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

2 Observation of scaling behavior in deep-inelastic scattering ν W 2 is the “form factor” for the deep-inelastic scattering, and is found to be independent of Q 2

3 Proton structure function from DIS Important features: –Q 2 -dependence is due to the quark-gluon coupling –Observed Q 2 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 Both DIS and Drell-Yan process are tools to probe the quark and antiquark structure in hadrons DIS Drell-Yan McGaughey, Moss, JCP, Ann.Rev.Nucl. Part. Sci. 49 (1999) 217

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)

Physics results from Fermilab dimuon experiments

8 Is in the proton? The Gottfried Sum Rule In 1992, New Muon Collaboration (NMC) obtains S G = ± ( 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)

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

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

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

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

16 J-PARC 50 GeV

17 No nuclear effects No assumption of charge-symmetry Large Q 2 scale

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

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

20 Unpolarized Polarized target Polarzied beam and target S L and S T : Target Polarizations; λe: Beam Polarization Sivers Transversity Boer-Mulders Transversity and Transverse Momentum Dependent PDFs are probed in Semi-Inclusive DIS

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

22 Boer-Mulders function h 1 ┴ Boer, PRD 60 (1999) ● Observation of large cos(2Φ) dependence in Drell-Yan with pion beam ● ● How about Drell-Yan with proton beam? 194 GeV/c π + W

23 With Boer-Mulders function h 1 ┴ : ν(π - W  µ + µ - X)~ [valence h 1 ┴ (π)] * [valence h 1 ┴ (p)] ν(pd  µ+µ-X)~ [valence h 1 ┴ (p)] * [sea h 1 ┴ (p)] Azimuthal cos2Φ Distribution in p+p and p+d Drell-Yan E866 Collab., Lingyan Zhu et al., PRL 99 (2007) ; PRL 102 (2009) Sea-quark BM functions are much smaller than valence quarks Smallνis observed for p+d and p+p D-Y

24 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.

25 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 Outstanding questions to be addressed by future Drell-Yan experiments

26 Modification of Parton Distributions in Nuclei EMC effect observed in DIS How are the antiquark distributions modified in nuclei? F 2 contains contributions from quarks and antiquarks (Ann. Rev. Nucl. Part. Phys., Geesaman, Saito and Thomas)

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

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

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

30 Nuclear modification of spin-dependent PDF? Bentz, Cloet, Thomas et al., arXiv: EMC effect for g 1 (x) Remains to be tested by experiments Measure the nuclear modification of Boer-Mulders functions with Drell-Yan ? (only unpolarized Drell-Yan is required)

31 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.