Looking for intrinsic charm at RHIC and LHC

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