Future of Transverse Spin at

1. Future of Transverse Spin at Anselm Vossen RSC Meeting, Ames, Iowa, May 15th

2. Motivation for Transverse Spin Physics • Interesting transverse spin effects help us understand QCD • Transverse Spin allows to probe Matrix elements via Interference • RHIC is the only place with polarized proton collisions in the foreseeable future • Test Factorization • Explore role of soft interactions • How and why is pp->hadrons different from SIDIS & DY • What contributes most of the visible mass in the universe? • Not Higgs: The QCD interaction! • SPIN is fundamental quantity:What role does it play in strong interactions?

3. Still not understood… • Several orders of magnitude in sqrt(s) • Several theoretical frameworks… • Effects strong in forward direction • Valence quark effect in parton picture AN(%)

4. Next decadal Plan: Full Forward Spectrometer North Muon Arm 145cm HCAL 80cm HCAL 68cm EMCAL 2T Solenoid EMCAL RICH Preshower 60cm Silicon Tracker VTX + 1 layer IP Silicon Tracker FVTX 1.2 < h < 2.7 8o < q < 37o • Coverage in 2 < h < 4 (2o < q < 30o) • Needs Open Geometry • replace current central detector with a new one covering |h| =< 1 • replace South muon arm by a endcap spectrometer able to do all the physics on the next slides

5. Subsystems HCAL EMCAL Tracking • Charged Particle Tracking • RICH allows PID up to high momenta: Flavor decomposition • EM Cal: Neutral particles • HCAL: Hadrons and jet reconstruction • Dedicated Magnet? • Jets! RICH

6. Mechanisms for AN (An Outline) • Spin dependent quark distributions • TMD picture: Sivers • Collinear Picture: Twist3 pdfs • Tests of Factorization • Spin dependent Fragmentation • Collins Effect • Interference Fragmentation Function • Flavor separation for all of the above • More forward physics • Charm AN • Lambda • … M. Boglione at DIS09

7. Collinear, Unpolarized Factorization is valid in the forward region

8. ST Spin Dependent Quark Distributions P twist-3 PRD 74, 114013 xP • Twist 3 • One hard scale (pt) • Sivers TMD + soft gluon interaction • One hard, one soft scale • TMD factorization not proven for pp->hX (counterexample) • DY should work

9. Scale Dependence PheniX AN in MPC: Turnaround At pT~ 3GeV?? In SIDIS turnover seems to be at around 1 GeV in pT Shape like Hermes Sivers measurement

10. Sivers in Different Configurations • Open Questions • Factorization: Does it break, how much? • How does PP compare to DY and DIS (Kinematics similar) Drell-Yan: repulsive Proton-Proton ? DIS: attractive (Werner Vogelsang)

11. Flavor Decomposition can answer differences between pp and SIDIS • Role of Strange Quarks • Additional interesting Channels • Vector Mesons

12. Sivers Channels • Crucial: Jet Measurements to get initial parton kinematics • Back To Back Jets • Photon-Jet • Possible Correlations • Forward – Forward • Forward – Central • Forward – Backward (isolated photons in MPC)

13. Q2 PT PT pT pT xF xF Q2 Kinematic Coverage of New Arm • Min Energy of 20GeV (inclusive pions) • One jet forward, EJet>20GeV, One jet in central arm Pythia, Tune100, sqrt(s)=200GeV, only hard processes, all units in GeV

14. Compass observed possible W dependence • One mechanism to explain Discrepancy to HERMES • More Input required W in DIS: Mass of hadronic system pp equivalent:

15. Kinematics Jets Q2 COMPASS HERMES xBj Inclusive Pions Q2 xBj

16. Inclusive pions W W Inclusive pions • W is not large • Jet energy > 20GeV • W can be reconstructed in di-jet events->Test of COMPASS observation h xF xF W W Jets xF h

17. Shape of Expected Sivers Asymmetries • Gauss around 0.3, width 0.4, Amp. 0.3 • Not taking into account the partial cancellation between u and d ASiv PT h

18. quark-gluon negligible T(f) = T(d) = 0 T(f) = T(d) trigluon T(f) = -T(d) With FVTX: Measure F, D type Sivers and Tri-Gluon Functions PRD 78,114013 model trigluon correlation functions using ordinary unpolarized gluon distribution function : A rough estimate Charm AN with FVTX: Vast improvement

19. Spin Dependent Fragmentation • Needs one reconstructed jet • Coupling to transversity • Collins effect (also Twist3 analogues) • Interference Fragmentation Function

20. _ Chiral odd FFs Collins effect + * * _ + q N _ + : Collins FF

21. The Collins effect in the Artru fragmentation model A simple model to illustrate that spin-orbital angular momentum coupling can lead to left right asymmetries in spin-dependent fragmentation: Jet direction π+ picks up L=1 to compensate for the pair S=1 and is emitted to the right. String breaks and a dd-pair with spin -1 is inserted. In Artru Model: favored (ie up+) and disfavored (ie up-) Collins function naturally of opposite sign

