1. 09/30/'06SPIN2006, T. Horaguchi1 Measurement of the direct photon production in polarized proton-proton collisions at  s= 200GeV with PHENIX CNS, University of Tokyo Takuma Horaguchi 09/30/’06 for the RSC Meeting

2. 09/30/'06SPIN2006, T. Horaguchi2 Contents Physics Motivation Experimental Setup –RHIC –PHENIX Direct Photon Production Cross Section Isolation Cut Method Double Spin Asymmetry Summary

3. 09/30/'06SPIN2006, T. Horaguchi3 Physics Motivation Spin Puzzle from polarized DIS experiment Origin of proton spin –Gluon spin –Orbital angular momentum of quark and gluon RHIC-Spin –The first polarized proton-proton collider –Interaction of quark-quark, quark-gluon, gluon-gluon –Direct photon production (qg→γg) ΔΣ ～ 20-30%

4. 09/30/'06SPIN2006, T. Horaguchi4 Relativistic Heavy Ion Collider The first polarized proton- proton collider Beam energy:50-250GeV in proton-proton collision √s=200GeV (2005) Beam polarization is 47%(2005). Luminosity is 3.8pb -1 (2005) The beam polarization and luminosity will be improved in 2006 Run. –Beam polarization : 60%. –Luminosity : 7.5pb -1 PHENIX STAR Brahms pp2pp

5. 09/30/'06SPIN2006, T. Horaguchi5 PHENIX Detector ElectroMagnetic Calorimeter (EMCal) –Measurement of photon & electron energy and position –Acceptance |η|< 0.35, Δφ=180 degree –Distance from collision point : 5m –High p T photon trigger Beam-Beam Counter (BBC) & Zero Degree Calorimeter (ZDC) –Used for relative luminosity measurement

6. 09/30/'06SPIN2006, T. Horaguchi6 Direct Photon Production A test of pQCD Measurement of the polarized gluon distribution function Determination of the sign of the gluon distribution function proton beam  or  gluon photon Quark-Gluon Compton Scattering

7. 09/30/'06SPIN2006, T. Horaguchi7 Direct photon cross section To be submitted soon Obtained the final plot of the Run2003 data Direct Photon signal –Subtraction of background Evaluation of the photons from hadron decay

8. 09/30/'06SPIN2006, T. Horaguchi8 Direct photon cross section To be submitted soon pQCD calculation describes the our data The 4 orders of magnitude on the cross section is obtained. Systematic error is as follows

9. 09/30/'06SPIN2006, T. Horaguchi9 Isolation-cut method Suppression of the photon from Jet Isolation Cut –ΣEi : The sum of the energy within R<0.5 –ΣPi : The sum of the energy within R<0.5 Isolation cut R  photon Direct photon R  Photon in Jet Photons and charged particles Single photon

10. 09/30/'06SPIN2006, T. Horaguchi10 Ratio of the direct photon Theory curves –Two fragmentation fuction –Three scale factors At high pT region (pT>7GeV/c) –The result shows many of direct photons are isolated. –Theory predictions agree well to the result For low pT region –The theory curve is higher. But the effect of underlying event is in the data Pi0 photons (from jet) are suppressed as we expected qualitatively.

11. 09/30/'06SPIN2006, T. Horaguchi11 From Run5 data X10 luminosity of Run3 Cross Section in Run2005 Pi0 tagging method and isolation cut method It is consistent to Run3 result Wider pT range

12. 09/30/'06SPIN2006, T. Horaguchi12 Double longitudinal spin asymmetry A LL Double longitudinal spin asymmetry (A LL ) –Measurement of the polarized gluon distribution –dσ ++ : Beam helicity is parallel. –dσ +- : Beam helicity is unti-parallel –P 1,2 : Beam polarization –R : Relative-Luminosity(L ++ /L +- ) Direct Photon A LL –Depend on the polarized gluon distribution function of the first degree. –Determination of the sign of the gluon distribution function

13. 09/30/'06SPIN2006, T. Horaguchi13 Effect of the Background The effect of the background A_LL The assumption is –A LL bg ～ A LL pi0 photon If GRSV-max is assumed –rA LL bg ～ 3% (p T =10GeV/c) Working on the measurement of the pi0 photon ALL from data Pi0 A_LL (GRSV-max) Isolation cut R=0.5, f=0.1 minE=0.15GeV Pmin=0.2GeV Pmax=15GeV

14. 09/30/'06SPIN2006, T. Horaguchi14 Outlook for the Future Run 2005 –Luminosity:3.8pb-1 –Polarization:47% Run 2006 –Luminosity:7.5pb-1 –Polarization:60% Working on the analysis of direct photon A_LL for the Run2005 data

15. 09/30/'06SPIN2006, T. Horaguchi15 Summary We obtained the final result of direct photon cross section in Run2003. It was submitted to the PRL. We obtained the preliminary result of the direct photon cross section with pi0 tagging method and isolation cut method in Run2005. We are working on the analysis of the direct photon A_LL for the Run2005 data.

16. 09/30/'06SPIN2006, T. Horaguchi16

17. 09/30/'06SPIN2006, T. Horaguchi17 Outlook for the Future Run 2005 –Luminosity:3.8pb-1 –Polarization:47% Run 2006 –Luminosity:7.5pb-1 –Polarization:60% Working on the analysis of direct photon A_LL for the Run2005 data

18. 09/30/'06SPIN2006, T. Horaguchi18 Signal fraction in the sample subtraction method (pi0 partner Emin=0.5GeV) all hadron all pi0 (tagged + missing partner) green band shows systematic error size. Common parts are cancelled. (normalization, acceptance) signal fraction in the sample. (Merged pi0 are already rejected by the photon shape cut)

19. 09/30/'06SPIN2006, T. Horaguchi19 (iso)Signal fraction in the sample pi0 isolated photon (with partner) isolated pi0 photon (missing partner) Isolation cut R=0.5, f=0.1 minE=0.15GeV Pmin=0.2GeV Pmax=15GeV isolation cut method (pi0 partner Emin=0.5GeV) The message: By applying a photon cut and an isolation cut, the purity is increased. Isolated signal fraction in the sample. (Merged pi0 are already rejected by the photon shape cut)

20. 09/30/'06SPIN2006, T. Horaguchi20 Analysis method Direct photon signal= All photon sample – photons from hadron’s decay (mainly pi0) All photon sample From EMCal clusters charge track veto Photon shape cut Estimation of photons from hadron’s decay Measurement of pi0 production cross section Estimate yield of photons based on pi0 Add other hadron’s (eta etc.) contribution Cocktail methodPi0 tagging method Tag pi0 photons with its partner Estimate them bin by bin Multiplied by the missing ratio to estimate the total Add other hadron’s (eta etc.) contribution Conventional method, It isn’t a direct count of the background Newly applied It is a simple method.