1 / 37

Marc Vanderhaeghen Johannes Gutenberg Universität, Mainz College of William & Mary

Overview of nucleon structure studies. Marc Vanderhaeghen Johannes Gutenberg Universität, Mainz College of William & Mary. Lattice 2008 Williamsburg, July 14-19, 2008. nucleon form factors. (generalized) parton distributions spin, tomography. nucleon resonances Δ (1232),….

fergal
Download Presentation

Marc Vanderhaeghen Johannes Gutenberg Universität, Mainz College of William & Mary

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Overview of nucleon structure studies Marc Vanderhaeghen Johannes Gutenberg Universität, Mainz College of William & Mary Lattice 2008 Williamsburg, July 14-19, 2008

  2. nucleon form factors (generalized) parton distributions spin, tomography nucleon resonances Δ(1232),…

  3. Pun05 Gay02 proton e.m. form factor : status green : Rosenbluth data (SLAC, JLab) JLab/HallA recoil pol. data new JLab/HallC recoil pol. exp. (spring 2008) : extension up to Q2 ≈ 8.5 GeV2 new MAMI/A1 data up to Q2 ≈ 0.7 GeV2

  4. neutron e.m. form factor : status MAMI JLab/HallC JLab/CLAS JLab/HallA new MIT-Bates (BLAST) data for both p and n at low Q2 new JLab/HallA double pol. exp. (spring 07) : extension up to Q2 ≈ 3.5 GeV2 completed

  5. Two-photon exchange effects Rosenbluth vs polarization transfer measurements of GE/GM of proton SLAC, Jlab Rosenbluth data Jlab/Hall A Polarization data Jones et al. (2000) Gayou et al. (2002) Two methods, two different results ! 2γ exchangeproposed as explanation Guichon, Vdh (2003)

  6. Observables including two-photon exchange Real parts of two-photon amplitudes

  7. Normal spin asymmetries in elastic eN scattering directly proportional to the imaginary part of 2-photon exchange amplitudes spin of beam OR target NORMAL to scattering plane OR on-shell intermediate state order of magnitude estimates : target : beam :

  8. Beam normal spin asymmetry New MAMI A4 data at backward angles Ee = 0.300 GeV Θe = 145 deg Ee = 0.570 GeV Θe = 35 deg Ee = 0.855 GeV Θe = 35 deg data : MAMI A4 theory : Pasquini & Vdh (2004) also : SAMPLE, Happex, G0, E-158

  9. Two-photon exchange calculations partonic calculation elastic contribution N GPDs Chen, Afanasev, Brodsky, Carlson, Vdh (2003) Blunden, Melnitchouk, Tjon (2003, 2005)

  10. Real part of Y2γ ε-independence of GEp/GMp in recoil polarization cross section difference in e+ and e- proton scattering non-linearity of Rosenbluth plot Also imaginary part from induced out-of-plane polarization single-spin target asymmetry Hall C 04-019, completed Hall B 07-005; Olympus/Doris with refurbished BLAST detector Hall C 05-017; being analyzed by-product of 04-019/04-108? Hall A 05-015 (3He ) whether two-photon exchange is entirely responsible for the discrepancy in the FF extraction is to be determined experimentally

  11. test ofε-dependence of Pt / Pl new JLab/Hall C data (2008) PRELIMINARY, not to be quoted 1γ result for Pt / Pl The preliminary data for Q2=2.5 GeV2 show no ε-dependence of GEp/GMp at the 0.01 level

  12. nucleon FF : lattice prospects F1V state of art : connected diagrams -> OK for isovector quantities LHPColl. full QCD lattice calculations Pion masses down to less than 300 MeV √(r2)1V chiral extrapolation to physical mass Leinweber, Thomas, Young (2001) next step : inclusion of disconnected diagrams

  13. LHPC results see talk : Meifeng Lin valence DWF on Asqtad staggered sea GEV new mπ = 293 MeV factor 4 reduction in error modest mπ dependence <r12>V

  14. RBC results see talk : T. Yamazaki arXiv:0802.0863 [hep-lat] 2 degenerate dynamical flavors of DWF F1V mπ= 0.493 GeV mπ= 0.607 GeV mπ= 0.695 GeV Puzzle: no strong chiral behavior expected at Q2 ≈ 1 GeV2 , however more than factor 2 deviation with data ! see also talks : J. Zanotti, Ph. Haegler, T. Korzec, H.-W. Lin, … F2V

  15. quark transverse charge densities in nucleon (I) q+ = q0 + q3 = 0 photon only couples to forward moving quarks quark charge density operator unpolarized nucleon

  16. quark transverse charge densities in nucleon (II) transversely polarized nucleon transverse spin e.g. along x-axis : dipole field pattern

  17. empirical quark transverse densities in proton ρ0 ρT induced EDM : dy= - F2p (0) . e / (2 MN) data : Arrington, Melnitchouk, Tjon (2007) densities : Miller (2007); Carlson, Vdh (2007)

  18. empirical quark transverse densities in neutron ρT ρ0 induced EDM : dy= - F2n (0) . e / (2 MN) data : Bradford, Bodek, Budd, Arrington (2006) densities : Miller (2007); Carlson, Vdh (2007)

  19. empirical transverse transition densities for N -> Δexcitation combination ofM1,E2,C2FFs data : MAID 2007 , Drechsel, Kamalov, Tiator (2007) densities : Carlson, Vdh (2007)

  20. monopole dipole quadrupole

  21. Generalized Parton Distributions : yield 3-dim quark structure of nucleon Burkardt (2000,2003) Belitsky,Ji,Yuan (2004) Elastic Scattering transverse quark distribution in coordinate space DIS longitudinal quark distribution in momentum space DES (GPDs) fully-correlated quark distribution in both coordinate and momentum space

