1. The Gluon’s spin contribution to the proton’s spin ---as seen at RHIC G. Bunce Moriond QCD, March 2008 I would like to thank Les Bland, Werner Vogelsang, Abhay Deshpande, Sasha Bazilevsky, Matthias Grosse Perdekamp, for their advice and many plots.

2. a history of the strong interaction: 1964: “quarks” …to understand the zoo of strongly interacting particles; “color” quantum number …to describe the Ω-  sss, S=3/2) 1967: quarks are real! …from hard inelastic scattering of electrons from protons at SLAC 1973: the theory of QCD …quarks and “gluons” and color; perturbative QCD 1980s to present: e-p and pbar-p colliders …beautiful precision tests of pQCD, unpolarized …………………………………………………………………. 1970s: polarized beams and targets 1988: the spin of the proton is not carried by its quarks! 1990s to present: confirmed in “DIS” fixed target experiments using electrons and muons to probe the spin structure of the proton 2001 to present: probe the spin structure of the proton using quarks and gluons (strongly interacting probes see both the gluons and quarks in the proton): RHIC

3. EMC at CERN: J. Ashman et al., NPB 328, 1 (1989): polarized muons probing polarized protons “proton spin crisis”

4. What else carries the proton spin ?  How are gluons polarized ?  How large are parton orbital angular mom. ?

5. DIS pp high p T

6. Probing  G in pp Collisions pp  hX Double longitudinal spin asymmetry A LL is sensitive to  G

7. RHIC Polarized Collider BRAHMS & PP2PP STAR PHENIX AGS LINAC BOOSTER Pol. H - Source Spin Rotators (longitudinal polarization) Siberian Snakes 200 MeV Polarimeter RHIC pC Polarimeters Absolute Polarimeter (H  jet) AGS pC Polarimeter Strong AGS Snake Helical Partial Siberian Snake PHOBOS Spin Rotators (longitudinal polarization) Siberian Snakes 2006: 1 MHz collision rate; P=0.6

8. Exquisite Control of Systematics

9. A LL (P) Polarization (L) Relative Luminosity (N) Number of pi0s ++ same helicity +  opposite helicity “Yellow” beam “Blue” beam

10. RHIC Spin Runs PL(pb^-1) Results 2002 15% 0.15 first pol. pp collisions! 2003 30%1.6 pi^0, photon cross section, A_LL(pi^0), 3 PRLs 2004 40%3.0 absolute beam polarization with polarized H jet 2005 50% 13 large gluon pol. ruled out (P^4 x L = 0.8) 2006 60% 46 first long spin run (P^4 x L = 6) 2007 no spin running 2008 50% (short) run in progress

11. RHIC Polarimetry PHOTO of Jet Pol Jet Polarization  for proton-proton elastic scattering

12. Polarization Measurements 2006 Run

13. PHENIX and STAR STAR STAR: Large acceptance with azimuthal symmetry Good tracking and PID Central and forward calorimetry PHENIX: High rate capability High granularity Good mass resolution and PID Limited acceptance

14. pp   X Cornerstones to the RHIC Spin program To appear PRD Rapid, hep-ex-0704.3599 0 Mid-rapidity: PHENIX Forward: STAR PRL 97, 152302 (2006)

15. And Jets and Direct  pp   X : PHENIX PRL 98, 012002 (2007) pp  jet X : STAR PRL 97, 252001 (2006)

16. A LL : jets Run3&4: PRL 97, 252001 10 20 pT(GeV) GRSV Models: “  G = G”:  G(Q 2 =1GeV 2 )=1.9 “  G = -G”:  G(Q 2 =1GeV 2 )=-1.8 “  G = 0”:  G(Q 2 =1GeV 2 )=0.1 “  G = std”:  G(Q 2 =1GeV 2 )=0.4 STAR Preliminary Run5 (  s=200 GeV) Large gluon polarization scenario is not consistent with data

