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Saturation and forward jets

Saturation and forward jets. Cyrille Marquet SPhT, Saclay. Low-x meeting, Prague, 2004. Contents. Introduction fixed-scale evolution and saturation Forward-gluon production in terms of dip o les in the eikonal approximation and at leading log(1/ x ) accuracy

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Saturation and forward jets

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  1. Saturation and forward jets Cyrille Marquet SPhT, Saclay Low-x meeting, Prague, 2004

  2. Contents • Introductionfixed-scale evolution and saturation • Forward-gluon production in terms of dipolesin the eikonal approximation and at leading log(1/x) accuracy • Fit to the HERA forward-jet datausing a GBW parametrization • Mueller-Navelet jetspredictions for the Tevatron and LHC • Conclusion and outlook

  3. Introduction

  4. *-* total cross-section: **  Xsuitable to test fixed-scale evolutionBFKLprediction: How does saturation set in?What is the saturation scale? *-* scattering • High-energy behavior:determined by dipole-dipole scattering • Tîmneanu, Kwiecinski and Motyka (2002) Kozlovand Levin (2003)

  5. p+*  jet+XQ, kT » QCD exp()» 1 Same kind of process than *-* but more statisticsdata from H1 and ZEUS Are saturation effects sizable at HERA? Forward-jet production • What is the relation with the dipole-dipole scattering?

  6. Forward-gluon production C. M. hep-ph/0409023

  7. Inclusive gluon production • The cross-section is derived for an arbitrary target and for an incident dipole of sizer0= x0-x1 • Approximations: • leading log(1/x) for the emitted gluon (y = log(1/x)) • the propagation through the target is eikonal and described by the Wilson lines

  8. An intermediate step • Doing the calculation in coordinate space, one obtains: • b=(x0+x1)/2 is the impact parameter • Tgg(x, x’) is the forward scattering amplitude of a gluon dipole on the target: see also Kovchegov and Tuchin PRD 65 (2002) 074026 for a target nucleus

  9. Final result • (gg)t(z) is the dipole(gg)-target total cross-section a dipole factorized form for the gluon-production cross-section • An alternative to write the cross-section:

  10. Gluon-production from an incident hadron evolution before the emission collinear limit r0»1 • gh is the gluon density inside the incident hadron •  is the factorization scale and xJ = exp(-y)

  11. Fitting the HERA data In collaboration with R. Peschanski and C. Royonhep-ph/0407011, to appear in PLB

  12. The forward-jet cross-section • x, y, Q2 : usual kinematic variables of DIS • xJ , k: longitudinal and transverse momentum of the jet •  = log(xJ /x) : rapidity interval with the hard cross-section given by

  13. The saturation model • An extension of the GBW model Tîmneanu, Kwiecinski and Motyka (2002)with • The saturation radius iswe fit the parameters  , 0and a normalization Q0  1 GeV

  14. Results of the fits • The first solution corresponds to significant saturation effects • The second solution corresponds to weak saturation effects • The intercept l is in both cases higher than what was found for F2 (lGBW = 0.288)

  15. The saturation fit

  16. The saturation scales • The saturation scale is QS 1/R0(Dh) • The plot represents • The weak saturation solution is compatible with the F2 parametrization • The other solution shows a harder saturation scale

  17. Mueller-Navelet jets C. M., R. Peschanski, PLB587 (2004) 201 C. M., R. Peschanski and C. Royon, hep-ph/0407011, to appear in PLB

  18. Mueller-Navelet jets • p+p  jet+X+jet :Q1, Q2 » QCD exp()» 1 • Can one reach saturation inthese processes?atthe Tevatron or LHC ? • The cross-section is

  19. Predictions for the LHC a suitable observable: a ratio studiedto test the BFKL evolution at the Tevatron (DØcollaboration, 1999) • The plot showsR 8/2 for Q1=Q2kT and the GBW parametrization • The two saturation solutions give different predictions this measurement at the LHC would distinguish between the two solutions

  20. Conclusion and outlook • Derivation of the cross-sectiondipole + target  forward gluon + X introduction of a dipole formalismfor the description of forward-jet emissions • Studies of saturation effects in forward jets at HERA using a GBW parametrization two solutions for the saturation scale: weak or significant saturation • Mueller-Navelet jets at Tevatron or LHC could distinguish between both solutions • Is the saturation scale universal?

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