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RHIC Results on Transverse Spin

2nd Workshop on the QCD Structure of the Nucleon June 12-16, 2006 Villa Mondragone Monte Porzio Catone, Rome, Italy. RHIC Results on Transverse Spin. Steve Heppelmann Penn State University. Three RHIC Experiments are producing results on Transverse Single Spin Asymmetries A N.

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RHIC Results on Transverse Spin

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  1. 2nd Workshop on the QCD Structure of the Nucleon June 12-16, 2006 Villa Mondragone Monte Porzio Catone, Rome, Italy RHICResults on Transverse Spin Steve Heppelmann Penn State University

  2. Three RHIC Experiments are producing results on Transverse Single Spin Asymmetries AN. • BRAHMS: Small XF Small angle (Charged (+/-) pion, kaon, nucleon) • PHENIX: Small angle Neutrons; Mid Rapidity 0, jets • STAR: Forward (larger XF) 0, jets, photons; Mid Rapidity charged tracks, pions, jets

  3. From Abhay Deshpande

  4. STAR detector layout (run 5) • TPC: -1.0 <  < 1.0 • FTPC: 2.8 <  < 3.8 • BBC : 2.2 <  < 5.0 • EEMC:1 <  < 2 • BEMC:0 <  < 1 • FPD: || ~ 3.3/3.7/4.0

  5. STAR Forward Calorimetry Recent History and Plans • Prototype FPD • Run 2 polarized proton data (published 2004 spin asymmetry and cross section) Prototype FMS Run 6 (FPD++) 2006 to present • Forward jet shape spin dependence. • Direct photon asymmetry (isolation) • High Statistics, High Polarization • FPD • Run 3-5 data • pp, dAu • (Preliminary An Results) FMS Forward Meson Spectrometer Run 7 2006 (hep-ex/0502040).

  6. FMS Design Forward Calorimeters FPD Run 3-5 (2003-2005) FPD++ Run 6 (2006) FMS Run 7- (2006- )

  7. y Barrel EMC Endcap EMC x -1 0 1 2 -units Opening angle kTx>0 kTx<0 STAR Central Region Reconstructed di-jets from EM calorimeter only trigger data: Run 2 PRELIMINARY 2002- No charged track An Seen @Pt~1.5 GeV An < .01 @Pt~4.5 GeV An < .16 2006- 3,000,000 dijets (-1<<2) will be sensitive to Sivers kT; measure predicted opening angle transverse spin dependence.

  8. Cross Sections and Analyzing Power published from RHIC Run 2 J. Adams et al. (STAR collaboration), Phys. Rev. Lett. 92 (2004) 171801 [hep-ex/0310058]. Similar asymmetry to many lower energy measurements. → R.D. Klem et al., Phys. Rev. Lett. 36 (1976) 929; W.H. Dragoset et al., Phys. Rev. D18 (1978) 3939; S. Saroff et al., Phys. Rev. Lett. 64 (1990) 995; B.E. Bonner et al., Phys. Rev. D41 (1990) 13; K. Krueger et al, Phys. Lett. B459 (1999); C.E. Allgower et al., Phys. Rev. D65 (2002) 092008. But now, for the first time, in a region where NLO PQCD calculations fairly accurately predict the cross section.

  9. Caveats: -RHIC CNI Absolute polarization still preliminary. -Result Averaged over azimuthal acceptance of detectors. -Positive XF (small angle scattering of the polarized proton). Run 2 Published Result. Run 3 Preliminary Result. -More Forward angles. -FPD Detectors. Run 3 Preliminary Backward Angle Data. -No significant Asymmetry seen. ( Presented at Spin 2004: hep-ex/0502040) Run 3 + Run 5 Preliminary <>=3.7,4.0 (Presented SPIN 2005 Dubna Sept 27-Oct 1)

  10. STAR pp  π0 + X cross sections at 200 GeV nucl-ex/0602011 • The error bars are statistical plus point-to-point systematic • Consistent with NLO pQCD calculations at 3.3 < η < 4.0 • Data at low pT trend from KKP fragmentation functions toward Kretzer. PHENIX observed similar behavior at mid-rapidity. NLO pQCD calculations by Vogelsang, et al.