22. Observables: Azimuthal Asymmetries of Hadrons around Jet Axis Tests Transversity at high x, high z • High x: Tensor Charge Connection to Lattice • Again: what does u, d quark sign difference mean for us? ACol pT z PT Mean z: 0.64 pt h

23. Lz Lz-1 _ Chiral odd FFs Interference Fragmentation Function + * * _ + q N _ +

24. Advantages of IFF • Independent Measurement • Favorable in pp: no Sivers • Transverse momentum is integrated • Collinear factorization • No assumption about kt in evolution • Universal function • Evolution known, collinear scheme can be used • Directly applicable to semi-inclusive DIS and pp • First experimental results from HERMES, COMPASS, PHENIX

25. IFF as Measured by BELLE Charm contributions unaccounted RHIC could shed light on flavor composition etc… Invariant mass in new Arm MInv

26. Combined Analysis: Extract Transversity Distributions Factorization + Universality ?! SIDIS ~ δq(x) x CFF(z) ~ δq(x) x IFF(z) e+e- ~ CFF(z1) x CFF(z2) ~ IFF(z1) x IFF(z2) pp  jets ~ G(x1) x δq(x2) x CFF(z) pp  h+ + h- + X ~ G(x1) x δq(x2) x IFF(z) pp  l+ + l- + X ~ δq(x1) x δq(x2) Transversity, δq(x) Tensor Charge Theory Lattice QCD: Tensor Charge

27. ANfor He3 • Predictions by Umberto D’Alesio, with DSS FF • Sign Flip due to isospin Measurement would test Universality, moderate & high x for u, d quarks

28. First Measurement of Forward Lambda’s • Lambda Kinematics with p, proton in Forward Arm pt pt xf h

29. Summary: What we will learn from Proton Proton • Transverse Spin essential! • Test QCD • Measure Sivers, Collins & IFF • Asymmetries expected to be large in forward direction • Cancellation between different flavors still unclear • Asymmetries should be smaller than SIDIS, but AN large • Color charges in initial and final states • Factorization • TMD, Collinear • Attractive, repulsive forces (color ‘anti-color’) • Transversity at high X (should be faster than JLab..) • Lambdas • Local Parity Violation, other TMDs… • RHIC is the only place… for a long time!! ….and finally we will understand An and can lay it to its well deserved rest..

31. Backup

33. DCAR Shape • μ decay from D, B and hadrons have different DCAR shapes in a given μ pT bin. • DCAR shape also depends on the parent particle and the decay μ pT. Distributions are normalized according to PHENIX cross sections. • Single particle shapes can be evaluated using MC. • They can be fitted together to the merged event shape, to get B, D and BG contributions.

34. c and b Separation -- Results With achieved statistics With 10 pb-1 statistics Limitations: Same pT spectra for B and D and same background sample are used in training sample and mixed sample. Systematic error need to be quantified.

37. DCAR DCAR = impact parameter projected onto μ pT.

38. Collins Fragmentation at Belle • First extraction of transversity quark distribution Together with HERMES, COMPASS First, still model dependent transversity Extraction : • Alexei Prokudin, DIS2008, update of Anselmino et al: hep-ex 0701006 Belle 547 fb-1 data set (Phys.Rev.D78:032011,2008.)

39. vs Invariant Mass of the Pair First measurement of IFF in pp beijing

40. Comparison to theory predictions Initial model description by Bacchetta,Checcopieri, Mukherjee, Radici : Phys.Rev.D79:034029,2009. Leading order, experimental results might contain effects from gluon radiation not contained in the model Mass dependence : Magnitude at low masses comparable, high masses significantly larger (some contribution possibly from charm ) Z dependence : Rising behavior steeper However: Theory contains parameters based on HERMES data.

41. Subprocess contributions (MC) Data not corrected for Charm contributions 8x8 m1 m2 binning charged B(<5%, mostly at higher mass) Neutral B (<2%) charm( 20-60%, mostly at highest masses) uds (main contribution) Charm Asymmetries in simulated data consistent with zero! To be checked with charm enhanced sample 41

42. Simulations: ~ 10(nb)-1

43. Other • Lambda • Local P viol

45. vs invariant mass of the pair No significant asymmetries seen at mid-rapidity. Added statistics from 2008 running NEW

46. Di-Hadron SSA in SIDIS (both on proton target, sign convention different)

47. Motivation: Transversity Quark Distributions δq(x)from Transverse Single Spin Asymmetries in Semi Inclusive Deep Inelastic Scattering Example: COMPASS results for Collins Asymmetries on proton target (see talk by H. Wollny) Collins- and IFF- asymmetries in semi-inclusive deep inelastic scattering (SIDIS) and pp measure ~ δq(x) x CFF(z)  combined analysis with CFF from e+e- annihilation

48. Definition of Vectors and Angles Bacchetta and Radici, PRD70, 094032 (2004) 48