Transcript Forward Physics in d+Au Collisions at PHENIX: Cold nuclear matter probed with J/ production and pion correlations Richard Seto for the PHENIX Collaboration University of.

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Forward Physics in d+Au Collisions
at PHENIX:
Cold nuclear matter probed with J/ production and pion correlations
Richard Seto
for the PHENIX Collaboration
University of California, Riverside
Rencontres de Moriond
QCD and High Energy Interactions
La Thuile, March 20-27, 2011
Thanks to my colleagues from whom
I have shameless stolen slides –
Particularly Matt Wysocki, Oleg Eyser
And Beau Meredith
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Why ask about Cold nuclear matter?
• sQGP – How is it born?
▫ τthermalization<1 fm but RsQGP~10
fm
 Explaining uniformity?
 Early Universe – inflation
▫ What sets initial condition of
Cold Nuclear Matter is the initial state
the sQGP?
 Preof
equilibrium
interest*interactions ?
 Turbulence
*also interesting in its own right
 Strongly
coupled (AdS/CFT)
 Weakly coupled (pQCD)
 What does the initial state
look like?
10 fm
τthermalization< 1 fm
 Structure functions ?
▫ BUT in the nucleus they are
xG(x)
altered
▫ In particular gluons x < 0.01
suppressed
Look at 2 models
x
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Model 1: gluon PDF and nuclear shadowing
Nuclear PDF  proton PDF
RG
Fit data on nuclei:
SLAC, NMC, EMC
DIS+DY+PHENIX
midrapidty π0
Lack of data
large uncertainly
in gluon pdf
at low-x
Pb
xGA ( x, Q2 )
( x, Q ) 
AxGp ( x, Q2 )
2
b=0-100%”
gluons
Large uncertainty
At lox-x
x
Eskola , Paukkunen, Salgado, JHP04 (2009)065
We will add two things:
1) Assume linear dependence on
2) For the J/ψ include σ br to account
density-weighted longitudinal
nuclear thickness
for the breakup of the cc pair while
 impact parameter (centrality)
passing through the nucleus
dependence
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Model 2: The Color Glass Condensate (CGC)
• Saturation of low-x
gluons
▫ high density
Recombination of
gluons, hence
suppression @ low-x
▫ Characterized by QS
▫ Nuclear Amplification
 xGA=A1/3xGp
Cartoon
x 
QS  Q0, S  0 
 x

Min-bias
Central
 We can exploit this
behavior vs centrality
• Region of validity: low-x
(forward rapidity)
Central:  =.23 Q0,2 S  2.5 GeV 2 x0  .01 (Kharzeev, Levin private communication)
Min Bias:  =.23 Q0,2 S  0.9 GeV 2 x0  .02 (Alacete,Marquet Phys.Lett.B687:174-179,2010)
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Comments:
Confuses
experimentalists
▫ plethora of effects e.g. Coherence, Higher twist effects, Initial
state energy loss
Strong coupling
• The CGC is a full QCD calculation in a particular limit which
should include all such effects
• Worry : CGC is a non-perturbative but weakly
coupled theory and requires αS(QS) to be
“small”. Much of the bulk (which makes up the
sQGP) may be from regions where αS is large
▫ Saturation calculation at strong coupling using AdS/CFT
Iancu, NPA(2011) 18. (a conformal theory with lots of other
stuff – but αS doesn’t change much at the phase transition...)
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Lets first look at the J/
+
• g+g  J/ψ dominant @RHIC e
Nice coverage in y or
equivalently x(Au)
forward y x~0.005
mid y
x~0.03
backward y x~0.1
μ+
μ-
μ+
e-
μ-
d
Central Arms
Au
• e+e- -0.35<<0.35
• μ+μ- 1.2<||<2.4
forward
mid
back
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J/ dN/dy vs. rapidity
S NN  200 GeV
p+p
 Suppression clearly
visible
 Now divide
d+Au
d
 d+Au is scaled by 1/Ncoll
 Ncoll=number of
binary collisions
Au
arXiv:1010.1246
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RdAu
1 Yield dAu

