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Study of J/ψ photoproduction in
ultra-peripheral Au+Au collisions
at √sNN=200GeV using the PHENIX
detector
Akihisa Takahara
CNS University of Tokyo,RIKEN
For THE PHENIX collaboration
Autum JPS 2011
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Ultra Peripheral Collision
b>2R
γ
γ
Characteristics of UPC
→strong  - source
(X) Z2 ~ 6·103
()  Z4 ~ 4·107
@Au(79)
No Nuclear overlap
→ low background
relativistic charged
particle generates
strong
electromagnetic
field in transverse
plane
~ large gamma flux
RHIC max. photon
energies(EPA):
3 GeV~γ/R
UPC J/ψ pT^2
distribution
(Theoretical)
Coherent(γAu):
low pt peak
Incoherent(γn):
wider pt distribution
(Incoherent + neutron
tagged :
Yellow shadow )
Wmax  6GeV
WNmax  34GeV
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UPC J/ψ physics
Low x PDF
Photoproduction process is sensitive
To gluon distribution
We can see Q2≒2.5, x≒0.01
region by UPC J/psi cross section
measurement at RHIC
Theoretical predictions
And 2004 result
Phys.Rev.C78:044904,2008
Large Uncertainty
UPC is good probe to study
low x R(x,Q^2)
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Previous result and motivation
J. Nystrand, Nucl. Phys. A
752(2005)470c; A.J. Baltz, S.R. Klein,
J. Nystrand, PRL 89(2002)012301;
S.R. Klein, J. Nystrand, Phys. Rev. C
60(1999)014903
M. Strikman, M. Tverskoy and M.
Zhalov, Phys. Lett. B 626 72 (2005)
V. P. Goncalves and M. V. T.
Machado, arXiv:0706.2810 (2007).
Yu. P. Ivanov, B. Z. Kopeliovich and I.
Schmidt, arXiv:0706.1532 (2007).
Coherent theoretical
prediction
Incoherent theoretical
prediction
PHENIX already measured total cross section at central rapidity
• To study more detail of low x PDF,
• pT dependence of cross section
• forward-rapidity measurement
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UPC measurement in PHENIX
(at 2007central rapidity)
n
e+
e-
Coherent UPC
50-60%
UPC trigger(for central arm)
1. No MB trigger:BBC VETO
2. 1 or 2 neutron :ZDC
3. Emcal (>1GeV):ε（pt）
Zvertex information was calculated from
Track extrapolation
√sNN=200GeV, AuAu ,530/μb
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Pt dependence of UPC J/ψ+Xn
cross section for 2007 run central
It is the first measurement of pT dependence of UPC J/psi
Coherent part(lower pT peak) is dominant.
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UPC measurement in PHENIX(at
2010 forward rapidity)
Due to nose cone(Fe,hadron
suppressor),
We can’t get Z vertex from track
extrapolation.
Then we required BOTH ZDC
tagging for forward rapidity
analysis
UPC trigger(for muon arms)
1. No MB trigger:BBC VETO:ε≒1
2. 1 or 2 neutron :ZDC:ε≒1
3. At least 2tracks reach middle of MUID
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√sNN=200GeV, AuAu ,1400/μb
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Pt dependence of UPC
J/ψ+Xn(N)+Xn(S) cross section for
2007 & 10 run
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UPC dσ/dy distribution
J/ψ+Xn(N)+Xn(S)
1n tagging data and
Theoretical curve
J. Nystrand, Nucl. Phys. A 752(2005)470c; A.J. Baltz,
If “both tagging ” doesn’t change rapidity shape,
Looks like strikman curve
Autum JPS 2011
S.R. Klein, J. Nystrand, PRL 89(2002)012301; S.R.
Klein, J. Nystrand, Phys. Rev. C 60(1999)014903
M. Strikman, M. Tverskoy and M. Zhalov, Phys. Lett.
B 626 72 (2005)
V. P. Goncalves and M. V. T. Machado,
arXiv:0706.2810 (2007).
Yu. P. Ivanov, B. Z. Kopeliovich and I. Schmidt,
arXiv:0706.1532 (2007).
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Summary and outlook
Summary
• PHENIX first measurement pt dependence of UPC J/psi cross section at
central and forward rapidity
Outlook
– Future measurement with silicon detector at PHENIX. We can get Z vertex
forward silicon
– ALICE measurement at lower bjorken x
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Back up
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RHIC and PHENIX
Relativistic Heavy Ion Collider,
at the Brookhaven National
Laboratory (NY,USA)
•About 4km circumference
(Second largest of Ion collider)
•Center of mass energy per nucleons
~200GeV(AuAu),~500GeV(pp)
•AuAu, pp, d+Au,CuCu
2007-RUN
2010-RUN
•AuAu
•“200GeV
•~530/μb
•AuAu
•“200GeV
~1400/μb
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The experimental signatures
and the analysis
UPC signatures
Only e+ e- pair in central arm
At least 1 neutron
Analysis cut
•Vertex cut:|Zvertex|<30cm
•ZDC north || south>30GeV
•Number of electron candidate
tracks==2
•No real track other than
2 electron candidate tracks.
