Flavor Symmetry of Parton Distributions and Fragmentation Functions

1. Flavor Symmetry of Parton Distributions and Fragmentation Functions Jen-Chieh Peng University of Illinois at Urbana-Champaign Workshop on “Future Prospects in QCD at High Energy” BNL, July 17-22, 2006

2. Outline

3. Is in the proton? = Test of the Gottfried Sum Rule New Muon Collaboration (NMC) obtains SG = 0.235 ± 0.026 ( Significantly lower than 1/3 ! )

4. Drell-Yan Measurements

5. Unpolarized Semi-Inclusive DIS Use SIDIS to extract parton distribution functions Universality of fragmentation functions (hep-ph/0011155)

6. Flavor structure of sea-quark distribution via SIDIS Assuming factorization is valid Require knowledge on the fragmentation function D’(z) SIDIS from HERMES Drell-Yan vs SIDIS

7. Future experiments to measureat large x

8. Future SIDIS for at small x ? HERMES: Semi-Inclusive DIS

9. Independent of nuclear effect in deuteron!

10. Garvey and Peng, nucl-ex/0109010

11. Models for asymmetry Meson Cloud Models Chiral-Quark Soliton Model Instantons Quark degrees of freedom in a pion mean-field nucleon = chiral soliton expand in 1/Nc Theses models also have implications on • asymmetry between and flavor structure of the polarized sea

12. Meson cloud model Analysis of neutrino DIS data Signal and Thomas Brodsky and Ma Melnitchouk and Malheiro Christiansen and Magnin Barone et al.

13. Result from NuTeV s(x) s-bar(x) D. Mason, DIS 2005 talk

14. 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

15. JCP, Eur. Phys. J. A18 (2003) 395

16. Flavor Structure of the Helicity Distributions No evidence for Measurement of W± production at RHIC-spin would provide new information

17. Drell-Yan decay angular distributions Θ and Φ are the decay polar and azimuthal angles of the μ+ in the dilepton rest-frame Collins-Soper frame A general expression for Drell-Yan decay angular distributions: In general :

18. Drell-Yan decay angular distributions Θ and Φ are the decay polar and azimuthal angles of the μ+ in the dilepton rest-frame Collins-Soper frame A general expression for Drell-Yan decay angular distributions:

19. Decay angular distributions in pion-induced Drell-Yan NA10 π- +W Z. Phys. 37 (1988) 545 Dashed curves are from pQCD calculations

20. Decay angular distributions in pion-induced Drell-Yan Is the Lam-Tung relation violated? 140 GeV/c 194 GeV/c 286 GeV/c Data from NA10 (Z. Phys. 37 (1988) 545)

21. Boer-Mulders function h1┴ 1=0.47, MC=2.3 GeV Boer, PRD 60 (1999) 014012

22. Motivation for measuring decay angular distributions in p+p and p+d Drell-Yan • No proton-induced Drell-Yan azimuthal decay angular distribution data • Provide constraints on models explaining the pion-induced Drell-Yan data. (h1┴ is expected to be small for sea quarks. The vacuum effects should be similar for p+N and π+N) • Test of the Lam-Tung relation in proton-induced Drell-Yan • Compare the decay angular distribution of p+p versus p+d

23. Decay angular distributions for p+d Drell-Yan at 800 GeV/c p+d at 800 GeV/c E866 Preliminary

24. Comparison of NA10 versus E866 Sea-quark Boer-Mulders function is relatively small

25. Comparison of p+d versus p+p

26. Many Quark Distributions 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

27. for large x SU(6) symmetry d/u →1/2 SZ = 0 dominance d/u→1/5 S = 0 dominance d/u→0

28. Can one probe the meson cloud directly? Scattering of electron off virtual pion was studied at HERA by tagging forward-going proton/neutron Pion structure functions at 10-4 < x < 10-2 were measured

29. BONUS at Hall-B Tagging slow-moving spectator protons This setup is ideal for detecting the scattering off the meson cloud: a) ep→e’pX (π0 cloud) b) ep→e’ΛX (K+ cloud)

30. Connections between parton distribution functions and fragmentation functions

32. Ma, Schmidt, Soffer, Yang assumes the following relations between fragmentation function and parton distributions: (hep-ph/0208122) CTEQ5 PDF BSB PDF Precise e+e-data at large z from Belle could shed light on the connection between PDF and fragmentation functions

33. Connection between PDF and FF for mesons? SMRS pion PDF Kretzer pion fragmentation function

34. Connection between PDF and FF for mesons? Kretzer pion fragmentation function

35. Flavor structure of the fragmentation functions 1) Hyperons Σ+ contains uus valence quarks (Alberg et al. hep-ph/9809243) Can be measured with Drell-Yan using Σ+ beam. Difficult experiment! X 2) Pions

36. Flavor structure of the fragmentation functions 3) Kaons Difficult to measure sea-quark distributions in K+!

37. What is known about kaon fragmentation functions? KKP global fit: This implies: Lingyan Zhu (PR-04-114) Connections between the parton distribution and fragmentation functions?

38. Summary • The flavor asymmetry of light sea quarks provides insight on nucleon sea. Future measurements of the sea quarks at higher and lower x and polarized sea are anticipated. • Flavor and spin structure of the nucleon are connected. • Complementarity between electron and hadron probes. • Connection between the parton distribution function and the parton fragmentation functions need to be better understood. • The flavor structure of nucleon and meson fragmentation functions could be an interesting area for further investigations.