Double Helicity Asymmetry of Inclusive Neutral Pion Production in Polarized pp Collisions at sqrt(s)=62.4 GeV

1. Double Helicity Asymmetry of Inclusive Neutral Pion Production in Polarized pp Collisions at sqrt(s)=62.4 GeV Kazuya Aoki For the PHENIX Collaborations. Kyoto Univ. / RIKEN

2. CONTENTS • Introduction • Motivation and physics channel • xT scaling • What we need to measure ALL • Experiment • RHIC beams and PHENIX global detectors. • Local Polarimeter • PHENIX Central Arms – EMC • p0 reconstruction • Results (ALL) • Conclusions

3. Introduction • Proton spin puzzle, triggered by EMC(’88), has stimulated various efforts towards the understanding of proton spin structure. • Measurement of DG • Double Helicity Asymmetry(ALL) of p0 production in pol pp collisions is sensitive to DG • p0 production is dominated by g+g , q+g s++= s+-= • PHENIX ‘s measuredALLp0 at This talk

4. Why 62.4GeV?– xT scaling Independent of s • xT scaling • Yield • Lower energy has higher yield at fixed xT (~ x500) xT • We can probe higher x with better statistics even by short run at 62GeV !! (compared to 200GeV)

5. Measurement of ALL N : p0 yield L : Luminosity R : Relative Lumi. • Beam polarization • Relative Luminosity • Spin-dependent p0 yield • ALL background subtraction • Remaining transverse component What we measure. What we want.

6. ZDC 10*10cm  2.8 mrad 3 module 150X0 5.1λI ZDC/BBC BBC dALL~0.0028 ZDC+SMD ( Local Polarimeter ) RHIC and PHENIX global detectors. • Run6(2006)<p>=48% , ~1week, 60nb-1 • BBC 3.0<|h|<3.9 • Quartz Cherenkov det. • Luminosity measurement • ZDC +/- 2.8mrad. • Hadron Calorimeter • Luminosity measurement • SMD (+ ZDC). • Scintillator hodoscopes. • Local polarimetry

7. Longitudinal 100% (-2.2%) Transverse 21% (1s uncertainty) ZDC detector neutron What we measure. What we want. Longitudinality Blue beam Forward Blue Beam Backward Horiz-position(cm) Horiz-position(cm) Yellow Beam Forward Yellow Beam Backward Red : Rotator OFF Blue : Rotator ON Horiz-position(cm) Horiz-position(cm)

8. PHENIX Central Arms for g detection. EMCal Trigger high energy cluster at EMCal. (~800MeV) w/o BBC • BBC efficiency for p0 event(hard scattering) is low (~40%) • Acceptance - |h|<0.35 , Df=90 x 2 • Energy resolution • Position resolution p0 reconstruction • Minimal photon energy cut • 0.1 GeV for PbSc • 0.2 GeV for PbGl • Shower profile cut • Energy asymmetry cut • Trigger tile matching. (for higher energy cluster)

9. pT = 1.~1.5GeV/c pT= 1.5~2GeV/c p0 cosmic rays + hadrons • Cosmic rays + hadrons peak move towards p0 peak. • The amount of the tail under p0 signal region is negligible up to used pT p0 pT= 2.~2.5GeV/c pT= 2.5-3.GeV/c pT= 3.~3.5GeV/c pT= 3.5~4.GeV/c

10. Results Theory curve by W. Vogelsang

11. Results 500GeV 1.8 pb-1 62.4GeV 0.06 pb-1

12. summary • Proton spin puzzle inspired measurements on DG • PHENIX has reported ALL of p0 at sqrt(s)=200GeV and gave constraint on DG. • Thanks to xT scaling, lower energy collisions can probe higher x region with better statistics. • ALL of p0 in pp collisions at sqrt(s)=62.4 GeV was measured at RHIC-PHENIX • RUN6 pp sqrt(s)=62.4GeV , <p>~48% , 60 nb-1 • Consistent with zero up to pT = 4GeV/c • When cross-section analysis finishes and tests pQCD applicability, ( to be shown in QM ) this measurement will have strong statement on DG.