10/03/'06 SPIN2006, T. Horaguchi 1 Measurement of the direct photon production in polarized proton-proton collisions at  s= 200GeV with PHENIX CNS, University of Tokyo Takuma Horaguchi for the PHENIX Collaboration for the PHENIX Collaboration 10/03/’06 for the SPIN2006

10/03/'06SPIN2006, T. Horaguchi2 Contents  Physics Motivation  Experimental Setup  RHIC  PHENIX  Direct Photon Production  Cross Section  Isolation Cut Method  Double Longitudinal Spin Asymmetry  Summary

10/03/'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→γq) ΔΣ ～ 20-30%

10/03/'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 3.4pb -1 (2005)  The beam polarization and luminosity were improved in 2006 Run.  Beam polarization : 60%.  Luminosity : 7.5pb -1 PHENIX STAR Brahms pp2pp

10/03/'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

10/03/'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

10/03/'06SPIN2006, T. Horaguchi7 Direct photon cross section  Obtained the final plot of the Run2003 data  pQCD calculation describes our data  The 4 orders of magnitude on the cross section is obtained.  Systematic error is as follows hep-ex/

10/03/'06SPIN2006, T. Horaguchi8 Isolation-cut method  Suppression of the photon from Jet  Isolation Cut  ΣEi : The sum of the energy of the photons within R<0.5  ΣPi : The sum of the momentum of the charged particles within R<0.5 Isolation cut R  photon Direct photon R  Photon in Jet Photons and charged particles Single photon

10/03/'06SPIN2006, T. Horaguchi9 Ratio of the direct photon  Theory curves  Two fragmentation function  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. hep-ex/

10/03/'06SPIN2006, T. Horaguchi10 X10 luminosity of Run3 Cross Section in Run2005  Pi0 tagging method  The wide p T range from 5GeV/c to 24GeV/c is covered.  The 4 orders of magnitude on the cross section is obtained.  pQCD calculation with CTEQ6M parton distribution function describes the data well over all measured p T region.  It is consistent to Run3 result

10/03/'06SPIN2006, T. Horaguchi11 Cross Section in Run2005  Isolation cut method  The wide p T range from 5GeV/c to 24GeV/c is covered.  The 4 orders of magnitude on the cross section is obtained.  It is consistent to Run3 result

10/03/'06SPIN2006, T. Horaguchi12 Double longitudinal spin asymmetry A LL  Double longitudinal spin asymmetry (A LL )  Measurement of the polarized gluon distribution  dσ ++ : Same-helicity protons  dσ +- : Opposite-helicity protons  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

10/03/'06SPIN2006, T. Horaguchi13 Effect of the Background  The effect of the background A LL  If we assumed as follows  A LL bg ～ A LL pi0 photon  For the meanwhile, we assumed the GRSV-max as a maximum A LL pi0 photon  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

10/03/'06SPIN2006, T. Horaguchi14 Outlook for the Future  Run 2005  Luminosity:3.8pb-1  Polarization:47%  Run 2006  Luminosity:7.5pb-1  Polarization:60%  The effect of the background A LL will decrease by the precise measurement of it  Working on the analysis of direct photon A_LL for the Run2005 data

10/03/'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 final result of direct photon cross section in Run2003. It was submitted to the PRL(hep-ex/ ).  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.

10/03/'06SPIN2006, T. Horaguchi16

10/03/'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

10/03/'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)

10/03/'06SPIN2006, T. Horaguchi19 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.