Apresentao do PowerPoint

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Looking for intrinsic charm at RHIC and
LHC
F.S. Navarra
University of São Paulo
V.P. Gonçalves
University of Pelotas
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Introduction
Origin of the sea quarks the proton?
valence
sea
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Charm sea
extrinsic
Perturbative parton branching
BFKL and DGLAP evolution
intrinsic
The pair knows in which hadron it is !
Non-perturbative effects
Brodsky, Hoyer, Peterson, Sakai, PLB 1980
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Bag with five quarks
Brodsky, Hoyer, Peterson, Sakai, PLB 1980
Probability to find a charm anticharm pair in
the proton
momentum of the parton i
Momentum distribution integrate P over
Heavy quark
Light quark
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Navarra, Nielsen, Nunes, Teixeira PRC
1996
Charm meson cloud
Paiva, Nielsen, Navarra, Durães, Barz
MPLA 1998
Carvalho, Durães, Navarra, Nielsen PRL
2001
both particles with similar momentum fraction
charm quarks carry most of the momentum
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Can we measure IC ?
Parton distributions measured in Deep Inelastic
Scattering
Gunion, Vogt, hep-ph/9706252
massless charm
extrinsic
extrinsic charm
intrinsic
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CTEQ6.5C recent analysis of DIS
Pumplin, Lai, Tung, hep-ph/0701220
extrinsic charm
intrinsic charm
Global fits of DIS data favor the existence of
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 Ds with large longitudinal
momentum !
IC
Excess of fast Ds can be explained with IC
PYTHIA
PYTHIA
large
small
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1999 2008 low x revolution
High densities non-linear evolution
gluon recombination g g -gt g
Saturation Color Glass Condensate
Non-linear evolution equations
JIMWLK and BK
Collinear factorization breaks down !
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grows slower with 1/x
Change from parton distributions to dipole cross
sections
color dipole
DIS
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amplitude
conjugate amplitude
abstract dipole
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Forward hadron production at RHIC
dilute
dense
dilute
CGC formula
quarkantiquark dipole cros section
theory data fitting
gluon-gluon dipole cros section
standard parton distributions in the proton
MRST, CTEQ, ...
standard parton fragmentation functions KKP, ...
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saturation scale
or
when
when
Physics is in the anomalous dimension
BRAHMS
(from approximate solutions of BFKL, BK)
Boer, Utermann, Wessels hep-ph/0701219
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Forward charm production at RHIC
collinear factorization formula
CGC formula
dilute
dense
dilute
gluon-gluon fusion
small at large
D suppression
quark-antiquark fusion
charm from CTEQ6.5C
Pumplin, Lai, Tung, hep-ph/0701220
recent fit from RHIC data
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
p p
extrinsic charm
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Ratio IC / No IC
p 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
no intrinsic charm
collinear factorization
standard parton distributions
overestimates the gluon density in the target
higher cross sections !
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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D transverse momentum spectra
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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 to 20
Results very sensitive to parton distributions...
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Qualitative prediction
Saturation reduces the number of gluons in the
target and the number of produced particles at
large rapidity
Nuclear modification ratio
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Saturation scale
Saturation condition target area completely
filled by gluons
QS saturation scale
dilute (linear)
dense (saturation)
LHC x may be small
eRHIC A may be large
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