1. Kazuya Aoki For the PHENIX Collaborations. Kyoto Univ. / RIKEN
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 Experiment Results (ALL) Conclusions
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 PHENIX ‘s measured ALL p0 at
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++=
ALL is defined as the asymmetry between helicity parallel and anti-parallel collisions.
s+-=
PHENIX ‘s measured ALL p0 at
This talk

4. Why 62.4GeV? – xT scaling xT scaling Yield xT
Independent of s
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. RHIC and PHENIX global detectors.
Run6(2006) <p>=48% , ~1week, 60nb-1
ZDC
10*10cm
 2.8 mrad
3 module
150X0 5.1λI
BBC <|h|<3.9
Quartz Cherenkov det.
Luminosity measurement
ZDC +/- 2.8mrad.
Hadron Calorimeter
SMD (+ ZDC).
Scintillator hodoscopes.
Local polarimetry
ZDC/BBC
dALL~0.0028
ZDC+SMD ( Local Polarimeter )
BBC
Proton beams are running in RHIC-beam pipes in transversely polarized state. Then it is rotated to ….

7. Longitudinality Longitudinal 100% (-2.2%)
neutron
Longitudinal 100% (-2.2%)
Transverse % (1s uncertainty)
What we want.
What we measure.
Blue beam
Forward
Blue Beam
Backward
Horiz-position(cm)
Horiz-position(cm)
ZDC detector
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
Acceptance - |h|<0.35 , Df=90 x 2
Energy resolution
Position resolution
high energy cluster at EMCal. (~800MeV) w/o BBC
BBC efficiency for p0 event(hard scattering) is low (~40%)
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. p0 Cosmic rays + hadrons peak move towards p0 peak.
pT =
1.~1.5GeV/c
pT =
1.5~2GeV/c
Cosmic rays + hadrons peak move towards p0 peak.
The amount of the tail under p0 signal region is negligible up to used pT
cosmic rays
+ hadrons 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 pb-1
62.4GeV 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.

13. backups

16. Measurement of ALL Beam polarization -- PB,PY Longitudinality
CNI polarimeter. <p> ~ 48%
Longitudinality
Measured by Local polarimeter ~98%
Relative Luminosity – R
BBC , ZDC are independent luminosity detector.
dALL ~
ALL background subtraction
N : p0 yield
L : Luminosity
R : Relative Lumi.

17. 200GeV  62GeV 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.

18. Systematic errors Scale uncertainty ( CNI pol. Meas.)
20%
Uncertainty of Relative Luminosity
dALL ~ 2.8 x 10-3
Effect of ATT
Remaining transverse component ~21%
0.212ATT ~ 0.04ATT on ALL

19. p0 reconstruction Energy calibration Cuts for photon or p0
Tower by tower -- done by Kenichi
Non linearity correction – same as In RUN5
Scale correction for PbSc – ( by Sasha )
x for PbSc
Cuts for photon or p0
Minimal photon energy cut
0.1 GeV for PbSc
0.2 GeV for PbGl
Shower profile cut > 0.02
Energy asymmetry cut a < 0.8
Trigger tile matching. (for higher energy cluster)
Cuts for global
ERT 2x2 triggered events

20. BBC trigger bias for pi0 f0 = N0(ERT2x2&BBC) / N0(ERT2x2)
PbSc vs PbGl
PbSc+PbGl
Results from PbSc and PbGl are well consistent
No global systematics shown (~2.5% expected), common for PbSc and PbGl
Trigger bias at sqrt(s)=62 GeV is pT dependent?
PYTHIA MC (without detector response simulation) at sqrt(s)=62 GeV shows qualitatively the similar effect: for jet pT=5, 10 and 20 GeV fMB~0.42, 0.27 and 0.05 correspondingly
At sqrt(s)=200 GeV fMB~0.79, no pT dependency (again, PYTHIA is in qualitative agreement)

21. ERT2x2 trigger efficiency for pi0
0 = N0(BBC&ERT2x2) / N0(BBC)
PbGl
PbSc
Plateau level: (882)%
MC: 88%
(7 of 64 SMs masked)
Plateau level: (98.10.5)%
MC: 98.5%
(2 of 108 SMs masked)

22. RHIC

23. NLO pQCD applicability
s=62GeV:Comparison to fit to data
s=200GeV:Comparison to data
D d’Enterria, AN291
Seems to work at both energies, within ~30% or so