Probing Spin and Flavor Structures of the Nucleon with Hadron Beams

1. Probing Spin and Flavor Structures of the Nucleon with Hadron Beams Jen-Chieh Peng University of Illinois • Flavor and spin structures of the nucleons • Overview and recent results • Future prospects • Fermilab, RHIC, J-PARC Workshop on Hadron Physics in China and Opportunities with 12 GeV JLab Lanzhou University, July 31-August 1, 2009 Outline

2. Flavor and spin structures of the nucleons Why is it interesting? • 99.97% of the visible mass of the Universe is composed of protons and neutrons • Quantum Chromodynamics (QCD) at the confinement scale remains to be understood • The progress of lattice QCD calculations allow direct comparison between the experiments and theory • They provide crucial inputs for describing hard processes in high energy collisions such as at LHC (p+p collider)

3. Electron beam as a powerful tool for probing partonic structure in nucleon SLAC e p  e’ X (DIS) DIS data vs. QCD calculation

4. Some open questions on nucleon partonic structures • What are the flavor structures of valence and sea quarks? • What are the origins of sea quarks in nucleons and nuclei? • Where does the proton’s spin come from? • How are the quark’s transverse spin distributions different from the helicity distributions? • What are the characteristics of various transverse-momentum-dependent (TMD) quark distribution functions?

5. Flavor structure of the parton distributions in the proton

6. Complimentality between DIS and Drell-Yan Drell-Yan DIS Both DIS and Drell-Yan process are tools to probe the quark and antiquark structure in hadrons

9. Meson cloud model Analysis of neutrino DIS data Thomas / Brodsky and Ma NuTeV, PRL 99 (2007) 192001

10. Predictions for sea-quark polarizations Meson Cloud Model Chiral-Quark Soliton Model Remain to be tested …..

11. J-PARC 50 GeV

12. Fermilab E906 dimuon experiment (expected to run ~2010-2011)

13. No nuclear effects No assumption of charge-symmetry Large Q2 scale

14. Using recent PDFs R. Z. Yang and JCP arXiv 0905.3783.

15. Charge Symmetry Violation in PDF? See recent review of Londergan, Peng, and Thomas (arXiv:0907.2352)

16. Charge Symmetry violation from MRST Global fits (Eur. Phys. J. C35, 325 (2004)) CSV for sea quarks CSV for valence quarks

17. Comparison between MRST and quark-model calculation Charge symmetry violation for valence quarks MRST Quark-model Eur. Phys. J. C35, 325 (2004) (Rodionov, Thomas, Londergan)

18. Charge symmetry violating Charge-symmetric (S. Yoon and Peng, 2006)

19. Gluon distributions in proton versus neutron? Lingyan Zhu et al., PRL, 100 (2008) 062301 (arXiv: 0710.2344) Gluon distributions in proton and neutron are very similar

20. Three parton distributions describing quark’s transverse momentum and/or transverse spin 1) Transversity 2) Sivers function 3) Boer-Mulders function

21. Transversity and TMD PDFs are probed in Semi-Inclusive DIS Unpolarized Boer-Mulders Transversity Polarized target Sivers Polarzied beam and target SL and ST: Target Polarizations;λe: Beam Polarization

22. Transversity and TMD PDFs are also probed in Drell-Yan

23. Boer-Mulders function h1┴ ● Observation of large cos(2Φ) dependence in Drell-Yan with pion beam ● How about Drell-Yan with proton beam? 252 GeV/c π + W Boer, PRD 60 (1999) 014012

24. cos2Φ Distribution in p+p and p+d Drell-Yan E866 Collab., Lingyan Zhu et al., PRL 99 (2007) 082301; PRL 102 (2009) 182001 Sea-quark BM functions are much smaller than valence BM

25. Polarized Drell-Yan with polarized proton beam? • Polarized Drell-Yan experiments have never been done before • Provide unique information on the quark (antiquark) spin Quark helicity distribution Quark transversity distribution Can be measured at RHIC, J-PARC, FAIR etc.

26. Outstanding questions in TMD to be addressed by future Drell-Yan experiments • Does Sivers function change sign between DIS and Drell-Yan? • Does Boer-Mulders function change sign between DIS and Drell-Yan? • Are all Boer-Mulders functions alike (proton versus pion Boer-Mulders functions) • Flavor dependence of TMD functions • Independent measurement of transversity with Drell-Yan

27. Future prospect for Drell-Yan experiments • Fermilab p+p, p+d, p+A • Unpolarized beam and target • RHIC • Polarized p+p collision • COMPASS • π-p and π-d with polarized targets • FAIR • Polarized antiproton-proton collision • J-PARC • Possibly polarizied proton beam and target

28. Summary • The Deep-Inelastic Scattering, together with Drell-Yan process in hadron collisions, have provide much information (and surprises) on the partonic structures of the hadrons • New Drell-Yan (and W-production) experiments using pion, proton, and antiproton beams will further elucidate the flavor and spin structures of the nucleons.

29. Double-spin asymmetry in polarized p-p at J-PARC 1) Double-spin asymmetry (ALL) with longitudinally polarized beam/target in Drell-Yan probe Quark helicity distributions 2) Double-spin asymmetry (ATT) with transversely polarized beam/target in Drell-Yan probe quark transversity distribution P24 proposal, Goto et al.

30. 950 pb-1 integrated luminosity R. Z. Yang and Peng (2007)

31. Leading-Twist Quark Distributions ( A total of eight distributions) No K┴ dependence K┴ - dependent, T-even K┴ - dependent, T-odd

32. Spin and flavor are closely connected Meson Cloud Model Pauli Blocking Model A spin-up valence quark would inhibit the probability of generating a spin-down antiquark Instanton Model Chiral-Quark Soliton Model Statistical Model

33. Peng, Eur. Phys. J. A18 (2003) 395