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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 1 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 ) Wmax 6GeV WNmax 34GeV Autum JPS 2011 2 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) Autum JPS 2011 3 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 Autum JPS 2011 4 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 Autum JPS 2011 5 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. 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 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 Autum JPS 2011 √sNN=200GeV, AuAu ,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) 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). 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 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 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|<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 13 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 Autum JPS 2011 14 Autum JPS 2011 15 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 Autum JPS 2011 16 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 Autum JPS 2011 17 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 Autum JPS 2011 just a trial. 18 Autum JPS 2011 19 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). 20 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 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- -0.62sigma •Kopeliovich: •Color dipole model+ gluon saturation effects •KST or GBW parameterization •+1.78- +1.05sigma Strikman looks better Autum JPS 2011 22 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) Autum JPS 2011 23 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 Autum JPS 2011 24 Fix pt vs 1-(1-eff_trg1)(1-eff_trg2) ~run 23500 run 23500~ nonpol pol Autum JPS 2011 25 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 Autum JPS 2011 26