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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