections GBW Golec-Biernat Wüstoff (1999) Satisfies unitarity and color transparency: or when when

  8. More generally: Most of the physics is in the “anomalous dimension”: when when (from approximate solutions of BFKL, BK)

  9. large dipoles BK BFKL small dipoles IIM Iancu, Itakura, Munier (2004) linear saturation

  10. KKT Kharzeev, Kovchegov, Tuchin (2004) KKTm Machado (2006) DHJ Dumitru, Hayashigaki, Jalilian-Marian (2006) GKMN Gonçalves, Kugeratski, Machado, F.S. N. (2006)

  11. Comparison with data Structure functions at HERA Forward hadron production at RHIC

  12. KKT KKT StructurefunctionsatHERA KKT

  13. Longitudinal structure functions at HERA KKT

  14. Structure functions at HERA DHJ

  15. Structure functions at HERA DHJ

  16. Forward hadron production at RHIC BRAHMS

  17. Conclusions I KKT and DHJ were fitted to RHIC data but do not fit HERA data The slightly modified versions KKTm and GKMN fit HERA data M.S. Kugeratski, V.P. Gonçalves, F.S. N., Eur. Phys. J. C44 577 (2005) M.S. Kugeratski, V.P. Gonçalves, M.V. Machado, F.S. N., Phys. Lett. B44 577 (2006) Future: Better numerical solutions of the evolution equations BK at NLO Albacete, PRL (2007) Impact parameter Global data analysis Better parametrizations (with more physical content)

  18. Electron-Ion Collisions

  19. Nuclear inclusive DIS We assume IIM and rescale Nuclear diffractive DIS Golec-Biernat, Wüsthoff (1999) We assume that

  20. Saturation reduces by a factor 2 (low x and large A) R = full / linear with IIM

  21. Ratio of Cross Sections It works for e-p ! grows with W falls with x falls with grows with A

  22. A Q2

  23. Nuclear diffractive structure functions Wüsthoff (1997); Golec-Biernat, Wüsthoff (1999) Forshaw,Sandapen,Shaw (2004)

  24. Nuclear diffractive structure functions

  25. A=2 A=197

  26. A=2 A=197

  27. grows weakly with W and falls weakly with x The ratio Conclusions II In the saturation region F2 is reduced with respect to the linear case by 20 % in ep and 50 % in eA (in the IIM model !) falls with Q2 and grows with A up to 0.37 with increasing A becomes flat in changed by saturation effects is less important for large A is very flat in this is due to saturation ! M.S. Kugeratski, V.P. Gonçalves, F.S. N., Eur. Phys. J. C46 413 (2006) M.S. Kugeratski, V.P. Gonçalves, F.S. N., Eur. Phys. J. C46 465 (2006)

  28. Recent Improvements Dipole cross section impact parameter dependent More realistic atomic number dependence No “nuclear diffractive slope” Comparison with existing data on nuclear DIS Comparison with collinear factorization models: DS, EPS-08 Cazaroto, Carvalho, Gonçalves, Navarra, arXiv 0805.1255 [hep-ph]

  29. A and b dependence N. Armesto (2002)

  30. H. Kowalski, L. Motika, G. Watt, hep-ph/0606.272 bCGC G. Watt, arXiv 0712.2670 Armesto – GBW N. Armesto (2002)

  31. Results Data: E665, ZPC (1995)

  32. Not very sensitive to saturation effects

  33. Diffraction Before: GBW (1999) Now: Kowalski, Lappi, Venugopalan (2008) Kowalski, Lappi, Marquet, Venugopalan (2008)

  34. Now Now Before Before

  35. Conclusion not very promising signals of saturation The ratio still grows with A up to 0.25 - 0.30 (not 0.30 – 0.40) Future Improve the dipole cross sections Diffractive structure function Kowalski, Lappi, Marquet, Venugopalan (2008)

  36. CGC visible when is large ! LHC : x may be small eRHIC : A may be large

  37. Diffractive overlap function: Saturation suppresses larger dipoles (more for larger nuclei)

  38. Eskola,Kohlinen,Salgado, EPJC (1999)

  39. Golec-Biernat and Wüsthoff, PRD(1999)

  40. Color dipole approach

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