Ncoll Yield pp
RdAu(0-100%)
RdAu for minimum bias collisions
Significant suppression at
mid and forward
rapidities.
y
Now compare to the
models..
Bars = point-to-point uncorrelated uncertainties
Boxes = point-to-point correlated uncertainties
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RdAu for minimum bias collisions
Compare to Model 1:
EPS09 nuclear PDF +
sbr = 4 mb (red curves).
sbr is the only free
parameter.
Reasonable agreement
Dashed lines are the
maximum variation
included in EPS09.
Note: EPS09, as published, is averaged over all b and we get decent
agreement with RdAu(0-100%).
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What about the CGC?
Kharzeev and Tuchin
NPA 770(2006) 40
 Include gluon saturation at low x
(affects forward rapidity)
 Enhancement from double gluon
____exchange with nucleus at midrapidity
We can break the data down further by dividing events into small and
large impact parameter.
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RdAu central and
peripheral
Model I: EPS09 nuclear PDF + sbr = 4 mb
is now deviating from the peripheral data
Gluon saturation again matches the
forward rapidity points relatively well,
but not mid-rapidity
We can further reduce systematics
by taking the ratio.
peripheral
central
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RCP
RCP
RdAu (central )

RdAu ( peripheral )
peripheral
RCP has the advantage of cancelling
most of the systematic uncertainties.
Now with reduced errors Model I with
the nuclear PDF and σbreakup=4mb does
not match the data
The CGC model works at least in the
forward region
•Is there something else we can look at which
• might be directly related to the condensate?
central
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Pion Correlations
• Gluons overlap and make a condensate
▫ Incoming quark interacts with condensate
coherently
▫ pT balanced by condensate leading to
“monoJets”
▫ Look for single “jets” (actually single particles)
with no correlated “jet” on opposite side
p
Jet
“monoJet”
deuteron
Gluon condensate
p
Jet
Au nucleus
The MPC (Muon Piston Calorimeters)
PHENIX
Central region
Side View
p0 or
clusters
1) Particle into MPC
e.g. π0 MPC (3.2> >3.8) pT>2.25
2) Choose 2nd particle with pT2>1.75
azimuthally opposite
3) plot 2 vs x2
Pythia simulation
π0 MPC (3.2> >3.8) pT>2.25
π pT2>1.75
MPC
p0 or h+/d
Au
2
Central Arms
2nd Particle in central arm: x2 ~ .03
2nd Particle in MPC: x2 ~ .001
Log(x2)
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The Nuclear Modification Factor
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 Correlation function
Same
side peak
will be
missing
Two-particle distribution
Including two-particle acceptance
Npairs
0
Crucial that we have
Models that can
Describe many
Aspects of the data
π
Coherent QCD
(rad)
Multiple
scattering
pT 1  1.5 GeV
pT 2  1 GeV
y1  4
y2  0
CGC calculation
Kharzeev, Levin, McLerran NPA 748,627(2006)
Two sides of
the same coin?
Qiu,Vitev PLB 692, 507(2006)
2π
The Nuclear Modification Factor
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 Correlation function
Same
side peak
will be
missing
Two-particle distribution
Including two-particle acceptance
Npairs
 Conditional yield
Number particle pairs per trigger particle
0
Including acceptance & efficiency
 Nuclear modification factor
Conditional yield ratio d+A/p+p
 Indicators of gluon saturation
IdA < 1
effect gets stronger with centrality
π
(rad)
2π
Central Arm - MPC Correlations
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<pTa>=2.00 GeV/c
2.0 <
GeV/c
pp
< 3.0
for all plots
Correlation
Function
pTt
dAu
60-88%
dAu
0-20%
0
p

peripheral to central
2p
Consistent with CGC
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Both particles in
MPC (work in progress)
• Correlation Functions
▫ Peripheral events
 pp and dAu are same
▫ Central events
 dAu looses correlated peak
Qualitative agreement
with a CGC picture
Quantitative Analysis
and a publication forthcoming
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Summary
• The data
▫ J/psi
 Unable to reconcile rapidity and centrality dependence with
Shadowing + naïve breakup cross section
 CGC hypothesis works at forward rapidity
▫ Pion Correlations
 Suppression with centrality in central-forward correlations
(moderate x)
 Suppression with centrality in forward-forward correlations
(low-x) in qualitative agreement with CGC model
• Closing thoughts
▫ Regime probed in present heavy experiments need new
non-pertubative QCD techniques e.g. CGC, AdS/CFT,
hydrodynamic codes to explain the data
▫ We must understand Cold Nuclear Matter - the initial
condition for the heavy ion reaction – if we are to
understand the sQGP