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JPS meeting March 26th, 2008 26pZF-11 Kohichi Sakashita ( Tokyo Tech )

Prompt Photon Production from Proton - proton Collisions at √ s = 62.4 GeV in PHENIX ( PHENIX 実験における重心系 62.4 GeV での陽子 - 陽子衝突からの 直接光子の生成断面積の測定 ). JPS meeting March 26th, 2008 26pZF-11 Kohichi Sakashita ( Tokyo Tech ) for the PHENIX Collaboration. Contents. Introduction

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JPS meeting March 26th, 2008 26pZF-11 Kohichi Sakashita ( Tokyo Tech )

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  1. Prompt Photon Production from Proton - proton Collisions at √s = 62.4 GeV in PHENIX( PHENIX実験における重心系62.4 GeVでの陽子-陽子衝突からの直接光子の生成断面積の測定 ) JPS meeting March 26th, 2008 26pZF-11 Kohichi Sakashita ( Tokyo Tech ) for the PHENIX Collaboration

  2. Contents • Introduction • PHENIX detector and data set • Method of prompt photon measurement • Result • Summary

  3. proton gluon proton quark prompt photon q(x), g(x) : PDF for quark, gluon : sub-process cross section 1-1. Introduction • Production of prompt photon • Quark - gluon scattering is dominant sub-process at pp collision in√s = 62.4 GeV • The related experiment • PHENIX √s = 200 GeV • R806, AFS, CCOR and CMOR using ISR collider at √s = 63 GeV in CERN • Test the applicability of perturbative QCD (pQCD) • Comparing the cross section of measurement to the one of pQCD calculation • pQCD calculation in qg scattering : • Once the applicable range of pQCD is determined, the framework of pQCD can be used to calculate other quantities of interest, in particular ALL

  4. 1-2. Introduction • Double helisity asymmetry ( ALL ) • Comparing to ALL in 200 GeV, large Bjorken’s x can be reached at 62.4 GeV √s = 200 GeV 0.02 0.04 0.06 0.08 0.1 xT

  5. 2. PHENIX Detector and Data Set • PHENIX central arm detector •  = 90° x 2, || < 0.35 • Data set • 2006 pp run • Integrated luminosity : 0.065 pb-1 • Basic analysis cuts • EMCal&BBC trigger • Vertex cut |z| < 30 cm • Remove 2 edge towers, dead and hot towers • Event selection • pT > 2 GeV/c • Shower shape cut • Charge veto with PC3 Proton beam prompt γ

  6. 3-1. Method of Prompt Photon Measurement • Main issue of prompt photon measurement • Evaluation of systematic uncertainties • 0 extraction and so on • Prompt photon yields is small signal of all photon • About 10 % at 3 GeV/c

  7. ’ωdecay photon The ratio of ’and 0 production to production The ratio of branching ratio of photon of ’and 0 to the branching ratio of photon of  A = Σσiσ Br i γ/ Br -> γγi : ’ω decay photon Detecting two photon ( Ntag ) Reconstruction invariant mass Missing one photon Evaluated by fast MC simulation The ratio ( R ) of the missing one photon to detecting two photon 3-2. Method of Prompt Photon Measurement Nall N prompt  x A*(1+R)* Ntag Ntag x R* Ntag N prompt  = Nall- (1+A)*(1+R)*Ntag By measuring Nalland Ntag, one can extractsmall Nprompt signal ( tagging method )

  8. 4-1. Result - cross section • Cross section : • pQCD calculation with NLO and CTEQ6M PDF agrees with experiment within theoretical uncertainty and experimental uncertainty

  9. 4-2. Result - comparison of PHENIX √s = 200 GeV and ISR experiments • Results of ISR agree with this result within the experimental uncertainty • Cross section slope at √s = 200 GeV is gentler than one at √s = 62.4 GeV Open black circle : PHENIX at √s =200 GeV ( 2005 year ) The others : ISR experiments at √s =63 GeV

  10. 5. Summary • Test the applicability of pQCD calculation • Data set • pp collision at 2006 year • √s = 62.4 GeV • Integrated luminosity : 0.065 pb-1 • Prompt photon yields as a function of pT are extracted by the 0 tagging method ( N prompt = Nall- (1+A)*(1+R)*Ntag ) with PHENIX central arm detector ( = 90° x 2, || < 0.35 ) • pQCD calculation with NLO and CTEQ6M PDF agrees with experiment within theoretical uncertainty and experimental uncertainty • Results of ISR agree with this result within the experimental uncertainty

  11. Back up

  12. 3-1. Method of Prompt Photon Measurement • Main issue of prompt photon measurement • Evaluation of systematic uncertainties • 0 extraction and so on • Prompt photon yields is small signal of all photon Prompt photon / All photon

  13. 4. Result - systematic errors • Error in N tag • Fit ( Gauss + pol.3 ) to the region of pi0 mass peak to extract 0 photon with 3( 105 < M< 165MeV/c2 ) • Difference of between N tag with pol.2 and Ntag with pol.3 and between N tagwith 3and N tag with 4 is assigned as the error • 3.4 % to the Ntag with pol.3 and 3at 2 GeV/c 2.8 % to the Ntag with pol.3 and 3 at 3.75 GeV/c

  14. 4. Result - systematic errors W = prompt / inclusive Error of C is scaled by 1/W - 1 Error in 1+A Dalitz decay pi0 partner photon conversion loss Error in Ntag Neutral hadron contamination Secondary origin Energy scale uncertainty Luminosity uncertainty Conversion error BBC bias uncertainty 1+R (acceptance) 1+R (Minimum E cut) 1+R (Pi0 cross section slope)

  15. xDG(x) present x-range GS-C x GS-C, ΔG = 1

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