1. 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 1Autum JPS 2011

2. Ultra Peripheral Collision Characteristics of UPC →strong  - source  (  X)  Z 2 ~ 6·10 3  (  )  Z 4 ~ 4·10 7 @Au(79) No Nuclear overlap → low background RHIC max. photon energies(EPA): 3 GeV~γ/R relativistic charged particle generates strong electromagnetic field in transverse plane ~ large gamma flux b>2R γ γ 2Autum JPS 20112 UPC J/ψ pT^2 distribution (Theoretical) Coherent( γAu ): low pt peak Incoherent( γn ): wider pt distribution (Incoherent + neutron tagged : Yellow shadow )

3. UPC J/ψ physics Low x PDF 3 We can see Q2 ≒ 2.5, x ≒ 0.01 region by UPC J/psi cross section measurement at RHIC Autum JPS 2011 Large Uncertainty UPC is good probe to study low x R(x,Q^2) Phys.Rev.C78:044904,2008 Photoproduction process is sensitive To gluon distribution Theoretical predictions And 2004 result

4. Previous result and motivation 4Autum JPS 2011 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 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).

5. UPC measurement in PHENIX (at 2007central rapidity) n e+ e- Coherent UPC 50-60% 5 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 Autum JPS 2011 √sNN=200GeV, AuAu,530/μb

6. Pt dependence of UPC J/ψ+Xn cross section for 2007 run central Autum JPS 20116 It is the first measurement of pT dependence of UPC J/psi Coherent part(lower pT peak) is dominant.

7. UPC measurement in PHENIX(at 2010 forward rapidity) Autum JPS 20117 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 √sNN=200GeV, AuAu,1400/μb

8. Pt dependence of UPC J/ψ+Xn(N)+Xn(S) cross section for 2007 & 10 run Autum JPS 20118

9. UPC dσ/dy distribution J/ψ+Xn(N)+Xn(S) Autum JPS 20119 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). 1n tagging data and Theoretical curve If “both tagging ” doesn’t change rapidity shape, Looks like strikman curve

10. 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 10Autum JPS 2011

11. Back up 11Autum JPS 2011

12. RHIC and PHENIX 12 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 ~530/μb Autum JPS 2011 2010-RUN AuAu “200GeV ~1400/μb

13. The experimental signatures and the analysis 13 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 Autum JPS 2011

14. RHIC and PHENIX 14 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 Autum JPS 2011

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16. RUN7 central UPC trigger UPC trigger 1.BBC detect no charge 2.EMCal energy threshold 1.0GeV 3.1 or 2 ZDC detects neutron n e+ e- Coherent UPC 50-60% Coherent UPC: γ+γ → e+e-, γ+A→ X+J/ψ: lower pt<0.3GeV Incoherent UPC: γ+n → n+J/ψ : wider pt 16 ee pairs from UPC J/psi is measured by tagging forward neutron emission Autum JPS 2011

17. Previous result Autum JPS 201117 PHENIX 2004 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 RHIC average photon energy corresponds to 24GeV HERA -ZEUS measured γp-> J/psi photo production cross section. However, In general σ(A)≠σ(p).

18. Comparison with HERA data coh:incoh rateAlpha_cohAlpha_incoh 30.4:30.40.94 (for run 4: 1.01 ± 0.07) 0.86 (for run 4: 0.92 ± 0.08) Strikman(40:27-29:21)x 60.8/(coh+incoh) 0.98-0.970.82-0.83 Koperiovich (53:21-61:24) x 60.8/(coh+incoh) 1.010.75 HERA data; Please note this calculation is just a trial. We don’t have enough statistic to separate coherent and incoherent Alpha=1Hard probe scaling Alpha=2/3 Soft probe scaling 18Autum JPS 2011

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20. Cross section compared to theoretical calculation 20 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 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). Some coherent prediction looks enough to explain the result. However measured pT spectra suggest both coherent and incoherent J/psi production

21. characteristics of continuum and coherent J/psi 21 γγ→ee Low pt peak Exp fitting (~exp(-2.1mass)) J/psi Coherent Low pt peak Gaussian fitting STARLIGHT model with GEANT simulation Same simulation for coherent UPC J/psi Autum JPS 2011 Likesign unlikesign pT<0.8

22. 2004-2007 combined result Autum JPS 201122 Compared to statistical error Strikman: Color dipole model Impluse or glauber approximation +0.47- -0.62sigma Kopeliovich: Color dipole model+ gluon saturation effects KST or GBW parameterization +1.78- +1.05sigma Run 4& 7 combined 60.8±13.7(stat)+10.5−10.1(sys) μb. Strikman looks better 1.2<|y|< 2.4 covered by PHENIX muon arm, and we have taken data at RUN 10 &7. Muon UPC will be analyzed

23. No likesign pair 43 ee pairs at m ee >2GeV Clear J/psi peak Clear γγ→ee(Continumm) Of course we have γγ→ee pair in J/psi region. Invariant mass 23 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) Autum JPS 2011

24. Pair pt 24 Red cross symbols correspond to this region Low J/psi pTpeak suggest s coherent UPC Some higher pT event s suggests Incoherent UPC We can see UPC coherent (γAu) &incoherent (γn) J/Ψ production Autum JPS 2011 Simulated data has 1000times larger Statistics. However their Max pT <0.8 At least, their incoherent events

25. Fix pt vs 1-(1-eff_trg1)(1-eff_trg2) ~run 23500run 23500~ nonpol pol 25Autum JPS 2011

26. Glauber_mc offline/analysis/glauber_mc Au Au 200GeV default setting Trial :500000 Ncoll>=1 :272216 Bbcnq==0||bbcsq==0:7388 Ineficiency=2.7% Average ncoll at bbcsq==0||bbcnq==0 1.72 bbcnq+bbcsq:for mass plotbbcnq+bbcsq:for sim At bbcnq==0||bbcsq==0 26Autum JPS 2011