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

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

3. From Abhay Deshpande

4. STAR 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 FMS Forward Meson Spectrometer Run 7 2006 ( hep-ex/0502040). FPD –Run 3-5 data –pp, dAu –(Preliminary A n Results)

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

8. 01 2  -units Barrel EMC Endcap EMC x y Reconstructed di-jets from EM calorimeter only trigger data: kTx<0 kTx>0 Opening angle 2002- No charged track A n Seen @Pt~1.5 GeV A n <.01 @Pt~4.5 GeV A n <.16 2006- 3,000,000 dijets (-1<  <2) will be sensitive to Sivers k T ; measure predicted opening angle transverse spin dependence. STAR Central Region

9. 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]. 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. Similar asymmetry to many lower energy measurements. → But now, for the first time, in a region where NLO PQCD calculations fairly accurately predict the cross section.

10. Caveats: -RHIC CNI Absolute polarization still preliminary. -RHIC CNI Absolute polarization still preliminary. -Result Averaged over azimuthal -Result Averaged over azimuthal acceptance of detectors. acceptance of detectors. -Positive X F (small angle -Positive X F (small angle scattering of the polarized proton). scattering of the polarized proton). Run 2 Published Result. Run 3 Preliminary Result. -More Forward angles. -More Forward angles. -FPD Detectors. -FPD Detectors. Run 3 Preliminary Backward Angle Data. Backward Angle Data. -No significant Asymmetry -No significant Asymmetry seen. 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)

11. pp  π 0 + X cross sections at 200 GeV NLO pQCD calculations by Vogelsang, et al. nucl-ex/0602011 STAR The error bars are statistical plus point-to-point systematic Consistent with NLO pQCD calculations at 3.3 < η < 4.0 Data at low p T trend from KKP fragmentation functions toward Kretzer. PHENIX observed similar behavior at mid-rapidity.

12. Combined A N (p T ) for x F > 0.4 from runs 3+5 (much higher statistic data recently collected) Online calibration of CNI polarimeter Data are consistent with the 1/p T expectation of pQCD

13. 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 A N (X F,p T )Greatly improve measurement of A N (X F,p T ) Determine if large asymmetry comes from the jet axis or is produced within the jet.Determine if large asymmetry comes from the jet axis or is produced within the jet.

14. BRAHMS Results

15.   K+K+ K-K- A N of proton and pbar

16. BRAHMS Summary (FROM DIS 2006) BRAHMS has obtained preliminary results for single transverse spin asymmetries for  ±,K ±, p, and pbar in √s =200 GeV pp collisions at RHIC in the x F range of 0.1 to 0.35 A N (   ): positive ~(<) A N (   ): negative: 5-10% in 0.1 < x F < 0.3 A N (   ) for 0.2 <x in agreement with Twist-3 calculations First SSA Results on K, p in 0.1 < x F < 0.3 - A N (K  ) ~ A N (K  ): positive - A N (p) ~0, A N (pbar): positive A N (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 X F.

17. The PHENIX Detector Philosophy –high resolution & high-rate at the cost of acceptance –trigger for rare events Central Arms –|  | < 0.35,  ~  – ,  , e,  +-,... – Identified –Momentum, Energy Muon Arms –1.2 < |  | < 2.4 –Momentum (MuTr) more on PHENIX analysis: see: Christine Aidala (tomorrow)

18. Phenix Statistics  s = 200 GeV 2001-2002 transverse P~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

19. Very Forward Neutron ～ 1800cm 10cm ±3 mrad D x magnet blue beamyellow beam BBC ZDC 3 modules: 150X 0 5.1λ I Forward counter SMD 1 ZDC SMD position measurement with scintillators

20. Calculation of A N Square-root formula Smearing effect -- simulation Without MinbiasWith Minbias LARGE!! neutron charged particles P~48%

21.  0 and charged hadrons for y~0 Run2 result with ~0.15pb -1, P~15% gg and qg processes are dominant (with small x B ) – transversity effect is suppressed May provide infomation on gluon-Sivers effect PRL 95 (2005) 202001 |  | < 0.35

22. Update on charged pions Improved polarization ： P=15% in 2001/02, P=47% in 2005 while statistics is smaller. A N is 0 within 1%  interesting contrast with forward  p T (GeV/c) ANAN

23. Conclusions From RHIC Transverse Running at √s=200 GeV Small pion/charged track A N asymmetry near y~0 Charged and Neutral Pion A N 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 A N (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 X F charged A N from BRAHMS (62 GeV running). Run 7 ?? (STAR forward left/right dijets)