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ForwardDi-Hadron Correlations
in d+Au Collisions in PHENIX
Searching for Gluon Saturationwith the MPC
ForwardDi-Hadron Correlations
in d+Au Collisions in PHENIX
Searching for Gluon Saturationwith the MPC
DIFFRACTION 2010, Sep. 10-15, Otranto, Italy
Oleg Eyser
Beau Meredith, Mickey Chiu, Matthias Perdekamp
for the PHENIX Collaboration
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Bremsstrahlung~ sln(1/x)
The gluon density at low x
Recombination~ sr
At small x we see an increase in gluons.
There must be a kinematic region in
which the gluon density reaches a saturation!
There must be a kinematic region in
which the gluon density reaches a saturation!
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log
x-1
log Q2
DGLAPnon
-pert
urb
ati
ve
log QCD2
Qs2(x)
SaturationScale
BKFL
PartonGas
Color Glass
Condensate
The color glass condensate
Hadronic probe Couple to gluons
High A Higher parton densities
Asymmetric Probe low x
Hadronic probe Couple to gluons
High A Higher parton densities
Asymmetric Probe low x
d Au
Mid Rapidity
Forward Rapidity
yT es
px 2
~
pT is
bala
nce
d b
y g
luons
4
0 meson||<0.35
PRL 97, 53203 (2006)
PRL 98, 172302 (2007)
CGC expectationsKharzeev, Kovchegov,,Tuchin, Phys.Rev.D68:094013,2003
Signatures of the CGC
PHENIX
BRAHMSSTAR
incre
ase
d
Gluon saturation is not the only explanation for
the reduced yields. There may be other
effects.
Gluon saturation is not the only explanation for
the reduced yields. There may be other
effects.
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pQCD 2→2 process = back-to-back di-jet With shadowing in nucleus
forward jet
mid-rapidity jet
p
d+Au in HIJING (A. Ogawa)
Shadowing in jet correlations
p
Au
d
Vitev, hep-ph/0405068v2
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Kharzeev, Levin, McLerran (NPA748, 627)
Mono-jets from the CGC
d
In the saturation regime the jet pT is balanced by many gluons.
Audense gluon field
The gluon field is increased in central vs. peripheral collisions.
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Correlation functionTwo-particle distributionIncluding two-particle acceptance
Conditional yieldNumber particle pairs per trigger particleIncluding acceptance & efficiency
Nuclear modification factorConditional yield ratio d+A/p+p
Indicators of gluon saturation IdA < 1 Angular de-correlation of widths
The Nuclear Modification Factor
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PHENIXSTAR
BRAHMSpp2ppd+Au vs p+p
high-x valence quarks
0.25 < xq < 0.7 on low-x gluons
0.001 < xg < 0.1Signatures of saturation suppressions of nuclear modification
factors angular de-correlations of di-jet
signals
d+Au vs p+phigh-x valence quarks
0.25 < xq < 0.7 on low-x gluons
0.001 < xg < 0.1Signatures of saturation suppressions of nuclear modification
factors angular de-correlations of di-jet
signals
Gluon Saturation @ RHIC
saturation is
expected at x≈10-4
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Azimuthal Correlations in PHENIX
Trigger particle Associate particle Correlation
Near side peak Away side peak
Central Arms | η | < 0.35Muon Arms 1.2 < | η | < 2.4Central Arms | η | < 0.35Muon Arms 1.2 < | η | < 2.4Muon Piston Calorimeter
3.1 < | η | < 3.9Muon Piston Calorimeter 3.1 < | η | < 3.9
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Azimuthal Correlations (prev.)
2003 data Trigger hadron from the muon arms Correlated hadron from the central arm
Phys.Rev.Lett.96:222301,2006
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invariant mass distribution
11 GeV < E < 15 GeV
o Signal pairso Mixed event pairs 0 yield
Electromagnetic Calorimetersat rapidity 3.1 < || < 3.9
2.2 x 2.2 x 18 cm3 PbWO4 crystals 220 cm from nominal interaction point
0 merging effects pT max ~ 2 GeV/c at outside ring
For higher pT Reconstructed 0s for 7 GeV < E < 22
GeV Clusters for E > 15 GeV (~ 85% 0)
The Muon Piston Calorimeters
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Forward Di-jet Signal with
0 orclusters
0 or h+/-
PHENIXCentral region
Side View
xgluon ~ 10-2
Aueffective xgluon ~ 10-3
d Au
peripheral to centralperipheral to central
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Forward correlations at = 3.4
0 orclusters
PHENIXCentral region
Side View
xgluon ~ 10-3
Aueffective xgluon ~ 10-4
d Au
Work in progress Area of away-side peak represents
conditional yield No efficiency correction No uncorrelated background yet Conditional yields, widths not
shown
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Trigger particle pT > 2 GeV/c
Associate particle pT > 0.875 GeV/c
Forward correlations (minBias)
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Forward correlations
peripheral central
Peripheral d+Au seems more similar to p+pCentral d+Au shows a reduced yield, maybe broadening
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pT,trigger
pT,associate
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pT,trigger
pT,associate
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Central/forward di-hadron correlations No significant broadening between d+Au vs pp Reduced IdA in more central collisions Model calculations are needed to understand
this effect
Forward/forward di-hadron correlations Qualitative indications of onset of gluon
saturation hypothesis in reduced yields Data also suggests width broadening More work needed on uncorrelated background!
Summary