looking for intrinsic charm at rhic and lhc
DESCRIPTION
Looking for intrinsic charm at RHIC and LHC. F.S. Navarra. University of São Paulo. V.P. Gonçalves. University of Pelotas. Winter Workshop on Nuclear Dynamics. 1 - 8 feb 2009. Charm sea. charm pair comes from the QCD DGLAP evolution. “extrinsic”. Perturbative QCD OK !. - PowerPoint PPT PresentationTRANSCRIPT
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