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

Charm sea

“extrinsic”

“intrinsic”

The pair knows in which hadron it is !

Strong non-perturbative effects

Brodsky, Hoyer, Peterson, Sakai, (80)

c

c

c

c

charm pair comesfrom the QCD DGLAP evolution

charm pair was there before evolution

Perturbative QCD OK !

Bag with five quarksProbability to find a charm – anticharm pair in the proton :

Momentum distribution : integrate P over

ccduu|

2220

][ MmPP

p

5

1

22

i i

i

xm

M ix momentum of the parton i

)()( 5 xcxP 4321 xxxx

Heavy quark Light quark

Brodsky, Hoyer, Peterson, Sakai, (80)

Charm meson cloud

proton protonc

D

cduc

cuD

MeVmD 1870

MeVm 2280

MeVmc 1500

both with similar momentum fraction

5.0x

MeVmc 300charm quarks are hard !

5.0cx

Paiva, Nielsen, Navarra, Durães, Barz (98)

Carvalho, Durães, Navarra, Nielsen (01)

Navarra, Nielsen, Nunes, Teixeira (96)

)(][

])([16

)( 2´22

2´

2´

max

tFmtmmtdtxgxf MBB

M

BBt

MBB

]1[

2´2

max xxmmt B

B

Can we measure IC ?

Parton distributions measured in Deep Inelastic Scattering :

)()(2 xcxF cXDp

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

Hadronic collisionsIC is hard and will produce charm at large momentum

Standard descrition in proton-proton collisions (PYTHIA)

ccgg ccqq

),(),(),(ˆ),(),( 2221

22

21

1

0

1

0212 TDcTDcccgggg

TDD

Xccpp

pxDpxDxxQxfQxfxdxdpdxdxd

d

collinear factorization formula

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

1x

2x

)( Fx

2

1ln21

xxy

21 xxxF

large

Fx y

small 2x

Fx

PYTHIA

FxdNd

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

),( 22 Qxf g

Change from parton distributions to dipole cross sections:

DIS

),,(2),( 2 brxNbdrxdip

colordipole

BRAHMS

Physics is in the “anomalous dimension”:

),( xr

})({exp1),( 22sQrrxN

}

1),( rxN when r or 0x22),( sQrrxN when 0r

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

xxQAQs 02

03/12

amplitude conjugate amplitude

abstract dipole

Forward hadron production at RHIC

),(),(),()2(1 22

1

222

)(

QxxDbp

xxNQxf

xx

xdbdpdxd

dxp

FqT

p

FFpq

x F

pp

TF

XhApp

F

F

),(),(),()2(1 22

1

2 QxxDbp

xxNQxf

xx

xdp

FgT

p

FApg

x F

pp

F

quark–antiquark dipole cros sectiongluon-gluon dipole cros section

FN

AN

standard parton distributions in the proton: MRST, CTEQ, ...

standard parton fragmentation functions: KKP, ...

qf

qD

dilute dense dilute

CGC formula Dumitru, HayashigakiJalilian-Marian (04)

Forward charm production at RHICcollinear factorization

formulaCGC formula

),(),(),()2(1 22

1

222

)(

QxxDbp

xxNQxf

xx

xdbdpdxd

dxp

FqT

p

FFpq

x F

pp

TF

XhApp

F

F

),(),(),()2(1 22

1

2 QxxDbp

xxNQxf

xx

xdp

FgT

p

FApg

x F

pp

F

dilute dense dilute

gluon-gluon fusionquark-antiquark fusion

small at large D suppression

qf charm from CTEQ6.5C

FN recent fit from RHIC data

Pumplin, Lai, Tung, hep-ph/0701220

Boer, Utermann, Wessels hep-ph/0701219

No new parameter!

Fx

The CTEQ 6.5 C parametrizations :

extrinsic charm

)(2 xcx

D transverse momentum spectra

extrinsic charm

p p

TpdydNd2

Ratio IC / No IC

p p

D transverse momentum spectra

TpdydNd2

Ratio IC / No IC

D transverse momentum spectra

extrinsic charm

Ratio IC / No IC

IC + CGC versus “standard physics”

PYTHIA: ccgg ccqq collinear factorization

overestimates the gluon density in the targethigher cross sections !

no intrinsic charm

standard parton distributions

STAR version (thanks to Thomas Ullrich!)

IC + CGC:

intrinsic charm fom CTEQdipole approach: dipole cross section from BUW

IC enhances the cross sections

gcgc

non-linear effects deplete the gluon density in the targetdecrease the cross sections

D transverse momentum spectra

D transverse momentum spectra

Complementary search of IC

sepxy

T1Kniehl, Kramer, Schienbein, Spisberger, arXiv: 0901.4130

IC / No-IC BHPS

Meson Cloud

Summary

Intrinsic charm is the non-perturbative component of the charm sea of the proton. Still to be confirmed...

IC explains HERA and ISR dataBest place to look for it: at RHIC at large rapidities (FPD)Intrinsic/extrinsic ~ 10 Results very sensitive to parton distributions...

AudR

)(GeVpT

T

ppT

pA

pp

pA

pA

pddA

pdd

AR

Nuclear modification ratio:

Saturation reduces the number of gluons in the target and the number of produced particles at large rapidity

Qualitative prediction :

QS : saturation scale

xxQAQs 02

03/12),( 2

22 QxGx

QnR s

Saturation condition: target area completely filled by gluons

nR 222sQQ 22sQQ nR 2

dilute (linear)

dense (saturation)

Saturation scale

)( 22

2

QWQx

220 0.1 GeVQ

40 10267.0 x

253.0

2sQ is large !CGC visible when

LHC : x may be smalleRHIC : A may be large

Introduction

Origin of the sea quarks the proton?

valence

sea

PYTHIA

IC

Perturbative parton branching