  11. Combined AN(pT) for xF > 0.4 from runs 3+5 (much higher statistic data recently collected) Online calibration of CNI polarimeter Data are consistent with the 1/pT expectation of pQCD

  12. Run6 – STAR Forward physics objectives • ♦ Forward jet shape ♦ Asymmetry for jet-like events • ♦ mapping ♦ ? • ♦ Inclusive/direct photon measurements FPD++ hardware-level calibration • Analysis of jets and jet shape from already collected in 2006 will • Greatly improve measurement of AN(XF,pT) • Determine if large asymmetry comes from the jet axis or is produced within the jet.

  13. BRAHMS Results

  14. p+ AN of proton and pbar p- K+ K-

  15. BRAHMS Summary (FROM DIS 2006) BRAHMS has obtained preliminary results for single transverse spin asymmetries for p±,K±, p, and pbar in √s =200 GeV pp collisions at RHIC in the xF range of 0.1 to 0.35 • AN(p+): positive ~(<) AN(p-): negative: 5-10% in 0.1 < xF < 0.3 AN(p+) for 0.2 <x in agreement with Twist-3 calculations • First SSA Results on K, p in 0.1 < xF < 0.3 - AN(K+) ~ AN(K-): positive - AN(p) ~0, AN(pbar): positive AN(K) in disagreement with naïve expectation from valence quark fragmentation. Need more theoretical inputs. Current 62 GeV run will allow Brahms to extend to higher XF.

  16. The PHENIX Detector • Philosophy • high resolution & high-rate at the cost of acceptance • trigger for rare events • Central Arms • |h| < 0.35, Df ~ p • g, p0, e, p+-, ... – Identified • Momentum, Energy • Muon Arms • 1.2 < |h| < 2.4 • Momentum (MuTr) more on PHENIX analysis: see: Christine Aidala (tomorrow)

  17. Phenix Statisticss = 200 GeV 2001-2002 transverseP~15% L= 0.15 pb-1 2003 longitudinal-spin run P~30% L=0.35 pb-1 2004 longitudinal spin P~40% L=0.12 pb-1 2005 longitudinal-spin run P~45% w/ short transverse run L=0.15 pb-1 2006 transverse (this run) (Radial polarization) P~55% L>2.4 pb-1

  18. ZDC Forward counter SMD 1 ZDC 3 modules: 150X0 5.1λI Very Forward Neutron ～1800cm 10cm blue beam yellow beam ±3 mrad Dx magnet SMD BBC position measurement with scintillators

  19. charged particles neutron neutron Calculation of AN P~48% • Square-root formula • Smearing effect -- simulation LARGE!! Without Minbias With Minbias

  20. p0 and charged hadrons for y~0 • Run2 result with ~0.15pb-1, P~15% • gg and qg processes are dominant (with small xB) • – transversity effect is suppressed • May provide infomation on gluon-Sivers effect |h| < 0.35 PRL 95 (2005) 202001

  21. Update on charged pions AN pT (GeV/c) • Improved polarization：　P=15% in 2001/02, P=47% in 2005 • while statistics is smaller. • AN is 0 within 1%  interesting contrast with forward p

  22. Conclusions From RHIC Transverse Running at √s=200 GeV • Small pion/charged track AN asymmetry near y~0 • Charged and Neutral Pion AN at Forward Angles large and qualitatively like E706 which took data at an order of magnitude lower energy. Corresponding backward º asymmetries small. • Unlike Lower Energy, the cross sections are in general agreement with perturbative QCD calculations. • Nature of forward AN (Collins/Sivers) to be examined with 2006 central di-jets and forward jet analysis. • Large Neutron Asymmetry at very small forward angles. • Central di-jet / di-hadron measurements (Sivers Effect) coming soon from Run 6 (STAR/PHENIX). • Forward Photon asymmetries, and Forward jet shape dependence coming soon from Run 6 (STAR). • Higher XF charged AN from BRAHMS (62 GeV running). • Run 7 ?? (STAR forward left/right dijets)

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