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Structure and Formation of Hadrons

Structure and Formation of Hadrons. Jen-Chieh Peng. University of Illinois at Urbana-Champaign. Flavor and spin structures of the nucleons Highlights of results from UIUC’s program Future Plans. NSF Site Visit, UIUC, Dec. 8-9, 2008. Outline. Flavor and spin structures of the nucleons.

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Structure and Formation of Hadrons

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  1. Structure and Formation of Hadrons Jen-Chieh Peng University of Illinois at Urbana-Champaign • Flavor and spin structures of the nucleons • Highlights of results from UIUC’s program • Future Plans NSF Site Visit, UIUC, Dec. 8-9, 2008 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. Observation of scaling behavior in deep-inelastic scattering SLAC e p  e’ X (DIS) DIS data vs. QCD calculation

  4. Open questions on nucleon and nuclear parton structures • 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? • How are the quark and gluon distributions modified in nuclei?

  5. Complimentality between DIS and Drell-Yan DIS Lepton beam Drell-Yan Hadron beam DIS and Drell-Yan (W-production) are tools to probe the quark and antiquark structure in hadrons

  6. Data from E866 Drell-Yan and HERMES Semi-Inclusive DIS(UIUC student, Joosten, is analyzing ~20 times larger Hermes data sample)

  7. Meson cloud model Analysis of neutrino DIS data Results from NuTeV/CCFR

  8. Predictions for sea-quark polarizations Meson Cloud Model Chiral-Quark Soliton Model

  9. Flavor Structure of the Helicity Distributions Polarized Semi-Inclusive DIS (SIDIS) HERMES SIDIS data Quark flavor is tagged by detecting π± and K± Five-flavor analysis PRD 71(2005) 012003 No indication for Δs < 0 (UIUC student Rubin’s thesis )

  10. Measurement of W± production in polarized p-p collision at RHIC would provide new information (Perdekamp’s talk)

  11. Towards DG at RHIC… (Perdekamp’s talk)

  12. Transversity • Remaining frontier of kT – independent structure functions. • Tensor charge (first moment of transversity distributions) can be calculated by Lattice QCD. • Connections to many other novel kT – dependent distribution and fragmentation functions. • Major experimental challenges to measure transversity.

  13. How to measure transversity? Chiral-odd → not accessible in DIS Require another chiral-odd object (either parton distribution function or fragmentation function) • Transversely Polarized Drell-Yan (transversity in both hadrons) • Semi-Inclusive DIS (transversity plus fragmentation function) • Single-hadron (Collins fragmentation function) • Two hadrons (Interference fragmentation function) • Vector meson polarization • Λ - polarization

  14. Semi-inclusive DIS can access all leading-twist quark distributions Leading-Twist Quark Distributions ( A total of eight distributions) Three have no K┴ dependence Transversity The other five are transverse momentum (K┴) dependent (TMD) Sivers function Boer-Mulders function

  15. 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

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

  17. Result from transv. pol. H target sin( + s) moments (Makins, SPIN2008 talk)

  18. Observation of the Collins Effect in e+e- Annihilation at Belle Ralf Seidl , UIUC, et al. Phys.Rev.D78:032011,2008 Collins Asymmetries in e+e- annihilation into hadrons e++e- π++ π- + X ~ Collins(z1) x Collins (z2) j2-p e- Q j1 e+ A12 cos(f1+f2) (Perdekamp’s talk)

  19. Sivers function from transversely polarized H target “Sivers” Moment (Makins, SPIN 2008 talk) Sivers function nonzero  orbital angular momentum of quarks

  20. Extraction of Sivers functions from the Sivers moment measurements Fits to the Hermes data Vogelsang and Yuan (hep-ph/0507266) Striking flavor dependence of the Sivers function We proposed to measure SIDIS at JLab using transversely polarized 3He target

  21. 3He↑(e,e’π+/-)x at JLab Hall A E06-010/06-011 Spokespersons:X. Jiang, J.P. Chen, E. Cisbani,H. Gao, J.C. Peng • Beam • 6 GeV, 15 μA e- beam • Target • Optically pumped Rb-K spin-exchange 3He target, 50 mg/cm2, ~42% polarization, transversely polarized with tunable direction • Electron detection • BigBite spectrometer, Solid angle = 60 msr, θLab = 300 • Charged pion/kaon detection • HRS spectrometer, θLab = -160 E06-010/06-011 thesis students:K. Allada, C. Dutta, X. Qian, M. Shabestari, Y. Wang (UIUC).

  22. Hall-A polarized 3He target 40-cm long Rb-K spin-exchange hybrid cell at 10 atm with beam current of 15 μA 42% target polarization with spin-flip frequency of 20 minutes (We reached 65%!!) A third set of Helmholtz coils (from UIUC), together with the laser optics, to allow for vertical polarization of the 3He target

  23. Predictions of Sivers asymmetry on neutron It can distinguish the predictions constrained by HERMES data.

  24. Currently taking data (since Nov. 20, 2008). Will run until Feb. 2009

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

  26. 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

  27. Azimuthal cos2Φ Distribution in p+d Drell-Yan Lingyan Zhu (UIUC) et al., PRL 99 (2007) 082301 ν (π-Wµ+µ-X) ~ [valence h1┴(π)] * [valence h1┴(p)] ν(pdµ+µ-X)~ [valence h1┴(p)] * [sea h1┴(p)] Sea-quark BM functions are much smaller than valence BM First result from Hermes SIDIS, R. Lamb and N. Makins New result for p+p Drell-Yan, Lingyan Zhu (UIUC) et al., (arXiv:0811.4589)

  28. PRL 83 (1999) 2304 New measurements can cover lower x at RHIC (Perdekamp’s talk), and higher x at Fermilab E906 (Makins’s talk)

  29. Fermilab E906 dimuon experiment at 120 GeV Expected to run ~ 2010-2011

  30. Summary • A broad program to study many novel aspects of parton structures in nucleons and nuclei is being pursued at various facilities by the UIUC group. • The various experimental activities address closely related physics topics using complementary high energy probes.

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