17. A LL :  0 pT(GeV) Run3,4,5: PRL 93, 202002; PRD 73, 091102; hep-ex-0704.3599 510 GRSV model: “  G = 0”:  G(Q 2 =1GeV 2 )=0.1 “  G = std”:  G(Q 2 =1GeV 2 )=0.4 Stat. uncertainties are on level to distinguish “std” and “0” scenarios? … PHENIX Preliminary Run6 (  s=200 GeV)

18. From A LL to  G (with GRSV) Calc. by W.Vogelsang and M.Stratmann  “std” scenario,  G(Q 2 =1GeV 2 )=0.4, is excluded by data on >3 sigma level:  2 (std)  2 min >9 Only exp. stat. uncertainties are included (the effect of syst. uncertainties is expected to be small in the final results) Theoretical uncertainties are not included “3 sigma”

19. Extending x range is crucial! Gehrmann-Stirling models GSC:  G(x gluon = 0  1) = 1  G(x gluon = 0.02  0.3) ~ 0 GRSV-0:  G(x gluon = 0  1) = 0  G(x gluon = 0.02  0.3) ~ 0 GRSV-std:  G(x gluon = 0  1) = 0.4  G(x gluon = 0.02  0.3) ~ 0.25 GSC:  G(x gluon = 0  1) = 1 GRSV-0:  G(x gluon = 0  1) = 0 GRSV-std:  G(x gluon = 0  1) = 0.4 Current data is sensitive to  G for x gluon = 0.02  0.3

20. unpol. u Expected start: 2009  q-  q at RHIC via W production

21. Transverse spin: pion A_N --very large forward asymmetries A N (  ) at 62 GeV Kyoto Spin2006 STAR

22. RHIC Spin Outline Spin structure of proton Strongly interacting probes ----------- P=60%, L=2x10^31, root(s)=200 GeV in 2006 Polarized atomic H jet: absolute P, pp elastic physics ---------- Cross sections for pi^0, jet, direct photon described by pQCD Helicity asymmetries: sensitivity to gluon spin contribution to proton ---------- W boson parity violating production: ubar and dbar polarizations in proton ---------- Very large transverse spin asymmetries in pQCD region ---------- Future: transverse spin Drell- Yan The key points for RHIC Spin are:

23. A Fundamental Test of Universality: Transverse Spin Drell Yan at RHIC vs Sivers Asymmetry in Deep Inelastic Scattering Important test at RHIC of recent fundamental QCD predictions for the Sivers effect, demonstrating… attractive vs repulsive color charge forces ---------------- Possible access to quark orbital angular momentum Requires very high luminosity (RHIC II) Both STAR and PHENIX can make important, exciting, measurements Discussion available at http://spin.riken.bnl.gov/rsc/

24. DIS: attractiveDrell-Yan: repulsive Attractive vs Repulsive “Sivers” Effects Unique Prediction of Gauge Theory ! Sivers = Dennis Sivers (predicted orbital angular momentum origin of transverse asymmetries)

25. 0.1 0.2 0.3 x Sivers Amplitude 0 0 Experiment SIDIS vs Drell Yan: Sivers| DIS = − Sivers| DY *** Probes QCD attraction and QCD repulsion *** HERMES Sivers ResultsRHIC II Drell Yan Projections Markus Diefenthaler DIS Workshop Munich, April 2007

26. Concluding Remarks High luminosity and high polarization achieved! -------------- Delta G: direct photon; global fits with RHIC, DIS; new vertex and forward detectors -------------- W boson parity violating production: ubar and dbar -------------- Very strong theoretical support -------------- Transverse spin renaissance  Drell Yan crucial test of our understanding of the underlying physics!

27. Spin is one of the most fundamental concepts in physics, deeply rooted in Poincare invariance and hence in the structure of space-time itself. All elementary particles we know today carry spin, among them the particles that are subject to the strong interactions, the spin ½ quarks and the spin 1 gluons. Spin, therefore, plays a central role also in our theory of the strong interactions, QCD, and to understand spin phenomena in QCD will help to understand QCD itself. To contribute to this understanding is the primary goal of the spin physics program at RHIC.