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Partonic Substructure of Nucleons and Nuclei with Dimuon Production

Partonic Substructure of Nucleons and Nuclei with Dimuon Production. Jen-Chieh Peng. University of Illinois. Partonic structures of the nucleons and nuclei with dimuon production Overview and recent results Future prospects Fermilab, RHIC, J-PARC, FAIR.

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Partonic Substructure of Nucleons and Nuclei with Dimuon Production

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  1. Partonic Substructure of Nucleons and Nuclei with Dimuon Production Jen-Chieh Peng University of Illinois • Partonic structures of the nucleons and nuclei with dimuon production • Overview and recent results • Future prospects • Fermilab, RHIC, J-PARC, FAIR ... Workshop on Achievements and New Directions in Subatomic Physics CSSM, Adelaide, February 15-19, 2010 Outline

  2. Observation of scaling behavior in deep-inelastic scattering νW2 is the “form factor” for the deep-inelastic scattering, and is found to be independent of Q2

  3. Proton structure function from DIS • Important features: • Q2-dependence is due to the quark-gluon coupling • Observed Q2 dependence can be well described by QCD • Challenges: • Compositions of various quarks and antiquarks • Spin structure of the proton • New types of structure functions • Models and lattice calculations for PDFs • Modifications of PDFs in nuclei

  4. Complimentality between DIS and Drell-Yan Drell-Yan DIS McGaughey, Moss, JCP, Ann.Rev.Nucl. Part. Sci. 49 (1999) 217 Both DIS and Drell-Yan process are tools to probe the quark and antiquark structure in hadrons

  5. Lepton-pair production provides unique information on parton distributions Probe antiquark distribution in nucleon Probe antiquark distribution in pion Probe antiquark distributions in antiproton Unique features of D-Y: antiquarks, unstable hadrons…

  6. Fermilab Dimuon Spectrometer (E605 / 772 / 789 / 866 / 906)

  7. Physics results from Fermilab dimuon experiments

  8. Is in the proton? = The Gottfried Sum Rule In 1992, New Muon Collaboration (NMC) obtains SG = 0.235 ± 0.026 ( Significantly lower than 1/3 ! )

  9. “A Limit on the Pionic Component of the Nucleon through SU(3) Flavor Breaking in the Sea” A.W. Thomas, Phys. Lett. 126B (1983) 97-100

  10. 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 (Piller and Thomas)

  11. Meson Cloud Models Chiral-Quark Soliton Model Instantons • nucleon = chiral soliton • expand in 1/Nc • Quark degrees of freedom in a pion mean-field Theory: Thomas, Miller, Kumano, Ma, Londergan, Henley, Speth, Hwang, Melnitchouk, Liu, Cheng/Li, etc. (For reviews, see Speth and Thomas (1997), Kumano (hep-ph/9702367 ), Garvey and Peng (nucl-ex/0109010)) Theses models also have implications on • asymmetry between and • flavor structure of the polarized sea Meson cloud has significant contributions to sea-quark distributions

  12. Meson cloud model Analysis of neutrino DIS data Signal and Thomas, 1987 NuTeV, PRL 99 (2007) 192001

  13. 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

  14. Eur. Phys. J. A18 (2003) 395 First measurements are now available (Talk by Don Geesaman)

  15. J-PARC 50 GeV

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

  17. Using recent PDFs Yang, Peng, Perdekamp, Phys. Lett. B680, 231 (2009) A comparison with D-Y could lead to extraction of CSV effect

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

  19. Transversity and Transverse Momentum Dependent 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

  20. Transversity and Transverse Momentum Dependent PDFs are also probed in Drell-Yan

  21. Boer-Mulders function h1┴ ● Observation of large cos(2Φ) dependence in Drell-Yan with pion beam ● ● How about Drell-Yan with proton beam? 194 GeV/c π + W Boer, PRD 60 (1999) 014012

  22. Azimuthal cos2Φ Distribution in p+p and p+d Drell-Yan E866 Collab., Lingyan Zhu et al., PRL 99 (2007) 082301; PRL 102 (2009) 182001 Smallνis observed for p+d and p+p D-Y With Boer-Mulders function h1┴: 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 quarks

  23. 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.

  24. Outstanding questions 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: Burkardt)? • Flavor dependence of Transverse Momentum Dependent distribution functions • Independent measurements of transversity and sea-quark polarization with Drell-Yan

  25. Modification of Parton Distributions in Nuclei EMC effect observed in DIS (Ann. Rev. Nucl. Part. Phys., Geesaman, Saito and Thomas) F2 contains contributions from quarks and antiquarks How are the antiquark distributions modified in nuclei?

  26. Drell-Yan on nuclear targets The x-dependence of can be directly measured PRL 64 (1990) 2479 PRL 83 (1999) 2304

  27. Flavor dependence of the EMC effects Isovector mean-field generated in Z≠N nuclei can modify nucleon’s u and d PDFs in nuclei Cloet, Bentz, and Thomas, arXiv:0901.3559

  28. The Drell-Yan Process: Drell-Yan ratios for p-A /p-d : Assuming dbar/ubar = 1.5 for the nucleons at x=0.15, then the above ratios are: 1.0 for 40Ca, 1.042 for 208Pb Can probably be measured at Fermilab E906

  29. Nuclear modification of spin-dependent PDF? EMC effect for g1(x) Bentz, Cloet, Thomas et al., arXiv:0711.0392 Remains to be tested by experiments Measure the nuclear modification of Boer-Mulders functions with Drell-Yan ? (only unpolarized Drell-Yan is required)

  30. Summary • Unique information on hadron structures has been obtained with dilepton production experiments using hadron beams. • On-going and future dilepton production experiments at various hadron facilities can address many important unresolved issues in the spin and flavor structures of nucleons and nuclei. • Many of the accomplishments and future plans were inspired by Tony’s ideas.

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