Double Helicity Asymmetry of Inclusive Neutral Pion Production

Double Helicity Asymmetry of Inclusive Neutral Pion Production in Polarized pp Collisions at sqrt(s)=62. 4 Ge. V Kazuya Aoki For the PHENIX Collaborations. Kyoto Univ. / RIKEN 1

CONTENTS • Introduction – Motivation and physics channel – x. T scaling – What we need to measure ALL • Experiment – RHIC beams and PHENIX global detectors. – Local Polarimeter – PHENIX Central Arms – EMC – 0 reconstruction • Results (ALL) • Conclusions 2

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 0 production in pol pp collisions is sensitive to DG – 0 production is dominated by g+g , q+g s++= s+-= • PHENIX ‘s measured ALL 0 at This talk 3

Why 62. 4 Ge. V? 　– x. T scaling • x. T scaling Independent of s • Yield • Lower energy has higher yield at fixed x. T (~ x 500) x. T • We can probe higher x with better statistics even by short 4 run at 62 Ge. V !! (compared to 200 Ge. V)

Measurement of ALL • • Beam polarization Relative Luminosity Spin-dependent 0 yield ALL background subtraction N : 0 yield L : Luminosity R : Relative Lumi. • Remaining transverse component What we measure. What we want. 5

RHIC and PHENIX global detectors. • BBC 3. 0<|h|<3. 9 – Quartz Cherenkov det. – Luminosity measurement • ZDC +/- 2. 8 mrad. – Hadron Calorimeter – Luminosity measurement <p>=48% , ~1 week, 60 nb-1 ZDC/BBC • Run 6(2006) BBC d. ALL~0. 0028 • SMD (+ ZDC). – Scintillator hodoscopes. – Local polarimetry 6 ZDC+SMD ( Local Polarimeter )

Longitudinality neutron Longitudinal 100% (-2. 2%) Blue Beam Blue beam Backward Forward 21% (1 s uncertainty) Transverse Horiz-position(cm) ZDC detector What we measure. Red : Rotator OFF Blue : Rotator ON Horiz-position(cm) What we want. Yellow Beam Backward Horiz-position(cm) Yellow Beam Forward 7 Horiz-position(cm)

PHENIX Central Arms for g detection. EMCal • Acceptance - |h|<0. 35 , Df=90 x 2 • Energy resolution • Position resolution Trigger high energy cluster at EMCal. (~800 Me. V) w/o BBC – BBC efficiency for 0 event(hard scattering) is low (~40%) 0 reconstruction • Minimal photon energy cut – 0. 1 Ge. V for Pb. Sc – 0. 2 Ge. V for Pb. Gl • Shower profile cut • Energy asymmetry cut • Trigger tile matching. (for higher energy cluster) 8

0 • Cosmic rays + hadrons peak move towards 0 peak. • The amount of the tail under 0 signal region is negligible up to used p. T = 1. ~1. 5 Ge. V/c p. T = 1. 5~2 Ge. V/c cosmic rays + hadrons 0 p. T = 2. ~2. 5 Ge. V/c p. T = 2. 5 -3. Ge. V/c p. T = 3. ~3. 5 Ge. V/c p. T = 3. 5~4. Ge. V/c 9

Results 10 Theory curve by W. Vogelsang

Results 500 Ge. V 1. 8 pb-1 62. 4 Ge. V 0. 06 pb-1 11

summary • Proton spin puzzle inspired measurements on DG • PHENIX has reported ALL of 0 at sqrt(s)=200 Ge. V and gave constraint on DG. • Thanks to x. T scaling, lower energy collisions can probe higher x region with better statistics. • ALL of 0 in pp collisions at sqrt(s)=62. 4 Ge. V was measured at RHIC-PHENIX – RUN 6 pp sqrt(s)=62. 4 Ge. V , <p>~48% , 60 nb-1 – Consistent with zero up to p. T = 4 Ge. V/c • When cross-section analysis finishes and tests p. QCD applicability, ( to be shown in QM ) this measurement will have strong statement on DG. 12

backups 13

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Measurement of ALL • Beam polarization -- PB, PY – CNI polarimeter. <p> ~ 48% • Longitudinality N : 0 yield L : Luminosity R : Relative Lumi. – Measured by Local polarimeter ~98% • Relative Luminosity – R • BBC , ZDC are independent luminosity detector. • d. ALL ~ 0. 0028 • ALL background subtraction 16

200 Ge. V 62 Ge. V from exp. point of view • BBC trigger bias ~80% ~40% – BBC coincidence was removed from trigger. • AN of neutron at forward rapidity decriese – Affected Local polarimeter performance. 17

Systematic errors • Scale uncertainty ( CNI pol. Meas. ) – 20% • Uncertainty of Relative Luminosity – d. ALL ~ 2. 8 x 10 -3 • Effect of ATT – Remaining transverse component ~21% – 0. 212 ATT ~ 0. 04 ATT on ALL 18

0 reconstruction • Energy calibration – Tower by tower -- done by Kenichi – Non linearity correction – same as In RUN 5 – Scale correction for Pb. Sc – ( by Sasha ) • x 0. 958 for Pb. Sc • Cuts for photon or 0 – Minimal photon energy cut • 0. 1 Ge. V for Pb. Sc • 0. 2 Ge. V for Pb. Gl – Shower profile cut > 0. 02 – Energy asymmetry cut a < 0. 8 – Trigger tile matching. (for higher energy cluster) • Cuts for global – ERT 2 x 2 triggered events 19

BBC trigger bias for pi 0 f 0 = N 0(ERT 2 x 2&BBC) / N 0(ERT 2 x 2) Pb. Sc vs Pb. Gl Pb. Sc+Pb. Gl Results from Pb. Sc and Pb. Gl are well consistent ü No global systematics shown (~2. 5% expected), common for Pb. Sc and Pb. Gl Trigger bias at sqrt(s)=62 Ge. V is p. T dependent? ü PYTHIA MC (without detector response simulation) at sqrt(s)=62 Ge. V shows qualitatively the similar effect: for jet p. T=5, 10 and 20 Ge. V f. MB~0. 42, 0. 27 and 0. 05 correspondingly ü At sqrt(s)=200 Ge. V f. MB~0. 79, no p. T dependency (again, PYTHIA is in qualitative 20 agreement)

ERT 2 x 2 trigger efficiency for pi 0 0 = N 0(BBC&ERT 2 x 2) / N 0(BBC) Pb. Gl Pb. Sc Plateau level: (98. 1 0. 5)% MC: 98. 5% (2 of 108 SMs masked) Plateau level: (88 2)% MC: 88% (7 of 64 SMs masked) 21

RHIC 22

NLO p. QCD applicability s=62 Ge. V: Comparison to fit to data s=200 Ge. V: Comparison to data D d’Enterria, AN 291 Seems to work at both energies, within ~30% or so 23

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