•BBC veto(offline)
•Electron(positron) id
•RICH associated
•Emcal matching
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RHIC and PHENIX
Relativistic Heavy Ion Collider,
at the Brookhaven National
Laboratory (NY,USA)
•About 4km circumference
(Second largest of Ion collider)
•Center of mass energy per nucleons
~200GeV(AuAu),~500GeV(pp)
•AuAu, pp, d+Au,CuCu
2007-RUN
•AuAu
•“200GeV
• Integrated Luminosity is4 times larger than last 2004 AuAu run
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RUN7 central UPC trigger
n
Coherent UPC:
γ+γ → e+e-, γ+A→ X+J/ψ:
lower pt<0.3GeV
Incoherent UPC:
γ+n → n+J/ψ :
wider pt
e+
Coherent UPC
e-
50-60%
ee pairs from UPC J/psi is measured by tagging forward neutron emission
UPC trigger
1. BBC detect no charge
2. EMCal energy threshold
1.0GeV
3. 1 or 2 ZDC detects
neutron
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Previous result
RHIC average
photon energy
corresponds to
24GeV
PHENIX 2004
•HERA -ZEUS measured γp-> J/psi photo
production cross section.
However , In general σ(A)≠σ(p).
•PHENIX measured UPC J/psi cross section at 2004.
•The result includes all theoretical predictions within 1sigma
Motivation
•To improve error to get enough quality to find fittest theoretical
predicition ->
2007 run has 4times statistics
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Comparison with HERA data
HERA data;
coh:incoh rate
Alpha_coh
Alpha_incoh
30.4:30.4
0.94
(for run 4:
1.01 ± 0.07)
0.86
(for run 4:
0.92 ± 0.08)
Please note this
calculation is
0.98-0.97
0.82-0.83
We don’t have
enough statistic to
separate coherent
and incoherent
Strikman(40:27-29:21)x
60.8/(coh+incoh)
Koperiovich
1.01
(53:21-61:24) x
60.8/(coh+incoh)
Alpha=1Hard probe scaling
Alpha=2/3 Soft probe scaling
0.75
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just a trial.
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Cross section compared to
theoretical calculation
Some coherent
prediction looks
enough to explain
the result.
However measured
pT spectra suggest
both coherent and
incoherent J/psi
production
J. Nystrand, Nucl. Phys. A 752(2005)470c; A.J. Baltz,
Run7:54.1±14.6 +10.3/-9.7μb
Run4(published data):76±31(stat)±11(sys) μb
Run 4& 7 combined
60.8±13.7(stat)+10.5−10.1(sys) μb. Autum JPS 2011
S.R. Klein, J. Nystrand, PRL 89(2002)012301; S.R.
Klein, J. Nystrand, Phys. Rev. C 60(1999)014903
M. Strikman, M. Tverskoy and M. Zhalov, Phys. Lett.
B 626 72 (2005)
V. P. Goncalves and M. V. T. Machado,
arXiv:0706.2810 (2007).
Yu. P. Ivanov, B. Z. Kopeliovich and I. Schmidt,
arXiv:0706.1532 (2007).
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characteristics of continuum and
coherent J/psi
γγ→ee
•Low pt peak
•Exp fitting
(~exp(-2.1mass))
J/psi
Coherent
•Low pt peak
•Gaussian fitting
STARLIGHT model with GEANT simulation
pT<0.8
Same simulation for coherent UPC J/psi
Likesign
unlikesign
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2004-2007 combined result
Run 4& 7 combined
60.8±13.7(stat)+10.5−10.1(sys) μb.
Compared to statistical error
•Strikman:
•Color dipole model
•Impluse or glauber approximation
1.2<|y|< 2.4 covered by
PHENIX muon arm, and
we have taken data
at RUN 10 &7.
Muon UPC will be analyzed
•+0.47- -0.62sigma
•Kopeliovich:
•Color dipole model+
gluon saturation effects
•KST or GBW parameterization
•+1.78- +1.05sigma
Strikman looks better
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Invariant mass
•No likesign pair
•43 ee pairs at mee>2GeV
•Clear J/psi peak
•Clear γγ→ee(Continumm)
Of course we have γγ→ee pair in J/psi region.
To estimate N(J/psi)
•Fitting function should be
Gaussian(J/psi) +continuum curve
•Continuum shape was estimated by
STARLIGHT simulation with PHENIX
detectors and trigger efficiency for
electrons
NJ/psi:18.75+-5.05(sta)+-0.25(sys)
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Pair pt
•Low J/psi pTpeak
suggest s
coherent UPC
•Some higher pT
event s suggests
Incoherent UPC
Red cross
symbols
correspond to
this region
Simulated data has
1000times larger
Statistics. However their
Max pT <0.8
At least, their incoherent events
We can see UPC
coherent (γAu) &incoherent (γn) J/Ψ production
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Fix pt vs 1-(1-eff_trg1)(1-eff_trg2)
~run 23500
run 23500~
nonpol
pol
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Glauber_mc
• offline/analysis/glauber_mc
•Au Au 200GeV default setting
•Trial
:500000
•Ncoll>=1
:272216
•Bbcnq==0||bbcsq==0:7388
Ineficiency=2.7%
bbcnq+bbcsq:for mass plot
Average ncoll at bbcsq==0||bbcnq==0
1.72
bbcnq+bbcsq:for sim
At bbcnq==0||bbcsq==0
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