Study of J photoproduction in ultraperipheral AuAu collisions

Study of J/ψ photoproduction in ultra-peripheral Au+Au collisions at √s. NN=200 Ge. V using the PHENIX detector Akihisa Takahara CNS University of Tokyo, RIKEN For THE PHENIX collaboration Autum JPS 2011 1

Ultra Peripheral Collision b>2 R γ γ Characteristics of UPC relativistic charged particle generates strong electromagnetic field in transverse plane ~ large gamma flux RHIC max. photon energies(EPA): 3 Ge. V~γ/R UPC J/ψ p. T^2 distribution (Theoretical) Coherent(γAu): low pt peak Incoherent(γn): wider pt distribution (Incoherent + neutron tagged : Yellow shadow ) →strong - source ( X) Z 2 ~ 6· 103 ( ) Z 4 ~ 4· 107 @Au(79) No Nuclear overlap → low background Autum JPS 2011 2

UPC J/ψ physics Low x PDF Photoproduction process is sensitive To gluon distribution We can see Q 2≒ 2. 5, x≒ 0. 01 region by UPC J/psi cross section measurement at RHIC Theoretical predictions And 2004 result Phys. Rev. C 78: 044904, 2008 Large Uncertainty UPC is good probe to study low x R(x, Q^2) Autum JPS 2011 3

Previous result and motivation J. Nystrand, Nucl. Phys. A 752(2005)470 c; 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, ar. Xiv: 0706. 2810 (2007). Yu. P. Ivanov, B. Z. Kopeliovich and I. Schmidt, ar. Xiv: 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, • p. T dependence of cross section • forward-rapidity measurement Autum JPS 2011 4

UPC measurement in PHENIX (at 2007 central 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 (>1 Ge. V): ε（pt） Zvertex information was calculated from Track extrapolation √s. NN=200 Ge. V, Au. Au , 530/μb Autum JPS 2011 5

Pt dependence of UPC J/ψ+Xn cross section for 2007 run central It is the first measurement of p. T dependence of UPC J/psi Coherent part(lower p. T peak) is dominant. Autum JPS 2011 6

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 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 2 tracks reach middle of MUID Autum JPS 2011 √s. NN=200 Ge. V, Au. Au , 1400/μb 7

Pt dependence of UPC J/ψ+Xn(N)+Xn(S) cross section for 2007 & 10 run Autum JPS 2011 8

UPC dσ/dy distribution J/ψ+Xn(N)+Xn(S) 1 n tagging data and Theoretical curve J. Nystrand, Nucl. Phys. A 752(2005)470 c; A. J. If “both tagging ” doesn’t change rapidity shape, Looks like strikman curve Autum JPS 2011 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, ar. Xiv: 0706. 2810 (2007). Yu. P. Ivanov, B. Z. Kopeliovich and I. Schmidt, ar. Xiv: 0706. 1532 (2007). 9

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 Autum JPS 2011 10

Back up Autum JPS 2011 11

RHIC and PHENIX Relativistic Heavy Ion Collider, at the Brookhaven National Laboratory (NY, USA) • About 4 km circumference (Second largest of Ion collider) • Center of mass energy per nucleons ~200 Ge. V(Au. Au), ~500 Ge. V(pp) • Au. Au, pp, d+Au, Cu. Cu 2007 -RUN 2010 -RUN • Au. Au • “ 200 Ge. V • ~530/μb • Au. Au • “ 200 Ge. V ~1400/μb Autum JPS 2011 12

The experimental signatures and the analysis UPC signatures Only e+ e- pair in central arm At least 1 neutron Analysis cut • Vertex cut: |Zvertex|<30 cm • ZDC north || south>30 Ge. V • 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 13

RHIC and PHENIX Relativistic Heavy Ion Collider, at the Brookhaven National Laboratory (NY, USA) • About 4 km circumference (Second largest of Ion collider) • Center of mass energy per nucleons ~200 Ge. V(Au. Au), ~500 Ge. V(pp) • Au. Au, pp, d+Au, Cu. Cu 2007 -RUN • Au. Au • “ 200 Ge. V • Integrated Luminosity is 4 times larger than last 2004 Au. Au run Autum JPS 2011 14

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RUN 7 central UPC trigger n Coherent UPC: γ+γ → e+e-, γ+A→ X+J/ψ: lower pt<0. 3 Ge. V 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. 0 Ge. V 3. 1 or 2 ZDC detects neutron Autum JPS 2011 16

Previous result RHIC average photon energy corresponds to 24 Ge. V 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 1 sigma Motivation • To improve error to get enough quality to find fittest theoretical predicition -> 2007 run has 4 times statistics Autum JPS 2011 17

Comparison with 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=1 Hard probe scaling Alpha=2/3 Soft probe scaling 0. 75 Autum JPS 2011 just a trial. 18

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Cross section compared to theoretical calculation Some coherent prediction looks enough to explain the result. However measured p. T spectra suggest both coherent and incoherent J/psi production J. Nystrand, Nucl. Phys. A 752(2005)470 c; A. J. Run 7: 54. 1± 14. 6 +10. 3/-9. 7μb Run 4(published data): 76± 31(stat)± 11(sys) μb Run 4& 7 combined Autum JPS 2011 60. 8± 13. 7(stat)+10. 5− 10. 1(sys) μb. 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, ar. Xiv: 0706. 2810 (2007). Yu. P. Ivanov, B. Z. Kopeliovich and I. Schmidt, 20 ar. Xiv: 0706. 1532 (2007).

characteristics of continuum and coherent J/psi γγ→ee • Low pt peak • Exp fitting (~exp(-2. 1 mass)) J/psi Coherent • Low pt peak • Gaussian fitting STARLIGHT model with GEANT simulation p. T<0. 8 Same simulation for coherent UPC J/psi Likesign unlikesign Autum JPS 2011 21

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. 62 sigma • Kopeliovich: • Color dipole model+ gluon saturation effects • KST or GBW parameterization • +1. 78 - +1. 05 sigma Strikman looks better Autum JPS 2011 22

Invariant mass • No likesign pair • 43 ee pairs at mee>2 Ge. V • 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) Autum JPS 2011 23

Pair pt • Low J/psi p. Tpeak suggest s coherent UPC • Some higher p. T event s suggests Incoherent UPC Red cross symbols correspond to this region Simulated data has 1000 times larger Statistics. However their Max p. T <0. 8 At least, their incoherent events We can see UPC coherent (γAu) &incoherent (γn) J/Ψ production Autum JPS 2011 24

Fix pt vs 1 -(1 -eff_trg 1)(1 -eff_trg 2) ~run 23500~ nonpol Autum JPS 2011 25

Glauber_mc • offline/analysis/glauber_mc • Au Au 200 Ge. V 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 Autum JPS 2011 26