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Hadron Structure with Dilepton Production

Hadron Structure with Dilepton Production. Jen-Chieh Peng. University of Illinois at Urbana-Champaign. • Brief historical review Recent highlights Future prospects. Workshop on “High-energy Hadron Physics with Hadron Beams”, KEK, January 6-8, 2010. Outline. First Dimuon Experiment.

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Hadron Structure with Dilepton Production

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  1. Hadron Structure with Dilepton Production Jen-Chieh Peng University of Illinois at Urbana-Champaign •Brief historical review • Recent highlights • Future prospects Workshop on “High-energy Hadron Physics with Hadron Beams”, KEK, January 6-8, 2010 Outline

  2. First Dimuon Experiment Lederman et al. PRL 25 (1970) 1523 Experiment originally designed to search for neutral weak boson (Z0) Missed the J/Ψ signal !

  3. Lepton-pair production is a powerful tool for finding new particles

  4. The Drell-Yan Process

  5. Lepton-pair production also 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. Deep-Inelastic Scattering versus Drell-Yan Drell-Yan DIS (hep-ph/9905409) Drell-Yan cross sections are well described by NLO calculations

  7. Quarkonium production provides complementary information Proceed via strong interaction Sensitive to gluons Calculations versus data Color evaporation model Gluon-gluon fusion F is the “fudge factor” Quark-antiquark annihilation Schuler, Vogt, PL B 387(1996)181

  8. (E605/772/789/866) Meson East Spectrometer 800 GeV proton beam Open-aperture Closed-aperture Beam-dump (Cu) J/Ψ J/Ψ Ψ’ σ(J/ψ) ~ 15 MeV σ(J/ψ) ~ 150 MeV σ(J/ψ) ~ 300 MeV

  9. Physics with High-Mass Dimuon Production

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

  11. 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

  12. 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, Londergan, Henley, Speth, Hwang, Liu, Cheng/Li, Ma, etc. (For reviews, see 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

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

  14. Predictions for sea-quark polarizations Meson Cloud Model Chiral-Quark Soliton Model First results are obtained from polarized DIS.Remain to be tested by W-production at RHIC

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

  19. Comparison between MRST and quark-model calculation Charge symmetry violation for valence quarks MRST Quark-model x(dVp-uVn) x(uVp-dVn) Eur. Phys. J. C35, 325 (2004) (Rodionov, Thomas, Londergan) Pion-induced D-Y can measure CSV effect (See arXiv:0907.2352 for a recent review on CSV and possible experimental tests)

  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 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

  22. Transversity and Transverse Momentum Dependent 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? 194 GeV/c π + W Boer, PRD 60 (1999) 014012

  24. 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

  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. (see talk by Goto)

  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. Modification of Parton Distributions in Nuclei EMC effect observed in DIS (Ann. Rev. Nucl. Part. Phys., Geesaman, Sato and Thomas) Extensive study by Kumano et al. and Strikman et al. F2 contains contributions from quarks and antiquarks How are the antiquark distributions modified in nuclei?

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

  30. Can there be other nuclear effects in Drell-Yan? 2) Drell-Yan 1) DIS μ+μ- e’ h e No initial state rescattering No final state rescattering Possible initial state rescattering No final state rescattering 3) Semi-inclusive DIS e’ Possible initial state rescattering effects in Drell-Yan need to be identified (and subtracted) Drell-Yan is analogous to semi-inclusive DIS (rather than DIS) e h No initial state rescattering Possible final state rescattering

  31. How to identify initial-state interaction in Drell-Yan? E772 Drell-Yan data Interaction would degrade the longitudinal momentum of the dimuons dσ/dxF would shift to more negative xF for Drell-Yan on nuclei Nuclear dependence would drop below 1 as xF -> 1 Nuclear modification of PDF depends on x2, initial-state effect depends on xF

  32. D-Y measurement at lower energies is important Fractional energy loss is larger at 50 GeV Garvey and JCP, PRL 90 (2003) 092302 Very sensitive measurement of quark energy loss at J-PARC is possible

  33. (first considered by Kumano et al.) Isovector mean-field generated in Z≠N nuclei can modify nucleon’s u and d PDFs in nucleons Cloet, Bentz, and Thomas, arXiv:0901.3559 What are the flavor dependences of the EMC effects?

  34. 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 be measured at J-PARC

  35. Nuclear modification of spin-dependent PDF? EMC effect for g1(x) Bentz, Cloet et al., arXiv:0711.0392 Very difficult to measure ! Easier to measure the nuclear modification of Boer-Mulders functions (only unpolarized targets are required)? (See Bianconi and Radici, J. Phys. G31 (2005) 645)

  36. Can one measure gluon distribution in nuclei with quarkonium production? p + A at 800 GeV/c E772 data σ(p+A) = Aασ(p+N) Strong xF - dependence Nuclear effects scale with xF, not x2→ Effects other than parton distribution modification need to be separated. See talk by Leitch

  37. Single muon measurement in E866 p+A Thesis of Stephen Klinksiek Targets (Z = -24.0”) 0 = Empty 1 = 0.502 “ Copper 2 = 2.036 “ Beryllium 3 = 1.004 “ Copper High-pT Single Muon Trigger High-pT single muon events are dominated by D-meson decays

  38. Preliminary E866 results on the single-muon (open-charm) nuclear-dependence Cu / Be Ratios Thesis of S. Klinksiek Rapidity (y) PT (GeV/C) PT and XF (y) dependences have similar trend as J/Ψ Can be further studied at J-PARC

  39. 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.

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