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Looking for intrinsic charm at RHIC and LHC University of São Paulo University of Pelotas F.S. Navarra V.P. Gonçalves Winter Workshop on Nuclear Dynamics 1 - 8 feb 2009

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Charm sea “extrinsic” “intrinsic” The pair knows in which hadron it is ! Strong non-perturbative effects Brodsky, Hoyer, Peterson, Sakai, (80) charm pair comes from the QCD DGLAP evolution charm pair was there before evolution Perturbative QCD OK !

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Bag with five quarks Probability to find a charm – anticharm pair in the proton : Momentum distribution : integrate P over momentum of the parton i Heavy quarkLight quark Brodsky, Hoyer, Peterson, Sakai, (80)

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Charm meson cloud proton both with similar momentum fraction charm quarks are hard ! Paiva, Nielsen, Navarra, Durães, Barz (98) Carvalho, Durães, Navarra, Nielsen (01) Navarra, Nielsen, Nunes, Teixeira (96)

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Can we measure IC ? Parton distributions measured in Deep Inelastic Scattering : Gunion, Vogt, hep-ph/9706252 massless charm extrinsic charm extrinsic intrinsic Pumplin, Lai, Tung, hep-ph/0701220 CTEQ6.5C : fits of DIS data favor 1-2 % IC

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Hadronic collisions IC is hard and will produce charm at large momentum Standard descrition in proton-proton collisions (PYTHIA) collinear factorization formula

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PYTHIA fails for D´s with large longitudinal momentum ! Excess of “fast” D´s can be explained with IC large small PYTHIA

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High densities: non-linear evolution Saturation gluon recombination g g -> g Non-linear evolution equations: JIMWLK and BK 1994 – 2008: low x “revolution “ Collinear factorization breaks down ! Color Glass Condensate

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Change from parton distributions to dipole cross sections: DIS color dipole

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BRAHMS Physics is in the “anomalous dimension”: when or when saturation scale Boer, Utermann, Wessels hep-ph/0701219 Help from approximate solutions of BFKL, BK Use N to fit data: Color dipoles also in hadron-hadron collisions

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amplitudeconjugate amplitude abstract dipole

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Forward hadron production at RHIC quark–antiquark dipole cros section gluon-gluon dipole cros section standard parton distributions in the proton: MRST, CTEQ,... standard parton fragmentation functions: KKP,... dilutedense dilute CGC formula Dumitru, Hayashigaki Jalilian-Marian (04)

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Forward charm production at RHIC collinear factorization formulaCGC formula dilutedense dilute gluon-gluon fusion quark-antiquark fusion small at large D suppression charm from CTEQ6.5C recent fit from RHIC data Pumplin, Lai, Tung, hep-ph/0701220 Boer, Utermann, Wessels hep-ph/0701219 No new parameter!

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The CTEQ 6.5 C parametrizations : extrinsic charm

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D transverse momentum spectra extrinsic charm p

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Ratio IC / No IC p

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D transverse momentum spectra

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Ratio IC / No IC

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D transverse momentum spectra extrinsic charm

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Ratio IC / No IC

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IC + CGC versus “standard physics” PYTHIA: collinear factorization overestimates the gluon density in the target higher cross sections ! no intrinsic charm standard parton distributions STAR version (thanks to Thomas Ullrich!) IC + CGC: intrinsic charm fom CTEQ dipole approach: dipole cross section from BUW IC enhances the cross sections non-linear effects deplete the gluon density in the target decrease the cross sections

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D transverse momentum spectra

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Complementary search of IC Kniehl, Kramer, Schienbein, Spisberger, arXiv: 0901.4130 IC / No-IC BHPS Meson Cloud

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Summary Intrinsic charm is the non-perturbative component of the charm sea of the proton. Still to be confirmed... IC explains HERA and ISR data Best place to look for it: at RHIC at large rapidities (FPD) Intrinsic/extrinsic ~ 10 Results very sensitive to parton distributions...

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Nuclear modification ratio: Saturation reduces the number of gluons in the target and the number of produced particles at large rapidity Qualitative prediction :

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

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Introduction Origin of the sea quarks the proton? valence sea

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PYTHIA IC Perturbative parton branching

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