1. Mid-rapidity pi0 production in pp collisions at sqrt(s)=62 and 200 GeV measured by the PHENIX detector at RHIC A.Bazilevsky Brookhaven National Laboratory for the PHENIX Collaboration QM2006 November 14-20, 2006 Shanghai, China  Provides precise reference for studying the evolution of hot/cold nuclear matter effects in heavy ion collisions with collision energy  Check applicability of NLO pQCD calculations  necessary ingredient to extract spin dependent pdf’s from RHIC data  Constrain gluon-to-pion fragmentation functions (PRL91, 241803)

2. PHENIX Detector Central Arms: |  |<0.35,  =2  90 0 Charged particle ID and tracking; photon ID Muon Arm: 1.2<|  |<2.4 Muon ID and tracking Global Detectors Collision trigger Collision vertex characterization Relative luminosity Local Polarimetry Philosophy: High rate capability & granularity Good mass resolution and particle ID  Sacrifice acceptance

3. PHENIX EMCal Lead-Scintillator (PbSc) Module Lead-Glass (PbGl) Super Module PbSc SectorPbGl Sector 6 PbSc sectors (15,552 channels) 2 PbGl sectors (9,216 channels)  =  0.35  =180 0 Granularity (  ) 0.011  0.0110.008  0.008 Energy resolution (%) Position resolution, orthog. imp. (mm) Time Resolution, photons (nsec) as in Test Beam data

4. Basics L * – integrated luminosity, measured with luminosity detector; in PHENIX: L= N BBC /  BBC,  BBC from vernier scan  s=200 GeV:  BBC = 23mb  9.7%  s=62 GeV: analysis ongoing  N – number of  0 s in the p T bin  p T wide; corrected for trigger bias geometrical acceptance smearing reconstruction efficiencies  

5.  0  reconstruction In different p T (GeV) bins

6. Data vs MC Data MC M  vs p T   vs p T Due to unfolding of close photons MC is used to confirm our understanding of EMCal performance MC is used to calculate corrections for geom. acceptance and smearing effect due to EMCal finite resolution This is the main plot to tune EMCal performance, Data vs MC: To tune EMCal global energy scale Confirm/check EMCal (non)linearity To tune EMCal energy resolution parameters

7. High pT photon trigger efficiency for pi0   0 = N  0 (BBC&Photon) / N  0 (BBC) 2x2 tile E thr =0.8 GeV 4x4 tile E thr =1.4 GeV Plateau level consistent with geom. acceptance covered by trigger tiles  s=62 GeV  s=200 GeV Used to collect high pT pi0s

8. High pT pi0 Merged pi0 can be clearly distinguished from a single photon up to at least pT=25 GeV/c using shower profile Probability for two photons to be clearly separated (two distinct clusters or a cluster with two local maxima) Pi0 photons start merging PbSc: at >10 GeV/c PbGl: at >15 GeV/c Separated  0 Merged  0  Consistent within stat. errors  Allows to do measurements at higher p T using “merged”  0

9. BBC (MB) trigger bias for pi0 f  0 = N  0 (Photon&BBC) / N  0 (Photon)  s=200 GeV  s=62 GeV 200 GeV: Doesn’t depend on pT 62 GeV: ~twice lower than at 200 GeV Drops with pT

10. Pi0 cross section  s=200 GeV  Provides precise reference for studying hot/cold nuclear matter effects in heavy ion collisions  Good agreement between NLO pQCD calculations and data  confirmation that pQCD can be used to extract spin dependent pdf’s from RHIC data.  s=62 GeV  Ongoing work on spectrum normalization (from vernier scan)