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Saturation at hadron colliders

Saturation at hadron colliders. Cyrille Marquet SPhT, Saclay. hep-ph/0312261 t o a pp ear in PLB. in collaboration with Robi Peschanski. Contents. Introduction gluon-initiated processes and saturation Framework the color dipoles, the GBW model and its extension

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Saturation at hadron colliders

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  1. Saturation at hadron colliders Cyrille Marquet SPhT, Saclay hep-ph/0312261 to appear in PLB in collaboration with Robi Peschanski

  2. Contents • Introductiongluon-initiated processes and saturation • Frameworkthecolor dipoles, the GBW model and its extension • Forward-jet production in terms of dipoles • Mueller-Navelet cross-sectionswith saturation effects • Conclusion and outlook

  3. Mueller-Navelet jets (1987): considered to test the BFKL evolution at the TevatronQ1, Q2 » QCD exp()» 1prediction: (>()2) Production of heavy-flavored and vector mesons Can we reach saturation inthese processes?atthe Tevatron or LHC ? How does one formulatesaturation in such processes? Gluon-initiated processes

  4. DIS: the Golec-Biernat and Wüsthoff (GBW) model (1998) forthe dipole-proton cross-section Saturation and the GBW model • photon-photon with an extension of the GBW model: a model for the dipole-dipole cross-section Tîmneanu, Kwiecinski and Motyka (2002)

  5. Dipole factorization for hardcross-sections • equivalent to BFKL+kT-factorization • in the present work, we assume this factorization property to hold in the presence of saturation

  6. thethree models exhibit color transparency • the model 3 correspondsto the two-gluon exchange betweenthe dipoles Extension of the GBW model TKM (2002) • the saturation radius iswe use the same parameters as those of dipole-proton = 0.288, 0 = 8.1 for Q0  1 GeV(universal saturation scale) • thethree scenarios we consider are 1. 2.3.

  7. the onium allows a perturbative calculation and the interpretation in the dipole formalism; in the collinear limitr0Q »1, f factorizes: Forward-jet in terms of dipoles Munier (2001), C.M. and R. P. (2003) collinear factorization dipole factorization

  8. large-size dipoleshave a contribution to  ; this is not the casefor in a photon-initiated process cannot be seen as a probability distribution the BFKL cross-sectionscalculated withare positive The dipole distribution in a forward jet Peschanski (2000), C.M. and R. P. (2003)

  9. Formulae for the hard total cross-sections C.M. and R. Peschanski (2003) for the different models : • the cross-sections are positivei > 0 • however2’s high-Q limit (no saturation) does not behave as 1/Q2

  10. Saturated cross-sections • model 3 withQ1= Q2  Q • the plot shows theexpected trend: a suppression of3in the domain Q<Qs 1/R0() Q0 = 1 GeV The rapidityintervals for the different curves are:  = 4, 6, 8, 10

  11. A suitable measurement • a ratio studiedto test theBFKL evolution at the Tevatron (DØcollaboration, 1999) • shows the influence of saturation in a more quantitative way • experimentally, Rwas obtained working at fixed andusing the factorization of the structure functionsinthe totalcross-sections: • R at LHC?

  12. An potentially interesting signal • thevalue of Rgoes downfrom the transparency limit towards the saturation regime whereR1 • one can observeasharper transition in the case of the gluon-initiated process • thevalues of Q at the transition are weak for jet cuts at the Tevatron • along with BFKL studies, the signal deserves to be studied at the LHC • alternatives to bypass the small-Q problem? Q0 = 1 GeV R 4.6/2.4 : ratiostudied attheTevatronR 8/4 : ratio realistic forthe LHC

  13. Other configurations • asymmetric configurations ? the transition towards saturation becomesreallysteep more interesting: the transition isshiftedtowardshigher Q Q0 = 1 GeV • alternatives to jets: heavy vector mesonsJ/ orD mesons withc quarks or B mesons with b quarks in asymmetric configurations?

  14. Conclusion and outlook • Introduction of the dipole formalismin the description of hadron-induced hard processes, such as Mueller-Navelet jets • Studies of saturation effects in these processes using an extension ofthe Golec-Biernat and Wüsthoff model • Proposal and predictions for an observable at hadron colliders To do • Studies of feasabilityforthe Tevatron and LHC:can we access the ratioR experimentally? for which values of Q? using jets or alternativelyheavy vector mesons, heavy flavors? Theoretical extensions • Improve our description of gluon-initiated processes in termsof dipoles:taking into account saturation effects in the emission vertex and kT-factorization breaking • StudyingpQCD saturation beyond GBW models

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