  22. * Q2 >> t = Δ2 x + ξ x - ξ P - Δ/2 P + Δ/2 GPD (x, ξ ,t) GPDs : ξ = 0 Fourier transform of GPDs : simultaneous distributions of quarks w.r.t. longitudinal momentum x P and transverse positionb

  23. y3 Handbag (bilocal) operator : new way to probe the nucleon Y- y0 y 0 generalized probe ( Y ≈ 0 ) ( W±, Z0 ) probe spin 2 (graviton) probe electroweak form factors energy-momentum form factors

  24. Why GPDs are interesting Unique tool to explore the internal landscape of the nucleon : 3D quark/gluon imaging of nucleon Access to static properties : constrained (sum rules) by precision measurements of charge/magnetization orbital angular momentum carried by quarks

  25. GPDs : transverse image of the nucleon (tomography) Hu(x, b? ) x Guidal, Polyakov, Radyushkin, Vdh (2005) b?(fm)

  26. quark contribution to proton spin X. Ji (1997) with parametrizations for E q : GPD : based on MRST2002 μ2 = 2 GeV2 lattice : full QCD, no disconnected diagrams so far see talks on Fri : hadron structure

  27. Bethe-Heitler DVCS on protonJLab/Hall A @ 6 GeV DVCS GPDs Difference of polarized cross sections Q2 ≈ 2 GeV2 xB = 0.36 Unpolarized cross sections also JLab/CLAS, HERMES, H1 / ZEUS

  28. DVCS on neutron 0 because F1(t) is small 0 because of cancelation of u and d quarks n-DVCSgives access to the least known and constrained GPD,E JLab /Hall A (E03-106) : preliminary data

  29. Sphere: Prolate: Q20=0 Q20/R2 > 0 Oblate: Q20/R2 < 0 electromagnetic N -> Δ(1232) transition J P=3/2+ (P33), M' 1232 MeV,  ' 115 MeV N ! transition:  N !  (99%),  N !  (<1%) non-zero values for E2 and C2 : measure of non-spherical distribution of charges spin 3/2 Role of quark core (quark spin flip) versus pion cloud

  30. Q2 dependence of E2/M1 and C2/M1 ratios data points : M1 MIT-Bates (Sparveris et al., 2005) MAMI : Q2 = 0 (Beck et al., 2000) Q2 = 0.06 (Stave et al., 2006) Q2 = 0.2 (Elsner et al., 2005, Sparveris et al., 2006) E2/M1 EFT calculation predicts the Q2 dependence C2/M1 no pion loops pion loops included Pascalutsa, Vdh (2005) also Gail, Hemmert

  31. mπ dependence of E2/M1 and C2/M1 ratios Q2 = 0.1 GeV2 quenched lattice QCD results : at mπ= 0.37, 0.45, 0.51 GeV linear extrapolation in mq ~ mπ2 Nicosia – MIT group :Alexandrou et al. (2005) EFT calculation discrepancy with lattice explained by chiral loops(pion cloud)! Pascalutsa, Vdh (2005) full QCD results available Alexandrou et al. data points : MAMI, MIT-Bates

  32. Magnetic Dipole Moment of (1232)- resonance octet baryonMDMs : precession in external magnetic fied • J P = 3/2+, M = 1232 MeV,  = 115 MeV • N ->  transition:  N ->  (99%),  N ->  (<1%) decuplet baryonMDMs : only Ω-lives long enough (weak decay) to be measurable by precession method how about other – strongly decaying -decuplet baryons ?  p! (+!’ + )!0 p

  33. Status of μΔ p! (+!’+ )!0 p forΔ+ : high precision exp. underway using Crystal Ball @ MAMI

  34. Chiral behavior of the -resonance magnetic moment quenched lattice points : Leinweber (1992) Cloet,Leinweber,Thomas (2003) Lee et.al. (2004) – revised (2006) chiral calculations Real parts Pascalutsa, Vdh (2004) Imag. parts

  35. full lattice QCD calculations : Ω- anisotropic clover dynamical lattices (JLab) background field method Periodic b.c. : magnetic flux continuous over boundary B = n . 2 π / L2 : Damgaard, Heller (1988) μΩ in physical nuclear magnetons NERSC mΩ= 1.65 GeV Kyklades @ WM EXP. -2.02 ± 0.05 C. Aubin JLab

  36. full lattice QCD calculations : Δ anisotropic clover dynamical lattices : 243 x 128,aS = 0.1, at = 0.036 fm background field method (patched) mπ= 366 MeV μΔ in physical nuclear magnetons C. Aubin

  37. Summary Nucleon form factors : -> high precision data at low Q2 : map out transverse quark densities in nucleon -> difference Rosenbluth vs polarization data GEp /GMp : mainly understood as due to two-photon exchange effects (new expt. planned) -> PV e-scattering : strangeness contributions to E and M distributions very small -> lattice QCD : state-of-art full QCD calculations go down to mπ~ 300 MeV, some puzzles GPDs : -> unifying theme in hadron physics (form factors, parton distributions) -> provide a tomographic image of nucleon -> access to angular momentum of quarks/gluons in nucleon -> encouraging experimental results coming out of HERMES, H1/ZEUS, JLab@6 GeV indicating twist-2 dominance -> future programs : COMPASS, dedictated JLab@12 GeV, EIC… Nucleon excitation spectrum : -> precision data on NΔform factors : shape of hadrons -> chiral EFT is used in dual role : describe both observables and use in lattice extrapolations strong non-analytic behavior in quark mass due to opening of πN decay channel (interplay of scales)

More Related